Viruses: A Very Short Introduction (Very Short Introductions) by Crawford Dorothy H

Author:Crawford, Dorothy H. [Crawford, Dorothy H.]
Language: eng
Format: epub
Publisher: Oxford University Press
Published: 2011-07-27T16:00:00+00:00

Chapter 7

Tumour viruses

The history of tumour virology began in 1908 when two Danish scientists, Wilhelm Ellermann and Oluf Bang, transmitted chicken leukaemia from a leukaemic bird to a healthy bird by injection of a filtered extract of leukaemic cells. The importance of this experiment was not fully appreciated at the time as leukaemia was not generally recognized as a malignant disease, and it was only after US scientist Peyton Rous transmitted a solid tumour from tumour-bearing to healthy chickens in 1911 that the findings had an impact. Both experiments indicated that some kind of ‘filterable agent’ was involved in tumour development, yet they pre-dated the identification and characterization of viruses. Due to this lack of knowledge and the fact that tumours do not generally behave like an infectious disease, the scientific community was slow to grasp their importance. Indeed, Rous had to wait over 50 years before he was awarded a Nobel Prize for his work on what became known as the ‘Rous sarcoma virus’.

Over the intervening years, other pioneering tumour virologists began to uncover the complex molecular mechanisms involved in tumour development. Using a combination of tumour-susceptible strains of laboratory animals and cell culture techniques, they identified specific viral genes which could convert, or transform, normal cells into tumour-like cells in a culture dish and also induce them to form tumours in laboratory animals. These genes are called viral oncogenes, and unravelling the various ways in which they transform cells has been instrumental in uncovering the molecular mechanisms involved in cancer development in general. Most importantly, the discovery in the 1980s that viral oncogenes have counterparts in the normal cellular genome (called proto-oncogenes) led to the realization that some time in the distant past these tumour viruses must have picked up, or transduced, their oncogenes from the cells they infect.

Tumours develop when a single cell in an organism is somehow released from the usual constraints that regulate its growth, and it replicates unchecked. This rogue cell then produces a mass of similar cells, forming a tumour (or cancer) that invades the surrounding tissues and may spread from its original site.

Healthy cells are subject to many complex chemical checks and balances which ensure that they grow and divide, age and die, only when appropriate. Not surprisingly, therefore, the development of a cancer cell involves mutations that alter the function of the genes that regulate these vital cellular controls. Both an increase in the action of genes that drive cell proliferation (called cellular oncogenes and including the proto-oncogenes that some tumour viruses have picked up) and a decrease in function of genes that inhibit cell division or induce cell death (called tumour suppressor genes) will have the effect of releasing the cell from normal constraints in favour of uncontrolled proliferation.

One in three people develop cancer at some time during their lives, resulting in nearly 11 million new cases, and wellfarming revolutionou depending on the over 6 million deaths worldwide every year. For most, the cause is unknown, although there are some well-known associations with environmental factors.

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