phosphothreonine and Lymphoma--B-Cell

The MYC proto-oncogene is a transcription factor implicated in a broad range of cancers. MYC is regulated by several post-translational modifications including SUMOylation, but the functional impact of this post-translational modification is still unclear. Here, we report that the SUMO E3 ligase PIAS1 SUMOylates MYC. We demonstrate that PIAS1 promotes, in a SUMOylation-dependent manner, MYC phosphorylation at serine 62 and dephosphorylation at threonine 58. These events reduce the MYC turnover, leading to increased transcriptional activity. Furthermore, we find that MYC is SUMOylated in primary B cell lymphomas and that PIAS1 is required for the viability of MYC-dependent B cell lymphoma cells as well as several cancer cell lines of epithelial origin. Finally, Pias1-null mice display endothelial defects reminiscent of Myc-null mice. Taken together, these results indicate that PIAS1 is a positive regulator of MYC.

Topics: Animals; Carcinogenesis; Cell Line; Cell Proliferation; Cell Survival; Gene Expression Regulation, Neoplastic; Half-Life; Humans; Lymphoma, B-Cell; Mice; Phosphorylation; Phosphothreonine; Protein Binding; Protein Inhibitors of Activated STAT; Proteolysis; Proto-Oncogene Mas; Proto-Oncogene Proteins c-myc; Sumoylation; Transcription, Genetic; Up-Regulation

A major goal of the Alliance for Cellular Signaling is to elaborate the components of signal transduction networks in model cell systems, including murine B lymphocytes. Due to the importance of protein phosphorylation in many aspects of cell signaling, the initial efforts have focused on the identification of phosphorylated proteins. In order to identify serine- and threonine-phosphorylated proteins on a proteome-wide basis, WEHI-231 cells were treated with calyculin A, a serine/threonine phosphatase inhibitor, to induce high levels of protein phosphorylation. Proteins were extracted from whole-cell lysates and digested with trypsin. Phosphorylated peptides were then enriched using immobilized metal affinity chromatography and identified by liquid chromatography-tandem mass spectrometry. A total of 107 proteins and 193 phosphorylation sites were identified using these methods. Forty-two of these proteins have been reported to be phosphorylated, but only some of them have been detected in B cells. Fifty-four of the identified proteins were not previously known to be phosphorylated. The remaining 11 phosphoproteins have previously only been characterized as novel cDNA or genomic sequences. Many of the identified proteins were phosphorylated at multiple sites. The proteins identified in this study significantly expand the repertoire of proteins known to be phosphorylated in B cells. The number of newly identified phosphoproteins indicates that B cell signaling pathways utilizing protein phosphorylation are likely to be more complex than previously appreciated.

Topics: Animals; Cell Line; Chromatography, Affinity; Chromatography, Liquid; Enzyme Inhibitors; Lymphoma, B-Cell; Marine Toxins; Mice; Oxazoles; Peptide Fragments; Phosphoproteins; Phosphoric Monoester Hydrolases; Phosphorylation; Phosphoserine; Phosphothreonine; Proteomics; Signal Transduction; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization