The normal function of NF1 is to promote the intrinsic GTPase function of the RAS oncogene. Mechanism:- RAS has an intrinsic GTPase activity that is accelerated by GTPase-activating proteins (GAPs), which bind to active RAS and augment its GTPase activity by more than 1000-fold, thereby terminating signal transduction. Thus, GAPs prevent uncontrolled RAS activity. When the Ras protein is bound to GTP, the growth-promoting function of the molecule is "ON". On hydrolysis of the GTP to GDP, Ras is conveed to an inactive state. GAPs (GTPase Activating Proteins), such as NF-1, suppress cell growth by stimulating GTP hydrolysis. Disabling mutations of neurofibromin 1, a GAP (GTPase-activating protein) encoded by the NF1 gene, are associated with the inherited cancer syndrome familial neurofibromatosis type 1. NF1 is therefore an example of a tumor suppressor gene that acts through negative regulation of RAS signaling (inhibitor of RAS/MAPK signaling). Other Options:- Caspases function to cleave cellular proteins once apoptosis is triggered Vascular endothelial growth factor promotes tumor angiogenesis RB and TP53 function as cell cycle checkpoint regulators