Rap-Interacting Proteins are Key Players in the Rap Symphony Orchestra

Rap, a member of the Ras-like small G-protein family, is a key node among G-protein coupled receptors (GPCR), receptor tyrosine kinases (RTKs), ion channels and many other downstream pathways. Rap plays a unique role in cell morphogenesis, adhesion, migration, exocytosis, proliferation, apoptosis and carcinogenesis. The complexity and diversity of Rap functions are tightly regulated by Rap-interacting proteins such as GEFs, GAPs, Rap effectors and scaffold proteins. These interacting proteins decide the subcellular localization of Rap, the interaction modes with downstream Rap effectors and tune Rap as an atypical molecular conductor, coupling extra- and intracellular signals to various pathways. In this review, we summarize four groups of Rap-interacting proteins, highlight their distinctions in Rap-binding properties and interactive modes and discuss their contribution to the spatiotemporal regulation of Rap as well as the implications of targeting Rap-interacting proteins in human cancer therapy.