HPK1, a KHS protein kinase, is an upstream activator of the stress-activated protein kinase (SAPK) signaling pathway. The protein has a structure similar to other GCK (Group I) kinases and contains four consensus SH3 binding motifs, which have been shown to interact with the SH3 motifs of the MAP kinase kinase kinases MLK3 and MEKK1 and several adapter proteins that couple to tyrosine kinases, including BASH, Blnk, Clnk, Crk, CrkL and Grb2. Additionally, HPK1 has been shown to be phosphorylated and activated by the tyrosine kinase c-Abl in response to genotoxic agents. At least two mRNA transcripts have been reported.Synonyms: HPK1, Hematopoietic progenitor kinase, MAPK/ERK kinase kinase kinase 1, MEKKK 1, Mitogen-activated protein kinase kinase kinase kinase 1