Cdc42 in Tumor Hypoxia: Molecular Mechanisms of Cellular Adaptation

Tumor hypoxia is a hallmark of solid tumors that promotes aggressiveness and resistance to therapy. Within hypoxic tumors, hypoxia-inducible factor (HIF)-dependent transcriptional programs drive metabolic reprogramming, lactate accumulation, extracellular acidosis, angiogenesis, immune suppression, and invasive phenotypes. Translation of these adaptations into increased tumor cell motility and invasion requires coordinated remodeling of the cytoskeleton and cell polarity machinery. Cdc42, a Rho-family small GTPase regulating actin dynamics, cell polarity, and migration, may therefore link hypoxic signaling to invasive tumor behavior. Here, we review current evidence on the regulation and function of Cdc42 in hypoxic solid tumors and its therapeutic implications. Available studies indicate that hypoxia can induce rapid and potentially reversible Cdc42 activation in selected cancer models. In some experimental systems, interference with Cdc42-associated signaling attenuates hypoxia-induced HIF-1α and VEGF responses, suggesting a role in pro-angiogenic adaptation. However, effects of hypoxia on Cdc42 expression, localization, and activation vary by tumor type, oxygen concentration, exposure duration, and microenvironmental context. Cdc42 therefore remains an emerging rather than validated therapeutic target. Future studies should employ physiologically relevant in vivo models of chronic and cycling hypoxia, directly measure Cdc42-GTP, and more accurately distinguish tumor-cell-intrinsic effects from those occurring in stromal components of the tumor microenvironment.