Quantitative Phosphoproteomics Revealed Glucose-Stimulated Responses of Islet Associated with Insulin Secretion

As central tissue of glucose homeostasis, islet has been an important focus of diabetes research. Phosphorylation plays pivotal roles in islet function, especially in islet glucose-stimulated insulin secretion. A systematic view on how phosphorylation networks were coordinately regulated in this process remains lacking, partially due to the limited amount of islets from an individual for a phosphoproteomic analysis. Here we optimized the in-tip and best-ratio phosphopeptide enrichment strategy and a SILAC-based workflow for processing rat islet samples. With limited islet lysates from each individual rat (20-47 mu g), we identified 8539 phosphosites on 2487 proteins. Subsequent quantitative analyses uncovered that short-term (30 min) high glucose stimulation induced coordinate responses of islet phosphoproteome on multiple biological levels, including insulin secretion related pathways, cytoskeleton dynamics, protein processing in ER and Golgi, transcription and translation, and so on. Furthermore, three glucose-responsive phosphosites (Prkar1a pT75pS77 and Tagln2 pS163) from the data set were proved to be correlated with insulin secretion. Overall, we initially gave an in-depth map of islet phosphoproteome regulated by glucose on individual rat level. This was a significant addition to our knowledge about how phosphorylation networks responded in insulin secretion. Also, the list of changed phosphosites was a valuable resource for molecular researchers in diabetes field.