Health-Medical-Fitness-Diet-zk: Critical

duminică, 5 august 2012

Critical Tumor Suppressor Identified For Cancer

Scientists from the Florida campus of The Scripps Research Institute have identified a protein that impairs the development and maintenance of lymphoma (cancer of the lymph nodes), but is repressed during the initial stages of the disease, allowing for rapid tumor growth.

While the study, published in the journal Cell, largely focuses on the role of this new tumor suppressor in lymphoma induced by Myc oncoproteins (the cancer-promoting products of Myc oncogenes), the authors show this circuit is apparently operational in all human tumors with MYC involvement, which is more than half of all human tumor types.

"This opens a new therapeutic avenue to exploit for cancers with Myc involvement - including relapsed metastatic tumors and refractory tumors, those that have not responded to treatment," said John Cleveland, a Scripps Research professor and chair of the Department of Cancer Biology, who led the study.

The Myc family of oncoproteins (c-Myc, N-Myc, and L-Myc) regulate critical pathways that contribute to tumors; c-Myc expression, which is activated in human Burkitt lymphoma, is sufficient to induce the growth of several tumor types in animal models.

In the new study, the scientists focused on precancerous and malignant Myc-expressing B cells, part of the immune system affected in human lymphoma. Using transgenic animal models, Cleveland and his team, led by the efforts of senior postdoctoral fellow Robert Rounbehler, showed that Myc-directed repression of a protein called tristetraprolin (TTP/ZFP36) was important for both the development and maintenance of cancer. The suppression of TTP is a hallmark of human cancers with MYC involvement, Cleveland noted.

The scientists' results showed that overriding this pathway by forced expression of TTP more than doubled the lifespan of Myc transgenic mice. Strikingly, Rounbehler discovered that re-introduction of TTP into Myc-driven lymphoma totally disabled these tumors, indicating an important therapeutic target.

The authors showed that Myc regulates hundreds of genes that contain adenylate-uridylate-rich elements (AU-rich elements), which play an important role in RNA stability and are found in many messenger RNAs (mRNAs) that code for oncogenes, nuclear transcription factors, and cytokines. AU-rich elements direct the mRNA for degradation; they are thought to be vital for controlling expression during cell growth.

"Myc regulates the expression of select AU-binding proteins to control the destruction of certain mRNAs," Cleveland said. "Also, our study strongly suggests that other AU-binding proteins may also, in fact, function as tumor suppressors in other cancers."

Article adapted by Medical News Today from original press release. Click 'references' tab above for source.
Visit our lymphoma / leukemia / myeloma section for the latest news on this subject. The first author of the study, "Tristetraprolin is a Tumor Suppressor That Impairs Myc-Induced Lymphoma and Abolishes the Malignant State," is Robert J. Rounbehler of Scripps Research. Other authors include Mohammad Fallahi, Chunying Yang, Meredith A. Steeves, Weimin Li, Joanne R. Doherty, and Franz X. Schaub of Scripps Research; Sandhya Sanduja and Dan A. Dixon of the University of South Carolina; and Perry J. Blackshear of the National Institute of Environmental Health Sciences.
The study was supported by the National Institutes of Health (grant numbers DK44158, CA167093, F32-CA115075, and CA134609), ThinkPink Kids Foundation, the State of Florida, the National City Charitable Contributions Committee, the Glenn W. Bailey Postdoctoral Fellowship, and the PGA National Women’s Cancer Awareness Days.
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Critical Molecular Switch Discovered That Regulates Autophagy

The body has a built-in system known as autophagy, or 'self-eating,' that controls how cells live or die. Deregulation of autophagy is linked to the development of human diseases, including neural degeneration and cancer.

In a study published online this week in the Proceedings of the National Academy of Sciences, scientists at the Ludwig Institute for Cancer Research in Oxford discovered a critical molecular switch that regulates autophagy. They also studied the links between autophagy and a cellular process called senescence that stops cell growth permanently.

The researchers identified ASPP2, a tumor suppressor, as a molecular switch that can dictate the ability of a common cancer gene, known as the RAS oncogene, to either stop or promote senescence.

As Yihua Wang and researchers in Xin Lu's group at the Ludwig Institute investigated the life cycle of fibroblast cells - the most common connective tissue cells in animals - they found that reduced levels of the ASPP2 protein increase RAS oncogene-induced autophagic activity. This in turn prevented cells from entering senescence. Without ASPP2, the cells continued to proliferate unchecked, thereby promoting tumor growth.

ASPP2 is known to play a role in suppressing tumor development. Mice that have a deficiency or malfunction in this protein have a predisposition to developing tumors. And low ASPP2 levels in patients are linked to poor prognoses in cancers, such as large B-cell lymphomas. Reduced ASPP2 expression has also been observed in highly metastatic breast tumors. But until now, researchers did not understand why.

"We found that in the presence of the common cancer-causing RAS oncogene, ASPP2 interacted with a protein complex that is responsible for deciding cell fate via autophagy," said Yihua Wang, PhD, Ludwig researcher in Oxford.

"What this means is that the cell's emergency stop button is disabled when ASPP2 expression is reduced or lost, allowing it to proliferate unchecked as with cancer," added Wang.

"The balance between the RAS oncogene and ASPP2 activity is crucial to determining whether or not tumor growth is promoted. Our next step will be to identify ways to alter ASPP2 activity at that critical switch point. This could be an effective way to treat cancers with reduced ASPP2 expression and mutated RAS, such as breast and colon cancers," concluded Wang.

"Some of the recently developed anti-cancer drugs are potent inducers of autophagy. The new findings may also offer an explanation as to why patient response to these drugs can vary dramatically. There are factors at play within the body that can dictate authophagic activity and impact clinical outcomes," said Xin Lu, PhD, director of Ludwig's Oxford Branch. "While further study is needed, these findings may in the longer term help doctors to identify patients who are more likely to respond well to autophagic inhibition," added Lu.

Article adapted by Medical News Today from original press release. Click 'references' tab above for source.
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