GM issues | Viral DNA dangers
Interesting new diseases to catch?
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
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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.
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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.
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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 (www.i-sis.uk):
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Cauliflower Mosaic Viral Promoter – A Recipe for Disaster (1999)
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Hazards of Transgenic Plants Containing the Cauliflower Mosaic Viral Promoter (2000)
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CaMV 35S promoter fragmentation hotspot confirmed, and it is active in animals (2000)
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New Evidence Links CaMV 35S Promoter to HIV Transcription (2009).