Role for c-Abl and p73 in the radiation response of male germ cells

p53 plays a central role in the induction of apoptosis of spermatogonia in response to ionizing radiation. In p53(-/) testes, however, spermatogonial apoptosis still can be induced by ionizing radiation, so p53 independent ap optotic pathways must exist in spermatogonia, Here we show that the p53 hom ologues p63 and p73 are present in the testis and that p73, but not p63, is localized in the cytoplasm of spermatogonia, Unlike p53, neither p63 nor p 73 protein levels were found to increase after a dose of 4 Gy of X-rays, Al though p73 protein levels did not increase, its interaction with the nonrec eptor tyrosine kinase c-Abl and its phosphorylation on tyrosine residues di d. c-Abl and p73 co-localize in the cytoplasm of spermatogonia and spermato cytes and in the residual bodies. Furthermore, c-Abl protein levels increas e after irradiation. p63 was not found to colocalize or interact with c-Abl neither before nor after irradiation. In conclusion, in the testis ionizin g radiation elevates cytoplasmic c-Abl that in turn interacts with p73, Thi s may represent an additional, cytoplasmic, apoptotic pathway. Although les s efficient than the p53 route, this pathway may cause spermatogonial apopt osis as observed in p53 deficient mice.