p70 S6 kinase and actin dynamics: A perspective.

p70 S6 kinase (p70(S6K)), a member of the AGC serine/threonine kinase family, was initially identified as a key player, together with its downstream effector S6, in the regulation of cellular growth and survival. The p70(S6K) protein has emerged in recent years as a multifunctional protein which also regulates the actin cytoskeleton and thus plays a role in cell migration. This new function is through two important activities of p70(S6K), namely actin cross-linking and Rac1 and Cdc42 activation. The testis is critically dependent on an intricate balance of fundamental cellular processes such as adhesion, migration, and differentiation. It is increasingly evident that Rho GTPases and actin binding proteins play fundamental roles in regulating spermatogenesis within the testis. In this review, we will discuss current findings of p70(S6K) in the control of actin cytoskeleton dynamics. In addition, the potential role of p70(S6K) in spermatogenesis and testicular function will be highlighted.