The Cdc42-interacting Protein-4 (CIP4) Gene Knock-out Mouse Reveals Delayed and Decreased Endocytosis

Abstract

The newly described F-BAR (Fer/CIP4 and Bin, amphiphysin, Rvs) family of proteins includes Cdc42-interacting protein-4 (CIP4), formin-binding protein-17 (FBP-17) and transactivator of cytoskeletal assembly-1 (Toca-1), and drives membrane deformation and invagination. Membrane remodeling affects endocytosis, vesicle budding, and cargo selection. The F-BAR family presents a novel family of proteins, which little is known about their in vivo function. We investigated the physiological role of CIP4, by creating Cip4-null mice through homologous recombination. Compared with their wild-type littermates, the Cip4-null mice displayed lower early post-prandial glucose levels. Adipocytes isolated from Cip4-null mice exhibited increased [ 14 C]2-deoxyglucose uptake compared with cells from wild-type mice. The enhanced insulin sensitivity was not due to higher levels of insulin or phospho-Akt, a critical player in insulin signaling. However, higher glucose transporter 4 (GLUT4) levels were detected in muscle membrane fractions in Cip4-null mice under insulin stimulation. Mouse embryonic fibroblasts from Cip4-null mice demonstrated decreased transferrin uptake, fluorescein isothiocyanate-dextran, and horseradish peroxidase uptake, indicating that CIP4 affects multiple modes of endocytosis. These studies demonstrate a physiological role for CIP4 in endocytosis leading to a whole animal phenotype.

Cooperative functions of the two F-BAR proteins Cip4 and Nostrin in regulating E-cadherin in epithelial morphogenesis

“…These data support an important role for F-BAR proteins in the regulation of membrane curvatures in a sequential manner during endocytosis (Suetsugu, 2010). Despite their pivotal functions in linking actin and membrane dynamics, recent single-knockout studies revealed that many F-BAR proteins are not essential for development and, thus, might have redundant or cooperative functions in vivo (Feng et al, 2010;Fricke et al, 2009). In fission yeast, the Cip4-like F-BAR proteins Cdc15 and Imp2 are examples for such synergistic function of two F-BAR proteins.…”

“…However, our understanding of how F-BAR proteins function in vivo in a physiological context is still incomplete because loss-offunction studies in higher organisms are limited. Mice that lack Cip4 are viable and show only a weak endocytosis defect of the insulin-responsive glucose transporter Glut4 (Feng et al, 2010). Mutant animals also display a reduced platelet production and defective integrin-dependent T-cell adhesion, both defects are probably caused by decreased WASP-dependent actin polymerization, rather than impaired endocytosis (Chen et al, 2013).…”

Cdc42-interacting protein 4 is a Src substrate that regulates invadopodia and invasiveness of breast tumors by promoting MT1-MMP endocytosis

“…CIP4-knockout mice are viable, but have altered glucose metabolism (Feng et al, 2010). This is consistent with cell-based studies implicating CIP4 in regulating both the trafficking of GLUT4 storage vesicles to the plasma membrane (Lodhi et al, 2007), as well as GLUT4 endocytosis via CIP4 interactions with N-WASP and dynamin-2 (Hartig et al, 2009).…”

Rho GTPases and their role in organizing the actin cytoskeleton

“…The N-WASP-WIP complex, together with Toca-1 or FBP17, activates actin polymerization on phosphatidylserinecontaining membranes (Takano et al, 2008). These roles have been confirmed with the observation that mouse Cip4-null cells have delayed and decreased endocytosis (Feng et al, 2010).…”