This finding posits RAS signaling as a key mediator of circadian output.

The fungus Neurospora crassa is one of the best studied laboratory systems for circadian rhythms. However, over the past 50 years, almost all of the work done on Neurospora has used laboratory strains carrying the band mutation, because it enables researchers to visualize the fungus' daily circadian growth cycles. Research on Neurospora using this strain has contributed to understanding the basis of jet lag as well as some affective disorders.

While the band mutation has facilitated Neurospora clock observation, researchers are only now realizing what protein is encoded by the band gene, and how the subtle nature of the disruption in the band gene affects Neurospora circadian rhythms.

The Dartmouth team demonstrate that the band mutation is a dominant point mutation in ras-1 that causes a slight increase in GTP exchange, and therefore slightly higher activity levels. Says Dunlap, "Understanding the molecular nature of band makes us all look at output from the circadian clock in a different and clearer way. It's been a long time coming."

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To narrow this field, investigators conducted a second group of screening procedures. Using a variety of genome-scale approaches, they sought to determine if genes for any of the five kinases were unusually abundant in cancer cells. They found extra copies of IKBKE, but not of the other genes -- and correspondingly high levels of the IKBKE protein. This pointed to IKBKE's role as a breast cancer oncogene.

In the third part of the study, the investigators explored whether breast cancer cells depend on IKBKE for survival. In an earlier study, they had used a technique called RNA interference -- whose discovery was recognized with the Nobel Prize in Medicine and Physiology last year -- which uses bits of genetic material to systematically stile certain genes. With a high-throughput version of this technique, they found that when IKBKE was switched off, the cancer cells tended to stop proliferating and died.

"This triple screening approach enabled us to study what happened to cells when IKBKE was turned on and when it was shut off, and to take a global look at the genetic alterations within breast cancer cell lines and tumors," Hahn says. "Integrating these techniques allowed us to identify a new breast cancer oncogene and show that it plays a crucial role in the formation and survival of tumors."

The discovery that mutated IKBKE helps sustain a sizable percentage of breast cancers may spur the development of new treatments for the disease, Hahn remarks. Drugs able to target the oncogene and shut it down could offer an effective therapy for women whose tumor cells harbor the mutation.

The three-stage approach to finding breast cancer genes may be used in other forms of cancer as well, Hahn continues. "Our study provides a framework for integrated genomic methods of oncogene discovery."

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