1,25-DIHYDROXYVITAMIN D-3, TRANSFORMING-GROWTH-FACTOR BETA-1, CALCIUM, AND ULTRAVIOLET-B RADIATION INDUCE APOPTOSIS IN CULTURED HUMAN KERATINOCYTES

Apoptosis is a cellular process of self-directed suicide that plays a key role during morphogenesis and in the maintenance of homeostasis in continuously renewing tissues, Currently, apoptosis is detected mainl y by gel electrophoresis of fragmented DNA and by typical ultrastructu ral features such as cell shrinkage and chromatin condensation, Recent ly, an in situ technique was developed that allows the detection of th e apoptotic process in cells and the quantitation of apoptosis in cell populations, We applied this technique to evaluate the apoptotic proc ess in cultured normal human keratinocytes under basic conditions and after stimulation with factors and agents that are presumed but have n ever been proved to induce apoptosis in these cells, Apoptosis was ana lyzed after stimulation with 1,25-dihydroxyvitamin D-3[1,25(OH)(2)D-3] , transforming growth factor beta 1 (TGF beta 1), calcium, UVB, or tum or necrosis factor alpha (TNF alpha), All these factors except TNF alp ha induced apoptosis in human keratinocytes. Whereas UVB and calcium w ere good apoptogenic stimuli at 6 and 24 h, respectively, the vitamin D derivative and TGF beta 1 induced apoptosis after 5 and 6 d in cultu re, Apoptosis was also established by DNA fragmentation and electron m icroscopy. Finally, TUNEL technique showed that the number of apoptoti c cells increases slightly (5-10%) from 24 to 144 h even in untreated keratinocytes, Our studies indicate that factors normally involved in the regulation of cell growth and differentiation can also control apo ptosis.