Breast Cancer Trigger?

NEW YORK CITY--Scientists have discovered that malignant breast tumor cells have high levels of an enzyme that tells cells to divide. The finding, announced at a press conference here today and described in the current issue of the Journal of Clinical Investigation, could provide a promising target for anticancer drugs.

Pharmacologist Craig Malbon and his team at the State University of New York, Stony Brook, found that levels of mitogen-activated protein (MAP) kinase, an enzyme involved in cell division, were five to 20 times higher in biopsied human breast tumor cells than in healthy cells from the same patients or in cells from benign tumors.

MAP kinase acts like a switch: When a phosphate group is added to it, it gets turned on and spurs cells to divide. But in the malignant cells, the researchers found, the MAP kinase was in its activated form: "Most [MAP-kinase] molecules were already phosphorylated," says Stony Brook molecular endocrinologist Hsien-yu Wang. How MAP kinase gets stuck in the "on" position in breast cancer cells is a mystery. It's also unknown, Malbon says, whether other tumor types have elevated MAP-kinase levels.

"It's an important study" that adds "another intriguing piece of the puzzle," says Bruce Stillman, director of the Cold Spring Harbor Laboratory on Long Island. He says drugs could be designed to inhibit MAP-kinase activity, which might interfere with tumor cell division. And if high enzyme levels are a hallmark of malignant cells, an assay for it in biopsied breast tissue could flag dangerous tumors.