Protein Kinase A-Independent cAMP Stimulation of Progesterone in a Luteal Cell Model Is Tyrosine Kinase Dependent but Phosphatidylinositol-3-Kinase and Mitogen-Activated Protein Kinase Independent1

Abstract

Comprehensive understanding of the cellular mechanisms utilized by luteal cells in response to extracellular hormonal signals resulting in the normal synthesis and secretion of their steroid and peptide products has yet to be achieved. Previous studies have established that cAMP functions as a second messenger in mediating gonadotropin stimulated luteal progesterone secretion. Classically, increased intracellular concentrations of cAMP result in activation of protein kinase A (PKA), which in turn phosphorylates gene regulatory transcription factors. Recent studies demonstrate that non-PKA mediated actions of cAMP exist, yet the mechanisms are not well understood. In addition to gonadotropic hormones, such growth factors as insulin, insulin-like growth factor 1, and epidermal growth factor have been shown to modulate luteal steroid hormone synthesis and steroidogenic enzyme expression as either independent effects or via amplification or modulation of the action of gonadotropic hormones or cAMP. Thus, mechanisms independent of cAMP and also downstream to cAMP that do not involve PKA are likely to be important in steroidogenesis in mammalian cells. The present studies were performed to help define the cellular mediators involved in cAMP-stimulated progesterone expression. Our data demonstrate that, in an in vitro steroidogenic cell model, 1) cAMP-stimulated progesterone occurs in a manner that is independent of PKA, 2) neither phosphatidylinositol-3-kinase nor mitogen-activated protein kinase are involved in PKA-independent cAMP-stimulated progesterone production, 3) tyrosine kinase activity does mediate cAMP-stimulated progesterone production, and 4) cAMP directly activates the Ras protein. These data suggest novel mediators of cAMP-stimulated progesterone production.

The progesterone receptor as a transcription factor regulates phospholipase D1 expression through independent activation of protein kinase A and Ras during 8-Br-cAMP-induced decidualization in human endometrial stromal cells

“…[23]). This mechanism occurs independently of PKA signalling: cAMP-stimulated progesterone expression occurs through direct activation of the Ras protein in an in vitro steroidogenic cell model [32]. A Ras-specific activator called CNrasGEF [cyclic nucleotide ras GEF (guanine-nucleotide-exchange factor)] is activated by cAMP in melanocytes, and Rap1, a member of the Ras family of GTPases, is activated by cAMP during endothelial cell-cell contact [33,34].…”

Produção de progesterona in vitro pelas células do corpo lúteo bovino ao longo da gestação

“…apresenta expressão máxima do mRNA do VEGF (Garbelotti 2006), o que pode contribuir para aumento da síntese de P4 nesta fase (Papa et al 2006, Needle et al 2007. No corpo lúteo cíclico de búfalos foi observada alta correlação existente entre a produção de progesterona e a expressão de mRNA e proteína do VEGF (Papa et al 2006) bem como entre produção de P4 e densidade vascular (Moura et al 2003).…”

“…Os fatores de crescimento, principalmente o VEGF (vascular endothelial growth factor) e o bFGF (basic fibroblastic growth factor), são responsáveis pelo desenvolvimento e manutenção da densa rede de capilares neo-formados, além de contribuírem de maneira parácrina e autócrina para a produção de P4 (Schams & Berisha 2002, Campos 2005, Needle et al 2007). Secundariamente, o hormônio luteinizante (LH) e o hormônio do crescimento (GH), possuem uma ação efetiva na regulação da atuação dos fatores de crescimento e estímulo à produção de P4; outros agentes, como peptídeos, esteróides e prostaglandinas são responsáveis pela modulação da função luteínica e regulação fina da glândula (Schams & Berisha 2004).…”