Hypoxia-inducible factor 1α promotes primary tumor growth and tumor-initiating cell activity in breast cancer

Abstract

IntroductionOverexpression of the oxygen-responsive transcription factor hypoxia-inducible factor 1α (HIF-1α) correlates with poor prognosis in breast cancer patients. The mouse mammary tumor virus polyoma virus middle T (MMTV-PyMT) mouse is a widely utilized preclinical mouse model that resembles human luminal breast cancer and is highly metastatic. Prior studies in which the PyMT model was used demonstrated that HIF-1α is essential to promoting carcinoma onset and lung metastasis, although no differences in primary tumor end point size were observed. Using a refined model system, we investigated whether HIF-1α is directly implicated in the regulation of tumor-initiating cells (TICs) in breast cancer.MethodsMammary tumor epithelial cells were created from MMTV-PyMT mice harboring conditional alleles of Hif1a, followed by transduction ex vivo with either adenovirus β-galactosidase or adenovirus Cre to generate wild-type (WT) and HIF-1α-null (KO) cells, respectively. The impact of HIF-1α deletion on tumor-initiating potential was investigated using tumorsphere assays, limiting dilution transplantation and gene expression analysis.ResultsEfficient deletion of HIF-1α reduced primary tumor growth and suppressed lung metastases, prolonging survival. Loss of HIF-1α led to reduced expression of markers of the basal lineage (K5/K14) in cells and tumors and of multiple genes involved in the epithelial-to-mesenchymal transition. HIF-1α also enhanced tumorsphere formation at normoxia and hypoxia. Decreased expression of several genes in the Notch pathway as well as Vegf and Prominin-1 (CD133)was observed in response to Hif1a deletion. Immunohistochemistry confirmed that CD133 expression was reduced in KO cells and in tumorspheres. Tumorsphere formation was enhanced in CD133hi versus CD133neg cells sorted from PyMT tumors. Limiting dilution transplantation of WT and KO tumor cells into immunocompetent recipients revealed > 30-fold enrichment of TICs in WT cells.ConclusionThese results demonstrate that HIF-1α plays a key role in promoting primary mammary tumor growth and metastasis, in part through regulation of TICs. HIF-1α regulates expression of several members of the Notch pathway, CD133 and markers of the basal lineage in mammary tumors. Our results suggest that CD133, which has not been profiled extensively in breast cancer, may be a useful marker of TICs in the PyMT mouse model. These data reveal for the first time that HIF-1α directly regulates breast TIC activity in vivo.

HIF-1 is involved in the negative regulation of AURKA expression in breast cancer cell lines under hypoxic conditions

“…The stabilization of the hypoxia-inducible transcription factor, HIF-1, is a crucial event that induces changes in the expression of many genes implicated in the growth and survival of neoplastic cells [22,23]. HIF-1 is made up of two subunits, a and b [24].…”

CD133 expression in circulating tumor cells from breast cancer patients: Potential role in resistance to chemotherapy

“…[20][21][22] CD133, which has not been profiled extensively in BC may also define tumor-initiating cells in BC tumors. 23 CD133-expressing tumor cells manifest cancer stem cell properties, characterized by the ability to self-renew in culture, to differentiate into cells that recapitulate original breast tumors, and to form tumors in animal models. Moreover, expression of stem cell associated genes, such as Notch1, ALDH1, Fgfr1 and Sox1, is increased in CD44 pos /CD24 neg and CD133 pos cells.…”

Hypoxia induces the breast cancer stem cell phenotype by HIF-dependent and ALKBH5-mediated m 6 A-demethylation of NANOG mRNA

“…In addition, HIF-1α is required for hypoxia-induced epithelial-mesenchymal transition (24), which is also linked to the BCSC phenotype (25). In contrast to WT cells, the capacity of mouse HIF-1α-KO (26) or human HIF-1α-knockdown (21) breast cancer cells to initiate tumorigenesis is markedly impaired.…”