The phenotype of individuals harboring loss-of-function or gain-of-function mutations of the lutropin receptor (LHR) clearly shows that this receptor is important for the proliferation and differentiation of Leydig cells and may even be involved in the neoplastic transformation of this cell type. The experiments proposed herein are driven by the hypothesis that the binding of agonist (LH/CG) to the LHR results in the activation of multiple signaling pathways, and that these pathways, either alone or in combination, stimulate the proliferation of Leydig cells. We seek to identify and characterize novel G protein-dependent and -independent pathways that are activated by the LHR and may control cell proliferation. In pursuing these experiments we will compare the behavior of the hLHR-wt and that of naturally occurring activating mutations of the hLHR associated with Leydig cell hyperplasia or Leydig cell tumors. Some experiments will be done in heterologous cell lines expressing these receptors but we will ultimately make use of the knowledge gained from these models to examine the ability of the LHR to induce the proliferation and neoplastic transformation of progenitor rat Leydig cells in primary culture.
The specific aims are as follows. (1) Examine the involvement of G proteins and the beta-arrestins (barrs) on the LH/CG-induced activation of Src, phosphatidylinositol 3 kinase (PI3K) and the mitogen-activated protein kinase (MAPK) cascade. (2) Define the residues of the LHR that bind the barrs and the relative importance of LHR activation vs. phosphorylation on the formation of the LHR/barr complex. (3) Define the molecular basis of the sorting of the internalized LHR and the impact of this sorting on signaling. (4) Compare the pathways involved in the trafficking of the hLHR-wt with the agonist-independent trafficking of activating mutations of the hLHR associated with Leydig cell hyperplasia and Leydig cell tumors. (5) Establish and characterize a new experimental system to test the mitogenic and oncogenic potential of the hLHR.
|Matzkin, Maria Eugenia; Yamashita, Soichi; Ascoli, Mario (2013) The ERK1/2 pathway regulates testosterone synthesis by coordinately regulating the expression of steroidogenic genes in Leydig cells. Mol Cell Endocrinol 370:130-7|
|Tai, Ping; Ascoli, Mario (2011) Reactive oxygen species (ROS) play a critical role in the cAMP-induced activation of Ras and the phosphorylation of ERK1/2 in Leydig cells. Mol Endocrinol 25:885-93|
|Yamashita, Soichi; Tai, Ping; Charron, Jean et al. (2011) The Leydig cell MEK/ERK pathway is critical for maintaining a functional population of adult Leydig cells and for fertility. Mol Endocrinol 25:1211-22|
|Tai, Ping; Shiraishi, Koji; Ascoli, Mario (2009) Activation of the lutropin/choriogonadotropin receptor inhibits apoptosis of immature Leydig cells in primary culture. Endocrinology 150:3766-73|
|Shiraishi, Koji; Ascoli, Mario (2008) A co-culture system reveals the involvement of intercellular pathways as mediators of the lutropin receptor (LHR)-stimulated ERK1/2 phosphorylation in Leydig cells. Exp Cell Res 314:25-37|
|Galet, Colette; Ascoli, Mario (2008) Arrestin-3 is essential for the activation of Fyn by the luteinizing hormone receptor (LHR) in MA-10 cells. Cell Signal 20:1822-9|
|Shiraishi, Koji; Ascoli, Mario (2007) Lutropin/choriogonadotropin stimulate the proliferation of primary cultures of rat Leydig cells through a pathway that involves activation of the extracellularly regulated kinase 1/2 cascade. Endocrinology 148:3214-25|
|Ascoli, Mario (2007) Potential Leydig cell mitogenic signals generated by the wild-type and constitutively active mutants of the lutropin/choriogonadotropin receptor (LHR). Mol Cell Endocrinol 260-262:244-8|
|Galet, Colette; Ascoli, Mario (2006) A constitutively active mutant of the human lutropin receptor (hLHR-L457R) escapes lysosomal targeting and degradation. Mol Endocrinol 20:2931-45|
|Shiraishi, Koji; Ascoli, Mario (2006) Activation of the lutropin/choriogonadotropin receptor in MA-10 cells stimulates tyrosine kinase cascades that activate ras and the extracellular signal regulated kinases (ERK1/2). Endocrinology 147:3419-27|
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