RELATIONSHIP BETWEEN MULTIPLE BIOLOGIC EFFECTS OF RAPAMYCIN AND THE INHIBITION OF PP70S6 PROTEIN-KINASE ACTIVITY - ANALYSIS IN MUTANT CLONES OF A T-CELL LYMPHOMA

Rapamycin (RAP) inhibits several biologic responses in the YAC-1 T cel l lymphoma, including the serum-driven proliferation and cyclin A mRNA expression, the induction of Ly-6E Ag expression by IFN, and the indu ction of IFN-gamma production by IL-1. RAP also suppresses the enzymat ic activity of the 70 kDa S6 protein kinase (pp70s6k). To define the m echanistic relationship between these multiple effects of RAP, we have generated stable somatic mutants with altered sensitivities to this d rug. A first series of mutants, represented by the R19, 4R16, and 10R1 3 clones, showed markedly reduced sensitivity to the inhibitory effect of RAP on all biologic responses tested and on pp70s6k activity. Two other mutant types, R103 and R125, were both highly sensitive to RAP-m ediated suppression of proliferation, of IL-1-induced IFN-gamma produc tion, and of pp70s6k activity but differed in their Ly-6E response. Th is response was not affected by RAP in the R125 clone and was enhanced in the R103 clone. Therefore, the inhibitory effects of RAP on prolif eration and IL-1-mediated IFN-gamma induction both appear associated w ith the inhibition of pp70s6k activity, whereas the modulation of Ly-6 E induction is independent from the latter. Moreover, the cellular bin ding of [H-3]dihydro-FK-506 was found to be blocked by RAP in all muta nt types to the same extent as in wild-type YAC-1 cells, suggesting th at the altered sensitivity to the effects of RAP in these mutants is n ot due to an inability of the drug to enter the cells or to interact w ith FKBP. Further biochemical characterization of the mutant cells des cribed here is expected to help clarify the mechanisms of RAP action.