P120 acts in cells by regulating the function of proteins called cadherins. Cadherins are membrane proteins that help cells stick to each other to form a tissue. On the outside of a cell's membrane, they act like Velcro, fusing to other cadherin proteins on adjacent cells. On the inside, they latch on to a chainwork of catenins, which are proteins that regulate a cell's shape and function. The best understood of the cadherins is E-cadherin, which binds all epithelial cells to each other, forming layers that cover the inside of organs and body cavities, and the outside skin of humans. In short, E-cadherin holds a human's cells and tissues together, Dr. Anastasiadis says.
P120 normally binds onto E-cadherin, strengthening cell-cell bonding. But in some cases it detaches from E-cadherin, which allows the cell to lose its adhesive grip to adjacent cells and switch on a program that promotes cell movement. The loss of E-cadherin expression during a process known as epithelial-mesenchymal transition (EMT) is one mechanism of activating p120's pro-migratory function, the researchers say. EMT is necessary during human development, or during wound healing in adults. But it is a process that is hijacked by tumors to allow cancer cells to migrate and colonize other organs. "When E-cadherin production is lost during the progression of cancer, p120 catenin induces invasion and metastasis," Dr. Anastasiadis says.
In this study, the researchers discovered that not only does p120 promote metastasis when it is not bound to E-cadherin, it also turns on growth-promoting genes and proteins. In laboratory and animal experiments, they found that "free" p120 makes cancer very aggressive, able to grow in conditions that other cancer cells can't. They specifically found that p120 activates a family of molecules that includes Ras and Rho, which promote cell growth and movement.
"What is really interesting here is that p120 is acting like a tu
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