The highly conserved 56 kDa multidomain cyclase associated protein 1 (CAP1) works in concert with cofilin and profilin to modulate actin filament turnover by facilitating cofilin-mediated actin filament severing and depolymerisation and catalysing profilin-mediated regeneration of actin monomers for reutilisation in growing filaments. CAP1 is abundant in platelets. Rap1 proteins are members of the Ras subfamily of small GTPases involved in many biological responses, including adhesion, cell proliferation, and differentiation. Like all small GTPases, they work as molecular allosteric units that are active in signaling only when associated with the proper membrane compartment. In obesity, adipose tissue secretes additional resistin, which prompts a proinflammatory effect through its action on adenylate cyclase-associated protein 1 (CAP1). The RETN and CAP1 polymorphisms and gene expression may be potential biomarkers for breast cancer risk. The expression of resistin and CAP1 in synovial tissue was stronger in RA than in osteoarthritis (OA). Resistin contributes to the pathogenesis of RA by increasing chemokine production by FLSs via CAP1 in synovial tissue.