ARHGEF39 is a Dbl-family guanine nucleotide exchange factor that functions primarily as a Rac1-GEF, promoting cell proliferation and migration through activation of small GTPase signaling cascades. As a Rac-GEF, ARHGEF39 facilitates GDP-to-GTP exchange on Rac1, driving actin cytoskeleton reorganization essential for cell motility 1. The protein operates through multiple signaling pathways depending on cellular context: in lung adenocarcinoma, ARHGEF39 mediates Rac1-dependent migration upon EGFR and c-Met activation 1; in gastric cancer, it promotes proliferation and migration via Akt/PI3K signaling 2; and in non-small cell lung cancer, it activates the Rac1/P38 MAPK/ATF2 axis, increasing expression of cell-cycle and invasion-associated proteins (Cyclin A2, Cyclin D1, MMP2) 3. In hepatocellular carcinoma, ARHGEF39 is transcriptionally regulated by E2F1 and promotes metastasis through enhanced fatty acid metabolism 4. Clinically, ARHGEF39 overexpression is significantly associated with poor prognosis across multiple cancer types including HCC, NSCLC, and gastric cancer, correlating with increased tumor size and reduced overall survival 53. Additionally, ARHGEF39 variants have been identified as African ancestry-specific risk loci for eosinophilic esophagitis 6 and putative neurological disorder susceptibility factors 7.