Collagens and PRL-Dependent Tyrosyl Phosphorylation of PAK1 Regulate MMP 1–3 and -9 Transcription. TMX2–28 cells stably overexpressing GFP, PAK1 WT, or PAK1 Y3F were plated and treated as in Figure 3. The mRNA level for MMP-1 (A), MMP-3 (B), MMP-2 (C), and MMP-9 (D) was analyzed by real-time RT-PCR. Bars represent mean ± SE. *, P < .05 compared with the same cells untreated with PRL. #, P < .05 compared with cells expressing GFP with the same treatment. Each experiment was repeated 3 times.