Rapl is a very close relative of Ras, but its function is likely to be distinct. A novel assay was developed to measure activation of Rapl and it was found that a large variety of extracellular stimuli are able to activate this small GTPase very rapidly. Common second messengers, like calcium, diacylglycerol and cAMP mediate this activation in a cell type dependent manner. We have studied the molecular mechanism of these activations and one of the striking results was the discovery of Epac, a novel binding protein of cAMP. Epac is a guanine nucleotide exchange protein for Rapl. This finding indicates that the common notion that all effects of cAMP are mediated by protein kinase A is incorrect. The function of Rapl is largely unknown. Recent evidence indicates that the hypothesis that Rapl functions as an antagonist of Ras effector signalling is probably incorrect. More like Rapl mediates a distinct pathway regulating processes related to the control of the actin cytoskeleton affecting vesicular traficking and/or cell adhesion.
展开▼
