The Formin family protein, formin homolog overexpressed in spleen, interacts with the insulin-responsive aminopeptidase and profilin IIa.
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.
Tojo
Hideaki
H
Discovery Research Laboratories II, Pharmaceutical Research Division, Takeda Chemical Industries Co., Ltd., Tsukuba, Ibaraki 300-4293, Japan. Tojo_Hideaki@takeda.co.jp
Kaieda
Isao
I
Hattori
Harumi
H
Katayama
Nozomi
N
Yoshimura
Koji
K
Kakimoto
Shigeya
S
Fujisawa
Yukio
Y
Presman
Eleonora
E
Brooks
Cydney C
CC
Pilch
Paul F
PF
D016475:3T3 Cells / Q000378:metabolism; D017667:Adipocytes / Q000378:metabolism; D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000626:Aminopeptidases / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002478:Cells, Cultured; D003285:Contractile Proteins / Q000235:genetics / Q000378:metabolism*; D005326:Fetal Proteins / Q000235:genetics* / Q000378:metabolism*; D000080865:Formins; D005786:Gene Expression Regulation; D005947:Glucose / Q000493:pharmacokinetics; D051275:Glucose Transporter Type 4; D006801:Humans; D007328:Insulin / Q000378:metabolism; D008297:Male; D051379:Mice; D008840:Microfilament Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D032342:Muscle Cells / Q000378:metabolism; D009124:Muscle Proteins; D018482:Muscle, Skeletal / Q000502:physiology; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism*; D051304:Profilins; D017434:Protein Structure, Tertiary; D051381:Rats; D017207:Rats, Sprague-Dawley; D013154:Spleen / Q000502:physiology*
D003285:Contractile Proteins; C120021:FHOD1 protein, human; D005326:Fetal Proteins; D000080865:Formins; D051275:Glucose Transporter Type 4; D007328:Insulin; D008840:Microfilament Proteins; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D009687:Nuclear Proteins; C495738:PFN1 protein, human; C495739:Pfn1 protein, mouse; C495743:Pfn2 protein, rat; D051304:Profilins; C495692:SLC2A4 protein, human; C495693:Slc2a4 protein, mouse; C495694:Slc2a4 protein, rat; D000626:Aminopeptidases; D005947:Glucose