Almost every GM crop ever created has included of a useful little piece of DNA copied from the 'Cauliflower Mosaic Virus' (CaMV). This chunk of DNA is referred to as 'CaMV 35S', and as its name suggests, it is part of the DNA found in a virus which commonly infects cauliflower and related vegetables. In infected plants, its normal function is to switch on the genes needed for the virus to replicate itself. In GM plants its function is to switch on the engineered DNA attached to it which otherwise would likely remain dormant: effectively it overpowers the host cell's own self-regulatory mechanisms to permanently turn on the inserted genes which then generate huge amounts of the transgenic proteins. The value of the CaMV 35S 'promoter' to genetic engineers lies in its promiscuity: it acts on all types of DNA in the genome of all types of plants.
Any suggestion that problems could arise from putting millions of copies of an aggressive viral promoter into every mouthful of our food have been reasoned out of existence by the biotech industry and regulators. Their argument goes something like: humanity has been eating such DNA in its natural form forever, besides which it won't survive processing, cooking and digestion, and, even if it did survive, it is plant-specific and so can't turn on the genes in mammals including humans, or gut bacteria, and, even if it did survive and get into such cells, it will only activate the gene to which it is attached ...
The Institute for Science in Society and other scientists have been warning of the inherent risk in using CaMV 35S in GM food for a decade (see references below). The scientific questions which GM proponents have reasoned they don't need to ask include can intact, functional CaMV 35S end up inside our cells and our intestinal flora, and if it gets there can it cause harm?
As industry and regulators look determinedly in the opposite direction, answers to these questions are gradually seeping out of the laboratory, and they are not reassuring.
Large chunks of DNA can and do survive digestion and enter animal cells (including human) and can end up in many vital organs; they can also enter microbial cells in the digestive tract. The CaMV 35S promoter can drive genes in any cell it ends up in, not only in plants but also microbes and animals. Engineered genes attached to a universal promoter can be taken up by all manner of living cells and can be functional.
The possibility of CaMV 35S promoters incorporated into the human genome raises all sorts of concerns:
- CaMV 35S is known to create a 'hotspot' of instability, meaning it can promote breakage and rearrangement of the DNA around it
- CaMV 35S has been found to activate not only the engineered gene to which it has been attached, but host genes elsewhere in the genome, even on other chromosomes; it has also been found to be able to switch on the host's own organ- and tissue-specific promoters, meaning it could drive gene expression in the wrong cells or at the wrong time.
- CaMV 35S promotes the biochemical mechanism in cells which viruses hijack to replicate themselves; parts of this mechanism are the same or similar in plants and humans.
- The cauliflower mosaic virus is related to certain serious human pathogenic viruses such as the 'human immune deficiency virus' (HIV) implicated in AIDS, and hepatitis B virus implicated in liver failure.
Such genomic disruptions could set the scene for a host of diseases, including cancers caused by the DNA damage, floods of toxic or allergenic proteins caused by inappropriate gene expression, and dormant viruses (especially related ones) being reactivated by the switching on of replication mechanisms. At least three experiments have now found signs of cell proliferation in animals fed GM chow; these have lead to speculation that the CaMV 35S promoter might well be stimulating the production of the animal's own growth factors which could lead to diseases such as cancer.
Other suggestions which have not yet been explored involve the unnatural genetic connections being forged by genetic engineers: a powerful piece of pathogenic viral DNA is being linked to engineered DNA copied from plants, bacteria, other viruses and animals. The copied DNA could act as a Trojan horse to take the CaMV 35S promoter into all manner of living cells. There are real concerns that the CaMV 35S promoter taken up by microbes in the gut could alter them permanently so as to disrupt the digestion with very serious consequences. Similarly, the CaMV 35S promoter taken up by microbes in the soil could alter them permanently so as to disrupt soil fertility with catastrophic consequences. The ultimate effect on an environment flooded with DNA constructs designed to 'mix-and-match' with all forms of organism living there and which include an 'on-switch' ensuring the genes can't lie inactive and the recipient can't control its own genes, may be devastating.
COMMENT If you want to catch some really interesting new disease in future, you may not need to look any further than your dinner plate.
SOURCES AND FURTHER READING
Terje Traavik, New research on survival of CaMV promoter in rat tissues, February 2004
Michael Antoniou, Updated comments on The Newcastle Feeding Trial, 23.09.03
Available from The Institute of Science in Society (http://www.i-sis.uk/):
- Cauliflower Mosaic Viral Promoter – A Recipe for Disaster (1999)
- Hazards of Transgenic Plants Containing the Cauliflower Mosaic Viral Promoter (2000)
- CaMV 35S promoter fragmentation hotspot confirmed, and it is active in animals (2000)
- New Evidence Links CaMV 35S Promoter to HIV Transcription (2009).