Regulation of Gonadotropin Receptors and Steroidogenic Responses in Cultured Leydig Tumor Cells

Ascoli, Mario; Freeman, Dale A.

doi:10.1007/978-1-4684-4634-0_20

Cited by 25 publications

(43 citation statements)

References 72 publications

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“…Treatment of MA10 Rasϩ and MA10 Src-Rasϩ cells were relatively unresponsive to either cholera toxin or 8-bromo cyclic AMP. This is somewhat at odds with a previous report that EGF-induced desensitization of MA10 cells was completely accounted for by a decrease in LH receptor number and that EGF pretreated cells were fully responsive to cholera toxin and 8-bromo cAMP [2]. However, that report also demonstrated that the EGF receptor was rapidly internalized, perhaps terminating the EGF signal, whereas LH receptor down-regulation and replenishment lagged far behind.…”

Section: Discussioncontrasting

confidence: 56%

“…Numerous reports have demonstrated that treatment of gonadal steroidogenic cells with growth factors such as epidermal growth factor (EGF), platelet-derived growth factors (PDGFs), and fibroblast growth factor results in an attenuation of gonadotropin-stimulated steroid secretion [1][2][3][4][5]. The mechanisms by which growth factor stimulation modulates steroidogenesis have yet to be fully elucidated.…”

Section: Discussionmentioning

confidence: 99%

“…Both the LH-R and FSH-R are primarily coupled to G s␣ which, upon activation, stimulates adenylate cyclase, leading to increased intracellular cAMP and activation of cAMP-dependent protein kinase A, with the end result of increased steroidogenesis and steroid secretion. Many studies have demonstrated that growth factors such as epidermal growth factor [1,2], platelet-derived growth factor [3,4], and the fibroblast growth factors [5] modulate gonadotropin-stimulated steroid secretion by gonadal steroidogenic cells, however, the mechanisms by 1 Supported by grant HD-36013 from the National Institutes of Health. Previous reports demonstrated that herbimycin A, a specific inhibitor of the Src family of nonreceptor tyrosine kinases, potentiated LH-stimulated progesterone secretion by rat thecal-interstitial cells [6].…”

Section: Introductionmentioning

confidence: 99%

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Src Tyrosine Kinase-Induced Loss of Luteinizing Hormone Responsiveness Is via a Ras-Dependent, Phosphatidylinositol-3-Kinase Independent Pathway1

Taylor¹

2002

Biology of Reproduction

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Gonadotropins stimulate gonadal cell steroid secretion primarily through activation of a cAMP-protein kinase A signal transduction pathway. Various growth factors have been shown to inhibit gonadotropin-stimulated steroidogenesis, however, the intracellular signaling cascades involved in growth factor inhibition have not been characterized. The present study investigated whether Src tyrosine kinase, a nonreceptor tyrosine kinase activated in response to growth factor stimulation and previously shown to inhibit LH-stimulated progesterone secretion, acts via activation of Ras stimulated pathways, phosphatidylinositol-3-kinase (PI3-kinase) stimulated pathways, or both in MA10 Leydig cells. Direct activation of Src in MA10 cells that express a temperature sensitive Src was associated with an increase in GTP-bound Ras, indicating increased Ras activity in response to Src activation. Direct activation of Ras by way of expression of a constitutively active Ras (Ras؉) was associated with a decrease in LH responsiveness. Coexpression of a dominant negative Src, which by itself increases LH responsiveness in MA10 cells, had no effect on Ras؉ inhibition on LH responsiveness, further demonstrating that Src is upstream of Ras. In addition, MA10 Ras؉ cells were relatively unresponsive to cholera toxin or 8-bromo cAMP, indicating the effects of Ras are independent of cAMP generation. Wortmannin, a PI3-kinase inhibitor, did not restore LH responsiveness to cells expressing activated Src or constitutively active Ras. These results demonstrate that Src activates a Ras pathway in MA10 Leydig cells, and that activation of Ras is associated with a loss of LH responsiveness that is independent of PI3-kinase.

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Section: Discussioncontrasting

confidence: 56%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Src Tyrosine Kinase-Induced Loss of Luteinizing Hormone Responsiveness Is via a Ras-Dependent, Phosphatidylinositol-3-Kinase Independent Pathway1

Taylor¹

2002

Biology of Reproduction

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“…This growth factor has been shown to cause a marked reducton (<97%) in the number of hCG receptors on MA-10 cells, a clonai line derived from a Leydig cell tumour (Ascoli, 1981), and on Leydig cells in primary culture (Welsh & Hsueh, 1982). In addition, EGF also inhibited hCG-stimulated production of testosterone, apparently by decreasing the activities of 17a-hydroxylase and 17,20-lyase (Welsh & Hsueh, 1982).…”

Section: Epidermal Growthfactor (Egf)mentioning

confidence: 99%

Growth factors as autocrine and paracrine modulators of male gonadal functions

Bellvé¹,

Zheng²

1989

Reproduction

155

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“…In both tissues, various hormones, growth factors and second messenger analogs can modulate the level of LHR expression. In particular, epidermal growth factor, phorbol esters and a high concentration of cAMP have been shown to down-regulate the numbers of LHR in Leydig cells and in differentiated granulosa cells (Ascoli 1981, Rebois & Fishman 1984, Rebois & Patel 1985, Wang et al 1991a. Besides the gonads, low levels of LHR expression have been reported in a number of extragonadal tissues (Ziecik et al 1986, Reshef et al 1990, Lei et al 1993, Reiter et al 1995, Hämäläinen et al 1999, Kero et al 2000.…”

Section: Introductionmentioning

confidence: 99%

Functional characterization of the basal promoter of the murine LH receptor gene in immortalized mouse Leydig tumor cells

Nikula¹,

Koskimies²,

El-Hefnawy³

et al. 2001

Journal of Molecular Endocrinology

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The nuclear proteins of the LH receptor (LHR) expressing murine Leydig tumor cells (mLTC-1), binding to the LHR primary promoter, were studied by gel retardation assays. Nuclear extracts of HeLa cells, not expressing LHR, were used as control. Protein binding was characterized to the first 173 base pairs (bp) of the LHR 5 -untranslated region, comprising the basal transcriptional promoter activity in mLTC-1 cells, and accounting for the Leydig cell-specific LHR expression. The promoter fragment is GC-rich and contains several Sp1 sites, one activating protein 2 (AP-2) site, and a putative SF-1 binding site. Three subfragments of the 173 bp promoter, I (bases 1 to 55), II ( 56 to 102) and III ( 103 to 173), were separately analyzed. Fragments II and III formed several complexes with mLTC-1 and HeLa cell nuclear extracts. One complex with fragments II and III, using mLTC-1 and HeLa cell extracts, was similar to that formed with purified Sp1, and it could be removed by an Sp1 oligo and supershifted by an Sp1 antibody. Both fragments formed additional complexes with mLTC-1 cell extracts with no specificity for Sp1. Partly similar, though weaker, complexes were seen with HeLa cell extracts. The most clearcut differences between the protein/DNA complexes formed with LHR expressing mLTC-1 cells and non-expressing (HeLa, COS, HEK 293 and MSC-1) cells were found with fragment I. Extracts of the non-expressing cells formed one prominent protein/DNA complex which was missing in mLTC-1 cells. Purified Sp1 also bound to this fragment. The fragment containing the putative SF-1 binding site did not form any protein/DNA complexes with mLTC-1 cell proteins. In conclusion, the murine LHR primary promoter binds, in addition to the Sp1 and AP-2 transcription factors, several other proteins. The Sp1 protein can bind into at least three different sites in the basal promoter. The other binding proteins differ most clearly between LHR expressing and nonexpressing cells in the promoter fragment closest to the translation start site, suggesting a key role for this part of the promoter in cell-specific LHR expression.

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Regulation of Gonadotropin Receptors and Steroidogenic Responses in Cultured Leydig Tumor Cells

Cited by 25 publications

References 72 publications

Src Tyrosine Kinase-Induced Loss of Luteinizing Hormone Responsiveness Is via a Ras-Dependent, Phosphatidylinositol-3-Kinase Independent Pathway1

Src Tyrosine Kinase-Induced Loss of Luteinizing Hormone Responsiveness Is via a Ras-Dependent, Phosphatidylinositol-3-Kinase Independent Pathway1

Growth factors as autocrine and paracrine modulators of male gonadal functions

Functional characterization of the basal promoter of the murine LH receptor gene in immortalized mouse Leydig tumor cells

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