Role of tyrosine phosphorylation in radiation-induced activation of c-jun protooncogene in human lymphohematopoietic precursor cells.

We examined the effects of ionizing radiation on c-jun expression in human lymphohematopoietic precursors. Radiation exposure increased the level of c-jun transcripts in a dose- and time-dependent manner, providing direct evidence that ionizing radiation can activate c-jun protooncogene in human lymphohematopoietic precursors. Notable gamma-rays failed to induce c-jun expression in cells pretreated with herbimycin, and the use of cycloheximide did not overcome the inhibitory effects of herbimycin. The lack of c-jun signal in herbimycin-treated cells was not due to nonspecific damage to the distal protein kinase C signaling pathway. Thus, protein tyrosine kinase activation precedes and perhaps mandates radiation-induced activation of c-jun protooncogene expression in human lymphohematopoietic precursors.