Intermediate basal cells of the prostate: In vitro and in vivo characterization

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Abstract
Background Progenitor cells within the prostate basal layer may play important roles in differentiation and carcinogenesis; however, prostate stem cell populations remain uncharacterized. Methods Immunohistochemical and immunoblot analyses were used to characterize prostate epithelial cells (PrEC), a commercially available prostate basal cell isolate. Results Proliferating PrECs exhibited immunophenotypic characteristics most consistent with basal cells, but during senescence PrECs up‐regulated androgen receptor (AR) mRNA, p27, and low‐molecular‐weight cytokeratin (LMWCK) expression, suggestive of partial differentiation. PrECs also stained strongly for involucrin, which marked a subset of intermediate prostate basal cells in vivo. Basal hyperplasia consisting of involucrin‐positive cells was prevalent in prostate tissue from androgen‐ablated patients, and formed epithelial clusters flanked by involucrin‐negative basal and luminal monolayers. Cultivation of PrECs on matrigel together with androgen‐treated stromal conditioned media resulted in dense aggregates, with a peripheral rim of basal‐like cells expressing p63 and basal cytokeratins. Conclusions PrEC represents an epithelial population whose basal characteristics are modified in response to matrigel, stromal factors, and senescence, consistent with a transient amplifying population. These cells may derive from a previously unrecognized, involucrin‐positive subset present in vivo. Prostate 55: 206–218, 2003.