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

Area of Science:

• Biochemistry
• Cell Biology
• Molecular Endocrinology

Background:

• The subcellular localization of 5 alpha-reductase isozymes, crucial for androgen metabolism, has been a subject of debate.
• Understanding their distribution is key to elucidating their distinct cellular functions.

Purpose of the Study:

• To definitively determine the subcellular localization of Type 1 and Type 2 5 alpha-reductase isozymes.
• To reconcile conflicting data regarding their cellular and tissue distribution.

Main Methods:

• Generation of specific and general antisera for 5 alpha-reductase isozymes.
• Western blotting and subfractionation of transfected COS cells expressing Type 1 or Type 2 cDNA.
• Cytoimmunofluorescence microscopy.
• Analysis of rat liver homogenates, including subfractionation and extraction studies.

Main Results:

• Both Type 1 and Type 2 5 alpha-reductase were detected at an apparent molecular weight of 26,000 Da.
• In transfected cells, both isozymes localized to the nuclear periphery.
• Rat liver Type 1 5 alpha-reductase was identified as an integral membrane protein in the outer nuclear membrane and rough endoplasmic reticulum.
• Homogenization procedures influenced the observed distribution between nuclear and cytosolic fractions.

Conclusions:

• Both Type 1 and Type 2 5 alpha-reductase are primarily localized to the nuclear periphery, specifically the outer nuclear membrane and endoplasmic reticulum.
• This finding resolves previous controversies regarding their subcellular distribution.
• The localization suggests shared functional roles at the nuclear envelope.