Speedy/RINGO regulation of CDKs in cell cycle, checkpoint activation and apoptosis.

Speedy/RINGO family members bind and activate cyclin dependent kinases (CDKs), although these proteins have no homology to known cyclin proteins. Members of this family are required for and enhance meiotic maturation, in addition to having novel roles in regulating the mitotic mammalian cell cycle and the DNA damage response. Here we discuss how the specialized functions of these proteins differ from classical cyclin-mediated activation of CDKs. Through atypical activation of CDKs, bypass of conventional inhibitory mechanisms, and unique substrate selection, Speedy/RINGO proteins contribute to cell cycle, checkpoint, and apoptotic regulation. Furthermore, we address the recently established correlation between Spy1 and cancer in terms of the specialized functions of the Speedy/RINGO family.