UNCOORDINATE INDUCTION AND DIFFERENTIAL REGULATION OF HLA CLASS-I ANDCLASS-II EXPRESSION BY GAMMA-INTERFERON IN DIFFERENTIATING HUMAN NEUROBLASTOMA-CELLS

Recombinant gamma-interferon (IFN-gamma) has recently been shown to be one of the most effective inducers of neuroblastoma (NB) cell differe ntiation. Since increasing evidence indicates that expression of MHC c lass-I and class-II antigens by tumour cells is important for immunore cognition and cell targeting, we tested whether induction of NB cell d ifferentiation by IFN-gamma is followed by expression of HLA class-I a nd class-II molecules. LAN-5 human NB cell line completely lacks HLA c lass-I antigens. Their expression was induced in a dose-dependent mann er by IFN-gamma. HLA class-II molecules are also absent on LAN-5 cells , but only DP antigens were dose-dependently induced by IFN-gamma, whi le DR and DQ molecules were unaffected by the treatment. To confirm an d extend the immunological data to all the class-II molecules, we perf ormed Northern blot analysis, observing that DPalpha mRNA was induced in a dose- and time-dependent manner. DObeta and DZalpha genes were al so induced peaking after 3 days of IFN-gamma treatment. DRbeta and DQb eta genes, which were not induced by IFN-gamma, gave a normal pattern of enzyme restriction by Southern blot. To get an insight into the reg ulation of HLA class-II gene expression in the neuronal model, we meas ured the decline of the steady-state HLA class-II mRNA. DObeta mRNA ra pidly returned to baseline level after removing IFN-gamma, while the d ecay rates of DPalpha and DZalpha mRNA were very slow. This might indi cate different regulation at the post-transcriptional level for DObeta mRNA with respect to DPalpha and DZalpha mRNA. To strengthen these fi ndings we evaluated the half-lives of the mRNA after IFN-gamma inducti on by means of actinomycin D treatment. HLA-DObeta mRNA had a shorter half-life, while DZalpha and DPalpha had a longer decay rate. Finally, we report that treatment of LAN-5 cells with cycloheximide did not al ter the rate of transcription of the HLA-DPalpha gene, suggesting that no protein factor(s) is/are needed to maintain DPalpha gene expressio n. (C) 1993 Wiley-Liss, Inc.