UV-B IRRADIATED CELL-LINES EXECUTE PROGRAMMED CELL-DEATH IN VARIOUS FORMS

We investigated changes typical for apoptosis in various cell lines af ter UV-B irradiation. Using established methods for detection of apopt osis we demonstrate changes of cellular morphology, phosphatidylserine (PS) exposure, oligonucleosomal DNA fragmentation and generation of h ypochrome nuclei, To isolated high-molecular-weight (hmwt) DNA fragmen ts we engaged a new method avoiding pulse field gel electrophoresis. M ost UV-B irradiated cell lines showed oligonucleosomal DNA fragmentati on, hypochrome nuclei: morphological changes, annexin-V binding and po sitive TUNEL reaction. However, no oligonucleosomal DNA fragmentation could be detected in Raji and HaCaT cells. Whereas HaCaT cells display ed all other changes typical for apoptosis, Raji cells were TUNEL nega tive, formed low amounts of hmwt DNA and showed an 'atypically' low hy pochrome shift, Nevertheless, UV-B irradiated Raji cells excluded prop idium iodide (PI), bound annexin-V and stopped proliferation, This sug gests that Raji cells underwent growth arrest with exposure of PS bein g the only feature of apoptosis. However, in the presence of phagocyte s expressing the phosphatidylserine receptor these cells would share t he removal pathway with apoptotic cells. Since UV-B induced programmed cell death differs in dependence of cells under investigation, the fa ilure to detect oligonucleosomal DNA fragmentation or chromatin conden sation is not suitable to exclude programmed (apoptotic?) cell death.