Final answer:
The statement is false. GEFs activate Rab GTPases by promoting the exchange of GDP for GTP, while GAPs stimulate the hydrolysis of GTP to GDP, which inactivates the Rab proteins.
Step-by-step explanation:
The question pertains to the functions of Guanine Nucleotide Exchange Factors (GEFs) and their effects on Rab GTPases. The statement provided is false. GEFs are in fact responsible for activating Rab proteins by facilitating the exchange of GDP for GTP, not for stimulating Rab to hydrolyze GTP. Rab proteins then promote various cellular events, such as vesicle trafficking, by being in the GTP-bound state. It is the GTPase-activating proteins (GAPs) that stimulate the hydrolysis of GTP to GDP, inactivating Rab and terminating the signaling event.
For instance, in the case of RAS G-proteins, if their intrinsic GTPase activity is inhibited, which means RAS cannot convert GTP to GDP, it can lead to continuous cell signaling and potentially uncontrolled cell growth.