PURPOSE: This study was designed to find out whether protein kinase C (PKC) may affect telomerase activity in human ovarian cancers. MATERIALS AND METHODS: To determine whether PKC modulators influence PKC activities, NIH: OVCAR-3 and CUMO-2, cells were treated with PKC inhibitors, G 6976 and bisindolyl maleimide I, and PKC activator, 12-O-tetradecanoyl phorbol 13-acetate (TPA). Telomerase acti vity was determined by telomeric repeat amplification protocol (TRAP). Analysis of the expres sion of each telomerase subunits, human telomerase RNA (hTR) and human telomerase reverse transcriptase (hTERT), was performed by RT-PCR. We also examined the alternative splicing of hTERT. RESULTS: G 6976 and bisindolylmaleimide I inhibited PKC activity. Telomerase activities appeared to be affected in a time-dependent manner by these two PKC inhibitors. PKC activities were increased in parallel with telomerase activity by TPA at the low dose (10 nM), but their activities were down-regulated at the high dose (1 micrometer). RT-PCR demonstrated the presence of hTR and hTERT mRNA before and after the treatment of PKC modulators, respectively, and showed the presence of one alternatively spliced transcript and full-length hTERT transcripts. CONCLUSION: These results showed that telomerase activity was affected by PKC and suggested PKC modulation may serve as an useful tool in the regulation of telomerase activity.