Signaling pathway activated during apoptosis of the prostate cancer cell line LNCaP: Overexpression of caspase-7 as a new gene therapy strategy for prostate cancer

We studied the molecular mechanisms of apoptosis in the prostate cancer cel l line LNCaP and whether overexpression of caspase activity could force thi s cell line to undergo apoptosis, The inhibitor of phosphom-evalonate decar boxylase, sodium phenylacetate, and the protein kinase inhibitor staurospor ine induced (a) release of cytochrome c from the mitochondria to the cytoso l; (b) reduction in mitochondrial transmembrane potential; (c) proteolytic processing of caspase-3 and -7 but not -2; (d) cleavage of the DEVD substra te and the death substrates poly(ADP-ribose) polymerase and DNA fragmentati on factor; and (e) apoptosis, The panspecific inhibitor of caspase activati on N-benzyloxycarbonyl-Val-Ala-Asp(OMe)-fluoromethylketone (z-VAD-FMK) prev ented all of these events except release of mitochondrial cytochrome c into the cytosol. None of these apoptotic signaling events were elicited by sta urosporine or sodium phenylacetate treatment of LNCaP-Bcl-2 cells that over express the oncoprotein Bcl-2, Because caspase-7 is activated in every mode l of apoptosis that we have characterized thus far, me wished to learn whet her overexpression of this protease could directly cause apoptosis of LNCaP cells. By using a replication-defective adenovirus, overexpression of casp ase-7 protein in both LNCaP and LNCaP-Bcl-2 cells was accompanied by induct ion of cleavage of the DEVD substrate and TUNEL. These studies have demonst rated that caspase-7 and -3 are critical mediators of apoptosis in LNCaP ce lls, Caspase-7 was proteolytically activated in every model of apoptosis th at me have developed, and the overexpression of it induced apoptosis of LNC aP and LNCaP-Bcl-2 cells, Thus, adenoviral-mediated transfer of caspase-7 m ay offer a new effective approach for the treatment of prostate cancer.