- Research Associate Professor, Medicine
- Ph.D. Pharmacology
- Peking University Health Science Center, Beijing, Beijing, China
- Hypoglycemic effects of Rosiglitazone
- University of Arizona, Tucson, Arizona (2016 - Ongoing)
- Arizona State Univesity (2010 - 2016)
- Arizona State University, Tempe, Arizona (2005 - 2010)
- University of Texas Health Science Center at San Antonio (1999 - 2004)
- Guangxi University of Chinese Medicine (1994 - 1996)
- Guangxi University of Chinese Medicine (1990 - 1994)
- Luzhai Pharmaceutical Factory (1982 - 1987)
No activities entered.
No activities entered.
- Luo, M., Ma, W., Sand, Z., Finlayson, J., Wang, T., Brinton, R. D., Willis, W. T., & Mandarino, L. J. (2019). Von Willebrand factor A domain-containing protein 8 (VWA8) localizes to the matrix side of the inner mitochondrial membrane. Biochemical and biophysical research communications.More infoVWA8 is a poorly characterized mitochondrial AAA + ATPase protein. The specific submitochondrial localization of VWA8 remains unclear. The purpose of this study was to determine the specific submitochondrial compartment within which VWA8 resides in order to provide more insight into the function of this protein. Bioinformatics analysis showed that VWA8 has a 34 amino acid N-terminal Matrix-Targeting Signal (MTS) that is similar to those in proteins known to localize to the mitochondrial matrix. Experiments in C2C12 mouse myoblasts using confocal microscopy showed that deletion of the VWA8 MTS (vMTS) resulted in cytosolic, rather than mitochondrial, localization of VWA8. Biochemical analysis using differential sub-fractionation of mitochondria isolated from rat liver showed that VWA8 localizes to the matrix side of inner mitochondrial membrane, similar to the inner mitochondrial membrane protein Electron Transfer Flavoprotein-ubiquinone Oxidoreductase (ETFDH). The results of these experiments show that the vMTS is essential for localization to the mitochondrial matrix and that once there, VWA8 localizes to the matrix side of inner mitochondrial membrane.
- Luo, M., Willis, W. T., Coletta, D. K., Langlais, P. R., Mengos, A., Ma, W., Finlayson, J., Wagner, G. R., Shi, C. X., & Mandarino, L. J. (2019). Deletion of the Mitochondrial Protein VWA8 Induces Oxidative Stress and an HNF4α Compensatory Response in Hepatocytes. Biochemistry.More infovon Willebrand A domain-containing protein 8 (VWA8) is a poorly characterized, mitochondrial matrix-targeted protein with an AAA ATPase domain and ATPase activity that increases in livers of mice fed a high-fat diet. This study was undertaken to use CRISPR/Cas9 to delete VWA8 in cultured mouse hepatocytes and gain insight into its function. Unbiased omics techniques and bioinformatics were used to guide subsequent assays, including the assessment of oxidative stress and the determination of bioenergetic capacity. Metabolomics analysis showed VWA8 null cells had higher levels of oxidative stress and protein degradation; assays of hydrogen peroxide production revealed higher levels of production of reactive oxygen species (ROS). Proteomics and transcriptomics analyses showed VWA8 null cells had higher levels of expression of mitochondrial proteins (electron transport-chain Complex I, ATP synthase), peroxisomal proteins, and lipid transport proteins. The pattern of higher protein abundance in the VWA8 null cells could be explained by a higher level of hepatocyte nuclear factor 4 α (HNF4α) expression. Bioenergetic assays showed higher rates of carbohydrate oxidation and mitochondrial and nonmitochondrial lipid oxidation in intact and permeabilized cells. Inhibitor assays localized sites of ROS production to peroxisomes and NOX1/4. The rescue of VWA8 protein restored the wild-type phenotype, and treatment with antioxidants decreased the level of HNF4α expression. Thus, loss of VWA8 produces a mitochondrial defect that may be sensed by NOX4, leading to an increase in the level of ROS that results in a higher level of HNF4α. The compensatory HNF4α response results in a higher oxidative capacity and an even higher level of ROS production. We hypothesize that VWA8 is an AAA ATPase protein that plays a role in mitochondrial protein quality.
- Pandey, R., Zhou, M., Islam, S., Chen, B., Barker, N. K., Langlais, P., Srivastava, A., Luo, M., Cooke, L. S., Weterings, E., & Mahadevan, D. (2019). Carcinoembryonic antigen cell adhesion molecule 6 (CEACAM6) in Pancreatic Ductal Adenocarcinoma (PDA): An integrative analysis of a novel therapeutic target. Scientific reports, 9(1), 18347.More infoWe investigated biomarker CEACAM6, a highly abundant cell surface adhesion receptor that modulates the extracellular matrix (ECM) in pancreatic ductal adenocarcinoma (PDA). The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) RNA-Seq data from PDA patients were analyzed for CEACAM6 expression and evaluated for overall survival, association, enrichment and correlations. A CRISPR/Cas9 Knockout (KO) of CEACAM6 in PDA cell line for quantitative proteomics, mitochondrial bioenergetics and tumor growth in mice were conducted. We found CEACAM6 is over-expressed in primary and metastatic basal and classical PDA subtypes. Highest levels are in classical activated stroma subtype. CEACAM6 over-expression is universally a poor prognostic marker in KRAS mutant and wild type PDA. High CEACAM6 expression is associated with low cytolytic T-cell activity in both basal and classical PDA subtypes and correlates with low levels of T- markers. In HPAF-II cells knockout of CEACAM6 alters ECM-cell adhesion, catabolism, immune environment, transmembrane transport and autophagy. CEACAM6 loss increases mitochondrial basal and maximal respiratory capacity. HPAF-II CEACAM6-/- cells are growth suppressed by >65% vs. wild type in mice bearing tumors. CEACAM6, a key regulator affects several hallmarks of PDA including the fibrotic reaction, immune regulation, energy metabolism and is a novel therapeutic target in PDA.
- Kruse, R., Krantz, J., Barker, N., Coletta, R., Rafikov, R., Luo, M., Hoejlund, K., Mandarino, L. J., & Langlais, P. R. (2017). The CLASP2 Protein Interaction Network in Adipocytes Links CLIP2 to AGAP3, CLASP2 to G2L1, MARK2, and SOGA1, and Identifies SOGA1 as a Microtubule-Associated Protein. Molecular & cellular proteomics : MCP.More infoCLASP2 is a microtubule-associated protein that undergoes insulin-stimulated phosphorylation and co-localization with reorganized actin and GLUT4 at the plasma membrane. To gain insight to the role of CLASP2 in this system, we developed and successfully executed a streamlined interactome approach and built a CLASP2 protein network in 3T3-L1 adipocytes. Using two different commercially available antibodies for CLASP2 and an antibody for epitope-tagged, overexpressed CLASP2, we performed multiple affinity purification coupled with mass spectrometry (AP-MS) experiments in combination with label-free quantitative proteomics and analyzed the data with the bioinformatics tool Significance Analysis of Interactome (SAINT). We discovered that CLASP2 co-immunoprecipitates (co-IPs) the novel protein SOGA1, the microtubule-associated protein kinase MARK2, and the microtubule/actin-regulating protein G2L1. The GTPase-activating proteins AGAP1 and AGAP3 were also enriched in the CLASP2 interactome, although subsequent AGAP3 and CLIP2 interactome analysis suggests a preference of AGAP3 for CLIP2. Follow-up MARK2 interactome analysis confirmed reciprocal co-IP of CLASP2 and also revealed MARK2 can co-IP SOGA1, glycogen synthase, and glycogenin. Investigating the SOGA1 interactome confirmed SOGA1 can reciprocal co-IP both CLASP2 and MARK2 as well as glycogen synthase and glycogenin. SOGA1 was confirmed to colocalize with CLASP2 and also with tubulin, which identifies SOGA1 as a new microtubule-associated protein. These results introduce the metabolic function of these proposed novel protein networks and their relationship with microtubules as new fields of cytoskeleton-associated protein biology.
- Luo, M., Mengos, A. E., Ma, W., Finlayson, J., Bustos, R. Z., Xiao Zhu, Y., Shi, C. X., Stubblefield, T. M., Willis, W. T., & Mandarino, L. J. (2017). Characterization of the novel protein KIAA0564 (Von Willebrand Domain-containing Protein 8). Biochemical and biophysical research communications, 487(3), 545-551.More infoThe VWA8 gene was first identified by the Kazusa cDNA project and named KIAA0564. Based on the observation, by similarity, that the protein encoded by KIAA0564 contains a Von Willebrand Factor 8 domain, KIAA0564 was named Von Willebrand Domain-containing Protein 8 (VWA8). The function of VWA8 protein is almost unknown. The purpose of this study was to characterize the tissue distribution, cellular location, and function of VWA8. In mice VWA8 protein was mostly distributed in liver, kidney, heart, pancreas and skeletal muscle, and is present as a long isoform and a shorter splice variant (VWA8a and VWA8b). VWA8 protein and mRNA were elevated in mouse liver in response to high fat feeding. Sequence analysis suggests that VWA8 has a mitochondrial targeting sequence and domains responsible for ATPase activity. VWA8 protein was targeted exclusively to mitochondria in mouse AML12 liver cells, and this was prevented by deletion of the targeting sequence. Moreover, the VWA8 short isoform overexpressed in insect cells using a baculovirus construct had in vitro ATPase activity. Deletion of the Walker A motif or Walker B motif in VWA8 mostly blocked ATPase activity, suggesting Walker A motif or Walker B motif are essential to the ATPase activity of VWA8. Finally, homology modeling suggested that VWA8 may have a structure most confidently similar to dynein motor proteins.
- Shi, C. X., Kortüm, K. M., Zhu, Y. X., Bruins, L. A., Jedlowski, P., Votruba, P. G., Luo, M., Stewart, R. A., Ahmann, J., Braggio, E., & Stewart, A. K. (2017). CRISPR Genome-Wide Screening Identifies Dependence on the Proteasome Subunit PSMC6 for Bortezomib Sensitivity in Multiple Myeloma. Molecular cancer therapeutics, 16(12), 2862-2870.More infoBortezomib is highly effective in the treatment of multiple myeloma; however, emergent drug resistance is common. Consequently, we employed CRISPR targeting 19,052 human genes to identify unbiased targets that contribute to bortezomib resistance. Specifically, we engineered an RPMI8226 multiple myeloma cell line to express Cas9 infected by lentiviral vector CRISPR library and cultured derived cells in doses of bortezomib lethal to parental cells. Sequencing was performed on surviving cells to identify inactivated genes responsible for drug resistance. From two independent whole-genome screens, we selected 31 candidate genes and constructed a second CRISPR sgRNA library, specifically targeting each of these 31 genes with four sgRNAs. After secondary screening for bortezomib resistance, the top 20 "resistance" genes were selected for individual validation. Of these 20 targets, the proteasome regulatory subunit PSMC6 was the only gene validated to reproducibly confer bortezomib resistance. We confirmed that inhibition of chymotrypsin-like proteasome activity by bortezomib was significantly reduced in cells lacking PSMC6. We individually investigated other members of the PSMC group (PSMC1 to 5) and found that deficiency in each of those subunits also imparts bortezomib resistance. We found 36 mutations in 19S proteasome subunits out of 895 patients in the IA10 release of the CoMMpass study (https://themmrf.org). Our findings demonstrate that the PSMC6 subunit is the most prominent target required for bortezomib sensitivity in multiple myeloma cells and should be examined in drug-refractory populations. .
- Zhu, Y. X., Shi, C. X., Bruins, L. A., Jedlowski, P., Wang, X., Kortüm, K. M., Luo, M., Ahmann, J. M., Braggio, E., & Stewart, A. K. (2017). Loss of Promotes Cell Survival in Myeloma. Cancer research, 77(16), 4317-4327.More infois one of the most recurrently mutated genes in multiple myeloma; however its role in disease pathogenesis has not been determined. Here we demonstrate that wild-type (WT) overexpression induces substantial cytotoxicity in multiple myeloma cells. In contrast, mutations found in multiple myeloma patients abrogate this cytotoxicity, indicating a survival advantage conferred by the mutant phenotype. WT FAM46C overexpression downregulated , and and upregulated immunoglobulin (Ig) light chain and / Furthermore, pathway analysis suggests that enforced expression activated the unfolded protein response pathway and induced mitochondrial dysfunction. CRISPR-mediated depletion of endogenous enhanced multiple myeloma cell growth, decreased Ig light chain and HSPA5/BIP expression, activated ERK and antiapoptotic signaling, and conferred relative resistance to dexamethasone and lenalidomide treatments. Genes altered in -depleted cells were enriched for signaling pathways regulating estrogen, glucocorticoid, B-cell receptor signaling, and ATM signaling. Together these results implicate FAM46C in myeloma cell growth and survival and identify mutation as a contributor to myeloma pathogenesis and disease progression via perturbation in plasma cell differentiation and endoplasmic reticulum homeostasis. .
- Luo, M., Mengos, A. E., Mandarino, L. J., & Sekulic, A. (2016). Association of liprin β-1 with kank proteins in melanoma. Experimental dermatology, 25(4), 321-3.
- Xu, Q., Hou, Y. X., Langlais, P., Erickson, P., Zhu, J., Shi, C. X., Luo, M., Zhu, Y., Xu, Y., Mandarino, L. J., Stewart, K., & Chang, X. B. (2016). Expression of the cereblon binding protein argonaute 2 plays an important role for multiple myeloma cell growth and survival. BMC cancer, 16, 297.More infoImmunomodulatory drugs (IMiDs), such as lenalidomide, are therapeutically active compounds that bind and modulate the E3 ubiquitin ligase substrate recruiter cereblon, thereby affect steady-state levels of cereblon and cereblon binding partners, such as ikaros and aiolos, and induce many cellular responses, including cytotoxicity to multiple myeloma (MM) cells. Nevertheless, it takes many days for MM cells to die after IMiD induced depletion of ikaros and aiolos and thus we searched for other cereblon binding partners that participate in IMiD cytotoxicity.
- Zhu, Y. X., Braggio, E., Shi, C. X., Kortuem, K. M., Bruins, L. A., Schmidt, J. E., Chang, X. B., Langlais, P., Luo, M., Jedlowski, P., LaPlant, B., Laumann, K., Fonseca, R., Bergsagel, P. L., Mikhael, J., Lacy, M., Champion, M. D., & Stewart, A. K. (2014). Identification of cereblon-binding proteins and relationship with response and survival after IMiDs in multiple myeloma. Blood, 124(4), 536-45.More infoCereblon (CRBN) mediates immunomodulatory drug (IMiD) action in multiple myeloma (MM). Using 2 different methodologies, we identified 244 CRBN binding proteins and established relevance to MM biology by changes in their abundance after exposure to lenalidomide. Proteins most reproducibly binding CRBN (>fourfold vs controls) included DDB1, CUL4A, IKZF1, KPNA2, LTF, PFKL, PRKAR2A, RANGAP1, and SHMT2. After lenalidomide treatment, the abundance of 46 CRBN binding proteins decreased. We focused attention on 2 of these-IKZF1 and IKZF3. IZKF expression is similar across all MM stages or subtypes; however, IKZF1 is substantially lower in 3 of 5 IMiD-resistant MM cell lines. The cell line (FR4) with the lowest IKZF1 levels also harbors a damaging mutation and a translocation that upregulates IRF4, an IKZF target. Clinical relevance of CRBN-binding proteins was demonstrated in 44 refractory MM patients treated with pomalidomide and dexamethasone therapy in whom low IKZF1 gene expression predicted lack of response (0/11 responses in the lowest expression quartile). CRBN, IKZF1, and KPNA2 levels also correlate with significant differences in overall survival. Our study identifies CRBN-binding proteins and demonstrates that in addition to CRBN, IKZF1, and KPNA2, expression can predict survival outcomes.
- Chao, A., Zhang, X., Ma, D., Langlais, P., Luo, M., Mandarino, L. J., Zingsheim, M., Pham, K., Dillon, J., & Yi, Z. (2012). Site-specific phosphorylation of protein phosphatase 1 regulatory subunit 12A stimulated or suppressed by insulin. Journal of proteomics, 75(11), 3342-50.More infoProtein phosphatase 1 (PP1) is one of the major phosphatases responsible for protein dephosphorylation in eukaryotes. So far, only few specific phosphorylation sites of PP1 regulatory subunit 12A (PPP1R12A) have been shown to regulate the PP1 activity. The effect of insulin on PPP1R12A phosphorylation is largely unknown. Utilizing a mass spectrometry based phosphorylation identification and quantification approach, we identified 21 PPP1R12A phosphorylation sites (7 novel sites, including Ser20, Thr22, Thr453, Ser478, Thr671, Ser678, and Ser680) and quantified 16 of them under basal and insulin stimulated conditions in hamster ovary cells overexpressing the insulin receptor (CHO/IR), an insulin sensitive cell model. Insulin stimulated the phosphorylation of PPP1R12A significantly at Ser477, Ser478, Ser507, Ser668, and Ser695, while simultaneously suppressing the phosphorylation of PPP1R12A at Ser509 (more than 2-fold increase or decrease compared to basal). Our data demonstrate that PPP1R12A undergoes insulin stimulated/suppressed phosphorylation, suggesting that PPP1R12A phosphorylation may play a role in insulin signal transduction. The novel PPP1R12A phosphorylation sites as well as the new insulin-responsive phosphorylation sites of PPP1R12A in CHO/IR cells provide targets for investigation of the regulation of PPP1R12A and the PPP1R12A-PP1cδ complex in insulin action and other signaling pathways in other cell models, animal models, and humans.
- Luo, M., Mengos, A. E., Stubblefield, T. M., & Mandarino, L. J. (2012). High Fat Diet-Induced Changes in Hepatic Protein Abundance in Mice. Journal of Proteomics & Bioinformatics, 5(060-066), 7. doi:10.4172/jpb.1000214
- Zhang, X., Højlund, K., Luo, M., Meyer, C., Geetha, T., & Yi, Z. (2012). Novel tyrosine phosphorylation sites in rat skeletal muscle revealed by phosphopeptide enrichment and HPLC-ESI-MS/MS. Journal of proteomics, 75(13), 4017-26.More infoTyrosine phosphorylation plays a fundamental role in many cellular processes including differentiation, growth and insulin signaling. In insulin resistant muscle, aberrant tyrosine phosphorylation of several proteins has been detected. However, due to the low abundance of tyrosine phosphorylation (
- Everman, S., Yi, Z., Langlais, P., Mandarino, L. J., Luo, M., Roberts, C., & Katsanos, C. S. (2011). Reproducibility of an HPLC-ESI-MS/MS method for the measurement of stable-isotope enrichment of in vivo-labeled muscle ATP synthase beta subunit. PloS one, 6(10), e26171.More infoWe sought to evaluate the reproducibility of a liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based approach to measure the stable-isotope enrichment of in vivo-labeled muscle ATP synthase β subunit (β-F1-ATPase), a protein most directly involved in ATP production, and whose abundance is reduced under a variety of circumstances. Muscle was obtained from a rat infused with stable-isotope-labeled leucine. The muscle was homogenized, β-F1-ATPase immunoprecipitated, and the protein was resolved using 1D-SDS PAGE. Following trypsin digestion of the isolated protein, the resultant peptide mixtures were subjected to analysis by HPLC-ESI-MS/MS, which resulted in the detection of multiple β-F1-ATPase peptides. There were three β-F1-ATPase unique peptides with a leucine residue in the amino acid sequence, and which were detected with high intensity relative to other peptides and assigned with >95% probability to β-F1-ATPase. These peptides were specifically targeted for fragmentation to access their stable-isotope enrichment based on MS/MS peak areas calculated from extracted ion chromatographs for selected labeled and unlabeled fragment ions. Results showed best linearity (R(2) = 0.99) in the detection of MS/MS peak areas for both labeled and unlabeled fragment ions, over a wide range of amounts of injected protein, specifically for the β-F1-ATPase(134-143) peptide. Measured stable-isotope enrichment was highly reproducible for the β-F1-ATPase(134-143) peptide (CV = 2.9%). Further, using mixtures of synthetic labeled and unlabeled peptides we determined that there is an excellent linear relationship (R(2) = 0.99) between measured and predicted enrichment for percent enrichments ranging between 0.009% and 8.185% for the β-F1-ATPase(134-143) peptide. The described approach provides a reliable approach to measure the stable-isotope enrichment of in-vivo-labeled muscle β-F1-ATPase based on the determination of the enrichment of the β-F1-ATPase(134-143) peptide.
- Geetha, T., Langlais, P., Luo, M., Mapes, R., Lefort, N., Chen, S. C., Mandarino, L. J., & Yi, Z. (2011). Label-free proteomic identification of endogenous, insulin-stimulated interaction partners of insulin receptor substrate-1. Journal of the American Society for Mass Spectrometry, 22(3), 457-66.More infoProtein-protein interactions are key to most cellular processes. Tandem mass spectrometry (MS/MS)-based proteomics combined with co-immunoprecipitation (CO-IP) has emerged as a powerful approach for studying protein complexes. However, a majority of systematic proteomics studies on protein-protein interactions involve the use of protein overexpression and/or epitope-tagged bait proteins, which might affect binding stoichiometry and lead to higher false positives. Here, we report an application of a straightforward, label-free CO-IP-MS/MS method, without the use of protein overexpression or protein tags, to the investigation of changes in the abundance of endogenous proteins associated with a bait protein, which is in this case insulin receptor substrate-1 (IRS-1), under basal and insulin stimulated conditions. IRS-1 plays a central role in the insulin signaling cascade. Defects in the protein-protein interactions involving IRS-1 may lead to the development of insulin resistance and type 2 diabetes. HPLC-ESI-MS/MS analyses identified eleven novel endogenous insulin-stimulated IRS-1 interaction partners in L6 myotubes reproducibly, including proteins play an important role in protein dephosphorylation [protein phosphatase 1 regulatory subunit 12A, (PPP1R12A)], muscle contraction and actin cytoskeleton rearrangement, endoplasmic reticulum stress, and protein folding, as well as protein synthesis. This novel application of label-free CO-IP-MS/MS quantification to assess endogenous interaction partners of a specific protein will prove useful for understanding how various cell stimuli regulate insulin signal transduction.
- Langlais, P., Yi, Z., Finlayson, J., Luo, M., Mapes, R., De Filippis, E., Meyer, C., Plummer, E., Tongchinsub, P., Mattern, M., & Mandarino, L. J. (2011). Global IRS-1 phosphorylation analysis in insulin resistance. Diabetologia, 54(11), 2878-89.More infoIRS-1 serine phosphorylation is often elevated in insulin resistance models, but confirmation in vivo in humans is lacking. We therefore analysed IRS-1 phosphorylation in human muscle in vivo.
- Luo, M., Langlais, P., Yi, Z., Lefort, N., De Filippis, E. A., Hwang, H., Christ-Roberts, C. Y., & Mandarino, L. J. (2007). Phosphorylation of human insulin receptor substrate-1 at Serine 629 plays a positive role in insulin signaling. Endocrinology, 148(10), 4895-905.More infoThe function of insulin receptor substrate-1 (IRS-1) is regulated by both tyrosine and serine/threonine phosphorylation. Phosphorylation of some serine/threonine residues in IRS-1 dampens insulin signaling, whereas phosphorylation of other serine/threonine residues enhances insulin signaling. Phosphorylation of human IRS-1 at Ser(629) was increased by insulin in Chinese hamster ovary cells expressing the insulin receptor (1.26 +/- 0.09-fold; P < 0.05) and L6 cells (1.35 +/- 0.29-fold; P < 0.05) expressing human IRS-1. Sequence analysis surrounding Ser(629) revealed conformity to the consensus phosphorylation sequence recognized by Akt. Phosphorylation of IRS-1 at Ser(629) in cells was decreased upon treatment with either an Akt inhibitor or by coexpression with kinase dead Akt, whereas Ser(629) phosphorylation was increased by coexpression with constitutively active Akt. In addition, Ser(629) of IRS-1 is directly phosphorylated by Akt in vitro. In cells, preventing phosphorylation of Ser(629) by a Ser(629)Ala mutation resulted in increased phosphorylation of Ser(636), a known negative regulator of IRS-1, without affecting phosphorylation of Tyr(632) or Ser(616). Cells expressing the Ser(629)Ala mutation, along with increased Ser(636) phosphorylation, had decreased insulin-stimulated association of the p85 regulatory subunit of phosphatidylinositol 3'-kinase with IRS-1 and decreased phosphorylation of Akt at Ser(473). Finally, in vitro phosphorylation of a Ser(629)-containing IRS-1 fragment with Akt reduces the subsequent ability of ERK to phosphorylate Ser(636/639). These results suggest that a feed-forward mechanism may exist whereby insulin activation of Akt leads to phosphorylation of IRS-1 at Ser(629), resulting in decreased phosphorylation of IRS-1 at Ser(636) and enhanced downstream signaling. Understanding the complex phosphorylation patterns of IRS-1 is crucial to elucidating the factors contributing to insulin resistance and, ultimately, the pathogenesis of type 2 diabetes.
- Yi, Z., Langlais, P., De Filippis, E. A., Luo, M., Flynn, C. R., Schroeder, S., Weintraub, S. T., Mapes, R., & Mandarino, L. J. (2007). Global assessment of regulation of phosphorylation of insulin receptor substrate-1 by insulin in vivo in human muscle. Diabetes, 56(6), 1508-16.More infoResearch has focused on insulin receptor substrate (IRS)-1 as a locus for insulin resistance. Tyrosine phosphorylation of IRS-1 initiates insulin signaling, whereas serine/threonine phosphorylation alters the ability of IRS-1 to transduce the insulin signal. Of 1,242 amino acids in IRS-1, 242 are serine/threonine. Serine/threonine phosphorylation of IRS-1 is affected by many factors, including insulin. The purpose of this study was to perform global assessment of phosphorylation of serine/threonine residues in IRS-1 in vivo in humans.
- Yi, Z., Luo, M., Mandarino, L. J., Reyna, S. M., Carroll, C. A., & Weintraub, S. T. (2006). Quantification of phosphorylation of insulin receptor substrate-1 by HPLC-ESI-MS/MS. Journal of the American Society for Mass Spectrometry, 17(4), 562-7.More infoSerine/threonine phosphorylation of insulin receptor substrate-1 (IRS-1) regulates the function and subsequent insulin signaling of this protein. Human IRS-1 has 1242 amino acid residues, including 182 serines and 60 threonines. The size, complexity, and relatively low abundance of this protein in biological samples make it difficult to map and quantify phosphorylation sites by conventional means. A mass spectrometry peak area based quantification approach has been developed and applied to assess the relative abundance of IRS-1 phosphorylation in the absence or presence of stimuli. In this method, the peak area for a phosphopeptide of interest is normalized against the average of peak areas for six selected representative IRS-1 peptides that serve as endogenous internal standards. Relative quantification of each phosphopeptide is then obtained by comparing the normalized peak area ratios for untreated and treated samples. Two non-IRS-1 peptides were added to each digest for use as HPLC retention time markers and additional standards as well as references to the relative quantity of IRS-1 in different samples. This approach does not require isotopic or chemical labeling and can be applied to various cell lines and tissues. Using this method, we assessed the relative changes in the quantities of two tryptic phosphopeptides isolated from human IRS-1 expressed in L6 cells incubated in the absence or presence of insulin or tumor necrosis factor-alpha. Substantial increases of phosphorylation were observed for Thr(446) upon stimulation. In contrast, no obvious change in the level of phosphorylation was observed for Ser(1078). This mass spectrometry based strategy provides a powerful means to quantify changes in the relative phosphorylation of peptides in response to various stimuli in a complex, low-abundance protein.
- Luo, M., Reyna, S., Wang, L., Yi, Z., Carroll, C., Dong, L. Q., Langlais, P., Weintraub, S. T., & Mandarino, L. J. (2005). Identification of insulin receptor substrate 1 serine/threonine phosphorylation sites using mass spectrometry analysis: regulatory role of serine 1223. Endocrinology, 146(10), 4410-6.More infoInsulin receptor substrate 1 (IRS-1), an intracellular substrate of the insulin receptor tyrosine kinase, also is heavily phosphorylated on serine and threonine residues, and several serine phosphorylation sites alter the function of IRS-1. Because of the large number of serine/threonine residues, position-by-position analysis of these potential phosphorylation sites by mutagenesis is difficult. To circumvent this, we have employed matrix-assisted laser desorption/ionization time-of-flight and HPLC-electrospray ionization tandem mass spectrometry techniques to scan for serine and threonine residues that are phosphorylated in full-length human IRS-1 ectopically expressed in cells using an adenoviral vector. This approach revealed 12 phosphorylation sites on serine or threonine residues, 10 of which were novel sites. Seven of these sites were in proline-directed motifs, whereas five were in arginine-directed sites. Sequence inspection suggested that phosphorylation of Ser1223 might alter the interaction of IRS-1 with the protein tyrosine phosphatase Src homology domain 2 (SH2)-containing phosphatase-2 (SHP-2). Mutation of Ser1223 to alanine to prevent phosphorylation resulted in increased association of SHP-2 with IRS-1, decreased insulin-stimulated tyrosine phosphorylation of IRS-1 in CHO/IR cells, and decreased insulin-stimulated association of the p85 regulatory subunit of phosphatidylinositol-3-kinase with IRS-1. This mutation had no effect on association of IRS-1 with the insulin receptor. Sequence analysis showed the Ser1223 region to be widely conserved evolutionarily. These data suggest that phosphorylation of Ser1223 dampens association of IRS-1 with SHP-2, thereby increasing net insulin-stimulated tyrosine phosphorylation.
- Yi, Z., Luo, M., Carroll, C. A., Weintraub, S. T., & Mandarino, L. J. (2005). Identification of phosphorylation sites in insulin receptor substrate-1 by hypothesis-driven high-performance liquid chromatography-electrospray ionization tandem mass spectrometry. Analytical chemistry, 77(17), 5693-9.More infoSerine phosphorylation of insulin receptor substrate-1 (IRS-1) can regulate tyrosine phosphorylation of IRS-1 and subsequent insulin signaling. The 182 serine and 60 threonine residues in IRS-1 make position-by-position analysis of potential phosphorylation sites by mutagenesis difficult. Tandem mass spectrometry provides a more efficient way to identify phosphorylated residues in IRS-1. Toward this end, we overexpressed glutathione S-transferase-IRS-1 fusion proteins in E. coli and treated them in vitro with various kinases followed by identification of phosphorylation sites using high-performance liquid chromatography-electrospray ionization tandem mass spectrometry. Nine phosphorylation sites were detected in the tryptic digests of middle and C-terminal regions of IRS-1 treated with protein kinase A or extracellular signal-regulated kinase 2. Of these sites, five have not previously been detected by any method and provide novel candidates for identification in cells or in vivo.
- Guo, Y., Luo, M., & Lin, Z. (2002). Establishment of Immune Insulin Resistance Model in Rat Induced by iv BCG. Acta Pharmaceutica Sinica, 37(321-325), 6.
- Luo, M., Guo, Y., & Lin, Z. (1999). Euglycemic Clamp Technique in Rats. Acta Pharmaceutica Sinica, 34(255-259), 5.