Gossypol-induced apoptotic DNA fragmentation correlates with inhibited protein kinase C activity in spermatocytes.

After exposure of cultured rat spermatocytes to gossypol acetic acid for five hours, DNA fragmentation in a ladder pattern was found in the medium and supernatants of cell lysates. The concentrations of gossypol used for the induction of apoptosis ranged from 100 microM to 300 microM. Within this dose range, gossypol was also found to be effective at inhibiting protein kinase C (PKC) activity. This inhibitory effect was demonstrated by measuring the PKC residing in cytosolic and particulate fractions. However, the gossypol-induced inhibition of PKC activity was protected by phorbol 12,13-dibutyrate (PDBu), an activator of PKC. Furthermore, the presence of PDBu prevented gossypol-induced DNA fragmentation. These results suggest that spermatocyte apoptosis induced by gossypol is correlated with the reduction of PKC activity, and that maintenance of PKC basal activity is essential for protecting the spermatocyte from apoptosis.