title: Downregulation of stromal BRCA1 drives breast cancer tumor growth via upregulation of HIF-1α, autophagy and ketone body production.
abstract: Our recent studies have mechanistically demonstrated that cancer-associated fibroblasts (CAFs) produce energy-rich metabolites that functionally support the growth of cancer cells. Also, several authors have demonstrated that DNA instability in the tumor stroma greatly contributes to carcinogenesis. To further test this hypothesis, we stably knocked-down BRCA1 expression in human hTERT-immortalized fibroblasts (shBRCA1) using an shRNA lentiviral approach. As expected, shBRCA1 fibroblasts displayed an elevated growth rate. Using immunofluorescence and immunoblot analysis, shBRCA1 fibroblasts demonstrated an increase in markers of autophagy and mitophagy. Most notably, shBRCA1 fibroblasts also displayed an elevation of HIF-1α expression. In accordance with these findings, shBRCA1 fibroblasts showed a 5.5-fold increase in ketone body production; ketone bodies function as high-energy mitochondrial fuels. This is consistent with the onset of mitochondrial dysfunction in BRCA1-deficient fibroblasts. Conversely, after 48 h of co-culturing shBRCA1 fibroblasts with a human breast cancer cell line (MDA-MB-231 cell), mitochondrial activity was enhanced in these epithelial cancer cells. Interestingly, our preclinical studies using xenografts demonstrated that shBRCA1 fibroblasts induced an ~2.2-fold increase in tumor growth when co-injected with MDA-MB-231 cells into nude mice. We conclude that a BRCA1 deficiency in the tumor stroma metabolically promotes cancer progression, via ketone production.
authors.affiliation: The Jefferson Stem Cell Biology and Regenerative Medicine Center, Thomas Jefferson University, Philadelphia, PA, USA.
authors.forename: Ahmed F
authors.initials: AF
authors.lastname: Salem
authors.forename: Anthony
authors.initials: A
authors.lastname: Howell
authors.forename: Marina
authors.initials: M
authors.lastname: Sartini
authors.forename: Federica
authors.initials: F
authors.lastname: Sotgia
authors.forename: Michael P
authors.initials: MP
authors.lastname: Lisanti
mesh_terms: D000818:Animals; D001343:Autophagy; D019313:BRCA1 Protein / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic; D018920:Coculture Techniques; D015536:Down-Regulation; D005260:Female; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D007657:Ketone Bodies / Q000378:metabolism*; D051379:Mice; D008819:Mice, Nude; D008928:Mitochondria / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D013385:Succinate Dehydrogenase / Q000378:metabolism; D019098:Telomerase / Q000378:metabolism; D014183:Transplantation, Heterologous; D059016:Tumor Microenvironment; D015854:Up-Regulation
chemical_list: D019313:BRCA1 Protein; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007657:Ketone Bodies; D034741:RNA, Small Interfering; C108095:SDHB protein, human; D013385:Succinate Dehydrogenase; C509186:TERT protein, human; D019098:Telomerase