Changes in tissue transglutaminase activity and expression during retinoicacid-induced growth arrest and apoptosis in primary cultures of human epithelial prostate cells

We treated primary epithelial cells from human normal prostate (NEPC) and p rostate cancer (CEPC) with all-trans-retinoic acid (RA) to study whether it regulates the activity of tissue transglutaminase (tTGase), an enzyme that accumulates in cells undergoing apoptosis. tTGase activity was assessed by [C-14]spermidine incorporation; tTGase, P53, Bcl-2, and p21 protein levels were evaluated by Western blotting; and RA receptors (RAR alpha, -beta, an d -gamma), tTGase, retinol-binding protein (RBP), and cellular REP type I t ranscripts were determined by semiquantitative RT-PCR. After 72-96 h of 10( -6) mol/L RA treatment, cell growth inhibition and apoptosis were associate d with increased tTGase activity in both NEPC and CEPC, and with increased tTGase protein and messenger ribonucleic acid levels only in NEPC. Moreover , RA down-regulated RAR alpha and -beta and increased REP messenger ribonuc leic acid levels in NEPC, whereas it increased RAR beta gene expression and decreased Bcl-2 protein levels in CEPC. Our results suggest that RA induce s tTGase gene expression and enzyme activity in normal prostate cells, and that RA-regulated pathways are impaired in cancer cells. Moreover, down-reg ulation of Bcl-2 protein and up-regulation of RAR beta suggest that retinoi d may act on the genetic defect responsible for prostate cancer progression .