ALTERNATIVE SPLICING OF HLA CLASS-I TRANSCRIPTS INDUCED BY IFN-GAMMA AND TNF IN FIBROBLASTS - RELEASE OF SOLUBLE HLA CLASS-I HEAVY-CHAIN AND AN ASSOCIATE PROTEIN

FS-4 fibroblasts were found to produce 37-kDa HLA class I heavy chain in response to IFN-gamma or TNF in a time- and dose-dependent fashion, and a synergism between IFN-gamma and TNF was observed. Immunoprecipi tation of IFN-gamma- or TNF-induced FS-4 cell culture supernatants by mAb A1.4 revealed an additional 33-kDa protein in association with the 37-kDa heavy chain. The 33-kDa protein appeared to be expressed in a 38-kDa form on the membrane of FS-4 cells induced by IFN-gamma or TNF, as A1.4 immunoprecipitated the 38-kDa band in association with the 44 -kDa transmembrane HLA class I heavy chain. Release of the 37-kDa heav y chain could well be due to an alternative RNA splicing with the dele tion of exon 5 encoding the hydrophobic transmembrane region of membra ne-anchored HLA class I heavy chain. Northern blot analysis and S1 nuc lease protection assay suggested the existence of HLA class I heavy ch ain mRNA lacking exon 5 in IFN-gamma- or TNF-induced FS-4 cells. South ern blot analysis on the products of reverse transcription-polymer ase chain reaction amplification from cytoplasmic RNA confirmed induction of alternative splicing by these cytokines. Our results suggest that cytokine-induced production of soluble HLA class I molecules may play important roles in the regulation of T cell interaction with antigen-p resenting cells. (C) 1995 Academic Press, Inc.