FIG. 5.

An integrin α2 cytoplasmic tail is needed for activation of a serine/threonine phosphatase PP2A. Saos-α2 and Saos-α2/α1 cells were serum starved, detached, and cultured inside collagen for 1.5 h (A and B) or cultured on fibronectin (C). Measurement of PP1-PP2A phosphatase activity was done from cell lysates using ³²P-labeled glycogen phosphorylase as a substrate. Two different Saos-α2 and Saos-α2/α1 single-cell clones were tested. The effect of 0.1 nM okadaic acid (OA) (inhibits half maximally PP2A but has no effect on PP1) was tested in the in vitro phosphatase reaction (B). Phosphatase activity relative to cell lysate protein content is shown. If the experiment was performed with several cell clones, the clone numbers are indicated (e.g., #2).