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Large crowds make many people uncomfortable, and—according to findings from a team of Huntsman Cancer Institute (HCI) researchers—some of our cells share the aversion.
Jody Rosenblatt, PhD, and her lab found the cells that make up normal epithelial tissue (those that line inner and outer surfaces of the body) have “personal space issues.” As new cells are formed, the tissue ejects older cells, causing them to die and easing overcrowding. The discovery was published in the April 2012 issue of Nature.
Rosenblatt, an HCI investigator and associate professor in the Department of Oncological Sciences at the University of Utah, and her team are the first to discover the link between cell birth (mitosis) and cell death (apoptosis). Earlier studies showed that dying cells are pushed out of the epithelium, or extruded, when researchers purposely trigger the process in the lab. “But it wasn’t clear what factors caused cells to die in normal tissues,” says Rosenblatt.
Epithelial tissue, which includes skin and the lining of the gastrointestinal tract, has the second quickest turnover of cells in the body—churning out billions of new cells each hour. When cells turn over at a rapid rate, extrusion becomes very important. If cells aren’t being pushed out, they pile up and form into masses.
In one experiment, Rosenblatt and her lab observed this phenomenon in sections of colon polyps. “In the polyps, which are precursors to colon cancer, there’s a similar pile-up of cells,” explains Rosenblatt. “If they behaved as normal colon tissue, we would have seen cells extrude, but polyps don’t seem to do it.”
Now that the link has been identified, investigators are searching for a reason why some epithelial tissues don’t extrude cells. “We still don’t know which cells are prone to die,” says Rosenblatt. “This is a very important question because it’s these cells that don’t die—though they should have—that may go on to form cancers.”
Rosenblatt notes this basic discovery may also have implications for diseases such as asthma and colitis, where too much cell death leads to poor barrier function, a primary role of epithelial tissue. Further research will continue to shed light on what controls cell turnover in epithelia, taking scientists closer to understanding the causes of cancers.