Regulation of cell adhesion by PP2A and SV40 small tumor antigen: an important link to cell transformation.

The serine/threonine protein phosphatase 2A (PP2A) represents a large family of highly conserved heterotrimeric enzymes. Their critical importance in cell homeostasis is underlined by the fact that they are targets of natural toxins like the tumor promoter okadaic acid, and of simian virus 40 small tumor antigen (SV40 small t), a viral protein known to promote cell transformation. Furthermore, mutated or lower expression levels of PP2A subunits have been found in certain cancers. One major known event in PP2A-dependent cell transformation is the alteration of key signaling pathways that control cell growth and survival. In this review, we focus on how PP2A enzymes also affect cell adhesion and cytoskeletal dynamics, the disruption of which is linked to loss of cell polarity, increased cell motility and invasiveness. We also examine how those various pathways participate in the transforming activity of SV40 small t.