In both cases, the result was a drastic reduction of TG2 expression (up to 94 percent) and telltale signs of autophagy in the cancer cells, which became riddled with cavities called vacuoles.
When autophagy occurs, a double membrane forms around a cell organ, or organelle. This autophagosome then merges with a digestive organelle called a lysosome and everything inside is consumed, leaving the vacuole and a residue of digested material. If enough of this happens, the cell dies.
Gabriel Lopez-Berestein, M.D., professor of experimental therapeutics and study co-author, notes that the research also shows that the self-consuming cell death prevented by TG2 is independent of a prominent molecular pathway also known to regulate autophagy called the mammalian target of rapamycin.
"Targeting TG2, or its activating protein PKC, or both, presents a novel and potentially effective approach to treating patients with pancreatic cancer," Lopez-Berestein said. Research in the mouse model remains in the early stages, the researchers caution.
The researchers also show that the TG2 pathway also is separate from another, better known, form of programmed cell death called apoptosis.
Apoptosis, like autophagy, is a normal biological defense mechanism that systematically destroys defective cells by forcing them to kill themselves. In apoptosis, the cells die via damage to their nucleus and DNA, with other cellular organelles preserved. Autophagy kills by degrading those other organelles while sparing the nucleus.
Mehta's lab reported in a Cancer Research paper last September that TG2 overexpression also activates a protein called nuclear factor-kB known to play a role in regulating cell growth, metastasis and apoptosis. This pathway, Mehta explained, could make TG2 an attractive target for other forms of cancer as well.
Co-authors with Mehta and Lopez-Berestein are: co-first authors