24 October 2007

Cancer Triggered By Viral Selection?

by Kate Melville

New research suggests that viruses may contribute to cancer by causing excessive death to normal cells while promoting the growth of surviving cells with cancerous traits. Writing in the journal PLoS ONE, the scientists behind the hypothesis say that viruses may act as forces of natural selection by wiping out normal cells that support the replication of viruses and leaving behind those cells that have acquired defects in their circuitry. When this process is repeated over and over, cancer can develop.

Viruses have been linked to many human cancers and scientists have proposed a number of mechanisms to explain the link. One commonly held belief is that when a virus infects a cell, its genetic material alters the cell, making it grow uncontrollably, eventually leading to cancer. But the new study's leader, Dr. Preet M. Chaudhary, proposes that viruses also can lead to cancer in a less direct manner.

"We believe a separate mechanism may be at play in which a cellular insult, such as infection with a virus, selects a few pre-existing mutated clones of cells, promotes their further growth and multiplication, eventually leading to the emergence of fully cancerous cells. Consequently, similar to the role played by natural selection during evolution, excessive cell death, rather than its absence, may be a defining force that drives the initial emergence of cancer," explained Dr. Chaudhary.

The new hypothesis is based on a study of cells infected with the Kaposi's sarcoma associated herpesvirus (KSHV, also known as human herpesvirus 8). The researchers examined a gene called K13 that activates a pathway previously implicated in cancer development. Cells with low K13 expression allowed KSHV to replicate, and these cells subsequently died off. Cells with higher expression of K13 emerged after KSHV replication and showed defective expression of two key proteins that are known to promote cancer. "If validated by further studies, [the new findings have] implications not only for an improved understanding of the processes involved in cancer, but also for the development of effective strategies for its prevention and treatment," said Dr. Chaudhary.

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Prof Questions Darwinian Dogma

Source: University of Pittsburgh Schools of the Health Sciences