Signaling through Extracellular Signal-regulated Kinase Is Required for Spermatogonial Proliferative Response to Stem Cell Factor

Susanna Dolci,Manuela Pellegrini,Silvia Di Agostino,Raffaele Geremia,Pellegrino Rossi

doi:10.1074/jbc.m105143200

Susanna Dolci, Manuela Pellegrini + Show 3 more

Open Access

https://doi.org/10.1074/jbc.m105143200

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Abstract

In vitro addition of stem cell factor (SCF) to c-kit-expressing A(1)-A(4) spermatogonia from prepuberal mice stimulates their progression into the mitotic cell cycle and significantly reduces apoptosis in these cells. SCF addition results in a transient activation of extracellular signal-regulated kinases (Erk)1/2 as well as of phosphatidylinositol 3-kinase (PI3K)-dependent Akt kinase. These events are followed by a rapid re-distribution of cyclin D3, which becomes predominantly nuclear, whereas its total cellular amount does not change. Nuclear accumulation of cyclin D3 is coupled to transient activation of the associated kinase activity, assayed using the retinoblastoma protein (Rb) as a substrate. These events were followed by a transient accumulation of cyclin E, stimulation of the associated histone H1-kinase activity, a delayed accumulation of cyclin A2, and Rb hyper-phosphorylation. All the events associated with SCF-induced cell cycle progression are inhibited by the addition of either a PI3K inhibitor or a mitogen-activated protein-kinase kinase (MEK) inhibitor, indicating that both MEK and PI3K are essential for c-kit-mediated proliferative response. On the contrary, the anti-apoptotic effect of SCF is not influenced by the separate addition of either MEK or PI3K inhibitors. Thus, SCF effects on mitogenesis and survival in c-kit expressing spermatogonia rely on different signal transduction pathways.

Highlights

The tyrosine kinase receptor encoded by the c-kit gene and its ligand stem cell factor (SCF)1 play a fundamental role in gametogenesis (1)
SCF Stimulates Cell Cycle Progression of c-kit Expressing Spermatogonia through Both mitogen-activated protein-kinase kinase (MEK) and phosphatidylinositol 3-kinase (PI3K) Signals—Cultures of germ cells obtained from 8-day-old mice are enriched in differentiating spermatogonia (25, 26), which express high levels of c-kit (5– 8, 14)
SCF Activates Both Extracellular Signal-regulated Kinases (Erk)1/2 and Akt Kinases in c-kit-expressing Spermatogonia— Since the MEK and PI3K inhibitors were effective in the inhibition of SCF-induced proliferation of spermatogonia, we studied the Erk1/2 and PI3K activation pathways induced by SCF

Summary

Introduction

The tyrosine kinase receptor encoded by the c-kit gene and its ligand stem cell factor (SCF)1 play a fundamental role in gametogenesis (1). We report evidence that SCF acts as a mitogenic factor in cultured c-kit-expressing spermatogonia and that both mitogen-activated protein kinase kinase (MEK)- and PI3K-dependent pathways are required for the proliferative response.

Results

Conclusion