Promotion of cathepsin L activity in newt spermatogonial apoptosis induced by prolactin.

We previously showed that prolactin (PRL) induces apoptosis in newt secondary spermatogonia and indicated that caspase activity is involved in the apoptosis. Since it was recently reported that Z-VAD-fmk, a pan-caspase inhibitor, blocks activity of cysteine cathepsins as well, we examined whether cathepsin is involved in the newt spermatogonial apoptosis. We found cathepsin L activity in the testis that was elevated by PRL in organ culture of testis, while E-64d, a lysosomal cysteine protease inhibitor, and Z-VAD-fmk suppressed it and chromosomal condensation. These results suggest that cathepsin L activity play a pivotal role in PRL-induced spermatogonial apoptosis.