Polyamine analogue induction of the p53-p21(WAF1/CIP1)-Rb pathway and G₁ Ar in human melanoma cells

Although polyamines are well recognized for their critical involvement in cell growth, the cell cycle specificity of this requirement has not yet been characterized with respect to the newly delineated regulatory pathways. We recently reported that polyamine analogues having close structural and functional similarities to the natural polyamines produce a distinct G₁ and G₂-M cell arrest in MALME-3M human melanoma cells. To determine a molecular basis for this observation, we examined the effects of N¹,N¹¹- diethylnorspermine on cell cycle regulatory proteins associated with G₁ arrest. The analogue is known to deplete polyamine pools by suppressing biosynthetic enzymes and potently inducing the polyamine catabolic enzyme spermidine/spermine N¹-acetyltransferase. Treatment of MALME-3M cells with 10 μM N¹,N¹¹-diethylnorspermine caused an increase in hypophosphorylated Rb, which correlated temporally with the onset of G₁ arrest of 16-24 h. Rb hypophosphorylation was preceded by an increase in wild-type p53 (~10-fold at maximum) and a concomitant increase in the cyclin-dependent kinase inhibitor, p21(WAF1/CIP1) (p21; ~5-fold at maximum). Another cyclin- dependent kinase inhibitor, p27(KIP1), and cyclin D1 increased slightly, whereas proliferating cell nuclear antigen and p130 remained unchanged. Induction of p21 protein was accompanied by an increase in p21 mRNA, whereas induction of p53 protein was not, suggesting transcriptional activation of the former and posttranscriptional regulation of the latter. SK-MEL-28 human melanoma cells, which contain a mutated p53, failed to induce p53 or p21 and did not arrest in G₁. Rather, these cells rapidly underwent programmed cell death within 48 h. Overall, these findings provide the first indication of the cell cycle regulatory pathways by which polyamine antagonists such as analogues might inhibit growth in cells containing wild-type p53 and further suggest a mechanistic basis for differential cellular responses to these agents.