35S CaMV promoter is active in some human intestinal cells
13 November 2005

Dear Friends and colleagues,

RE: 35S CaMV promoter is active in some human intestinal cells

The 35S promoter of the cauliflower mosaic virus (CaMV) is a general, strong plant promoter. It has been used to secure expression of the transgene in most genetically engineered (GE) crop plants commercialized so far.

It has been claimed that the 35S promoter is plant-specific and would not be active in mammalian cells, and hence would not pose risks linked to the consumption of GE food and feed in the event that plant DNA fragments are taken up from the mammalian gastrointestinal tract. However, this claim has not been supported by experimental data.

On the contrary, there have already been published reports indicating that this assumption might be incorrect, for example, previous research has indicated the potential of the 35S promoter to be active in mammalian systems. More recently, direct evidence that the 35S promoter is active in mammalian cell cultures has been presented.

Of particular importance are the cells lining the intestinal wall, given that the gastrointestinal tract will be the first site of exposure to GE food and feed.

In a recently published paper, scientists have demonstrated that the 35S CaMV promoter was able to drive the expression of two reporter genes (gfp and luc) in the human cell line Caco-2, which share a number of characteristics with human enterocytes (cells lining the intestinal wall).

While the protein expression levels were modest compared to results obtained with strong mammalian promoters, the significant observation remains that the 35S CaMV promoter, generally assumed to be plant specific, initiated significant protein expression levels in host cells that share important characteristics with those lining parts of the human gastrointestinal tract.

These results, taken together with other published papers, leads the scientists to conclude that the 35S CaMV promoter is capable of initiating gene expression in some mammalian cell lines under a range of different conditions and circumstances. Computer based searches further indicate that transcriptional activation by the 35S promoter may be stronger in other human and animal cell types than those investigated so far.

This research clearly warrants further serious investigation, including by in vivo means.

Whether there are GE food safety implications would be linked to the process of foreign DNA uptake from the human gastrointestinal tract. The uptake of food-derived DNA fragments from the intestines into the blood stream and some organs has already been demonstrated in various animal species and recently also in humans.

Given the potential for the 35S promoter to initiate gene expression in some mammalian cells, if the intact 35S promoter is taken up, the biological consequences are potentially great (for example, inappropriate expression of genes may occur).

The abstract of the paper is attached.

With best wishes,
Lim Li Ching
Third World Network
121-S Jalan Utama
10450 Penang
Email: This email address is being protected from spambots. You need JavaScript enabled to view it.
Website: and

REF: Doc.TWN/Biosafety/2005/C

The 35S CaMV plant virus promoter is active in human enterocyte-like cells
European Food Reseach and Technology (2005)
DOI 10.1007/s00217-005-0154-3
Marit R. Myhre (2, 4), Kristin A. Fenton (4), Julia Eggert (3), Kaare M. Nielsen (3) and Terje Traavik (1, 2)

(1) GENOK-Norwegian Institute of Gene Ecology, Science Park, N-9294 Tromsø, Norway
(2) Department of Microbiology and Virology, Institute of Medical Biology, University of Tromsø, N-9037 Tromso, Norway
(3) Department of Pharmacy, University of Tromsø, N-9037 Tromsø, Norway
(4) Both authors have contributed equally, University of Tromso, N-9037 Tromso, Norway

Received: 22 May 2005 Accepted: 5 September 2005 Published online: 20 October 2005


The 35S cauliflower mosaic virus (CaMV) promoter is commonly used to drive transgene expression in the genetically engineered (GE) crop plants that have been commercialized so far. Whether, and how far, the 35S promoter might be active in mammalian cells has been scientifically unsettled and controversial. Very recently it was established that the 35S promoter is transcriptionally active following transient reporter gene transfections in continuous cell lines of human [J Biotechnol 103:197 202, 2003] and hamster ovary [Environ Biosafety Res 3:41 47, 2004] fibroblasts. The initial exposure of a human organism to DNA from GE food takes place in the gastrointestinal tract (GIT). Hence, we have now investigated the promoter capacity of 35S in human enterocyte-like cells. We constructed expression vectors with 35S promoter inserted in front of two reporter genes encoding firefly luciferase and green fluorescent protein (GFP), respectively, and performed transient transfection experiments in the human enterocyte-like cell line Caco-2. It was demonstrated that the 35S CaMV promoter was able to drive the expression of both reporter genes to significant levels, although the protein expression levels might seem modest compared to those obtained with the strong promoters derived from human cytomegalo virus (hCMV) and simian virus 40 (SV40). Furthermore, computer-based searches of the 35S CaMV DNA sequence for putative mammalian transcription factor binding motifs gave a high number of hits. Some of the identified motifs indicate that transcriptional activation by the 35S CaMV promoter may be stronger in other human and animal cell types than in those investigated so far.