A major question in cell biology is how molecular specificity is achieved by different growth factor receptors that activate apparently identical signaling events. For the neurotrophin family, a distinguishing feature is the ability to maintain a prolonged duration of signal transduction. However, the mechanisms by which neurotrophin receptors assemble such a sustained signaling complex are not understood. Here we report that an unusual ankyrin-rich transmembrane protein (ARMS+kidins220) is closely associated with Trk receptor tyrosine kinases, and not the EGF receptor. This association requires interactions between transmembrane domains of Trk and ARMS. ARMS is rapidly tyrosine phosphorylated after binding of neurotrophins to Trk receptors and provides a docking site for the CrkL-C3G complex, resulting in Rap1-dependent sustained ERK activation. Accordingly, disruption of Trk-ARMS or the ARMS-CrkL interaction with dominant-negative ARMS mutants, or treatment with small interference RNA against ARMS substantially reduce neurotrophin-elicited signaling to ERK, but without any effect upon Ras or Akt activation. These findings suggest that ARMS acts as a major and neuronal-specific platform for prolonged MAP kinase signaling by neurotrophins

Phospholipase Cepsilon (PLCepsilon) is a novel PLC that has a CDC25 guanine nucleotide exchange factor (GEF) domain and two Ras association (RA) domains of which the second (RA2) is critical for Ras activation of the enzyme. In the present studies, we examined hormonal stimulation to elucidate receptor-mediated pathways that functionally regulate PLCepsilon. We demonstrate that epidermal growth factor (EGF), a receptor tyrosine kinase (RTK) agonist, and lysophosphatidic acid (LPA), sphingosine-1-phosphate (S1P), and thrombin, G protein-coupled receptor agonists, stimulate PLCepsilon overexpressed in COS-7 cells. EGF stimulated PLCepsilon in an RA2-dependent manner through Ras and Rap. In contrast, LPA, S1P and thrombin stimulated PLCepsilon by both RA2-independent and dependent mechanisms. To determine the G proteins that mediate the effects of these GPCR agonists, we coexpressed constitutively active G proteins with PLCepsilon and found that Galpha12, Galpha13, Rho, Rac and Ral stimulate PLCepsilon in an RA2-independent manner; whereas, TC21, Rap1A, Rap2A and Rap2B stimulate in an RA2-dependent manner similar to H-Ras. Of these G proteins, we show that Galpha12/13 and Rap partly mediate the effects of LPA, S1P, and thrombin to stimulate PLCepsilon. In addition, the stimulation by LPA and S1P is also partly sensitive to pertussis toxin. These studies demonstrate diverse hormonal regulation of PLCepsilon by distinct and overlapping pathways.