Prostate epithelium and stem cells

Human prostate is an exocrine gland that consists of basal, luminal and neuroendocrine cell types embedded in a fibro-muscular stroma. The basal cells are relatively undifferentiated, not dependent on androgens and hence express low levels of androgen receptors (ARs). Additionally, basal cells generate some secretory products such as CD44 [5], p63 [6], p27kip and c-Met [7], cytokeratin 5 (CK 5) and CK 14 [8]. In contrast to the basal layer of cells, luminal (or secretory) cells are terminally differentiated and specifically secrete the prostate like prostate specific antigen (PSA) and prostatic acid phosphatase (PAP) into the glandular medulla in response to androgens. Because, survival of these luminal cells depend on andro-gens they express ARs on a high level; whereas, their other specific secretory products are CD57 [5], CK 8 and CK 18 [8]. The third type of cell in the cellular organization of the prostate epithelium is the neuroendocrine (NE) cell. The specific functions of NE cells have not been deduced so far. However, Bonkhoff suggested that they are post-mitotic cells derived from luminal secretory cells [9]. NE cells are terminally differentiated, androgen insensitive and scattered throughout the epithelium. Unlike the luminal cells, NE cells do not express AR or PSA; but, they do express NE-specific markers such as chromogranin A and synapto-physin [10]. Basal and luminal cells can also be distinguished by comparing expression profiles of other genes; like basal cells do mainly express CK 5 and CK 14, whereas luminal cells express CK 8 and CK 18 [8]. Morphologically basal cells are small, flattened cells with condensed chromatin and small amounts of cytoplasm. Luminal cells instead have increased cytoplasm and their chromatin appear more opened [11]. Finally, the stroma is located under the epithelial layer of prostate. Stromal cells are androgen responsive and they do express AR. Development, maintenance and differentiation of epithelial cells are provided by these stromal cells [12].

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