The inflammatory response elicited by various stimuli such as microbial products or cytokines is determined by differences in the pattern of cellular gene expression. We have used the differential display RT-PCR (DDRT-PCR) strategy to identify mRNAs that are differentially expressed in various murine cell types stimulated with pro-inflammatory cytokines, microbial products or anti-inflammatory drugs. Mouse embryonic fibroblasts (MEFs) were treated with IFNs, TNF, or sodium salicylate. Also, peritoneal macrophages from C3H/Hej mice were stimulated with T. cruzi-derived GPI-mucin and/or IFN-g. After DDRT-PCR, various cDNA fragments that were differentially represented on the sequencing gel were recovered, cloned and sequenced. Here, we describe a summary of several experiments and show that, when 16 of a total of 28 recovered fragments were tested for differential expression, 5 (31%) were found to represent mRNAs whose steady-state levels are indeed modulated by the original stimuli. Some of the identified cDNAs encode for known proteins that were not previously associated with the inflammatory process triggered by the original stimuli. Other cDNA fragments (8 of 21 sequences, or 38%) showed no significant homology with known sequences and represent new mouse genes whose characterization might contribute to our understanding of inflammation. In conclusion, DDRT-PCR has proven to be a potent technology that will allow us to identify genes that are differentially expressed when cells are subjected to changes in culture conditions or isolated from different organs.

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Using DDRT-PCR, we compared the mRNA content of untreated and TNF-treated mouse embryonic fibroblasts (MEFs). Among differentially represented fragments, we identified and cloned a novel TNF-stimulated gene named Tsg-5. This gene, mapped to mouse chromosome 14, has three exons that can be alternatively spliced giving rise to two mRNA species, one spanning three exons and another that skips the second exon. Analysis of full-length Tsg-5 cDNA revealed a potential start codon within exon 2 encoding an ORF of 40 amino-acids. No homology with known mouse or human sequences, neither at the nucleotide nor at the amino-acid level could be found in public databases. In MEFs, Tsg-5 is induced by tumor necrossis factora (TNF) and IL-1b, albeit with distinct kinetics. TNF-induced Tsg-5 expression is NF-kB-dependent as it was inhibited by MG132, lactacystin, Bay 11-7083, and Bay 11-7085. Analysis of Tsg-5 expression in vivo revealed that the gene and its encoded polypeptide are constitutively expressed in the thymus and ovary, whereas, in LPS-treated mice, Tsg-5 mRNA can be detected in the spleen, lung, and brain. Our data suggest that Tsg-5 encodes a new, rare transcript, with a very tight regulation of expression and differential splicing.

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