RAP1A is a small GTPase that serves multiple critical functions in vascular biology and cellular signaling. As a primary function, RAP1A regulates endothelial barrier integrity and vascular homeostasis through distinct mechanisms from its closely related isoform RAP1B 1. RAP1A specifically modulates endothelial calcium homeostasis by restricting Orai1-mediated store-operated calcium entry, thereby limiting inflammatory responses and vascular permeability 2. The protein also plays essential roles in integrin activation, where constitutively active RAP1A can bypass PKCα requirements and promote formation of integrin activation complexes containing talin and RIAM 3. In hepatocytes, RAP1A regulates glucose homeostasis by suppressing gluconeogenic gene expression through Akt-mediated FoxO1 inhibition, with its activity dependent on geranylgeranylation 4. RAP1A also controls PCSK9 expression post-transcriptionally via the RhoA-ROCK pathway, influencing cholesterol homeostasis 5. Additionally, RAP1A participates in neutrophil extracellular trap formation through the C5aR1/LTB4R1-Rap1a/B-Raf/ERK signaling pathway 6. Clinically, RAP1A dysfunction is associated with inflammatory lung injury, glucose intolerance, statin-induced metabolic side effects, and compromised immune responses in low birth weight newborns 246.