Steroidogenesis and early response gene expression in MA-10 Leydig tumor cells following heterologous receptor down-regulation and cellular desensitization

Abstract

The Leydig tumor cell line, MA-10, expresses the luteinizing hormone receptor, a G protein-coupled receptor that, when activated with luteinizing hormone or chorionic gonadotropin (CG), stimulates cAMP production and subsequent steroidogenesis, notably progesterone. These cells also respond to epidermal growth factor (EGF) and phorbol esters with increased steroid biosynthesis. In order to probe the intracellular pathways along with heterologous receptor down-regulation and cellular desensitization, cells were preincubated with EGF or phorbol esters and then challenged with CG, EGF, dibutryl-cyclic AMP, and a phorbol ester. Relative receptor numbers, steroid biosynthesis, and expression of the early response genes, JUNB and c-FOS, were measured. It was found that in all cases but one receptor down-regulation and decreased progesterone production were closely coupled under the conditions used; the exception involved preincubation of the cells with EGF followed by addition of CG where the CG-mediated stimulation of steroidogenesis was considerably lower than the level of receptor down-regulation. In a number of instances JUNB and c-FOS expression paralleled the decreases in receptor number and progesterone production, while in some cases these early response genes were affected little if at all by the changes in receptor number. This finding may indicate that even low levels of activated signaling kinases, e.g. protein kinase A, protein kinase C, or receptor tyrosine kinase, may suffice to yield good expression of JUNB and c-FOS, or it may suggest alternative pathways for regulating expression of these two early response genes.

Flurbiprofen Inhibits Androgen Productions in Rat Immature Leydig Cells

“…Pituitary-secreted gonadotropin luteinizing hormone (LH) via bloodstream reaches Leydig cells, where it binds the membrane LH/choriogonadotropin receptor (LHCGR). The LHCGR has seven membrane-spanning domains . Upon binding of LH to the external portion of the LHCGR, a transduction of the signal activates the G protein and the latter further activates the adenosine cyclase, elevating intracellular cAMP .…”

“…8 Upon binding of LH to the external portion of the LHCGR, a transduction of the signal activates the G protein and the latter further activates the adenosine cyclase, elevating intracellular cAMP. 8 After a series of signal cascades via protein kinase A (PKA), steroidogenic acute regulatory protein (StAR) is phosphorylated and activated, 9 which mobilizes intracellular cholesterol into the mitochondrial inner membrane, where CYP11A1 is located and the first catalysis begins. Cholesterol is converted by CYP11A1 into pregnenolone (P5) via intermediate steroid, 22R-OH-cholesterol (22R).…”