Hematopoietic progenitor kinase 1 associates physically and functionally with the adaptor proteins B cell linker protein and SLP-76 in lymphocytes

B cell linker protein (BLNK) is a SLP-76-related adaptor protein essential for signal transduction from the BCR. To identify components of BLNK-associ ated signaling pathways, we performed a phosphorylation-dependent yeast two -hybrid analysis using BLNK probes. Here we report that the serine/threonin e kinase hematopoietic progenitor kinase 1 (HPK1), which is activated upon antigen-receptor stimulation and which has been implicated in the regulatio n of MAP kinase pathways, interacts physically and functionally with BLNK i n B cells and with SLP-76 in T cells. This interaction requires Tyr(379) of HPK1 and the Src homology 2 (SH2) domain of BLNK/SLP-76. Via homology mode ling, we defined a consensus binding site within ligands for SLP family SH2 domains. We further demonstrate that the SH2 domain of SLP-76 participates in the regulation of AP-1 and NFAT activation in response to T cell recept or (TCR) stimulation and that HPK1 inhibits AP-1 activation in a manner par tially dependent on its interaction with SLP-76. Our data are consistent wi th a model in which full activation of HPK1 requires its own phosphorylatio n on tyrosine and subsequent interaction with adaptors of the SLP family, p roviding a mechanistic basis for the integration of this kinase into antige n receptor signaling cascades.