THE EFFECTS OF THE BROAD-BAND UVA RADIATION ON MYELOID-LEUKEMIA CELLS- THE POSSIBLE ROLE OF PROTEIN-KINASE-C IN MEDIATION OF UVA-INDUCED EFFECTS

We examined the effects of broadband UVA radiation (320-400 nm) on a r at myeloid leukemia cell line-chloroma (ChL), A Phillips face tanner m odel HE 171/A was used as a light source, Chloroma were irradiated thr ough a 5 mm thick glass filter that cut off all of the UVB contaminati on, The irradiances were measured, from 250 to 400 nm, with a well-cha racterized and calibrated double-grating spectroradiometer Optronic 74 2, The overall uncertainty of dose evaluation was estimated to he +/- 15% (2 sigma), The cells were irradiated with UVA doses of 4 and 8 J/c m(2) and cultured thereafter for 24 h, After this period of time, a ma rked decline up to 50% was observed in cell proliferation in UVA-irrad iated ChL cultures, The cell proliferation decline was found to be cau sed by simultaneously occurring G2/M phase cell cycle arrest and apopt osis in part of the UVA-irradiated ChL population, Concomitantly, with the decline in cell proliferation, an increase was observed in the ex pression of the major histocompatibility (MHC) class I and II antigens , Because protein kinase C (PKC) is known to regulate cell proliferati on, apoptosis and expression of MHC antigens, and because UVA was show n to regulate PKC activity/expression, we therefore examined whether U VA irradiation has any effect on the expression of isozymes of PKC. We stern blots revealed that ChL express alpha, beta I, delta, epsilon, e ta, and zeta/l isozymes of PKC and that expression of all isozymes dec lined 24 h after UVA irradiation (8 J/cm(2)), Finally, PKC activation in ChL by exposure to phorbol ester caused cell cycle arrest in G1 pha se but did not induce apoptosis, This suggests that the previously sho wn WA-induced PKC activation in ChL might be responsible for the induc tion of MHC antigens but the simultaneously observed ChL apoptosis is likely to be mediated by PKC down-regulation, All together, our result s suggest that UVA, at irradiance levels that resemble the outdoor exp osure, may have profound effects on the immune-related properties of l eukocytes, Thus, we speculate that in vivo the immune functions of leu kocytes passing through dermal capillaries might be altered by exposur e to solar UVA radiation.