POU5F1 and Familial prostate cancer: In addition, since RWPE-1 cell cultures contain a stem/progenitor cell population [21] and Dkk-3 promotes differentiation of embryonic stem cells [22], we examined the stem cell genes SOX2, OCT4 (POU5F1), and NANOG. We also measured the expression of s-SHIP, which encodes an isoform of SHIP1 (SH2-containing Inositol 5ʹ-Phosphatase) that lacks the N-terminal domain [23] and is upregulated in RWPE-1 stem/progenitor cells [24] and ALDH1A1, a prostate cancer stem cell marker that may be a myofibroblast marker in prostate stroma [25, 26].