FOXO3a-dependent up-regulation of Mxi1-0 promotes hypoxia-induced It apoptosis in endothelial cells
CELLULAR SIGNALLING
Authors: Hu, Zhenzhen; Wang, Feng; Wu, Zhen; Gu, Hao; Dong, Na; Jiang, Xiuqin; Xu, Jinjin; Wu, Zhiwei; Wechsler, Daniel S.; Zheng, Datong
Abstract
Endothelial cell apoptosis induced by hypoxia is implicated in the pathogenesis of vascular diseases. However, the underlying mechanism is not clearly elucidated. In this study, we found that hypoxia increased Mxi1-0 expression, and the Mxi1-0 siRNA could inhibit caspase-8 activation and apoptosis in HUVECs induced by hypoxia. In addition, hypoxia induced FOXO3 activation, while Mxi1-0 expression and apoptosis were inhibited by transfection with FOXO3 siRNA. Using ChIP assay, we confirmed that FOXO3a binds to the Mxi1-0 promoter region. Furthermore, hypoxia treatment leads to remarkable production of reactive oxygen species (ROS), while ROS scavenger N-acetyl-L-cysteine (NAC) inhibits hypoxia-induced ROS production, apoptosis and FOXO3 amediated Mxi1-0 up-regulation. Finally, we found that the HIF-1 alpha siRNA inhibited hypoxia-induced HIF-1 alpha expression and ROS production, as well as FOXO3a/Mxi1-0 activation and apoptosis in HUVECs. Taken together, this study identifies a HIF-1 alpha/FOXO3a/Mxil-0/caspase-8 signaling pathway in hypoxia-induced endothelial cell apoptosis. These data also indicate that HIF-1 alpha-dependent ROS production is required for FOXO3a-mediated Mxi1-0 up-regulation and apoptosis in hypoxic endothelial cells.
Subjugation of TGF beta Signaling by Human Papilloma Virus in Head and Neck Squamous Cell Carcinoma Shifts DNA Repair from Homologous Recombination to Alternative End Joining
CLINICAL CANCER RESEARCH
Authors: Liu, Qi; Ma, Lin; Jones, Trevor; Palomero, Luis; Angel Pujana, Miquel; Martinez-Ruiz, Haydeliz; Ha, Patrick K.; Murnane, John; Cuartas, Isabel; Seoane, Joan; Baumann, Michael; Linge, Annett; Barcellos-Hoff, Mary Helen
Abstract
Purpose: Following cytotoxic therapy, 70% of patients with human papillomavirus (HPV)-positive oropharyngeal head and neck squamous cell carcinoma (HNSCC) are alive at 5 years compared with 30% of those with similar HPV-negative cancer. Loss of TGF beta signaling is a poorly studied consequence of HPV that could contribute to patient outcome by compromising DNA repair. Experimental Design: Human HNSCC cell lines (n = 9), patient-derived xenografts (n = 9), tissue microarray (n = 194), TCGA expression data (n = 279), and primary tumor specimens (n = 10) were used to define the relationship between TGF beta competency, response to DNA damage, and type of DNA repair. Results: Analysis of HNSCC specimens in situ and in vitro showed that HPV associated with loss of TGF beta signaling that increased response to radiation or cisplatin. TGF beta suppressedmiR-182, which inhibited both BRCA1, necessary for homologous recombination repair (HRR), and FOXO3, required for ATM kinase activity. TGF beta signaling blockade by either HPV or inhibitors released miR182 control, compromised HRR and increased response to PARP inhibition. Antagonizing miR-182 rescued the HRR deficit in HPV-positive cells. Loss of TGF beta signaling unexpectedly increased repair by error prone, alternative end-joining (alt-EJ). Conclusions: HPV-positive HNSCC cells are unresponsive to TGF beta. Abrogated TGF beta signaling compromises repair by HRR and increases reliance on alt-EJ, which provides a mechanistic basis for sensitivity to PARP inhibitors. The effect of HPV in HNSCC provides critical validation of TGF beta's role in DNA repair proficiency and further raises the translational potential of TGF beta inhibitors in cancer therapy.