Specific association of a set of molecular chaperones including HSP90 and Cdc37 with MOK, a member of the mitogen-activated protein kinase superfamily

We have recently identified and cloned a novel member of mitogen-activated protein kinase superfamily protein, MOK (Miyata, Y,, Akashi, M,, and Nishid a, E, (1999) Genes Cells 4, 299-309), To address its regulatory mechanisms, we searched for cellular proteins that specifically associate with MOK by co-immunoprecipitation experiments. Several cellular proteins including a m ajor 90-kDa molecular chaperone HSP90 were found associated with MOK, Treat ment of cells with geldanamycin, an HSP90-specific inhibitor, rapidly decre ased the protein level of MOK, and the decrease was attributed to enhanced degradation of MOK through proteasome-dependent pathways. Our data suggest that the association with HSP90 may regulate intracellular protein stabilit y and solubility of MOK, Experiments with a series of deletion mutants of M OK indicated that the region encompassing the protein kinase catalytic subd omains I-IV is required for HSP90 binding. Closely related protein kinases (male germ cell-associated kinase and male germ cell-associated kinase-rela ted kinase) were also found to associate with HSP90, whereas conventional m itogen-activated protein kinases (extracellular signal-regulated kinase, p3 8, and c-Jun N-terminal kinase/ stress-activated protein kinase) were not a ssociated with HSP90. In addition, we found that other molecular chaperones including Cdc37, HSC70, HSP70, and HSP60 but not GRP94, FKBP52, or Hop wer e detected specifically in the MOK-HSP90 immunocomplexes. These results tak en together suggest a role of at specific set of molecular chaperones in th e stability of signal-transducing protein kinases.