H-, K- and N-Ras inhibit myeloid leukemia cell proliferation by a p21^WAF1-dependent mechanism

Abstract

Mutated ras genes are frequently found in human cancer. However, it has been shown that oncogenic ras inhibits growth of primary cells, through pathways involving p53 and the cell cycle inhibitors p16^INK4a and p19^ARF. We have analysed the effect of the ectopic expression of the three mammalian ras genes on the proliferation of K562 leukemia cells, which are deficient for p53, p16^INK4a, p15^INK4b and p19^ARF genes. We have found that high expression levels of both wild-type and oncogenic H-, K- and N-ras inhibit the clonogenic growth of K562 cells. Induction of H-rasV12 expression in K562 transfectants retards growth and this effect is accompanied with an increase of p21^WAF1 mRNA and protein levels. Furthermore, p21^WAF1 promoter is activated potently by oncogenic ras and less pronounced by wild-type ras. This induction is p53-independent since a p21^WAF1 promoter devoid of the p53 responsive elements is still activated by Ras. Finally, inhibition of p21^WAF1 expression by an antisense construct partially overcomes the growth inhibitory action of oncogenic H-ras. Altogether, these results indicate that the antiproliferative effect of ras in myeloid leukemia cells is associated to the induction of p21^WAF1 expression and suggest the existence of p19^ARF and p16^INK4a-independent pathways for ras-mediated growth inhibition.