The Basolateral Localization Signal of the Follicle-stimulating Hormone Receptor

Abstract

The follicle-stimulating hormone receptor (FSHR) is physiologically localized in the basolateral compartment of the membrane of Sertoli cells. This localization is also observed when the receptor is experimentally expressed in Madin-Darby canine kidney cells. We thus used in vitro mutagenesis and transfection into these polarized cells to delineate the basolateral localization signal of the receptor.The signal was localized in the C-terminal tail of the intracellular domain (amino acids 678 -691) at a marked distance of the membrane. Mutation of individual amino acids highlighted the importance of Tyr 684 and Leu 689 . The 14-amino acid sequence was grafted onto the p75 neurotrophin receptor and redirected this apical protein to the basolateral cell membrane compartment. Deletion of amino acids 677-695 did not modify the internalization of the FSHR, showing that the basolateral localization signal of the FSHR is not colinear with its internalization signal.The FSH 1 receptor (FSHR), along with the LH and TSH receptors, belongs to a subgroup of G protein-coupled receptors (reviewed in Refs. 1-5). These highly homologous proteins are unusual among G protein-coupled receptors in that they contain a very large extracellular hormone binding domain. FSH transduction pathways involve mainly G s proteins coupling and the ensuing activation of adenylate cyclase (5).The FSH receptor has a central role in reproduction through the control of gonadal development and gamete production (5). In males it is expressed in testicular Sertoli cells. These cells form an epithelial blood barrier and control the development of spermatogenesis (6). In females, the FSHR is expressed in the granulosa cells of the ovaries. It controls follicular growth and, in cooperation with the LH receptor, ovarian steroidogenesis (2).Little is known of the intracellular trafficking of G proteincoupled receptors and, more specifically, of this subgroup of receptors. The pathways of internalization of the LH and TSH receptors have been studied at the ultrastructural level (7), 2 but the molecular signals involved are still unknown. The LH receptor is also present in the vascular endothelium of the testes (8). This endothelial LH receptor is involved in receptormediated hormone transcytosis, leading to the accumulation of the hormone in close proximity to the target cells. FSHR has been detected in the vascular endothelial cells of the testes (9), but its role in hormone transcytosis has not been studied to date.Another particularity of gonadotrophin and thyrostimulin receptors is their polarized cellular expression in several target tissues. Immunocytochemical studies with monoclonal antibodies have shown that the FSH receptor in Sertoli cells and the TSH receptor in thyroid follicular cells have a polarized basolateral expression (9, 10). By contrast, the LH receptor is expressed circumferentially in the ovarian granulosa and theca cells and in the testicular Leydig cells (11,12). This difference in receptor distribution could result from either a diffe...

Differential time course of FSH/FSH receptor complex endocytosis within sertoli and germ cells during rat testis development

“…Previous data, using antibodies directed against the receptor peptide complex, described its presence at the plasma membrane of Sertoli cells (Dattatreyamurty and Reichert, 1993;Beau et al, 1998). In the present study, by developing deconvolution microscopy, we have confirmed the location of FSH receptors on Sertoli cell plasma membranes but also demonstrated their presence within the cytoplasms of these cells and in germ cells such as spermatogonia and spermatocytes.…”

Charged residues in the C-terminus of the P2Y1 receptor constitute a basolateral-sorting signal

“…Indeed, the FSH receptor has two alternatively spliced forms in addition to the primary transcript (Touyz et al, 2000), one of which results in a different C-tail lacking the basolateral-targeting signal identified by Beau and colleagues (Beau et al, 1998). Although the targeting of this alternatively spliced receptor has not (A)A series of P2Y 1 receptor mutants was constructed in which total charge within the BLC was reduced while maintaining the charge balance at +1 by mutating both a basic and acidic amino acid to alanine (R and K residues are shown in blue; E and D residues in red; mutated A residues in purple; unchanged amino acids in green).…”

“…The presence of two targeting signals in a 7TM receptor has been observed previously. For example, the follicle-stimulating hormone receptor (FSH receptor), which is normally located on the basolateral surface of polarized epithelial cells, is redirected to the apical membrane upon removal of its basolateral-targeting signal in the C-tail (Beau et al, 1998). Thus, a precedent exists for a G-protein-coupled receptor containing two independent targeting signals, although the reasons for the existence of several signals in a single protein are unknown.…”

“…Previous studies have revealed that the C-tails of GPCRs often contain crucial sorting information (Beau et al, 1998;Chuang and Sung, 1998;Darmon et al, 1998;Jolimay et al, 2000;Qi et al, 2005). To determine the role of the C-tail in basolateral targeting of the P2Y 1 receptor, we deleted the C-tail of the receptor (P2Y 1 -334Z), as well as replaced the C-tail of both the apically sorted P2Y 2 receptor and the unsorted B2 bradykinin receptor (BK2) with the C-tail of the P2Y 1 receptor (P2Y 2 /P2Y 1 CT and BK2/P2Y 1 CT, respectively), and determined the steady-state distribution of the receptors in polarized monolayers of MDCK(II) cells.…”

Polarity and lipid raft association of the components of the ciliary neurotrophic factor receptor complex in Madin-Darby canine kidney cells

“…2C). This is an unusual finding since most receptors studied so far have shown a clear preference for one plasma membrane domain, usually the basolateral one (Beau et al, 1998;Maratos-Flier et al, 1987;Matter et al, 1994). A physiological relevance for an apical localisation of the LIF-R could lie in its role during blastocyst implantation in the uterus.…”