Biosynthesis and Function of All-trans- and 9-cis-Retinoic Acid in Parathyroid Cells

Abstract We demonstrate that cultured human and bovine parathyroid cells incubated with all- trans -[11,12- 3 H]-retinol convert this tracer into all- trans - and 9- cis -retinoic acid. By using RT-PCR, cellular retinol-binding protein type I (CRBP I), cellular retinoic acid binding protein I and II (CRABP I and II), retinoic acid receptors (RARs) α, β and γ, and 9- cis -retinoic acid receptor (RXR) α transcripts were detected in human parathyroid cDNA. CRBP I and CRABP I expression was confirmed by immunohistochemistry. Both 9- cis - and all- trans -RA were found to suppress parathyroid hormone (PTH) secretion from dispersed human adenomatous parathyroid cells, which was augmented by combined treatment with 1mM RA and 100 nM 1,25 (OH) 2 D 3 . The present data establish parathyroid gland as a target for retinoids and as a site of synthesis of the hormonal forms of vitamin A (retinol), all- trans - and 9- cis -retinoic acid.