Apoptosis can be induced in response to hypoxia. The severity of hypoxia determines whether cells become apoptotic or adapt to hypoxia and survive. A hypoxic environment devoid of nutrients prevents the cell undergoing energy dependent apoptosis and cells become necrotic. Apoptosis regulatory proteins are delicately balanced. In solid tumours, hypoxia is a common phenomenon. Cells adapt to this environmental stress, so that after repeated periods of hypoxia, selection for resistance to hypoxia induced apoptosis occurs. These resistant tumours probably have a more aggressive phenotype and may have decreased responsiveness to treatment. The key regulator of this process, hypoxia inducible factor 1 (HIF-1), can initiate apoptosis by inducing high concentrations of proapoptotic proteins, such as BNIP3, and can cause stabilisation of p53. However, during hypoxia, antiapoptotic proteins, such as IAP-2, can be induced, whereas the proapoptotic protein Bax can be downregulated. During hypoxia, an intricate balance exists between factors that induce or counteract apoptosis, or even stimulate proliferation. Understanding the regulation of apoptosis during hypoxia and the mechanisms of resistance to apoptosis might lead to more specific treatments for solid tumours.

BACKGROUNDHypoxia‐inducible factor‐1 (HIF‐1) is a transcription factor that plays an important role in tumor growth and metastasis by regulating energy metabolism and inducing angiogenesis to survive cellular hypoxia. Increased levels of HIF‐1α, the O2‐regulated subunit of HIF‐1, were noted during breast carcinogenesis. In this study, the prognostic value of HIF‐1α expression and its correlation with various clinicopathologic variables in patients with invasive breast carcinoma were investigated.METHODSExpression levels of HIF‐1α, HER‐2/neu, estrogen receptor, and progesterone receptor were analyzed in 150 patients with early‐stage breast carcinoma by immunohistochemistry. HER‐2/neu gene amplification was investigated with automated fluorescent in situ hybridization. The mitotic activity index, histologic grade, and tumor type were assessed in hematoxylin and eosinstained specimens. Clinical data included disease‐free survival, overall survival, lymph node status, and tumor size. The data were analyzed with two‐sided univariate and multivariate tests, with P values < 0.05 considered significant.RESULTSHigh levels of HIF‐1α had an association of borderline significance with decreased overall survival (P = 0.059) and disease‐free survival (P = 0.110) that was ascribed completely to the subgroup of women with lymph node negative tumors (n = 81 patients; P = 0.008 and P = 0.004, respectively). HER‐2/neu immunoreactivity (P < 0.001) and gene amplification (P < 0.001), vascular endothelial growth factor expression (P = 0.016), and Ki‐67 expression (P < 0.001) were correlated strongly with HIF‐1α positivity, although none of those factors had an independent effect on survival.CONCLUSIONSIncreased levels of HIF‐1α were associated independently with shortened survival in patients with lymph node negative breast carcinoma. Therefore, the use of immunohistochemical assessment of HIF‐1α as a new predictor of poor outcome may improve clinical decision‐making regarding adjuvant treatment of patients with lymph node negative breast carcinoma. Cancer 2003;97:1573–81. © 2003 American Cancer Society.DOI 10.1002/cncr.11246

The hypoxia-inducible factor 1 (HIF-1) plays a critical role in cellular responses to hypoxia. The aim of the present study was to evaluate which genes are induced by hypoxia, and whether this induction is mediated by HIF-1, by expression microarray analysis of wt and HIF-1alpha null mouse fibroblasts. Forty-five genes were up-regulated by hypoxia and 40 (89%) of these were regulated by HIF-1. Of the 114 genes down-regulated by hypoxia, 19 (17%) were HIF-1-dependent. All glycolytic enzymes were strongly up-regulated by hypoxia in a HIF-1-dependent manner. Genes already known to be related to hypoxia, such as glucose transporter 1, BNIP3, and hypoxia-induced gene 1, were induced. In addition, multiple new HIF-1-regulated genes were identified, including genes involved in metabolism (adenylate kinase 4, galactokinase), apoptosis (galectin-3 and gelsolin), and invasion (RhoA). Genes down-regulated by hypoxia were involved in cytoskeleton maintenance (Rho kinase), mRNA processing (heterogeneous nuclear ribonucleoprotein H1 and splicing factor), and DNA repair (REV3). Furthermore, seven cDNAs from genes with unknown function or expressed sequence tags (ESTs) were up-regulated and 27 such cDNAs were down-regulated. In conclusion, hypoxia causes down- rather than up-regulation of gene expression and HIF-1 seems to play a major role in the regulation of hypoxia-induced genes.

Background:Intratumorous hypoxia triggers a broad cellular response mediated by the transcription factor hypoxia inducible factor 1 (HIF-1). HIF-1α concentrations increase during breast carcinogenesis, and are associated with poor prognosis. An earlier study noted two HIF-1α overexpression patterns: diffuse scattered throughout the tissue and confined to perinecrotic cells.Aims:To investigate the prognostic impact of these different HIF-1α overexpression patterns in relation to its downstream effectors carbonic anhydrase (CA) IX and glucose transporter 1 (GLUT-1).Methods:HIF-1α, CA IX, and GLUT-1 expression was studied by immunohistochemistry, including double staining for CA IX and HIF-1α. Clinical data included disease free survival, lymph node status, and tumour size.Results:HIF-1α overexpression (44% of cases) had a perinecrotic (13.5%) or diffuse staining pattern (30.5%). CA IX expression was detectable in 12.5% of breast cancers, whereas GLUT-1 expression was seen in 29%, with both showing perinecrotic membrane staining. Perinecrotic HIF-1α overexpression was highly associated with CA IX and GLUT-1 overexpression, and double staining for HIF-1α and CA IX showed strong expression in the same cells. Diffusely overexpressed HIF-1α was not associated with CA IX or GLUT-1 expression. Patients with diffuse HIF-1α staining had a significantly better prognosis than patients with perinecrotically overexpressed HIF-1α.Conclusions:Different regulation pathways of HIF-1α overexpression exist in breast cancer: (1) hypoxia induced, perinecrotic HIF-1α overexpression with strong expression of hypoxia associated genes (CA IX and GLUT-1), which is associated with a poor prognosis; and (2) diffuse HIF-1α overexpression lacking major hypoxia associated downstream effects, resulting in a more favourable prognosis.

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