The role of protein kinase C (PKC)-α in endothelin-1 (ET-1)-induced proliferation of human myometrial cells was investigated. Inhibition of conventional PKC with Gö 6976 eliminated the proliferative effect of ET-1. Treatment of myometrial cells with an antisense oligonucleotide against PKCα efficiently reduced PKCα protein expression without effect on other PKC isoforms and resulted in the loss of ET-1-induced cell growth. Immunocytochemistry using an antibody against PKCα revealed that there was no PKCα immunoreactivity in the nuclei of quiescent nonconfluent untreated cells, whereas it is evenly distributed throughout the cytoplasm. Exposure of myometrial cells to ET-1 for 15 min caused the PKCα to shift towards the perinuclear area, and incubation for 60 min caused a shift towards the nucleus. These results reveal that PKCα is required for ET-1-induced human myometrial cell growth and suggest that targeting of PKCα by antisense nucleotides might be an important approach for the development of anticancer treatments.