EXPLORING THE CROSSTALK BETWEEN AUTOPHAGY AND APOPTOSIS IN HYPOXIC TUMOR MICROENVIRONMENTS

Abstract

Hypoxia is a hallmark of the tumor microenvironment that drives profound metabolic and molecular changes in cancer cells. This study investigates the dynamic crosstalk between autophagy and apoptosis in response to hypoxic stress using in vitro models of solid tumors. Our quantitative findings demonstrate that under early hypoxic conditions, autophagy is significantly upregulated as a pro-survival response, evidenced by increased LC3B-II/LC3B-I ratios and p62 degradation, while apoptotic markers remain relatively suppressed. However, prolonged exposure to hypoxia results in a marked shift toward apoptosis, characterized by increased Bax/Bcl-2 ratios, mitochondrial depolarization, caspase-3/7 activation, and loss of cell viability. HIF-1α expression was consistently elevated, triggering transcription of autophagy-related genes such as BNIP3 and ULK1, yet also contributing to oxidative stress and ER stress pathways that activate intrinsic apoptosis. Assays for cell functions indicated that interrupting autophagy in cells increases the likelihood of cell death from hypoxia, whereas stopping apoptosis allows cells to survive by relying on autophagy. The use of flow cytometry, JC-1 staining, MTT viability assays and clonogenic survival increases the evidence for a shift from protective autophagy to death by apoptosis. Using integrated approaches of protein and gene expression, coupled with imaging and function analysis, it was found that cell type is determined by the delicate balance of molecules in response to hypoxia time and pathway changes. Thanks to these results, we can see how stress in tumors changes over time and how controlling autophagy-apoptosis interactions may help treat cancer more effectively when tumors lack oxygen.