Protein turnover in relation to growth status and the cell cycle in cultured mammalian cells

Protein turnover during cell growth can be extensive. It is by no means proven that, as a result of accelerated growth, protein degradation declines. Indeed, it is argued that in absolute terms it will almost certainly increase. The question, however, is raised as to what regulates changes in growth rate, irrespective of whether it operates primarily through effects on protein synthesis or on protein degradation. Although "growth factors" can entrain cells into cycle, the fundamental problem within the cell is how does this lead to integration and insertion of new material as growth. It is argued that the forces which stabilize or destabilize "structures" (any functional association of molecules) have still to be appreciated and their controls understood. Degradation is in general seen as a passive rather than an active ongoing process, whose level of activity is governed by the degree to which structures are destabilized and their proteins render at greater risk to proteolysis.