Diacylglycerol kinase-alpha phosphorylation by Src on Y335 is required for activation, membrane recruitment and Hgf-induced cell motility.

Diacylglycerol (DAG) kinases (Dgk), which phosphorylate DAG to generate phosphatidic acid, act as either positive or negative key regulators of cell signaling. We previously showed that Src mediates growth factors-induced activation of Dgk-alpha, whose activity is required for cell motility, proliferation and angiogenesis. Here, we demonstrate that both hepatocytes growth factor (HGF) stimulation and v-Src transformation induce tyrosine phosphorylation of Dgk-alpha on Y335, through a mechanism requiring its proline-rich C-terminal sequence. Moreover, we show that both proline-rich sequence and phosphorylation of Y335 of Dgk-alpha mediate: (i) its enzymatic activation, (ii) its ability to interact respectively with SH3 and SH2 domains of Src, (iii) its recruitment to the membrane. In addition, we show that phosphorylation of Dgk-alpha on Y335 is required for HGF-induced motility, while its constitutive recruitment at the membrane by myristylation is sufficient to trigger spontaneous motility in absence of HGF. Providing the first evidence that tyrosine phosphorylation of Dgk-alpha is required for growth-factors-induced activation and membrane recruitment, these findings underscore its relevance as a rheostat, whose activation is a threshold to elicit growth factors-induced migratory signaling.

The use of the H reflex in serial evaluation of nerve conduction velocity.

Conduction velocity (CV) in the H pathway, expressed by a mixed (sensorimotor) index (HCV), showed a very reduced intra-individual variability when compared to conventional conduction parameters in normal subjects. HCV, tested serially over increasing intervals of time, was about 4 times more stable than motor CV in deep peroneal nerve and about 6 times more stable than the sensory CV in sural nerve. The HCV was so accurate in showing marginal conduction changes that it clearly revealed, in normal persons, a circadian rhythm of conduction velocity, well correlated with circadian variations of body temperature, which totally escaped conventional conduction parameters. owing to its reduced variability, this conduction parameter represents, within the limits in which it can be reliably used in clinical application, a first choice tool for longitudinal conduction studies.