A retinoblastoma susceptibility gene product, RB, targeting protease is regulated through the cell cycle

Degradation of cyclin B and ;cyclin-dependent kinase inhibitor, p27, at a specific time has been shown to play a critical role in regulating the cell cycle, SPase, a nuclear and cytosol protease with cathepsin B-and L-like proteolytic activity, has been identified in several cell lines, This proteolytic enzyme selectively degraded nuclear proteins such as retinoblastoma susceptibility gene product, RE, and transcription factor, SP-1., High levels of SPase activity were detected at the G(1)/S, moderate levels at the G(1) and S phases, and undetectable activity at the M phase of synchronized CV-1 cells, suggesting that SPase activity is regulated through the cell cycle, Degradation of RE correlated with SPase activity throughout the cell cycle, suggesting that SPase regulates RE, which has a functional role in regulating cell cycle, These results demonstrated that SPase plays an integral role in regulating the nuclear regulator, RE, in controlling cell cycle progression, (C) 1998 Federation of European Biochemical Societies.