Tumor-promoting Phorbol Ester and Activated Ha-ras Synergistically Reduce the Interleukin 3 Requirement in a Mast Cell Line1

Infection of the bone marrow-derived mast cell line PB-3c with a retrovirus carrying oncogenic c-Ha-rai or v-Ha-ras reduced the interleukin 3 (IL-3) growth requirement and induced a state of tumorigenicity. In contrast, normal c-Ha-ruîhad no effect on the IL-3 requirement of this cell line nor did the cells become tumorigenic. A factor reduction similar to that caused by activated lin-ras was transiently obtained with 12-0-tetradecanoylphorbol-13-acetate in the PB-3c cells expressing nor mal c-Ha-ras. The analogous stimulation of protein kinase C (PKC) in PB-3c cells producing oncogenic I l:i-i-«.v led to an additional reduction of the IL-3 requirement during the first 24 h. In the absence of IL-3, the prolonged exposure of the cells to 12-CMetradecanoylphorbol-13-acetate for 72 h resulted in a stimulation of growth when activated but not when normal Uà -ras was expressed. PB-3c cell lines expressing activated Ha ras neither revealed differences in the amounts nor in the subcellular distribution of PKC activity but displayed elevated levels of immunoreactive ß-PKCcompared to the parental PB-3c cells. Upon 12-O-tetradecanoylphorbol-13-acetate treatment, a protracted down-regulation of the immunodetectable a-PKC as well as constitutive!}' high levels of cfos mRNA were observed when oncogenic Ha-ras was expressed. These data suggest the involvement of specific PKC subtypes and ofc-fos in the reduction of the IL-3 requirement caused by activated Ha-ras in this particular hematopoietic cell line.