College of LAS « Illinois

Cellular and Structural Biology

Protein Plays Key Role as Regulator of Cell Growth and Division

A protein located in the cytoplasm between a mammalian cell membrane and nucleus is more important than previously believed. It shuttles in and out of the nucleus as part of a "nuclear experience" that helps regulate cell growth and division, LAS scientists say.

The presence of FKBP12-rapamycin-associated protein (FRAP) in the nucleus previously was considered an artifact of research. New research indicates that the protein regulates signal transduction, a membrane-to-cytoplasm communication network that governs cellular response to outside stimuli such as growth factors, hormones or foreign agents. If FRAP fails to briefly enter and exit the nucleus, then some crucial proteins fail to synthesize.

"What we found is a brand new mechanism for cell signaling, a fundamental one that was not realized until it was shown in yeast," says Jie Chen, a professor of cell biology. "Our research is the first to show this activity in mammalian systems."

A similar finding involving a different protein in yeast cells was published in 1999 in the journal Cell by Harvard Medical School researchers. The two reports taken together, Chen says, offer new insight on the regulation of the protein-synthesis machinery in living cells.

"This knowledge is important because of the link to human diseases, especially cancer, which are basically cases of cell growth gone awry," she says. "What we have found is a regulatory mechanism for normal cell growth. If we understand normal cell growth better, we can come up with better ways to fight deregulated cell growth."

The idea that FRAP could enter the nucleus on its own, especially considering its size, had been dismissed until new molecular technologies opened research doors, Chen says.

Summer 2002