5 alpha-Reductase type 1 is localized to the outer nuclear membrane.

Mol Cell Endocrinol

Department of Medicine, University of Ottawa, Loeb Institute for Medical Research, Ottawa Civic Hospital, Canada.

Published: April 1995

AI Article Synopsis

  • The study focuses on the subcellular distribution of the two isozymes of 5 alpha-reductase, highlighting the generation of specific antisera for better identification of these proteins.
  • Extensive experiments in COS cells and rat liver demonstrate that both isozymes are found at a mass of 26,000 and are localized primarily to the nuclear periphery and rough endoplasmic reticulum.
  • It concludes that Type 1 5 alpha-reductase in rat liver is an integral membrane protein situated in the outer nuclear membrane, which contrasts with prior beliefs about its tissue distribution.

Article Abstract

The subcellular distribution of the two isozymes of 5 alpha-reductase has been controversial. To resolve this issue which could provide clues about the respective functions of the two isozymes, two antisera were generated, one which was specific for the Type 1 5 alpha-reductase and one which recognized both isozymes. In COS cells transfected separately with the Type 1 or Type 2 cDNA, both isozymes were detected on Western blots at an M(r) of 26,000. Subfractionation of the COS cells resulted in the partitioning of both isozymes between the crude nuclear and cytosolic fractions, while cytoimmunofluorescence localized both reductases to the nuclear periphery. In rat liver homogenate, the 5 alpha-reductase was also detected at M(r) 26,000. The 5 alpha-reductase immunoreactivity was increased after castration of the animals with no further effect when castrated animals were treated with androgens. Although the rat liver expresses only the Type 1 5 alpha-reductase, the 5 alpha-reductase was distributed about equally between crude nuclear and cytosolic subfractions; this distribution could be shifted to the cytosolic fractions with harsher homogenization procedures. Further extensive subfractionation and extraction studies identified the rat liver Type 1 5 alpha-reductase as an integral membrane protein present in the outer nuclear membrane of the nuclear envelope and in rough endoplasmic reticulum. Thus, the subfractionation and cytoimmunofluorescence studies are consistent with the localization of the Type 1 5 alpha-reductase to the outer nuclear membrane of the nuclear envelope which is continuous with and indistinguishable from the endoplasmic reticulum. This study is the first to localize rat liver Type 1 5 alpha-reductase to the nuclear envelope to which the prostatic 5 alpha-reductase activity previously had been localized. We conclude that, contrary to previous tissue distribution studies, but consistent with investigations in transfected cells, both isozymes are similarly localized to the nuclear periphery.

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Source
http://dx.doi.org/10.1016/0303-7207(95)03526-dDOI Listing

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