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Kinetically differentiated post‐translational modifications in a transcription factor, Bcl11b

Bcl11b is a highly modified transcription factor that is required for T cell development. Stimulation of primary thymocytes through the MAP kinase pathways leads to a series of post‐translational modifications of Bcl11b that ultimately alter its function from a repressor to a derepressor of a model target gene. These modifications include hyperphosphorylation and desumoylation at 5 min, significant dephosphorylation at 30 min and then subsequent resumoylation at 60 min, followed ultimately by ubiquitination‐mediated degradation at 4 to 8 hours. We sought to define the sites of Bcl11b phosphorylation and sumoylation to better understand the role of these modifications in integrating the signals from extracellular stimulation into alterations of the gene network in developing thymocytes. We identified 23 sites of phosphorylation and one site of sumoylation by mass spectrometry analysis. We identified a second sumoylation site by site‐directed mutagenesis. For the phosphorylation sites, we have begun to define the kinetics of each site following thymocyte stimulation. Thus far, four distinct kinetic patterns are observed among the 23 sites. Further, we have found differential association of the activated ERK kinase and PP6 phosphatase subunits in complex with Bcl11b. (This work was supported by the NIH, grant R15 GM096243, and the OSU College of Pharmacy.)