title: Hexose-6-phosphate dehydrogenase confers oxo-reductase activity upon 11 beta-hydroxysteroid dehydrogenase type 1.
abstract: Two isozymes of 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) interconvert active cortisol and inactive cortisone. 11 beta-HSD2 (renal) acts only as a dehydrogenase, converting cortisol to cortisone. 11 beta-HSD1 (liver) is a bi-directional enzyme in cell homogenates, whereas in intact cells it typically displays oxo-reductase activity, generating cortisol from cortisone. We recently established that cortisone reductase deficiency is a digenic disease requiring mutations in both the gene encoding 11 beta-HSD1 and in the gene for a novel enzyme located within the lumen of the endoplasmic reticulum (ER), hexose-6-phosphate dehydrogenase (H6PDH). This latter enzyme generates NADPH, the co-factor required for oxo-reductase activity. Therefore, we hypothesized that H6PDH expression may be an important determinant of 11 beta-HSD1 oxo-reductase activity. Transient transfection of chinese hamster ovary (CHO) cells with 11 beta-HSD1 resulted in the appearance of both oxo-reductase and dehydrogenase activities in intact cells. Co-transfection of 11 beta-HSD1 with H6PDH increased oxo-reductase activity whilst virtually eliminating dehydrogenase activity. In contrast, H6PDH had no effect on reaction direction of 11 beta-HSD2, nor did the cytosolic enzyme, glucose-6-phosphate dehydrogenase (G6PD) affect 11 beta-HSD1 oxo-reductase activity. Conversely in HEK 293 cells stably transfected with 11 beta-HSD1 cDNA, transfection of an H6PDH siRNA reduced 11 beta-HSD1 oxo-reductase activity whilst simultaneously increasing 11 beta-HSD1 dehydrogenase activity. In human omental preadipocytes obtained from 15 females of variable body mass index (BMI), H6PDH mRNA levels positively correlated with 11 beta-HSD1 oxo-reductase activity, independent of 11 beta-HSD1 mRNA levels. H6PDH expression increased 5.3-fold across adipocyte differentiation (P < 0.05) and was associated with a switch from 11 beta-HSD1 dehydrogenase to oxo-reductase activity. In conclusion, H6PDH is a crucial determinant of 11 beta-HSD1 oxo-reductase activity in intact cells. Through its interaction with 11 beta-HSD1, H6PDH may represent a novel target in the pathogenesis and treatment of obesity.
authors.affiliation: Division of Medical Sciences, Endocrinology, Institute of Biomedical Research, Medical School, University of Birmingham, Birmingham, B15 2TT, UK.
authors.forename: Iwona J
authors.initials: IJ
authors.lastname: Bujalska
authors.forename: Nicole
authors.initials: N
authors.lastname: Draper
authors.forename: Zoi
authors.initials: Z
authors.lastname: Michailidou
authors.forename: Jeremy W
authors.initials: JW
authors.lastname: Tomlinson
authors.forename: Perrin C
authors.initials: PC
authors.lastname: White
authors.forename: Karen E
authors.initials: KE
authors.lastname: Chapman
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Walker
authors.forename: Paul M
authors.initials: PM
authors.lastname: Stewart
mesh_terms: D043205:11-beta-Hydroxysteroid Dehydrogenase Type 1 / Q000235:genetics / Q000378:metabolism*; D000328:Adult; D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D016466:CHO Cells; D002237:Carbohydrate Dehydrogenases / Q000235:genetics / Q000378:metabolism*; D006224:Cricetinae; D017931:DNA Primers; D005260:Female; D006801:Humans; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics
chemical_list: D017931:DNA Primers; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D002237:Carbohydrate Dehydrogenases; C020552:galactose-6-phosphate dehydrogenase; D043205:11-beta-Hydroxysteroid Dehydrogenase Type 1