Since the late 1990s, researchers have known that a gene called PTEN (short for phosphatase and tensin homolog on chromosome 10) encodes a signaling protein that suppresses tumor growth. What wasn't known, however, was what mechanism activated PTEN. The answer was found by a group of researchers led by University of Illinois at Chicago chemistry professor Wonhwa Cho. They report their findings in the June 9 online edition of the Proceedings of the National Academy of Sciences.
"The role of PTEN is to counterbalance the action of an enzyme that induces cell growth," said Cho. "Over-activation of the enzyme can lead to cancer. So if you lose a PTEN gene and its cellular activity, the cell goes out of control. It's like a car with an accelerator but without the brakes."
It was generally thought that PTEN was activated by binding to other proteins, giving it a signal to interact with the cell membrane. But Cho said that's not the case.
Cho's group found that PTEN itself can be activated by phosphorylation, or the chemical addition of a phosphate tag.
"We found that the phosphorylation of certain sites of the PTEN protein worked as a switch to completely change its electrostatic property," said Cho. "It switched from being neutral to positively charged, then recognized the opposite charge on the membrane to bind there." Once the bind took hold, the cancer suppression action went to work.
Cho's laboratory used a biophysical technique called surface plasmon resonance analysis and cellular microscopic analysis of green fluorescence protein-labeled PTEN to unlock the secret of its activation. The UIC chemist believes the mechanism described for PTEN is a relatively common way to regulate membrane binding and activation of many cellular proteins involved in cell signaling and membrane traffickin
Contact: Paul Francuch
University of Illinois at Chicago