Cofilin phosphorylation and actin reorganization activities of testicular protein kinase 2 and its predominant expression in testicular Sertoli cells

We previously identified testicular protein kinase 1 (TESK1), which phospho rylates cofilin and induces actin cytoskeletal reorganization. We now repor t identification and characterization of another member of a TESK family, t esticular protein kinase 2 (TESK2), with 48% amino acid identity with TESK1 . Like TESK1, TESK2 phosphorylated cofilin specifically at Ser-3 and induce d formation of actin stress fibers and focal adhesions. Both TESK1 and TESK 2 are highly expressed in the testis, but in contrast to TESK1, which is pr edominantly expressed in testicular germ cells, TESK2 is expressed predomin antly in nongerminal Sertoli cells. Thus, TESK1 and TESK2 seem to play dist inct roles in spermatogenesis. In HeLa cells, TESK1 was localized mainly in the cytoplasm, whereas TESK2 was localized mainly in the nucleus, which me ans that TESK1 and TESK2 likely have distinct cellular functions. Because t he kinase-inactive mutant of TESK2 was localized in the cytoplasm, nuclear/ cytoplasmic localization of TESK2 depends on its kinase activity. A TESK2 m utant lacking the C-terminal noncatalytic region had about a 10-fold higher kinase activity in vitro and, when expressed in HeLa cells, induced puncta te actin aggregates in the cytoplasm and unusual condensation and fragmenta tion of nuclei, followed by apoptosis. Thus, we propose that the C-terminal region plays important roles in regulating the kinase activity and cellula r functions of TESK2.