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Toshio Hosaka

Publications and source records attributed to Toshio Hosaka.

4 recordsLinked to original sources
PubMed2006

Molecular cloning of a murine glycerol-3-phosphate acyltransferase-like protein 1 (xGPAT1).

A novel murine glycerol-3-phosphate acyltransferase-like protein 1 (named xGPAT1) has been cloned. The mouse xGPAT1 gene is located on mouse Chromosome 2, spans >19 kb, and consists of at least 23 exons. The protein is 32% identical and 72% similar to mouse mitochondrial GPAT (mtGPAT) on the amino acid level. Sequencing analysis confirmed that xGPAT1 has a 2403-bp open reading frame (ORF) that encodes an 801-amino acid protein with an estimated molecular mass of 89.1 kDa. A hydropathy plot of the deduced xGPAT1 protein showed a high degree of similarity with that of the mtGPAT protein. Using 5'-rapid amplification of cDNA ends, two alternate, untranslated exon 1 (1a and b) isoforms were obtained, generating variants xGPAT1-v1 and xGPAT1-v2. xGPAT1-v1 is expressed in mouse heart, liver, spleen, kidney and murine inner medullary collecting duct 3 (mIMCD3) cells, while xGPAT1-v2 is expressed in mouse liver, spleen, kidney, white and brown adipose tissues and 3T3-L1 pre- and post-adipocytes. xGPAT1 was distributed in the membrane fraction and showed GPAT activity when epitope-tagged xGPAT1 was expressed in Chinese hamster ovary (CHO)-K1 cells.

Amino Acid Sequence↗
PubMed2005

Dynamics of lipid droplet-associated proteins during hormonally stimulated lipolysis in engineered adipocytes: stabilization and lipid droplet binding of adipocyte differentiation-related protein/adipophilin.

In mature adipocytes, triglyceride is stored within lipid droplets, which are coated with the protein perilipin, which functions to regulate lipolysis by controlling lipase access to the droplet in a hormone-regulatable fashion. Adipocyte differentiation-related protein (ADRP) is a widely expressed lipid droplet binding protein that is coexpressed with perilipin in differentiating fat cells but is minimally present in fully differentiated cultured adipocytes. We find that fibroblasts ectopically expressing C/EBPalpha (NIH-C/EBPalpha cells) differentiate into mature adipocytes that simultaneously express perilipin and ADRP. In response to isoproterenol, perilipin is hyperphosphorylated, lipolysis is enhanced, and subsequently, ADRP expression increases coincident with it surrounding intracellular lipid droplets. In the absence of lipolytic stimulation, inhibition of proteasomal activity with MG-132 increased ADRP levels to those of cells treated with 10 mum isoproterenol, but ADRP does not surround the lipid droplet in the absence of lipolytic stimulation. We overexpressed a perilipin A construct in NIH-C/EBPalpha cells where the six serine residues known to be phosphorylated by protein kinase A were changed to alanine (Peri A Delta1-6). These cells show no increase in ADRP expression in response to isoproterenol. We propose that ADRP can replace perilipin on existing lipid droplets or those newly formed as a result of fatty acid reesterification, under dynamic conditions of hormonally stimulated lipolysis, thus preserving lipid droplet morphology/structure.

Adipocytes↗
PubMed2005

p115 Interacts with the GLUT4 vesicle protein, IRAP, and plays a critical role in insulin-stimulated GLUT4 translocation.

Insulin-regulated aminopeptidase (IRAP) is an abundant cargo protein of Glut4 storage vesicles (GSVs) that traffics to and from the plasma membrane in response to insulin. We used the amino terminus cytoplasmic domain of IRAP, residues 1-109, as an affinity reagent to identify cytosolic proteins that might be involved in GSV trafficking. In this way, we identified p115, a peripheral membrane protein known to be involved in membrane trafficking. In murine adipocytes, we determined that p115 was localized to the perinuclear region by immunofluorescence and throughout the cell by fractionation. By immunofluorescence, p115 partially colocalizes with GLUT4 and IRAP in the perinuclear region of cultured fat cells. The amino terminus of p115 binds to IRAP and overexpression of a N-terminal construct results in its colocalization with GLUT4 throughout the cell. Insulin-stimulated GLUT4 translocation is completely inhibited under these conditions. Overexpression of p115 C-terminus has no significant effect on GLUT4 distribution and translocation. Finally, expression of the p115 N-terminus construct has no effect on the distribution and trafficking of GLUT1. These data suggest that p115 has an important and specific role in insulin-stimulated Glut4 translocation, probably by way of tethering insulin-sensitive Glut4 vesicles at an as yet unknown intracellular site.

3T3-L1 Cells↗