title: Galactose-1 phosphate uridylyltransferase (GalT) gene: A novel positive regulator of the PI3K/Akt signaling pathway in mouse fibroblasts.
abstract: The vital importance of the Leloir pathway of galactose metabolism has been repeatedly demonstrated by various uni-/multicellular model organisms, as well human patients who have inherited deficiencies of the key GAL enzymes. Yet, other than the obvious links to the glycolytic pathway and glycan biosynthetic pathways, little is known about how this metabolic pathway interacts with the rest of the metabolic and signaling networks. In this study, we compared the growth and the expression levels of the key components of the PI3K/Akt growth signaling pathway in primary fibroblasts derived from normal and galactose-1 phosphate uridylyltransferase (GalT)-deficient mice, the latter exhibited a subfertility phenotype in adult females and growth restriction in both sexes. The growth potential and the protein levels of the pAkt(Thr308), pAkt(Ser473), pan-Akt, pPdk1, and Hsp90 proteins were significantly reduced by 62.5%, 60.3%, 66%, 66%, and 50%, respectively in the GalT-deficient cells. Reduced expression of phosphorylated Akt proteins in the mutant cells led to diminished phosphorylation of Gsk-3β (-74%). Protein expression of BiP and pPten were 276% and 176% higher respectively in cells with GalT-deficiency. Of the 24 genes interrogated using QIAGEN RT(2) Profiler PCR Custom Arrays, the mRNA abundance of Akt1, Pdpk1, Hsp90aa1 and Pi3kca genes were significantly reduced at least 2.03-, 1.37-, 2.45-, and 1.78-fold respectively in mutant fibroblasts. Both serum-fasted normal and GalT-deficient cells responded to Igf-1-induced activation of Akt phosphorylation at +15 min, but the mutant cells have lower phosphorylation levels. The steady-state protein abundance of Igf-1 receptor was also significantly reduced in mutant cells. Our results thus demonstrated that GalT deficiency can effect down-regulation of the PI3K/Akt growth signaling pathway in mouse fibroblasts through distinct mechanisms targeting both gene and protein expression levels.
authors.affiliation: Division of Medical Genetics, Department of Pediatrics, University of Utah School of Medicine, USA.
authors.forename: Bijina
authors.initials: B
authors.lastname: Balakrishnan
authors.affiliation: Division of Medical Genetics, Department of Pediatrics, University of Utah School of Medicine, USA.
authors.forename: Wyman
authors.initials: W
authors.lastname: Chen
authors.affiliation: Division of Medical Genetics, Department of Pediatrics, University of Utah School of Medicine, USA.
authors.forename: Manshu
authors.initials: M
authors.lastname: Tang
authors.affiliation: Division of Genetics and Genomics, Department of Pediatrics, Harvard Medical School, USA.
authors.forename: Xiaoping
authors.initials: X
authors.lastname: Huang
authors.affiliation: Division of Genetics and Genomics, Department of Pediatrics, Harvard Medical School, USA.
authors.forename: Didem Demirbas
authors.initials: DD
authors.lastname: Cakici
authors.affiliation: Department of Pathology and Laboratory Medicine, University of Florida College of Medicine, USA.
authors.forename: Anwer
authors.initials: A
authors.lastname: Siddiqi
authors.affiliation: Division of Genetics and Genomics, Department of Pediatrics, Harvard Medical School, USA.
authors.forename: Gerard
authors.initials: G
authors.lastname: Berry
authors.affiliation: Division of Medical Genetics, Department of Pediatrics, University of Utah School of Medicine, USA. Electronic address: kent.lai@hsc.utah.edu.
authors.forename: Kent
authors.initials: K
authors.lastname: Lai
mesh_terms: D000818:Animals; D059865:Endoplasmic Reticulum Stress; D005260:Female; D005347:Fibroblasts / Q000378:metabolism*; D005693:Galactosemias / Q000378:metabolism* / Q000473:pathology; D015971:Gene Expression Regulation, Enzymologic; D008297:Male; D051379:Mice; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D005694:UTP-Hexose-1-Phosphate Uridylyltransferase / Q000378:metabolism*
chemical_list: D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D005694:UTP-Hexose-1-Phosphate Uridylyltransferase
keywords: 3-Phosphoinositide-dependent kinase-1 (Pdk1); Endoplasmic reticulum (ER) stress; Galactose-1 phosphate uridylyltransferase (GalT); Galactosemia; Heat shock protein 90 (Hsp90); Protein kinase B (Akt)