RESUMEN
Hypoxia-inducible factors (HIFs) are master regulators of the transcriptional response to low oxygen and play essential roles in embryonic development, tissue homeostasis, and disease. Recent studies have demonstrated that hematopoietic stem cells (HSCs) within the bone marrow localize to a hypoxic niche and that HIF-1α promotes HSC adaptation to stress. Because the related factor HIF-2α is also expressed in HSCs, the combined role of HIF-1α and HIF-2α in HSC maintenance is unclear. To this end, we have conditionally deleted the HIF-α dimerization partner, the aryl hydrocarbon receptor nuclear translocator (ARNT) in the hematopoietic system to ablate activity of both HIF-1α and HIF-2α and assessed the functional consequence of ARNT deficiency on fetal liver and adult hematopoiesis. We determined that ARNT is essential for adult and fetal HSC viability and homeostasis. Importantly, conditional knockout of both Hif-1α and Hif-2α phenocopied key aspects of these HSC phenotypes, demonstrating that the impact of Arnt deletion is primarily HIF dependent. ARNT-deficient long-term HSCs underwent apoptosis, potentially because of reduced B-cell lymphoma 2 (BCL-2) and vascular endothelial growth factor A (VEGF-A) expression. Our results suggest that HIF activity may regulate HSC homeostasis through these prosurvival factors.
Asunto(s)
Translocador Nuclear del Receptor de Aril Hidrocarburo/metabolismo , Hematopoyesis/fisiología , Células Madre Hematopoyéticas/citología , Células Madre Hematopoyéticas/metabolismo , Animales , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/metabolismo , Diferenciación Celular/fisiología , Supervivencia Celular , Subunidad alfa del Factor 1 Inducible por Hipoxia/metabolismo , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Reacción en Cadena en Tiempo Real de la PolimerasaRESUMEN
Hypoxia-inducible factors (HIFs) accumulate in both neoplastic and inflammatory cells within the tumor microenvironment and impact the progression of a variety of diseases, including colorectal cancer. Pharmacological HIF inhibition represents a novel therapeutic strategy for cancer treatment. We show here that acriflavine (ACF), a naturally occurring compound known to repress HIF transcriptional activity, halts the progression of an autochthonous model of established colitis-associated colon cancer (CAC) in immunocompetent mice. ACF treatment resulted in decreased tumor number, size and advancement (based on histopathological scoring) of CAC. Moreover, ACF treatment corresponded with decreased macrophage infiltration and vascularity in colorectal tumors. Importantly, ACF treatment inhibited the hypoxic induction of M-CSFR, as well as the expression of the angiogenic factor (vascular endothelial growth factor), a canonical HIF target, with little to no impact on the Nuclear factor-kappa B pathway in bone marrow-derived macrophages. These effects probably explain the observed in vivo phenotypes. Finally, an allograft tumor model further confirmed that ACF treatment inhibits tumor growth through HIF-dependent mechanisms. These results suggest pharmacological HIF inhibition in multiple cell types, including epithelial and innate immune cells, significantly limits tumor growth and progression.
Asunto(s)
Neoplasias Colorrectales/genética , Neoplasias Colorrectales/patología , Subunidad alfa del Factor 1 Inducible por Hipoxia/genética , Acriflavina/administración & dosificación , Acriflavina/farmacología , Animales , Antineoplásicos/administración & dosificación , Antineoplásicos/farmacología , Translocador Nuclear del Receptor de Aril Hidrocarburo/genética , Translocador Nuclear del Receptor de Aril Hidrocarburo/metabolismo , Línea Celular Tumoral , Proliferación Celular/efectos de los fármacos , Neoplasias Colorrectales/metabolismo , Modelos Animales de Enfermedad , Progresión de la Enfermedad , Femenino , Humanos , Subunidad alfa del Factor 1 Inducible por Hipoxia/metabolismo , Macrófagos/efectos de los fármacos , Macrófagos/metabolismo , Macrófagos/patología , Ratones , Neovascularización Patológica/tratamiento farmacológico , Neovascularización Patológica/genética , Transducción de Señal/efectos de los fármacos , Transcripción Genética/efectos de los fármacos , Carga Tumoral/efectos de los fármacos , Carga Tumoral/genética , Ensayos Antitumor por Modelo de XenoinjertoRESUMEN
Solid tumors exhibit heterogeneous microenvironments, often characterized by limiting concentrations of oxygen (O2), glucose, and other nutrients. How oncogenic mutations alter stress response pathways, metabolism, and cell survival in the face of these challenges is incompletely understood. Here we report that constitutive mammalian target of rapamycin complex 1 (mTORC1) activity renders hypoxic cells dependent on exogenous desaturated lipids, as levels of de novo synthesized unsaturated fatty acids are reduced under low O2. Specifically, we demonstrate that hypoxic Tsc2(-/-) (tuberous sclerosis complex 2(-/-)) cells deprived of serum lipids exhibit a magnified unfolded protein response (UPR) but fail to appropriately expand their endoplasmic reticulum (ER), leading to inositol-requiring protein-1 (IRE1)-dependent cell death that can be reversed by the addition of unsaturated lipids. UPR activation and apoptosis were also detected in Tsc2-deficient kidney tumors. Importantly, we observed this phenotype in multiple human cancer cell lines and suggest that cells committed to unregulated growth within ischemic tumor microenvironments are unable to balance lipid and protein synthesis due to a critical limitation in desaturated lipids.