ITSN1 regulates SAM68 solubility through SH3 domain interactions with SAM68 proline-rich motifs.

SAM68 is an mRNA-binding protein involved in mRNA processing in the nucleus that forms membraneless compartments called SAM68 Nuclear Bodies (SNBs). We found that intersectin 1 (ITSN1), a multidomain scaffold protein harboring five soluble SH3 domains, interacts with SAM68 proline-rich motifs (PRMs) surrounded by self-adhesive low complexity domains. While SAM68 is poorly soluble in vitro, the interaction of ITSN1 SH3 domains and mRNA with SAM68 enhances its solubility.

The atypical Rho GTPase RhoU interacts with intersectin-2 to regulate endosomal recycling pathways.

Rho GTPases play a key role in various membrane trafficking processes. RhoU is an atypical small Rho GTPase related to Rac/Cdc42, which possesses unique N- and C-terminal domains that regulate its function and its subcellular localization. RhoU localizes at the plasma membrane, on endosomes and in cell adhesion structures where it governs cell signaling, differentiation and migration.

WIP/ITSN1 complex is involved in cellular vesicle trafficking and formation of filopodia-like protrusions.

WIP (WASP interacting protein) together with N-WASP (neural Wiskott-Aldrich syndrome protein) regulates actin polymerization that is crucial for invadopodia and filopodia formation. Recently, we reported the WIP interaction with ITSN1 which is highly implicated in endo-/exocytosis, apoptosis, mitogenic signaling and cytoskeleton rearrangements. Here we demonstrate that the WIP/ITSN1 complex is involved in the transferrin receptor recycling and partially co-localizes with a marker of the fast recycling endosomes, RAB4.

Ubiquitin-ligase AIP4 controls differential ubiquitination and stability of isoforms of the scaffold protein ITSN1.

At present, the role of ubiquitination of cargoes internalized from the plasma membrane is better understood than the consequences of ubiquitination of proteins comprising the endocytic machinery. Here, we show that the E3 ubiquitin ligase AIP4/ITCH contributes to the differential ubiquitination of isoforms of the endocytic scaffold protein intersectin1 (ITSN1). The major isoform ITSN1-s is monoubiquitinated, whereas the minor one, ITSN1-22a undergoes a combination of mono- and oligoubiquitination.

Mammalian verprolin CR16 acts as a modulator of ITSN scaffold proteins association with actin.

Actin cytoskeleton rearrangements are required for normal cell functioning, and their deregulation leads to various pathologies. Members of two mammalian protein families - ITSNs (ITSN1 and ITSN2) and verprolins (WIP, CR16 and WIRE) are involved in Cdc42/N-WASP/Arp2/3 signaling pathway-mediated remodeling of the actin cytoskeleton. Recently we demonstrated that ITSNs interact with the actin-regulating protein WIP.