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: Iwona J Bujalska, Nicole Draper, Zoi Michailidou, Jeremy W Tomlinson, Perrin C White, Karen E Chapman, Elizabeth A Walker, Paul M Stewart
• Journal: Journal of molecular endocrinology (J Mol Endocrinol) Vol. 34 Issue 3 Pg. 675-84 (Jun 2005) ISSN: 0952-5041 [Print] England
• PMID: 15956339 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• DNA Primers
• RNA, Messenger
• RNA, Small Interfering
• Carbohydrate Dehydrogenases
• galactose-6-phosphate dehydrogenase
• 11-beta-Hydroxysteroid Dehydrogenase Type 1

Topics

• 11-beta-Hydroxysteroid Dehydrogenase Type 1 (genetics, metabolism)
• Adult
• Animals
• Base Sequence
• Blotting, Western
• CHO Cells
• Carbohydrate Dehydrogenases (genetics, metabolism)
• Cricetinae
• DNA Primers
• Female
• Humans
• Polymerase Chain Reaction
• RNA, Messenger (genetics)
• RNA, Small Interfering (genetics)