STAT5A and pachyonychia congenita: To evaluate whether the activation of endogenous Stat5 is sufficient to induce AR-FL and AR-V mRNA, CWR22Rv1, we treated CWR22Pc and LAPC4 cells with the cytokine prolactin (Prl), which is known to activate the canonical Jak2-Stat5 pathway in PC cells (35, 50).