Follicle-stimulating Hormone Inhibits All-trans-retinoic Acid-induced Retinoic Acid Receptor α Nuclear Localization and Transcriptional Activation in Mouse Sertoli Cell Lines

Abstract

The regulation of retinoic acid receptor alpha (RAR␣) signal transduction has not been well characterized. In this study, we determined whether all-trans-retinoic acid (tRA) and follicle-stimulating hormone (FSH) modulate RAR␣ receptor subcellular localization, leading to changes in its transcriptional activity and protein expression in mouse Sertoli cell lines. We found that tRA induced the nuclear localization of RAR␣ within 30 min and that longer term exposure increased the receptor transcriptional activity and RAR␣ protein expression. Conversely, FSH suppressed the tRA-induced nuclear localization, transcriptional transactivation, and protein expression of RAR␣. Treatment with two different protein kinase A-selective antagonists reversed the inhibitory actions of FSH on tRA-dependent RAR␣ nuclear localization and transcriptional activity. These results are consistent with the involvement of protein kinase A in mediating the inhibitory effects of FSH. For the first time, we demonstrate a unique signaling convergence between the RAR␣ and the FSH-mediated signaling pathways, which may have significant implications in the testis because both are critical regulators of testis physiology.Vitamin A is required for various fundamental physiological processes including vertebrate development, cellular differentiation, vision, and reproduction (1, 2). The biologically active form of vitamin A is retinoic acid, which includes all-transretinoic acid (tRA) 1 and 9-cis-retinoic acid (3). The biological response of retinoic acid is mediated through two families of nuclear receptors, the retinoic acid receptors (RARs) and the retinoid X receptors, each of which consists of three receptor subtypes, ␣, ␤, and ␥ (4). Retinoid receptors are transcription factors that regulate the transcription of retinoic acid-responsive genes.Retinoid receptors belong to the larger superfamily of steroid/thyroid hormone receptors. Several members of this superfamily including the progesterone, the glucocorticoid, the estradiol, and the peroxisome proliferator-activated receptors are regulated at the level of nuclear trafficking (5-9). It was demonstrated that activation of cellular kinases increased the nuclear translocation and transcriptional activity of these receptors (8, 9). However, little is known about the regulation of RAR␣ subcellular localization and how this may affect its subsequent transcriptional activity. Previously, Tahayato et al. (10) reported that down-regulation of protein kinase C decreased RAR␣ nuclear localization and subsequent retinoic acid response element (RARE)-dependent transcriptional activity. In addition, although the regulation of nuclear trafficking was not examined, cAMP-dependent protein kinase (PKA) has been shown to decrease the transcriptional activity of RAR␣ and to inhibit the tRA-induced expression of all three retinoic acid receptor mRNAs in PC12, B16 melanoma, and F9 teratocarcinoma cells (11-13). In contrast, other reports indicate that the phosphorylation of RAR␣ on serine 369 by an overexpresse...

A Novel Cytoplasmic Adaptor for Retinoic Acid Receptor (RAR) and Thyroid Receptor Functions as a Derepressor of RAR in the Absence of Retinoic Acid*

“…However, some studies have demonstrated that RAR and TR are retained in the cytoplasm and move to the nucleus when ligands are supplied (13)(14)(15)(16). In particular, we also found that RAR␣ shuttles between the cytoplasm and the nucleus in the Sertoli cell line TM4 in response to AtRA (Fig.…”

“…6C), we can speculate on the function of CART1 in testis development. Although ligand-induced RAR cytoplasm-to-nucleus shuttling has been reported in testis Sertoli cells (15,16), little is known about the role of the putative cytoplasmic retention factor CART1 in testis. Recent data suggest that Rab11, another partner of CART1, is essential for fertility in the fruit fly (41).…”

“…39 and 40), little is known about their regulation in the cytoplasm. Recently, a few reports have indicated that RAR and TR can shuttle from the cytoplasm to the nucleus in response to ligand (13)(14)(15)(16). However, it is largely unknown which cellular factor(s) is responsible for the FIGURE 7.…”

“…Cells-It has been reported that apoRAR␣ is cytoplasmic and holo-RAR␣ is nuclear in mouse testis Sertoli cell lines (15,16). These findings led us to investigate the role of CART1 in the intracellular distribution of RAR␣ in Sertoli cells.…”

“…A few reports have suggested that TRs (TR␣1 and TR␤1) actively shuttle between the nucleus and cytoplasm and that the ligand promotes cytoplasm-to-nucleus shuttling (13,14). In some Sertoli cell lines derived from mouse testis, RAR␣ is ordinarily located in the cytoplasm and rapidly moves to the nucleus in response to its ligand RA (15,16). In both cases, ligands are required for the promotion of nuclear translocation.…”