Biomedical subjects

M Ascoli

Publications and source records attributed to M Ascoli.

At least 37 records · Page 2Linked to original sources

PubMed1998

The agonist-induced phosphorylation of the rat follitropin receptor maps to the first and third intracellular loops.

Previous results from this laboratory have shown that the rat FSH receptor (rFSHR) becomes phosphorylated on S/T residues upon stimulation of transfected cells with human (h)FSH and that a truncation of the C-terminal tail that removes 12 of the 25 intracellular S/T residues does not affect phosphorylation. Based on the results of phosphopeptide-mapping experiments we analyzed three new mutants. rFSHR-1L and rFSHR-3L were constructed by mutating the S/T residues in the first intracellular loop or the third intracellular loop, respectively. rFSHR-(3L+CT) was constructed by mutating all the S/T residues in the third loop as well as S624, the only C-terminal tail residue that was not previously eliminated as a potential phosphorylation site. All mutants were biologically active. The agonist-induced phosphorylation of rFSHR-3L and rFSHR-(3L+CT) were partially reduced, while that of rFSHR-1L was almost completely lost. The agonist-induced uncoupling of rFSHR-1L and rFSHR-3L are retarded to about the same extent, while the agonist-induced internalization is retarded only in rFSHR-1L. Four major conclusions can be made from the present studies: 1) the phosphorylated rFSHR is a common molecular intermediate in agonist-induced uncoupling and internalization; 2) agonist-induced phosphorylation of the rFSHR maps to the first and third intracellular loops; 3) the phosphorylation of the third intracellular loop facilitates agonist-induced uncoupling but is not necessary for agonist-induced internalization; 4) agonist-induced internalization is facilitated by phosphorylation but it is not known if only the first loop, only the third loop, or both the first and third loops need to be phosphorylated for this response.

Amino Acid Sequence↗

PubMed1997

Molecular basis of the regulation of the lutropin/choriogonadotropin receptor.

The studies summarized here clearly show that the phosphorylation of one or more serine residues (S635, S639, S649 and/or S652) present in the C-terminal tail of the LHR is necessary, but not sufficient, for the agonist-induced uncoupling of the LHR from adenylate cyclase and for the endocytosis of the agonist-receptor complex. Simultaneous mutation of these four serines to alanines decreases the rate of agonist-induced uncoupling and the rate of agonist-induced internalization. This mutation does not affect the magnitude of agonist-induced uncoupling attained upon a long incubation with agonist, nor does it reduce the rate of internalization of the agonist-bound LHR to that of the free LHR. Thus additional molecular interactions and/or post-translational modifications of the LHR are needed for uncoupling and down-regulation.

Adenylyl Cyclases↗

PubMed1997

Phosphorylation of the lutropin/choriogonadotropin receptor facilitates uncoupling of the receptor from adenylyl cyclase and endocytosis of the bound hormone.

Stably transfected cell lines expressing the wild-type rat LH/CG receptor (rLHR) or a full-length rLHR in which S635, T638, S639, S649 and S653 were simultaneously mutated to alanine residues (designated rLHR-5S/T-->A) were used to probe the importance of receptor phosphorylation on the regulation of receptor functions. The mutant receptor binds hCG with high affinity and transduces the hormonal signal into increases in cAMP and inositol phosphate accumulation comparable in magnitude to those elicited by the wild-type receptor. In contrast to cells expressing rLHR-wt, which respond to hCG or phorbol 12-myristate 13-acetate stimulation with an increase in rLHR phosphorylation, the phosphorylation of rLHR in cells expressing rLHR-5S/T-->A is severely blunted. Likewise, the phorbol 12-myristate 13-acetate-induced desensitization of hCG-induced cAMP accumulation is drastically reduced in cells expressing rLHR-5S/T-->A. In contrast, the hCG-induced desensitization of hCG-induced cAMP accumulation is delayed, but not abolished, in cells expressing rLHR-5S/T-->A. Lastly, the rate of internalization of the receptor-bound hCG is slower in cells expressing rLHR-5S/T-->A than in cells expressing rLHR-wt. These results show that phosphorylation of rLHR is necessary, but not sufficient, for uncoupling of the receptor from adenylyl cyclase and for endocytosis of the receptor-bound hormone.

Adenylyl Cyclases↗

PubMed1996

Functional consequences of the phosphorylation of the gonadotropin receptors.

When target cells are exposed to a hormone, their responsiveness wanes with time, in spite of the continuous presence of the hormone. This phenomenon, referred to as desensitization, is due to regulatory steps that occur at the level of the hormone receptor as well as at post-receptor steps. While post-receptor events may be specific for the metabolic pathways activated in a given target cell, receptor events are more general in nature and conserved within a given family of receptors. There are at least two categories of regulatory events that occur at the level of the receptor and contribute to the process of desensitization. One of them, referred to as receptor uncoupling, will be used here to denote a change in the functional properties of a constant number of receptors resulting in a reduction in the ability of the receptor to activate its most proximal effector system. The other, referred to as receptor down-regulation, will be used here to denote a reduction in the density of cell surface receptors. Uncoupling is generally faster than down-regulation, and is believed to be due to post-translational modifications of the receptor. Down-regulation, on the other hand, is slower, and could be due to an increase in the rate of receptor internalization, sequestration or degradation, and/or to a decrease in the rate of receptor externalization, processing or synthesis. In this paper, recent studies from my laboratory designed to directly address the potential involvement of gonadotropin receptor phosphorylation in the process of uncoupling have been reviewed.

Amino Acid Sequence↗

PubMed1996

Two mutations of the lutropin/choriogonadotropin receptor that impair signal transduction also interfere with receptor-mediated endocytosis.

The experiments presented herein were designed to probe a potential role for the activation of the LH/CG receptor (LHR) on the receptor-mediated endocytosis of human CG (hCG). Two mutants of the rat LHR (rLHR) that bind the hormone with high affinity but are deficient in signal transduction were prepared by mutating highly conserved residues that have been previously shown to be important in signal transduction in other members of the G protein-coupled receptor family. Mutation of a highly conserved aspartic acid in the second transmembrane domain of the rLHR (designated rLHR-D383N) does not affect hCG binding but impairs signal transduction. When compared with cells expressing an equivalent density of wild type rLHR (rLHR-wt), concentration-response curves for the hCG-stimulated cAMP accumulation in cells expressing rLRH-D383N- are characterized by an 18-fold increase in the EC50 but no change in the maximal response. Cells expressing rLHR-D383N also display a 4- to 5-fold increase in the half-life of internalization of hCG. Mutation of a highly conserved arginine in the second intracellular loop of the rLHR (designated rLHR-R442H) also does not affect hCG binding but impairs signal transduction. When compared with cells expressing an equivalent density of rLHR-wt, concentration-response curves for the hCG-stimulated cAMP accumulation in cells expressing rLHR-R442H are characterized by a 7-fold increase in the EC50 and a 6- to 10-fold decrease in the maximal response. Cells expressing rLHR-R442H also display a 1.5- to 2-fold increase in the half-life of internalization of hCG. These results, together with the finding that an antagonist of hCG is internalized more slowly than hCG, suggest that the activation of the LHR is needed for the efficient endocytosis of the bound hCG.

Arginine↗

PubMed1996

Progressive cytoplasmic tail truncations of the lutropin-choriogonadotropin receptor prevent agonist- or phorbol ester-induced phosphorylation, impair agonist- or phorbol ester-induced desensitization, and enhance agonist-induced receptor down-regulation.

Stably transfected human kidney 293 cells expressing the wild type rat LH/CG receptor (rLHR) or receptors with C-terminal tails truncated at residues 653, 631, or 628 (designated rLHR-t653, rLHR-t631, and rLHR-t628) were used to probe the importance of this region on the regulation of hormonal responsiveness. The chosen cells line express comparable densities of cell surface rLHR, bind human CG (hCG) with high affinity, and respond to hCG with increases in cAMP and inositol phosphate accumulation. Cells expressing rLHR-wt or rLHR-t653 responded to hCG, or phorbol 12-myristate-13-acetate (PMA) stimulation with a similar increase in rLHR phosphorylation. Neither of these two stimuli increased rLHR phosphorylation in cells expressing rLHR-t631 or rLHR-t628, however. The cell line expressing rLHR-t653, the phosphorylation-positive receptor mutant, desensitized normally in response to PMA or hCG stimulation. This truncated form of rLHR also was down-regulated normally in response to hCG stimulation. In contrast, the cell lines expressing rLHR-t631 or rLHR-t628, the two phosphorylation-negative receptor mutants, showed a delay in the early phase of hCG-induced desensitization, a complete loss of PMA-induced desensitization, and an increase in the rate of hCG-induced receptor down-regulation. These results clearly show that residues 632-653 in the C-terminal tail of the rLHR are involved in PMA-induced desensitization, hCG-induced de-sensitization, and hCG-induced down-regulation. These results also establish a positive correlation between rLHR phosphorylation and desensitization and a negative correlation between rLHR phosphorylation and down-regulation.

Binding Sites↗

PubMed1995

Truncation of the C-terminal tail of the follitropin receptor does not impair the agonist- or phorbol ester-induced receptor phosphorylation and uncoupling.

We have recently shown that addition of follitropin (FSH) or a phorbol ester (phorbol 12-myristate 13-acetate (PMA)) to cells expressing the recombinant follitropin receptor (FSHR) results in both phosphorylation and uncoupling of the FSHR from adenylyl cyclase. In the light of findings reported with other G protein-coupled receptors we have proposed that phosphorylation of the FSHR mediates the uncoupling from adenylyl cyclase. The experiments described herein represent the first attempt to determine the location of the amino acid residues that become phosphorylated in FSHR and to test the hypothesis that phosphorylation is responsible for uncoupling of FSHR from adenylyl cyclase. As a first step in identifying which residues may be phosphorylated in response to hFSH and PMA, we constructed a mutant of the FSHR cDNA in which the C-terminal cytoplasmic tail was truncated at residue 635 (FSHR-t635), thus removing all but one of the potential phosphorylation sites present in the C-terminal tail. Cells expressing FSHR-t635 bind hFSH with the appropriate affinity and respond with increases in cAMP and inositol phosphate accumulation. The maximal cAMP and inositol phosphate responses of cells expressing FSHR-t635 are higher than those of cells expressing the wild type FSHR, but the concentration of hFSH required to elecit these responses is similar in both cell lines. Immunoprecipitation of FSHR-t635 shows that the truncated receptor is still effectively phosphorylated in response to hFSH or PMA. Phosphoamino acid analysis reveals that, like the wild-type FSHR, FSHR-t635 phosphorylation occurs on serine and threonine residues. Peptide mapping suggests that the phosphorylated residues in the FSHR and FSHR-t635 are located within the same areas of the intracellular regions of the receptors. In addition to stimulating phosphorylation of FSHR-t635, hFSH and PMA also effectively uncouple the truncated receptor from adenylyl cyclase. Taken together, these data show that hFSH and PMA can both phosphorylate and uncouple a FSH receptor species with a cytoplasmic tail truncated at residue 635.

Adenylyl Cyclases↗

PubMed1995

Decreased stathmin expression does not affect the actions of human choriogonadotropin or epidermal growth factor in Leydig tumor cells.

Although hCG and mouse epidermal growth factor (mEGF) activate different signaling systems in a clonal strain of murine Leydig tumor cells (designated MA-10), both compounds ultimately elicit several common effects such as increased steroidogenesis, decreased transcription of the LH receptor gene and attenuation of adenylyl cyclase. A 21-kilodalton protein whose phosphorylation state increases after hCG and mEGF stimulation has previously been described and identified as stathmin. To determine whether stathmin is involved in the signaling pathways of hCG and mEGF, an expression vector containing the full-length stathmin complementary DNA in an antisense orientation was constructed and used to establish two novel clonal MA-10 cell lines that have a decreased level of stathmin expression. Characterization of these mutant cell lines revealed no differences from MA-10 cells or neomycin-resistant subclones of MA-10 cells with respect to the ability of hCG or mEGF to increase steroidogenesis, decrease transcription of the LH receptor, or attenuate the adenylyl cyclase activity. Thus, it appears that stathmin is not involved in mediating the common actions of hCG and mEGF in MA-10 cells.

Adenylyl Cyclases↗

PubMed1995

The lutropin/choriogonadotropin receptor is palmitoylated at intracellular cysteine residues.

Most members of the family of G protein-coupled receptors have one or more conserved cysteine residues in their carboxy-terminal cytoplasmic tails which are believed to be consensus sites for palmitoylation. Indeed, a growing number of G protein-coupled receptors (rhodopsin, beta 2-, and alpha 2-adrenergic receptors) have now been shown to have palmitic acid covalently attached to this position. In the case of the beta 2-adrenergic receptor, it was also reported that mutation of the palmitoylated cysteine to glycine greatly diminished the ability of this receptor to interact with and activate Gs. Mutation of this conserved cysteine appears to have little or no effect on the ability of other members of this receptor family (rhodopsin, alpha 2-adrenergic and M2 muscarinic) to activate their cognate G proteins, however. The studies presented here were designed to determine whether another Gs-coupled receptor, the LH/CG receptor, is palmitoylated, and whether this modification is important for receptor function. To facilitate biochemical analysis, we examined these issues using cell lines stably transfected with the wild type LH/CG receptor (LHR-wt) or with a mutant receptor in which the two conserved cysteins were mutated to alanines (designated LHR-C621,622A). Our results show that LHR-wt is palmitoylated but that LHR-C621,622A is not. We also show that LHR-C621,622A is capable of binding human CG (hCG) and transducing the cAMP signal. The main difference that we detected between the wild type and mutant receptor is that the latter is trapped intracellularly and does not appear to mature into the 85 kilodalton protein previously identified as the mature cell surface LH/CG receptor.

Animals↗

PubMed1995

Human chorionic gonadotropin (CG)- and phorbol ester-stimulated phosphorylation of the luteinizing hormone/CG receptor maps to serines 635, 639, 649, and 652 in the C-terminal cytoplasmic tail.

In a number of instances, binding of a ligand to its receptor results in receptor phosphorylation that mediates receptor uncoupling from its effector. Recently, we showed that human CG (hCG)- or phorbol ester- [phorbol 12-myristate-13-acetate (PMA)] stimulation of cells transfected with the LH/CG receptor induced rapid LH/CG receptor phosphorylation and a reduced cAMP response upon reexposure to hCG. The fact that hCG and PMA both phosphorylate and uncouple the LH/CG receptor suggests a common mechanism of action, namely the activation of protein kinase C. The studies presented here were designed to investigate the role of the C kinase in LH/CG receptor phosphorylation and to locate the phosphorylation site(s) within the receptor protein. The experiments presented here show that although hCG activates the C kinase in these cells, phosphorylation of the LH/CG receptor in response to hCG is maintained in C kinase-deficient cells. This suggests that activation of protein kinase C is not required for hCG-induced phosphorylation of its receptor. As a first step in locating the phosphorylation sites within the receptor polypeptide, we performed phosphoamino acid analysis of the phosphorylated LH/CG receptor. Only phosphoserine residues were detected. Based on the assumption that the phosphoserine(s) must be located within the intracellular regions of the receptor, we isolated cell lines expressing the wild type LH/CG receptor or receptors with cytoplasmic tails truncated at residue 653 or 631.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

PubMed1994

Follitropin (FSH) and a phorbol ester stimulate the phosphorylation of the FSH receptor in intact cells.

Using a cell line stably transfected with the rat follitropin (FSH) receptor cDNA we demonstrate that the FSH receptor becomes phosphorylated when cells are exposed to FSH. Since binding of FSH to its receptor results in an increase in cAMP and inositol phosphate accumulation, we examined the potential involvement of protein kinase A and C in mediating receptor phosphorylation. Stimulation of protein kinase A does not appear to be necessary because hFSH-induced receptor phosphorylation was minimally impaired in a cell line that overexpresses cAMP phosphodiesterase. Moreover, stimulation of the protein kinase A pathway with other agonists result in minimal phosphorylation of the FSH receptor. Stimulation of the protein kinase C with a phorbol ester did result in an increase in receptor phosphorylation, and down-regulation of the protein kinase C decreased, but did not abolish, the FSH-induced receptor phosphorylation. The possible impact of phosphorylation on the functions of the receptor was examined by testing if conditions that lead to phosphorylation decrease the ability of FSH to stimulate cAMP synthesis. Our data show that as with the addition of FSH, addition of a phorbol ester also results in a decrease in the ability of FSH to stimulate cAMP synthesis.

Adenylyl Cyclases↗

PubMed1994

Leydig tumor cell protein phosphorylated in response to stimulation with choriogonadotropin or epidermal growth factor is identified as stathmin.

Although hCG and mouse epidermal growth factor activate different signaling systems in a clonal strain of Leydig tumor cells (designated MA-10), both compounds are capable of increasing steroidogenesis, decreasing transcription of the LH/CG receptor gene, and attenuating adenylyl cyclase. We have recently identified a 21-kilodalton protein (p21) that is a potential intermediary in the actions of mouse epidermal growth factor and hCG. Characterization of p21 revealed similarities to stathmin, a ubiquitous phosphoprotein whose phosphorylation is associated with diverse second messenger pathways. Using two different experimental approaches, Western blotting and immunoprecipitation, we present data that identify p21 as stathmin.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed1994

Characterization of the functional properties and nuclear binding proteins of the rat luteinizing hormone/chorionic gonadotropin receptor promoter in Leydig cells.

The experiments presented herein were designed to study the molecular basis of the restricted cellular localization and transcriptional regulation of the LH/CG receptor in Leydig cells. Using luciferase fusion constructs transfected into Leydig and Sertoli cell lines, we show that the proximal 186 basepairs (relative to the translation start site) of the 5'-flanking region of the rat LH/CG receptor represent a basal promoter that accounts for the Leydig cell-specific expression of this receptor. A region that confers negative transcriptional regulation by cAMP maps to nucleotides -40 to -70 of this basal promoter. Using mobility shift and deoxyribonuclease footprinting assays, we also report the detection of Leydig cell-specific protein(s) that bind to the basal LH/CG receptor promoter. The binding of this protein(s) to the promoter involves an AP-2 consensus sequence beginning at nucleotide -59 as well as additional sequences that remain to be identified. In spite of the fact that the AP-2 site is involved, the protein-DNA complexes detected in Leydig cells are not recognized by an antibody to AP-2.

Animals↗

PubMed1993

The lutropin/choriogonadotropin receptor ... 4 years later.

A comparison of this review with the review on the LH/CG receptor that we published in this journal 4 yr ago (1) clearly shows that the field has advanced tremendously in this short period of time. Many of the questions that were unanswered then have now been conclusively answered. On the other hand, as is always the case, the new knowledge generated has also resulted in many new questions that are yet to be answered. Hopefully it is clear from this review that the knowledge and experimental tools generated during the last 4 yr have given us new ammunition to address such important issues as the elucidation of the structural determinants of the LH/CG receptor that are involved in the different functions of this receptor, as well as on the molecular bases of receptor activation, inactivation, and regulation. In fact, since we finished writing this review in September of 1992, we are certain that some of the questions left unanswered here will already have an answer in 1993 when this review is published.

Amino Acid Sequence↗

PubMed1993

The use of genetic manipulation of MA-10 Leydig tumor cells to demonstrate the role of mitochondrial proteins in the acute regulation of steroidogenesis.

The true rate-limiting step in steroidogenesis is the delivery of cholesterol to the inner mitochondrial membrane where it is converted to pregnenolone by the cholesterol side-chain cleavage complex. This process is known to require de novo protein synthesis. We have previously described the synthesis of a family of 37, 32, and 30 kilodalton mitochondrial proteins in response to hormone stimulation in MA-10 mouse Leydig tumor cells and have proposed that these proteins are involved in the acute regulation of steroidogenesis. In this study we have used two subclones of MA-10 cells to further demonstrate the correlation between the quantity of these proteins and the production of steroids in response to hormone treatment. One of these, designated MA-10(K3), has been transfected with a mutant gene of the type 1 regulatory subunit of the cAMP-dependent protein kinase under the control of a metallothionein promoter, whereas the other, designated MA-10(P+29), is a constitutive overproducer of a cAMP-phosphodiesterase (PDE). MA-10 parent cells designated (P), produce large amounts of progesterone in response to LH, human CG, and (Bu)2cAMP. The MA-10(K3) cells, on the other hand, whereas significantly higher than controls, produce much less steroid than the parent cells in response to hormone stimulation. Activation of the mutant gene with Zn+2 results in yet a further decrease in the amount of steroid produced. The MA-10(P+29) cells display greatly reduced progesterone production when stimulated with LH, because of the presence of high amounts of PDE, but return to maximally stimulated levels when a PDE inhibitor is present. Quantitation of the synthesis of the mitochondrial proteins described above in MA-10(K3) cells in the presence and absence of Zn+2 and in MA-10(P+29) cells in the presence and absence of PDE inhibitor clearly demonstrate that the amount of the 30 kilodalton mitochondrial proteins present in these cells closely parallels that of progesterone production. The high degree of correlation between the appearance and quantity of these mitochondrial proteins and the production of steroids make them strong candidates for the putative proteins involved in acute regulation of steroidogenesis.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed1993

Biochemical properties of the agonist-induced desensitization of the follicle-stimulating hormone and luteinizing hormone/chorionic gonadotropin-responsive adenylyl cyclase in cells expressing the recombinant gonadotropin receptors.

In most experiments done in cell-free systems, the LH/CG-induced desensitization of the ovarian LH/CG-responsive adenylyl cyclase has been reported to be dependent on GTP. Little is known, however, about the molecular basis of this phenomenon or about the FSH-induced desensitization of the FSH-responsive adenylyl cyclase. We report here that, contrary to most previous findings, ATP is required for desensitization of the LH/CG- and FSH-responsive adenylyl cyclase in human kidney cells stably transfected with the complementary DNAs for the rat LH/CG or FSH receptor. This requirement does not seem to be peculiar to transfected cells because under our experimental conditions ATP is also preferred over GTP for the human CG-induced desensitization of the LH/CG-responsive adenylyl cyclase in highly purified plasma membranes from MA-10 Leydig tumor cells. Maximal desensitization of both FSH- and LH/CG-sensitive adenylyl cyclase in membranes from the transfected cells was achieved with millimollar concentrations of Mg2+ and ATP and did not appear to correlate with activation of the enzyme. In both of these systems, GTP, uridine triphosphate, and cytidine triphosphate were not able to substitute for ATP. In MA-10 membranes, however, there was some desensitization even without added nucleotide triphosphates, and ATP was more potent than GTP. Last, desensitization of the gonadotropin-sensitive adenylyl cyclase could not be explained by a decrease in the functional activities of stimulatory guanine nucleotide binding protein or of the catalytic moiety of the enzyme. A change in the functional properties of the gonadotropin receptors appears to be the most likely mechanism for desensitization.

Adenosine Triphosphate↗

PubMed1993

Identification of a Leydig tumor cell protein that is phosphorylated in response to stimulation with choriogonadotropin or epidermal growth factor.

Although hCG and mouse epidermal growth factor (mEGF) activate different signaling systems in a clonal strain of murine Leydig tumor cells (designated MA-10), both compounds ultimately elicit several common effects, such as increased steroidogenesis, decreased transcription of the LH/CG receptor gene, and attenuation of adenylyl cyclase. Based on this information, it was hypothesized that hCG and mEGF may induce phosphorylation of a common protein or set of proteins. Studies were performed to identify such a protein if it exists. MA-10 cells were metabolically labeled with [32P]orthophosphate, and phosphorylation patterns were examined and quantitated using two-dimensional gel electrophoresis. A 21-kilodalton protein whose phosphorylation state increased after hCG and mEGF stimulation was identified. Three isoforms of this protein were visible after hCG stimulation, with approximate pI values of 5.9, 6.0, and 6.1, while only two isoforms were visible after mEGF stimulation, with approximate pI values of 6.0 and 6.1. This protein is phosphorylated on serine residues in response to either hCG or mEGF. Since this protein may play a role in eliciting the common actions of hCG and mEGF, its time course of phosphorylation and concentration responsiveness to hCG and mEGF were also characterized.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed1993

A polyclonal antibody to a synthetic peptide derived from the rat follicle-stimulating hormone receptor reveals the recombinant receptor as a 74-kilodalton protein.

We have prepared a polyclonal antibody (AntiF) against a synthetic peptide comprising residues 19-29 of the rat FSH receptor. The specificity of this antibody was documented using human embryonic kidney (293) cells and stable transfectants of 293 cells expressing the recombinant LH/CG and FSH receptors. The data presented show that AntiF inhibits the binding of FSH, but not that of LH/CG, to their cognate receptors. AntiF also recognizes a specific protein(s) representing the FSH receptor in Western blots or by immunoprecipitation of cells transfected with the FSH receptor. This protein(s) is not present in untransfected 293 cells or in 293 cells permanently transfected with the LH/CG receptor. Finally, addition of the 19-29 peptide prevents immunoprecipitation of the FSH receptor by AntiF, whereas an unrelated peptide corresponding to residues 637-647 has no effect. In Western blots of 293 cells transfected with the FSH receptor, AntiF reveals the recombinant receptor as a heterogenous glycoprotein with a molecular mass of 58,000-83,000 daltons (in the absence of thiol-reducing agents) or 69,000-81,000 (in the presence of thiol reducing agents). Pulse-chase experiments with metabolically labeled cells show that the mature FSH receptor is a 74-kilodalton protein derived from 67- and 72-kilodalton precursors.

Amino Acid Sequence↗