CSK and breast cancer: In the SHP2 knockdown breast cancer cell lines, however, the P4-increased p-cSrcY416 level was abolished, and P4 increased the levels of p-caveolin-1, p-Csk and p-cSrcY527 (Figures 4A–D, 5A–D, 6A–D), PR-cSrc negative regulatory proteins (Figures 4B, 5B, 6B), Csk-PRA, Csk-PRB, Csk-p-PRA, Csk-p-PRB, and Csk-p140Cap (Figures 4C, 5C, 6C), caveolin-1-Csk, and caveolin-1-p140Cap (Figures 4D, 5D, 6D).