Mitogen Activated Protein Kinase Kinase Kinase Kinase 1 (MAP4K1)

Using a subtractive hybridization between a mouse cDNA granulocyte-macrophage progenitor and an erythrocyte megakaryocyte progenitor, Hu et al. (1996) identified a human hematopoietic serine/threonine protein kinase that they called hematopoietic progenitor kinase-1, or HPK1.

The authors detected 2 major distinct HPK1 transcripts (2.8 kb and 6.0 kb) primarily in hematopoietic organs, such as bone marrow and fetal liver. HPK1 encodes an 833-amino acid polypeptide with a predicted molecular weight of 90 kD and an actual weight of 97 kD. HPK1 is distantly related to the p21/Cdc42/Rac1-activated kinase (PAK) and yeast STE20 implicated in the mitogen-activated protein kinase (MAPK) cascade.