c-fos and c-jun overexpression in malignant cells reduces their tumorigenic and metastatic potential, and affects their MHC class I gene expression.

Reduced co-expression of the c-fos and c-jun protooncogenes has been correlated with the down regulation of H-2K class I major histocompatibility antigens in high-metastatic cell lines from the Lewis lung carcinoma, B16 melanoma and the K1735 melanoma. Transfection of c-jun and c-fos genes into the high metastatic clones D122 (3LL) and F10.9 (B16 melanoma) resulted in activation of H-2 class I gene expression. D122 transfectants expressing high levels of c-jun and c-fos and F10.9 transfectants expressing high levels of c-fos exhibited markedly reduced tumorigenicity and were of low metastatic potential. In contrast, transfection of junB into the low metastatic, high H-2Kb, Db expressor clone A9 (3LL), reduced MHC class I gene expression, and converted the parental low, into high-metastatic cells. The data demonstrate the involvement of genes from the fos and jun family in regulation of MHC class I expression and consequently in regulation of immunogenicity and metastatic competence of tumor cells.

A Leuconostoc lactis protein with homology to ribosomal protein S1 shares common epitopes and common DNA binding properties with a mammalian DNA binding nuclear factor.

A mouse testis cDNA expression library (Clontech) was screened with a synthetic oligonucleotide ligand containing CT-rich motifs derived from the rat skeletal muscle actin gene promoter. These motifs bind nuclear proteins, and seem to be involved in the regulation of the gene. Analysis of isolated clones, which expressed proteins that specifically bind the oligonucleotide, indicated that they were derived from a single gene. This gene was identified as a contaminant of bacterial origin (Leuconostoc lactis). The cloned gene from L. lactis encodes a protein with significant homology to bacterial ribosomal protein S1, which we designated LrpS1-L. Band shift analysis and competition experiments indicated that both the bacterial protein and a mouse nuclear protein specifically bind to the same CT-rich motif of the skeletal muscle actin promoter. Furthermore, antibodies against the recombinant bacterial protein interfered with the formation of complex between the CT-rich element and the mouse nuclear protein. These results indicate that the bacterial LrpS1-L protein and the mammalian protein bind the same CT-rich motif and share common antigenic epitopes.

TAFII105 mediates activation of anti-apoptotic genes by NF-kappaB.

The transcription factor NF-kappaB is important for expression of genes involved in immune responses, viral infections, cytokine signaling and stress. In addition NF-kappaB plays a crucial role in protecting cells from TNF-alpha-induced apoptotic stimuli, presumably by activating anti-apoptotic genes. Here we report that the sub-stoichiometric TFIID subunit TAFII105 is essential for activation of anti-apoptotic genes in response to TNF-alpha, serving as a transcriptional coactivator for NF-kappaB. The putative coactivator domain of TAFII105 interacts with the activation domain of the p65/RelA member of the NF-kappaB family, and further stimulates p65-induced transcription in human 293 cells. Moreover, inhibition of TAFII105 activity by overexpression of a dominant negative mutant of TAFII105 decreased NF-kappaB transcriptional activity and severely reduced cell survival in response to TNF-alpha. Similarly, expression of anti-sense TAFII105 RNA sensitized the cells to TNF-alpha cytotoxicity. These results suggest that TAFII105 is involved in activation of anti-apoptotic genes by NF-kappaB.

Interaction of TAFII105 with selected p65/RelA dimers is associated with activation of subset of NF-kappa B genes.

TAF(II)105, a substoichiometric coactivator subunit of TFIID, is important for activation of anti-apoptotic genes by NF-kappaB in response to the cytokine tumor necrosis factor (TNF)-alpha. In the present study we have analyzed the mechanism of TAF(II)105 function with respect to its regulation of p65/RelA, a component of NF-kappaB. We found two independent p65/RelA-binding domains within the N terminus of TAF(II)105. One of these domains appears to be crucial for TAF(II)105-mediated anti-apoptotic gene activation in response to TNF-alpha. Analysis of the interaction between TAF(II)105 and different NF-kappaB complexes has revealed substantial differences in the affinity of TAF(II)105 toward different p65/RelA-containing dimers. We have identified the TNF-alpha induced anti-apoptotic A20 gene as a target gene of TAF(II)105. A20 has a differential protective effect on cell death induced by TNF-alpha in the presence of either the dominant negative mutant of TAF(II)105 (TAF(II)105DeltaC) or the superdominant IkappaBalpha. The results suggest that the inhibitory effect of TAF(II)105DeltaC on NF-kappaB-dependent genes is restricted to a subset of anti-apoptotic genes while the effect of IkappaBalpha is more general. Thus, an interaction between NF-kappaB and a specific coactivator is important for specifying target gene activation.