Alteration of Bcl11b upon stimulation of both MAP Kinase- and Gsk3-dependent signaling pathways in double negative thymocytes.

Bcl11b is a transcription factor critical for thymocyte development. We previously characterized the kinetic post-translational modifications (PTMs) of Bcl11b in double positive (DP) thymocytes during stimulation of the T cell receptor-activated MAP kinase pathway. However, the PTMs of Bcl11b in thymocytes from other developmental stages in the thymus, primarily double negative (DN) cells, have not been previously identified. We found that kinetic modifications of Bcl11b in DN cells are somewhat different than the patterns observed in DP cells. Distinct from DP thymocytes, phosphorylation and sumoylation of Bcl11b in DN cells were not oppositely regulated in response to activation of MAP kinase, even though hyper-phosphorylation of Bcl11b coincided with near complete desumoylation. Additionally, prolonged stimulation of the MAP kinase pathway in DN cells, unlike DP thymocytes, did not alter Bcl11b levels of sumoylation or ubiquitinylation, or stability. On the other hand, activation of Wnt/Gsk3-dependent signaling in DN cells resulted in composite dephosphorylation and sumoylation of Bcl11b. Moreover, stimulation of MAP kinase and/or Wnt signaling pathways differentially affects gene expression of some Bcl11b target and maturation- associated genes. Defining the signaling pathways and regulation of sequence-specific transcription factors (SSTFs) by PTMs at various stages of thymopoiesis may improve our understanding of leukemogenesis.