A new study has uncovered the link between hepatitis C (HCV) and cancer of the liver.1
Protein-Blocking Link Found
Scientists at the University of Texas Medical Branch at Galveston have identified a key biochemical connection between the virus and hepatocellular carcinoma.
The link is similar to that between the human papilloma virus (HPV) and cancer of the cervix, according to Stanley Lemon, MD, the study's lead investigator.
"What we've found is that one of the hepatitis C virus proteins targets a cell protein that is critical for suppressing the development of tumors, interfering with its ability to control [cancer] cell proliferation," explained Lemon, who is director of the Institute for Human Infections and Immunity and a professor of Microbiology & Immunology and Internal Medicine. "By knocking out this 'tumor suppressor' and promoting the proliferation of liver cells, this viral protein is setting up the liver for cancer."
Latching on to a Beneficial Protein
The tumor-blocking protein is known as the retinoblastoma protein. It normally lassos growing cancer cells, but when HCV is present, scientists have found that the protein is greatly reduced in liver cells. These cells contain a hepatitis C "replicon", a piece of HCV genetic material that is able to reproduce itself in liver cells used in lab experiments, and can also produce proteins made by the hepatitis C virus.
What Lemon and his colleagues found was a viral protein that latches on to the retinoblastoma protein, preventing it from halting cancer. "The replicon experiments enabled us to identify a protein known as NS5B that attaches to the retinoblastoma protein, a critical tumor suppressor, and accelerates its breakdown," Lemon explained.
"The way NS5B docks with the retinoblastoma protein is biochemically almost identical to the way a protein made by human papilloma virus does so to produce similar cancer-promoting results. That's interesting," he says, "because the two viruses are so different; HPV is a DNA virus, while hepatitis C is composed of RNA."
Paving the Way to Better Treatment?
Understanding exactly how the hepatitis C virus leads to the development of hepatocellular carcinoma is critically important, Lemon noted. Since there is no "silver bullet" treatment for hepatitis C on the horizon, researchers must use the knowledge they've gained in medical research to maximize the effectiveness of various cancer-fighting therapies currently under development. This will help doctors manage people with chronic illnesses like hepatitis C in more effective ways with the aim of helping them avoid cancer, he said.
According to the Centers for Disease Control and Prevention (CDC), about 3.9 million Americans have been infected with HCV, of whom approximately 2.7 million have chronic infection.2
It's also estimated that about 17,500 new cases of primary liver cancer were diagnosed in 2005, and that some 15,400 people died from the disease that year. While there are various forms of liver cancer, the most common in adults is hepatocellular carcinoma. This cancer has different growth patterns. Some begin as a single tumor that grows outward, while others grow in many parts of the liver and spread even further.3
Liver cancer is more common in developing countries in Africa and East Asia than in the United States. In many of these countries, it is the most common form of cancer.3
1. Munakata T, Nakamura M, Liang Y, Li K, Kemon SM. Down-regulation of the retinoblastoma tumor suppressor by the hepatitis C virus NS5B RNA-dependent RNA polymerase. Proc Natl Acad Sci USA 2005 ec 13;102(50);18159-64. Epub 2005 Dec 6.
2. Centers for Disease Control and Prevention (CDC). Viral Hepatitis C. Available at: http://www.cdc.gov/ncidod/diseases/hepatitis/c/fact.htm. Accessed December 30, 2005.
3. American Cancer Society. What is Liver Cancer? Available at: http://www.cancer.org/docroot/cri/content/
cri_2_2_1x_what_is_liver_cancer_25.asp. Accessed December 30, 2005.
John Martin is a long-time health journalist and an editor for CuraScript. His credits include overseeing health news coverage for the website of Fox Television's The Health Network, and articles for the New York Post and other consumer and trade publications.
