Functional characterization of two 20β-hydroxysteroid dehydrogenase type 2 homeologs from Xenopus laevis reveals multispecificity.

The African clawed frog, Xenopus laevis, is a versatile model for biomedical research and is largely similar to mammals in terms of organ development, anatomy, physiology, and hormonal signaling mechanisms. Steroid hormones control a variety of processes and their levels are regulated by hydroxysteroid dehydrogenases (HSDs). The subfamily of 20β-HSD type 2 enzymes currently comprises eight members from teleost fish and mammals. Here, we report the identification of three 20β-HSD type 2 genes in X. tropicalis and X. laevis and the functional characterization of the two homeologs from X. laevis. X. laevis Hsd20b2.L and Hsd20b2.S showed high sequence identity with known 20β-HSD type 2 enzymes and mapped to the two subgenomes of the allotetraploid frog genome. Both homeologs are expressed during embryonic development and in adult tissues, with strongest signals in liver, kidney, intestine, and skin. After recombinant expression in human cell lines, both enzymes co-localized with the endoplasmic reticulum and catalyzed the conversion of cortisone to 20β-dihydrocortisone. Both Hsd20b2.L and Hsd20b2.S catalyzed the 20β-reduction of further C steroids (17α-hydroxyprogesterone, progesterone, 11-deoxycortisol, 11-deoxycorticosterone), while only Hsd20b2.S was able to convert corticosterone and cortisol to their 20β-reduced metabolites. Estrone was only a poor and androstenedione no substrate for both enzymes. Our results demonstrate multispecificity of 20β-HSD type 2 enzymes from X. laevis similar to other teleost 20β-HSD type 2 enzymes. X. laevis 20β-HSD type 2 enzymes are probably involved in steroid catabolism and in the generation of pheromones for intraspecies communication. A role in oocyte maturation is unlikely.