HCV Link to Cancer Found

by John C. Martin




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