TGF-β cytokines increase senescence-associated beta-galactosidase activity in human prostate basal cells by supporting differentiation processes, but not cellular senescence

Abstract

The family of transforming growth factors betas ( TGF- βs) comprises molecules involved in growth inhibition, stress-induced premature senescence, epithelial mesenchymal transition and differentiation processes. The aim of this study was to clarify the effect of long term exposure of human prostate basal cells to TGF- βs, which are found in high concentrations in prostatic fluid and areas of benign prostatic hyperplasia (BPH). Basal cell cultures established from prostate explants ( n=3) were either grown into cellular senescence, or stimulated with TGF- β1, β2 and β3. Similar to cellular senescence, TGF- β stimulation resulted in an increase of SA-beta galactosidase ( SA- β- gal) activity, flattened and enlarged cell morphology, and down-regulation of the inhibitor of differentiation Id-1. TGF- β-treated prostate epithelial cells neither showed terminal growth arrest nor induction of important senescence-relevant genes, such as p16 INK4A, IFI-6-16, IGFBP-3 or Dkk-3. Cells stained positive for cytokeratins 8/18, but did not express other lumenal markers, such as prostate-specific antigen and androgen-receptors. TGF- βs increased also the expression of the mesenchymal marker vimentin, indicating that basal epithelial cells underwent differentiation with lumenal and mesenchymal features. In contrast, in vitro-differentiated neuroendocrine-like cells from prostate organoide cultures, expressing chromogranin A and cytokeratin 18, strongly stained positive for SA-β-gal. Thus, SA-β-gal activity is not only a marker for senescence, but also for differentiation of human prostate epithelial cells. With regard to the in vivo situation, in addition to cellular senescence, TGF-β could contribute to the increased number of SA-β-gal positive epithelial cells in BPH.