The Formin Family Protein, Formin Homolog Overexpressed in Spleen, Interacts with the Insulin-Responsive Aminopeptidase and Profilin IIa

• Published in: Molecular endocrinology (Baltimore, Md.) Md.), 2003-07, Vol.17 (7), p.1216-1229
• Main Authors: Tojo, Hideaki, Kaieda, Isao, Hattori, Harumi, Katayama, Nozomi, Yoshimura, Koji, Kakimoto, Shigeya, Fujisawa, Yukio, Presman, Eleonora, Brooks, Cydney C, Pilch, Paul F
• Format: Article
• Language: English
• Subjects: 3T3 Cells - metabolism; Adipocytes - metabolism; Alternative Splicing; Amino Acid Sequence; Aminopeptidases - genetics; Aminopeptidases - metabolism; Animals; Cells, Cultured; Contractile Proteins - genetics; Contractile Proteins - metabolism; Fetal Proteins - genetics; Fetal Proteins - metabolism; Gene Expression Regulation; Glucose - pharmacokinetics; Glucose Transporter Type 4; Humans; Insulin - metabolism; Male; Mice; Microfilament Proteins - genetics; Microfilament Proteins - metabolism; Molecular Sequence Data; Monosaccharide Transport Proteins - metabolism; Muscle Cells - metabolism; Muscle Proteins; Muscle, Skeletal - physiology; Nuclear Proteins - genetics; Nuclear Proteins - metabolism; Profilins; Protein Structure, Tertiary; Rats; Rats, Sprague-Dawley; Spleen - physiology
• ISSN: 0888-8809; 1944-9917
• DOI: 10.1210/me.2003-0056

Insulin stimulates translocation of glucose transporter isoform type 4 (GLUT4) and the insulin-responsive aminopeptidase (IRAP) from an intracellular storage pool to the plasma membrane in muscle and fat cells. A role for the cytoskeleton in insulin action has been postulated, and the insulin signaling pathway has been well investigated; however, the molecular mechanism by which GLUT4/IRAP-containing vesicles move from an interior location to the cell surface in response to insulin is incompletely understood. Here, we have screened for IRAP-binding proteins using a yeast two-hybrid system and have found that the C-terminal domain of FHOS (formin homolog overexpressed in spleen) interacts with the N-terminal cytoplasmic domain of IRAP. FHOS is a member of the Formin/Diaphanous family of proteins that is expressed most abundantly in skeletal muscle. In addition, there are two novel types of FHOS transcripts generated by alternative mRNA splicing. FHOS78 has a 78-bp insertion and it is expressed mainly in skeletal muscle where it may be the most abundant isoform in humans. The ubiquitously expressed FHOS24 has a 24-bp insertion encoding an in-frame stop codon that results in a truncated polypeptide. It is known that some formin family proteins interact with the actin-binding profilin proteins. Both FHOS and FHOS78 bound to profilin IIa via their formin homology 1 domains, but neither bound profilin I or IIb. Overexpression of FHOS and FHOS78 resulted in enhanced insulin-stimulated glucose uptake in L6 cells to similar levels. However, overexpression of FHOS24, lacking the IRAP-binding domain, did not affect insulin-stimulated glucose uptake. These findings suggest that FHOS mediates an interaction between GLUT4/IRAP-containing vesicles and the cytoskeleton and may participate in exocytosis and/or retention of this membrane compartment.