BIOSYNTHESIS AND FUNCTION OF ALL-TRANS-RETINOIC AND 9-CIS-RETINOIC ACID IN PARATHYROID CELLS

We demonstrate that cultured human and bovine parathyroid cells incuba ted with all-trans-[11,12-H-3]-retinol convert this tracer into all-tr ans- and 9-cis-retinoic acid. By using RT-PCR, cellular retinol-bindin g protein type I (CRBP I), cellular retinoic acid binding protein I an d II (CRABP I and II), retinoic acid receptors (RARs) alpha, beta and gamma, and 9-cis-retinoic acid receptor (RXR) alpha transcripts were d etected in human parathyroid cDNA. CRBP I and CRABP I expression was c onfirmed by immunohistochemistry. Both 9-cis- and all-trans-RA were fo und to suppress parathyroid hormone (PTH) secretion from dispersed hum an adenomatous parathyroid cells, which was augmented by combined trea tment with 1mM RA and 100 nM 1,25 (OH)(2)D-3. The present data establi sh parathyroid gland as a target for retinoids and as a site of synthe sis of the hormonal forms of vitamin A (retinol), all-trans- and 9-cis -retinoic acid. (C) 1996 Academic Press.