Critical and Distinct Roles of p16 and Telomerase in Regulating the Proliferative Life Span of Normal Human Prostate Epithelial Progenitor Cells

Abstract

Normal human prostate (NHP) epithelial cells undergo senescence in vitro and in vivo, but the underlying molecular mechanisms remain obscure. Here we show that the senescence of primary NHP cells, which are immunophenotyped as intermediate basal-like cells expressing progenitor cell markers CD44, ␣2␤1, p63, hTERT, and CK5/CK18, involves loss of telomerase expression, up-regulation of p16, and activation of p53. Using genetically defined manipulations of these three signaling pathways, we show that p16 is the primary determinant of the NHP cell proliferative capacity and that hTERT is required for unlimited proliferative life span. Hence, suppression of p16 significantly extends NHP cell life span, but both p16 inhibition and hTERT are required to immortalize NHP cells. Importantly, immortalized NHP cells retain expression of most progenitor markers, demonstrate gene expression profiles characteristic of proliferating progenitor cells, and possess multilineage differentiation potential generating functional prostatic glands. Our studies shed important light on the molecular mechanisms regulating the proliferative life span of NHP progenitor cells.The prostatic glands contain neuroendocrine (NE) 7 cells and two epithelial cells: 1) luminal cells expressing cytokeratin 8 (CK8) and CK18, androgen receptor (AR), prostate-specific antigen (PSA), prostatic acid phosphatase, CD26, CD57, and 15-lipoxygenase 2 (15-LOX2) and 2) basal cells expressing CK5/CK14, CD44, CD104 (integrin ␤4), Bcl-2, p63, telomerase, and glutathione S-transferase-(1-3). It has been proposed that a common stem/progenitor cell may generate both basal and luminal cells (4). Alternatively, basal cells may function as progenitors to luminal cells (5, 6).The adult rodent prostate possesses regenerative stem cells (SCs) (6 -8). Whether adult human prostate contains definitive SCs is less certain, although there exists strong evidence that the basal cell layer harbors regenerative cells (1, 6, 9 -12), and several candidate populations of human prostate stem/progenitor cells, preferentially localized in the basal layer, have been reported. These include the cells that preferentially express CD44 (13), ␣2␤1 (i.e. ␣2␤1 hi ) (14), or CD133 (15, 16) and the side population (17), whose phenotype is mediated by multidrug resistance family proteins, such as MDR-1 and ABCG2 (18). Interestingly, the ABCG2 ϩ cells in the benign prostate constitute Ͻ1% of total basal cell population and share essentially the same transcriptome as the side population cells (19 * This work was supported, in whole or in part, by National Institutes of Health Grants R01-AG023374, R01-ES015888, and R21-ES015893-01A1. This work was also supported by American Cancer Society Grant RSG MGO-105961, Department of Defense Grants W81XWH-07-1-0616 and PC073751, the Prostate Cancer Foundation, the Elsa Pardee Foundation (to D. G. T.), and two Center Grants, CCSG-5 P30 CA166672 and ES07784. The costs of publication of this article were defrayed in part by the payment of page charges. This article m...

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