Negatively regulates TGF-beta-induced signaling; in cooperation with SKI prevents the translocation of SMAD2 from the nucleus to the cytoplasm in response to TGF-beta. Acts as an adapter that mediates the specific recognition of LIMK1 by CDC42BPA and CDC42BPB in the lamellipodia. LRAP25-mediated CDC42BPA/CDC42BPB targeting to LIMK1 and the lamellipodium results in LIMK1 activation and the subsequent phosphorylation of CFL1 which is important for lamellipodial F-actin regulation. Interacts with SKI (By similarity). Interacts (via LRR repeat) with CDC42BPA (via AGC-kinase C-terminal domain) and CDC42BPB (via AGC-kinase C-terminal domain) (PubMed:25107909). Interacts (via LRR repeat) with LIMK1 (via LIM zinc-binding domains). Forms a tripartite complex with CDC42BPA, CDC42BPB and LIMK1 (By similarity). Co-localizes with CDC42BPA, CDC42BPB and LIMK1 in the lamellipodium. Additional isoforms seem to exist. Belongs to the FAM89 family.