Lipid metabolismPathways for kidney-specific uptake of the steroid hormone 25-hydroxyvitamin D3Willnow, Thomas E.a; Nykjaer, AndersbAuthor Information aMax Delbrück Center for Molecular Medicine and Medical Faculty of the Free University of Berlin, Berlin, Germany, and bDepartment of Medical Biochemistry, University of Aarhus, Aarhus, Denmark Correspondence to Thomas E. Willnow, Max Delbrück Center for Molecular Medicine, Robert-Roessle-Strasse 10, D-13125 Berlin, Germany. Tel: +49 30 9406 2569; fax: +49 30 9406 3382; e-mail: firstname.lastname@example.org Current Opinion in Lipidology: June 2002 - Volume 13 - Issue 3 - p 255-260 Buy Abstract Steroid hormones are believed to enter cells solely by free diffusion through the plasma membrane. However, recent work on the uptake of 25-hydroxyvitamin D3 into the kidney has identified an endocytic pathway that is responsible for the delivery of this steroid to renal tissues. This finding led to a new perception that endocytosis may play an important role in the cell-type-specific targeting and uptake of steroid hormones. In the present review, we describe the molecular components (e.g. steroid carriers, endocytic receptors and intracellular transport proteins) that constitute this novel pathway for tissue-specific uptake of vitamin D metabolites. © 2002 Lippincott Williams & Wilkins, Inc.