We have analysed the structure of mRNA isoforms of the human gene encoding tryptophanyl-tRNA synthetase (Trp-tRNA synthetase) expressed in the epithelial CaOv cells and MT-4 lymphocytes. The Trp-tRNA synthetase gene is induced by interferon-y in both lines and, in MT-4 lymphocytes, also by interferon-a. Four Trp-tRNA synthetase mRNA isoforms have different combinations of the first exons TA, 1B and 11. Two transcription initiation sites (PI and P2) were detected 90 bp from each other. Processing of the primary transcript initiated from the PI start site generates the mRNA isoform where exon IA joins to exon 11. The other three isoforms are produced by alternative splicing of the primary transcript produced from the P2 start site. Isoform 2 has a 3'-end fragment of exon IA joined to exon 11. Isoform 3 contains exons IA and IB. Isoform 4 contains exon IA and exon I11 and lacks exon I1 encoding the Nterminus of the Trp-tRNA synthetase. Therefore, the two primary transcripts of the Trp-tRNA synthetase gene differ only in the 5' flank sequence between PI and P2, and this fragment regulates their processing.Both interferon-a and interferon-y induce exon IA-containing and exon IB-containing isoforms of the Trp-tRNA synthetase mRNA.

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SUMMARYNitric oxide is a diffusible messenger with multiple biological functions. We show here that NO-generating compound, S-nitrosoglutathione (GSNO) induces apoptosis in human chondrocytes and causes necrosis-like celt death in human epithelial CaOv cell line. Pretreatment of chondrocytes with low-dose GSNO or with y-interferon enhances their tolerance to the second high-concentration GSNO exposure. On the contrary, in CaOv cells low-dose GSNO pretreatment diminishes the resistance and increases cytolysis at the second GSNO exposure. We conclude that human chondrocytes possess specific and inducible mechanism preventing celt killing by nitric oxide.

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