Subcellular localization of the five members of the human steroid 5α-reductase family

In humans the steroid 5a-reductase (SRD5A) family comprises five integral membrane enzymes that carry out reduction of a double bond inlipidic substrates: D4-3-keto steroids, polyprenol and trans-enoyl CoA. The best-characterized reaction is the conversion of testosterone into themore potent dihydrotestosterone carried out by SRD5A1-2. Some controversy exists on their possible nuclear or endoplasmic reticulumlocalization.We report the cloning and transient expression in HeLa cells of the five members of the human steroid 5a-reductase family as both N- and Cterminusgreen fluorescent protein tagged protein constructs. Following the intrinsic fluorescence of the tag, we have determined that thesubcellular localization of these enzymes is in the endoplasmic reticulum, upon expression in HeLa cells. The presence of the tag at either end ofthe polypeptide chain can affect protein expression and, in the case of trans enoyl-CoA reductase, it induces the formation of protein aggregates.