G Proteins Also Signal on Internal Cell Membranes (Golgi Body); Finding May Have Relevance to Solid Tumor Cancer Metastasis

A family of proteins called G proteins are a recognized component of the communication system the human body uses to sense hormones and other chemicals in the bloodstream and to send messages to cells. In work that further illuminates how cells work, researchers at the University of California, San Diego (UCSD) School of Medicine have discovered a new role for G proteins that may have relevance to halting solid tumor cancer metastasis. The study was reported online on April 9, 2015 in Developmental Cell. The article is titled “Activation of Gαi at the Golgi by GIV/Girdin Imposes Finiteness in Arf1 Signaling.” "Our work provides the first direct evidence that G proteins are signaling on membranes inside cells, not just at the cell surface as has been widely believed for several decades," said Pradipta Ghosh, M.D., Associate Professor and senior author. "This is significant because the G-protein pathway is a target of at least 30 percent of all current drugs on the market." Specifically, the UCSD-led team used live cell imaging of fluorescent proteins and other biological assays to show that G proteins in cultured human cells are active on a series of pancake-shaped membranes, called the Golgi body. The Golgi body sorts, packages, and directs the distribution of newly synthesized proteins to various locations within a cell. It also secretes enzymes, including matrix metalloproteases that enable cancer cells to digest surrounding tissue, escape, and spread. In addition to documenting G protein activity on the Golgi, the scientists also identified the protein that turns on G proteins as the GIV protein, which is widely recognized in the cancer research community for its role in facilitating metastasis.
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