Multidrug Resistance Protein Pumps:
Nature's Common Currency

Story By Alison Davis
Illustrated by Andrea Foust


 The pudgy "fat innkeeper" worm Urechis caupo, which looks more like a frankfurter than a worm, tunnels through the salty mudflats of Elkhorn Slough, California. It collects food by spinning a sinewy, mucous net. But the muddy cocktail trapped within the net contains more than lunch: within lies a virtual potpourri of chemical toxins, some natural and some man-made, that aren't meant to be eaten. Yet as soon as the poisons find their way into the marine worm's belly, they are spit back out into the mire.

At a nearby hospital, a breast cancer patient is losing her battle against cancer because the tenaciously dividing cancer cells in her body are using the same molecular gadgetry to jettison chemotherapy drugs back into her bloodstream, preventing them from attacking her tumor.

The fates of the worm and the woman are linked by a sub-microscopic pumping mechanism. A protein called a "multidrug resistance," or MDR pump, is nature's common currency here. Embedded within a cell's membrane, this protein protects a cell by ejecting a variety of molecules in many cases, toxins on contact. The cell might be a bacterium, in which case the "toxins" are antibiotics. With cancer cells, the "poisons" are chemotherapy drugs. MDR pumps are being discovered in almost every organism searched, including Urechis caupo that calls polluted, toxin-laden mud home, says Stanford University embryologist David Epel. Detecting traces of MDR in such a wide array of organisms is leading scientists like Epel to believe that this line of defense has persisted for a long, long time in biology, usually the signature of a very important molecule.


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