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CAMP activates Rap1 in differentiating mouse male germ cells: a new signaling pathway mediated by the cAMP-activated
1Department of Biology, University of Milan, Via Celoria 26, 20133 Milano, Italy. giovanna.berruti@unimi.it
Abstract:
Rap1, a Ras-like G-protein, is implicated in the signaling of various cellular processes as morphogenesis, differentiation, cell adhesion and spreading, and maintenance of T cell anergy and B cell activation. The effectors that mediate Rap1 signaling have not yet been definitely identified, with the exception of B-Raf which, however, is restricted to neuronal tissues and a small subset of other cell types, including in particular male germ cells. We previously showed that in mouse spermatids Rap1 could interact with B-Raf giving rise to a signaling complex. Here we investigated about the possible molecules which "switch on" Rap1 finding that cAMP could in vivo activate endogenous Rap1. Spermatid-enriched cell cultures stimulated with 8-(4-chlorophenylthio)-cyclic AMP yielded higher levels of GTP-bound Rap1 than unstimulated cells. Since cAMP-induced Rap1 activation is actually retained to occur through Epac, we checked whether this recently discovered Rap1 exchange factor is expressed in male germ cells. Our findings indicate that Epac is present in spermatogenic cells and exhibits a preferential subplasmalemmal localization, although it shows also an intracellular location, more or less pronounced depending on the type of spermatogenic cell examined. Taken together, our data show that cAMP activates Rap1 in differentiating male germ cells which express the cAMP sensor Epac, thus suggesting that this activation might occur directly through Epac.
Insights
Cyclic adenosine monophosphate (cAMP) activates Rap1 signaling in male germ cells. This process involves the cAMP sensor Epac, suggesting a direct activation pathway crucial for cell differentiation.
Area of Science:
- Molecular Biology
- Cell Signaling
- Reproductive Biology
Background:
- Rap1, a Ras-like G-protein, regulates key cellular functions including differentiation and cell adhesion.
- Identifying Rap1's upstream activators and effectors is crucial for understanding its signaling pathways.
- B-Raf is a known Rap1 effector, but its expression is limited, necessitating the search for other activators, particularly in male germ cells.
Purpose of the Study:
- To investigate the in vivo activators of Rap1 in male germ cells.
- To determine if cyclic adenosine monophosphate (cAMP) activates Rap1 in these cells.
- To examine the expression and localization of Epac (a cAMP-activated Rap1 exchange factor) in male germ cells.
Main Methods:
- Utilized spermatid-enriched cell cultures.
- Stimulated cells with 8-(4-chlorophenylthio)-cyclic AMP, a cAMP analog.
- Assessed levels of GTP-bound Rap1 to measure Rap1 activation.
- Performed immunofluorescence to determine Epac expression and localization in spermatogenic cells.
Main Results:
- Spermatid cultures stimulated with the cAMP analog showed increased levels of GTP-bound Rap1 compared to unstimulated controls.
- Epac (Exchange protein directly activated by cAMP) was found to be expressed in spermatogenic cells.
- Epac exhibited a preferential subplasmalemmal localization, with some intracellular presence varying by cell type.
Conclusions:
- Cyclic adenosine monophosphate (cAMP) activates endogenous Rap1 in differentiating male germ cells.
- The presence and localization of Epac in male germ cells suggest it acts as the cAMP sensor for Rap1 activation.
- This cAMP-Epac-Rap1 pathway is likely a key mechanism for regulating Rap1 signaling during male germ cell differentiation.
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