Glucose-6-phosphate isomerase deficiency results in mTOR activation, failed translocation of lipin 1α to the nucleus and hypersensitivity to glucose: Implications for the inherited glycolytic disease

• Published in: Biochimica et biophysica acta 2011-11, Vol.1812 (11), p.1393-1402
• Main Authors: Haller, Jorge F., Krawczyk, Sarah A., Gostilovitch, Lubov, Corkey, Barbara E., Zoeller, Raphael A.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Anemia, Hemolytic, Congenital Nonspherocytic - etiology; Animals; Blotting, Western; Cell Nucleus - metabolism; CHO Cells; Cloning, Molecular; Cricetinae; Electrophoretic Mobility Shift Assay; Fructosephosphates - metabolism; Glucose - pharmacology; Glucose-6-Phosphate - metabolism; Glucose-6-Phosphate Isomerase - genetics; Glucose-6-Phosphate Isomerase - metabolism; Glucose-6-phosphate isomerase deficiency; Glycolipids; Lipin 1; Lipodystrophy; Microscopy, Fluorescence; Molecular Sequence Data; Mutant; Non-spherocytic anemia; Organic Chemicals - metabolism; Phosphatidate Phosphatase - metabolism; Phospholipid biosynthesis; Protein Transport; Sequence Homology, Amino Acid; TOR Serine-Threonine Kinases - metabolism
• ISSN: 0925-4439; 0006-3002; 1879-260X
• DOI: 10.1016/j.bbadis.2011.07.007

Inherited glucose-6-phosphate isomerase (GPI) deficiency is the second most frequent glycolytic erythroenzymopathy in humans. Patients present with non-spherocytic anemia of variable severity and with neuromuscular dysfunction. We previously described Chinese hamster (CHO) cell lines with mutations in GPI and loss of GPI activity. This resulted in a temperature sensitivity and severe reduction in the synthesis of glycerolipids due to a reduction in phosphatidate phosphatase (PAP). In the current article we attempt to describe the nature of this pleiotropic effect. We cloned and sequenced the CHO lipin 1 cDNA, a gene that codes for PAP activity. Overexpression of lipin 1 in the GPI-deficient cell line, GroD1 resulted in increased PAP activity, however it failed to restore glycerolipid biosynthesis. Fluorescence microscopy showed a failure of GPI-deficient cells to localize lipin 1α to the nucleus. We also found that glucose-6-phosphate levels in GroD1 cells were 10-fold over normal. Lowering glucose levels in the growth medium partially restored glycerolipid biosynthesis and nuclear localization of lipin 1α. Western blot analysis of the elements within the mTOR pathway, which influences lipin 1 activity, was consistent with an abnormal activation of this system. Combined, these data suggest that GPI deficiency results in an accumulation of glucose-6-phosphate, and possibly other glucose-derived metabolites, leading to activation of mTOR and sequestration of lipin 1 to the cytosol, preventing its proper functioning. These results shed light on the mechanism underlying the pathologies associated with inherited GPI deficiency and the variability in the severity of the symptoms observed in these patients. ► Lipin 1α mislocalization is due to a mutation in the GPI gene. ► Demonstrated glucose sensitivity in a GPI-deficient cell line. ► Altered lipid biosynthesis as a pathological factor in inherited GPI deficiency. ► First sequencing of lipin 1 cDNA from hamster.