Contribution of protein kinase C to ET-1-induced proliferation in human myometrial cells

The role of protein kinase C (PKC) in endothelin-1 (ET-l)-induced prolifera tion of human myometrial cells was investigated. ET-1 dose dependently stim ulated DNA synthesis and the number of cultured myometrial cells. Inhibitio n of PKC by calphostin C or Ro-31-8220 or downregulation of PKC eliminated the proliferative effects of ET-I. The failure of two protein tyrosine kina se (PTK) inhibitors (tyrphostin 51 and tyrphostin 23) to affect ET-l-induce d proliferation supports the hypothesis of noninvolvement-of the tyrosine k inase signaling pathway in this process. The expression and distribution of PKC isoforms were examined by Western blot analysis. The five PKC isoforms (PKC-alpha, -beta(1), -beta(2), -zeta; -epsilon) evidenced in human myomet rial tissue were found to be differentially expressed in myometrial cells, with a predominant expression of PKC-alpha and PKC-zeta. Treatment with pho rbol 12,13-dibutyrate (PDBu) resulted in the translocation of all five isof orms to the particulate fraction, whereas ET-1 induced a selective increase in particulate PKC-beta(1), PKC-beta(2), and PKC-epsilon. Our findings tha t multiple PKC isoforms are differentially responsive to ET-1 or PDBu sugge st that they play distinct roles in the myometrial growth process.