Cycling in Switzerland

Abstract

Progression through the cell cycle is mediated by the sequential activation of a number of cyclins that form active kinase complexes when bound to one of several cyclin-dependent kinases (CDKs). In GI, these kinases phosphorylate, amongst others, the retinoblastoma protein, which, when phosphorylated, releases the E2F transcription factor, which, in turn, drives cells into S phase. CDKs can be negatively regulated by CKIs (cyclin-dependent kinase inhibitors), which also come in several flavors. Thus, cell-cycle-control proteins either promote division (such as the cyclins, CDKs and E2Fs) or inhibit cell cycling (RB and CKIs). In this relatively simple view of the cell-cycle world, the former are potential oncogenes, the latter are possible tumor suppressors.