Hypoxia activates all components of the unfolded protein response (UPR), a stress response initiated by the accumulation of unfolded proteins within the endoplasmic reticulum (ER). Our group and others have shown previously that the UPR, a hypoxia-inducible factor -independent signaling pathway, mediates cell survival during hypoxia and is required for tumor growth. Identifying new genes and pathways that are important for survival during ER stress may lead to the discovery of new targets in cancer therapy. Using the set of 4,728 homozygous diploid deletion mutants in budding yeast, Saccharomyces cerevisiae, we did a functional screen for genes that conferred resistance to ER stress -inducing agents. Deletion mutants in 56 genes showed increased sensitivity under ER stress conditions. Besides the classic UPR pathway and genes related to calcium homeostasis, we report that two additional pathways, including the SLT2 mitogen-activated protein kinase (MAPK) pathway and the osmosensing MAPK pathway, were also required for survival during ER stress. We further show that the SLT2 MAPK pathway was activated during ER stress, was responsible for increased resistance to ER stress, and functioned independently of the classic IRE1/HAC1 pathway. We propose that the SLT2 MAPK pathway is an important cell survival signaling pathway during ER stress. This study shows the feasibility of using the yeast deletion pool to identify relevant mammalian orthologues of the UPR. (Mol Cancer Res 2005;3(12):669 -77)

AT has an ICER comparable to those for other widely used interventions. Longer clinical follow-up is warranted to evaluate the long-term efficacy and toxicity of different AT regimens.

Hypoxia within solid tumors decreases therapeutic efficacy, and identification of hypoxia markers may influence the choice of therapeutic modality. Here, we used a proteomic approach to identify hypoxia-regulated proteins and validated their use as endogenous indicators of tumor hypoxia. Using two-dimensional gel electrophoresis and PowerBlot (antibody-based array), we identified a group of 20 proteins that are increased >1.5-fold during hypoxia. The majority of these proteins such as IB kinase ␤ (IKK␤), MKK3b, highly expressed in cancer (HEC), density-regulated protein 1, P150 glued , nuclear transport factor 2, binder of ARL 2, Paxillin, and transcription termination factor I have not been previously reported to be hypoxia inducible. The increase in these proteins under hypoxia was mediated through posttranscriptional mechanisms. We additionally characterized the role of IKK␤, a regulator of the nuclear factor-B transcription factor, during hypoxia. We demonstrated that IKK␤ mediates cell survival during hypoxia and is induced in a variety of squamous cell carcinoma cell lines. Furthermore, we showed that IKK␤ expression from tumor specimens correlated with tumor oxygenation in patients with head and neck squamous cell carcinomas. These data suggest that IKK␤ is a novel endogenous marker of tumor hypoxia and may represent a new target for anticancer therapy.

<div>Abstract<p>Hypoxia within solid tumors decreases therapeutic efficacy, and identification of hypoxia markers may influence the choice of therapeutic modality. Here, we used a proteomic approach to identify hypoxia-regulated proteins and validated their use as endogenous indicators of tumor hypoxia. Using two-dimensional gel electrophoresis and PowerBlot (antibody-based array), we identified a group of 20 proteins that are increased ≥1.5-fold during hypoxia. The majority of these proteins such as IκB kinase β (IKKβ), MKK3b, highly expressed in cancer (HEC), density-regulated protein 1, P150^glued, nuclear transport factor 2, binder of ARL 2, Paxillin, and transcription termination factor I have not been previously reported to be hypoxia inducible. The increase in these proteins under hypoxia was mediated through posttranscriptional mechanisms. We additionally characterized the role of IKKβ, a regulator of the nuclear factor-κB transcription factor, during hypoxia. We demonstrated that IKKβ mediates cell survival during hypoxia and is induced in a variety of squamous cell carcinoma cell lines. Furthermore, we showed that IKKβ expression from tumor specimens correlated with tumor oxygenation in patients with head and neck squamous cell carcinomas. These data suggest that IKKβ is a novel endogenous marker of tumor hypoxia and may represent a new target for anticancer therapy.</p></div>