Cutting edge: hypoxia-inducible factor 1alpha and its activation-inducible short isoform I.1 negatively regulate functions of CD4+ and CD8+ T lymphocytes.

To evaluate the role of hypoxia-inducible factor 1alpha (HIF-1alpha) and its TCR activation-inducible short isoform I.1 in T cell functions, we genetically engineered unique mice with: 1) knockout of I.1 isoform of HIF-1alpha; 2) T cell-targeted HIF-1alpha knockdown; and 3) chimeric mice with HIF-1alpha gene deletion in T and B lymphocytes. In all three types of mice, the HIF-1alpha-deficient T lymphocytes, which were TCR-activated in vitro, produced more proinflammatory cytokines compared with HIF-1alpha-expressing control T cells. Surprisingly, deletion of the I.1 isoform, which represents < 30% of total HIF-1alpha mRNA in activated T cells, was sufficient to markedly enhance TCR-triggered cytokine secretion. These data suggest that HIF-1alpha not only plays a critical role in oxygen homeostasis but also may serve as a negative regulator of T cells.

Misfolded proteins are competent to mediate a subset of the responses to heat shock in Saccharomyces cerevisiae.

Cells may sense heat shock via the accumulation of thermally misfolded proteins. To explore this possibility, we determined the effect of protein misfolding on gene expression in the absence of temperature changes. The imino acid analog azetidine-2-carboxylic acid (AZC) is incorporated into protein competitively with proline and causes reduced thermal stability or misfolding. We found that adding AZC to yeast at sublethal concentrations sufficient to arrest proliferation selectively induced expression of heat shock factor-regulated genes to a maximum of 27-fold and that these inductions were dependent on heat shock factor. AZC treatment also selectively repressed expression of the ribosomal protein genes, another heat shock factor-dependent process, to a maximum of 20-fold. AZC treatment thus strongly and selectively activates heat shock factor. AZC treatment causes this activation by misfolding proteins. Induction of HSP42 by AZC treatment required protein synthesis; treatment with ethanol, which can also misfold proteins, activated heat shock factor, but treatment with canavanine, an arginine analog less potent than AZC at misfolding proteins, did not. However, misfolded proteins did not strongly induce the stress response element regulon. We conclude that misfolded proteins are competent to specifically trigger activation of heat shock factor in response to heat shock.