Serum starvation induces density-dependent apoptosis via HIF-1 activation and JNK suppression

Serum deprivation is a well-established inducer of apoptosis, yet the molecular mechanisms governing this process remain incompletely understood. Here, we show that serum starvation selectively triggers intrinsic apoptosis in high-density murine embryonic fibroblasts (MEFs) through coordinated HIF-1α activation and JNK signaling suppression. Knockdown of HIF-1α abolishes caspase-3 activation and apoptosis induced by serum deprivation, whereas upregulation of HIF-1α in low-density cells recapitulates the apoptotic response observed in high-density cultures. Simultaneously, serum deprivation leads to the suppression of the JNK pathway, which contributes to apoptosis. Notably, combined HIF-1α activation and JNK inhibition in low-density cells fully mimics the apoptotic phenotype of high-density conditions, underscoring the interplay between these pathways. Together, these findings define a density-dependent apoptotic switch in which HIF-1α drives metabolic stress adaptation, whereas JNK suppression removes a critical survival signal, converging to promote mitochondrial-mediated cell death. This work provides a mechanistic framework for understanding nutrient stress-induced apoptosis and suggests potential therapeutic targets for diseases characterized by aberrant cell survival.