Dissection of the insulin signaling pathway via quantitative phosphoproteomics

The insulin signaling pathway is of pivotal importance in metabolic diseases, such as diabetes, and in cellular processes, such as aging. Insulin activates a tyrosine phosphorylation cascade that branches to create a complex network affecting multiple biological processes. To understand the full spectrum of the tyrosine phosphorylation cascade, we have defined the tyrosine-phosphoproteome of the insulin signaling pathway, using high resolution mass spectrometry in combination with phosphotyrosine immunoprecipitation and stable isotope labeling by amino acids in cell culture (SILAC) in differentiated brown adipocytes. Of 40 identified insulin-induced effectors, 7 have not previously been described in insulin signaling, including SDR, PKC delta binding protein, LRP-6, and PISP/PDZK11, a potential calcium ATPase binding protein. A proteomic interaction screen with PISP/PDZK11 identified the calcium transporting ATPase SERCA2, supporting a connection to calcium signaling. The combination of quantitative phosphoproteomics with cell culture models provides a powerful strategy to dissect the insulin signaling pathways in intact cells.