Guanine Nucleotide Exchange Factors and Small GTPases: Their Regulation and Functions, Diseases, and Therapeutic Targets

Guanine nucleotide exchange factors (GEFs) and their small GTPase substrates constitute a fundamental regulatory system that governs diverse cellular processes, including cytoskeletal dynamics, membrane trafficking, and transcriptional regulation. Since their discovery, GEFs have been recognized as molecular switches that activate small GTPases by catalyzing GDP‐to‐GTP exchange, thereby playing pivotal roles in cellular signaling and homeostasis. Despite extensive research, key gaps remain in understanding the spatiotemporal regulation of GEF isoforms, their functional redundancy in disease, and the development of isoform‐specific drugs. This review examines the regulatory mechanisms and physiological roles of GEFs, highlighting their growing potential as therapeutic targets. We explore the phylogenetic classification of GEFs into major families (Ras, Rho, Rab, and ArfGEFs) and their regulatory networks, which encompass subcellular localization, posttranslational modifications, and scaffolding interactions. Special emphasis is placed on GEF–H1, a microtubule‐regulated RhoGEF, and its roles in cytoskeletal remodeling, cancer metastasis, and immune responses. We also examine GEF dysregulation in diseases like cancer, neurodegeneration, and cardiovascular disorders, and assess current therapies, such as small‐molecule inhibitors and emerging PROTAC technology. This review connects GEF biology with clinical applications by combining basic research with translational insights, providing guidance for precision medicine and novel therapeutic strategies targeting GEF‐related diseases.