Hematopoietic lineage cell specific protein 1 associates with and down-regulates protein kinase CK2

The catalytic (alpha) subunit of protein kinase CK2 and the hematopoietic s pecific protein 1 (HS1) display opposite effects on Ha-ras induced fibrobla st transformation, by enhancing and counteracting it, respectively. Here me show the occurrence of physical association between HS1 and CK2 alpha as j udged from both far Western blot and plasmon resonance (BIAcore) analysis. Association of HS1 with CK2a is drastically reduced by the deletion of the HS1 C-terminal region (403-486) containing an SH3 domain. HS1, but not its deletion mutant HS1 Delta 324-393, lacking a sequence similar to an acidic stretch of the regulatory B-subunit of CK2, inhibits calmodulin phosphoryla tion by CK2a. These data indicate that HS1 physically interacts with CK2a a nd down-regulates its activity by a mechanism similar to the P-subunit. (C) 1999 Federation of European Biochemical Societies.