Abstract
Recombinant γ‐interferon (IFN‐γ) has recently been shown to be one of the most effective inducers of neuroblastoma (NB) cell differentiation. Since increasing evidence indicates that expression of MHC class‐I and class‐II antigens by tumour cells is important for immunorecognition and cell targeting, we tested whether induction of NB cell differentiation by IFN‐γ is followed by expression of HLA class‐I and class‐II molecules. LAN‐5 human NB cell line completely lacks HLA class‐I antigens. Their expression was induced in a dose‐dependent manner by IFN‐γ. HLA class‐II molecules are also absent on LAN‐5 cells, but only DP antigens were dose‐dependently induced by IFN‐γ, while DR and DQ molecules were unaffected by the treatment. To confirm and extend the immunological data to all the class‐II molecules, we performed Northern blot analysis, observing that DPα mRNA was induced in a dose‐ and time‐dependent manner. DOβ and DZα genes were also induced peaking after 3 days of IFN‐γ treatment. DRβ and DQβ genes, which were not induced by IFN‐γ, gave a normal pattern of enzyme restriction by Southern blot. To get an insight into the regulation of HLA class‐II gene expression in the neuronal model, we measured the decline of the steady‐state HLA class‐II mRNA. DOβ mRNA rapidly returned to baseline level after removing IFN‐γ, while the decay rates of DPα and DZα mRNA were very slow. This might indicate different regulation at the post‐transcriptional level for DOβ mRNA with respect to DPα and DZα mRNA. To strengthen these findings we evaluated the half‐lives of the mRNA after IFN‐γ induction by means of actinomycin D treatment. HLA‐DOβ mRNA had a shorter half‐life, while DZα and DPα had a longer decay rate. Finally, we report that treatment of LAN‐5 cells with cycloheximide did not alter the rate of transcription of the HLA‐DPα gene, suggesting that no protein factor(s) is/are needed to maintain DPα gene expression.