Member of GRP1 signaling complexes that are acutely recruited to plasma membrane ruffles in response to insulin receptor signaling. May function as a scaffolding protein that regulates epithelial cell polarity by connecting ARF6 activation with the PAR3 complex (PubMed:20080746). Plays a redundant role with FRMD4A in epithelial polarization (PubMed:20080746). Interacts with CYTH3 (PubMed:11445584, PubMed:20080746). Interacts with PARD3 (PubMed:20080746). Interacts with CYTH1. Colocalized with PARD3 at adherens junction and tight junction (PubMed:20080746). Isoform 1 is expressed in the brain. Isoform 2 is expressed in the lung (at protein level). Extended N-terminus.