Dynamic membrane patterning, signal localization and polarity in living cells.

We review the molecular and physical aspects of the dynamic localization of signaling molecules on the plasma membranes of living cells. At the nanoscale, clusters of receptors and signaling proteins play an essential role in the processing of extracellular signals. At the microscale, "soft" and highly dynamic signaling domains control the interaction of individual cells with their environment. At the multicellular scale, individual polarity patterns control the forces that shape multicellular aggregates and tissues.

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.

Diagnosis of juvenile hemochromatosis in an 11-year-old child combining genetic analysis and non-invasive liver iron quantitation.

UNLABELLED: Juvenile or type2 hemochromatosis is a rare autosomal recessive disorder which leads to severe iron overload early in life. As in the classic adult form of the disease iron toxicity causes liver cirrhosis, cardiomyopathy, and endocrine complications, but the onset of the disease is anticipated in the second to third decades of life. Experience of this disease in children is limited. Molecular diagnosis is unfeasible because the type2 hemochromatosis gene is still unknown, although it is known that the disease locus maps to chromosome 1q. Combining linkage analysis with markers encompassing chromosome 1 locus and a non-invasive method for liver iron quantitation we diagnosed juvenile hemochromatosis in a presymptomatic stage in an 11-year-old Italian child. A regular phlebotomy protocol reduced iron overload preventing all the disease complications. CONCLUSION: Juvenile hemochromatosis patients have severe iron overload within the first years of life, strengthening the greater iron absorption that occurs in this as compared to other types of hemochromatosis. Early detection is essential, because treatment in presymptomatic stages prevents organ damage.