Cutting edge: the class II transactivator prevents activation-induced cell death by inhibiting Fas ligand gene expression.

The Fas:Fas ligand pathway is critical in regulating immune homeostasis by eliminating activated T cells that proliferated in response to an infection. Here, we show that the MHC class II transactivator (CIITA) can suppress this pathway by inhibiting transcription of the Fas ligand gene. CIITA can effectively repress transcription from the Fas ligand promoter in both T cell lines as well as primary cells. The repression appears to be at least partly due to interference of NFAT-mediated induction of Fas ligand gene transcription. T cells that express CIITA constitutively do not up-regulate Fas ligand on the cell surface after activation via the TCR. Consequently, these cells lack the ability to undergo activation-induced cell death, and to kill Fas-bearing target cells.

MHC class II transactivator inhibits IL-4 gene transcription by competing with NF-AT to bind the coactivator CREB binding protein (CBP)/p300.

The MHC class II transactivator (CIITA) activates the expression of multiple genes involved in Ag presentation, but inhibits Th2-type cytokine production, including IL-4, during Th1 cell differentiation. Th1 cells derived from CIITA-deficient mice produce both Th1- and Th2-type cytokines, and the introduction of CIITA to Th2 cells down-regulates Th2-type cytokine gene transcription. Here we show that the IL-4 promoter is regulated by multiple protein-protein interactions among CIITA, NF-AT, and coactivator CBP/p300. The introduction of CBP/p300 and NF-AT enhances the IL-4 promoter activity, and this activation was repressed by CIITA. Furthermore, our data show that CIITA competes with NF-AT to bind CBP/p300 and that this competition dramatically influences transcriptional activation of the IL-4 promoter. We identified two domains of CIITA that interact with two distinct domains of CBP/p300 that are also recognized by NF-AT. CIITA mutants that retain the ability to interact with CBP/p300 are sufficient to inhibit NF-AT-mediated IL-4 gene expression.

A novel role for the major histocompatibility complex class II transactivator CIITA in the repression of IL-4 production.

Class II transactivator (CIITA) is known as a coactivator for MHC class II gene expression in antigen-presenting cells. Surprisingly, when CIITA-/- CD4 T cells were stimulated in the presence of IL-12, they produced not only IFNgamma but also high levels of IL-4. The IL-4 production is due to the accumulation of IL-4 gene transcripts in Th1 cells. This transcriptional control is observed in T cells differentiating to the Th1 but not Th2 lineage, consistent with induction of expression of the CIITA gene in T cells by IFNgamma. Thus, in addition to its role in transactivation of genes involved in antigen presentation, CIITA plays a critical role during the T cell differentiation by negatively regulating the IL-4 gene transcription.

Diva, a Bcl-2 homologue that binds directly to Apaf-1 and induces BH3-independent cell death.

We have identified and characterized Diva, which is a novel regulator of apoptosis. Sequence analysis revealed that Diva is a member of the Bcl-2 family of proteins containing Bcl-2 homology domain 1, 2, 3, and 4 (BH1, BH2, BH3, and BH4) regions and a carboxyl-terminal hydrophobic domain. The expression of Diva mRNA was detected in multiple embryonic tissues but was restricted to the ovary and testis in adult mice. The expression of Diva promoted the death of 293T, Ramsey, and T47D cells as well as that of primary sensory neurons, indicating that Diva is a proapoptotic protein. Significantly, Diva lacks critical residues in the conserved BH3 region that mediate the interaction between BH3-containing proapoptotic Bcl-2 homologues and their prosurvival binding partners. Consistent with this, Diva did not bind to cellular Bcl-2 family members including Bcl-2, Bcl-XL, Bcl-w, Mcl-1, and A1/Bfl-1. Furthermore, mutants of Diva lacking the BH3 region fully retained their proapoptotic activity, confirming that Diva promotes apoptosis in a BH3-independent manner. Significantly, Diva interacted with a viral Bcl-2 homologue (vBcl-2) encoded by the Kaposi's sarcoma-associated herpesvirus. Consistent with these associations, apoptosis induced by Diva was inhibited by vBcl-2 but not by Bcl-XL. Importantly, Diva interacted with Apaf-1, an adapter molecule that activates caspase-9, a central death protease of the apoptotic pathway. The expression of Diva inhibited the binding of Bcl-XL to Apaf-1, as determined by immunoprecipitation assays. Thus, Diva represents a novel type of proapoptotic Bcl-2 homologue that promotes apoptosis independently of the BH3 region through direct binding to Apaf-1, thus preventing Bcl-XL from binding to the caspase-9 regulator Apaf-1.

Wool production in transgenic sheep: results from first-generation adults and second-generation lambs.

In sheep transgenic for a sheep insulin-like growth factor 1 (IGF-1) cDNA driven by a mouse keratin promoter, we assessed wool production and properties in 51 adults of the first generation (G1) and in 56 lambs of the second generation (G2). Transgenic G1 sheep had an increased rate of wool production during spring and summer of year 2 compared with nontransgenic half-sibs, with a maximum increase of 17% in December, but during the winter nadir rates were similar. At second- and third-year shearing, however, fleece weights were not significantly different. There was a trend for transgenic animals to have coarser wool of lower staple strength. A controlled feeding trial revealed no significant differences in feed intake. The transgene was expressed not only in skin but also in a wide range of other tissues. Circulating IGF-1 concentrations were not significantly different between transgenic and nontransgenic animals, suggesting that local mechanisms were more important than systemic mechanisms for wool production, but were significantly higher in males than in females. In the G2 sheep, transgenic fleece weight did not differ significantly from nontransgenic either as lambs or at the end of the lamb year. Although the transgene was inherited in Mendelian fashion and was widely expressed, the production advantage seen in animals of the first generation did not persist in the second generation.

Legionnaires' disease in Vancouver.

A female patient presented at the end of a holiday cruise with the pneumonitis of Legionnaires' disease. The radiographic appearance was indistinguishable from any other cause of air-space consolidation.