Bruton's Tyrosine Kinase Phosphorylates cAMP-responsive Element-binding Protein at Serine 133 during Neuronal Differentiation in Immortalized Hippocampal Progenitor Cells

Bruton's tyrosine kinase (BTK) is a member of the Tec family of kinases, which is a subgroup of the nonreceptor cytoplasmic protein tyrosine kinases. BTK has been shown to be important in the proliferation, differentiation, and signal transduction of B cells. Mutations in BTK result in B cell immune deficiency disorders, such as X-linked agammaglobulinemia in humans and X-linked immunodeficiency in mice. Although BTK plays multiple roles in the life of a B cell, its functional role in neuronal cells has not been elucidated. In the present study, we demonstrate that BTK activates transcription factor, cAMP response element (CRE)-binding protein (CREB), and subsequent CRE-mediated gene transcription during basic fibroblast growth factor (bFGF)-induced neuronal differentiation in immortalized hippocampal progenitor cells (H19-7). The kinase activity of BTK is also induced by bFGF, and BTK directly phosphorylates CREB at Ser-133 residue, indicating that BTK has a dual protein kinase activity. In addition, blockading BTK activation significantly inhibits CREB phosphorylation as well as the neurite outgrowth induced by bFGF in H19-7 cells. These results suggest that the activation of BTK and the subsequent phosphorylation of CREB at Ser-133 are important in the neuronal differentiation of hippocampal progenitor cells.