The role of bacteria in cancer development

[mark!]

It is known that a high amount of bacterial DNA is often present near cancer cells. There are about 7000 pieces of bacterial DNA in healthy cells, but researchers found 691,000 inserted pieces of bacterial DNA in cancer cells. That’s almost 200 times as much, which implies that there is a correlation between some types of bacteria and the development of cancer. In addition, quite a few of them were in so called cancer genes, making them more active, which accelerated tumor growth.

Bacteria species that are known to be harmful, like Fusobacterium Nucleatum (who normally habitates the mouth), or Streptococcus Bovis (often present in intestinal tumors) are the usual suspects to be present near cancer cells. It is also known of some the unusual suspects (bacteria that normally are not harmful in their behavior) are behaving rather moderate and quiet in normal circumstances, but might derail and all of a sudden begin helping to overthrow the immune system, if they’re being encouraged to do so by these harmful bacteria.

I’d like to know more about how and which bacteria are involved with the development of cancer. Does anybody know where I could find such information?

 

[SemM]

http://www.ciencias.unal.edu.co/unciencias/data-file/user_29/file/How%20bacteria%20could%20cause%20cancer%20one%20step%20at%20a%20time.pdf

 

[Ygggdrasil]

It is known that a high amount of bacterial DNA is often present near cancer cells. There are about 7000 pieces of bacterial DNA in healthy cells, but researchers found 691,000 inserted pieces of bacterial DNA in cancer cells. That’s almost 200 times as much, which implies that there is a correlation between some types of bacteria and the development of cancer. In addition, quite a few of them were in so called cancer genes, making them more active, which accelerated tumor growth.

Do you have the source for these numbers?

 

[SemM]

Do you have the source for these numbers?

In general it is not surprising that infections can cause cancer, but it may be difficult to prove. Take for instance the bacteriophage, should it inject is DNA in the bacterias transcription gene for polymerase II, it will have immediately fatal consequences. Should a virus , such as influenza, inject its DNA in a gonad cell in a human, at the p53 suppressor gene, then that gonad cell may replicate under poor if no control at all.

But this can't really be proved, because the site of insertion of the virus DNA in a cell cannot readily be identified more than once, i .e. the same insertion site doesn't happen twice. So any experiment wouldn't be reproducible.

 

[mark!]

http://www.ciencias.unal.edu.co/unciencias/data-file/user_29/file/How%20bacteria%20could%20cause%20cancer%20one%20step%20at%20a%20time.pdf

Thanks a lot! This is the kind of paper I was looking for

Do you have the source for these numbers?

Yes I do. On page 16 of this paper, it states: "Taken together, putative integrations of bacterial DNA in human tissues, including tumors, can be detected with nextgeneration sequencing. Such integrations were detected 210 x more frequently in tumor samples than normal samples"

 

[SemM]

Thanks a lot! This is the kind of paper I was looking for

You're welcome.

Yes I do. On page 16 of this paper, it states: "Taken together, putative integrations of bacterial DNA in human tissues, including tumors, can be detected with nextgeneration sequencing. Such integrations were detected 210 x more frequently in tumor samples than normal samples"

Interesting! Worthwhile a follow-up study with in vivo cultures of various types of cancer!

 

[Ygggdrasil]

In general it is not surprising that infections can cause cancer, but it may be difficult to prove. Take for instance the bacteriophage, should it inject is DNA in the bacterias transcription gene for polymerase II, it will have immediately fatal consequences. Should a virus , such as influenza, inject its DNA in a gonad cell in a human, at the p53 suppressor gene, then that gonad cell may replicate under poor if no control at all.

But this can't really be proved, because the site of insertion of the virus DNA in a cell cannot readily be identified more than once, i .e. the same insertion site doesn't happen twice. So any experiment wouldn't be reproducible.

It is well established that viral infections can cause cancer. For example, the 2008 Nobel Prize in Physiology or Medicine was awarded, in part, for the discovery that almost all cases of cervical cancer are caused by infection with human papilloma virus. However, this thread is about bacteria and bacteria are not viruses.

Furthermore, not all viruses integrate their genetic material into the host cell's DNA. In the case of HPV, HPV specifically causes cancer because the virus encodes proteins (E6 and E7) that inhibit important tumor suppressor genes (p53 and pRb) in the host cell. You are correct that some viruses can also contribute to cancer by disrupting tumor suppressor genes during proviral integration (e.g. Human T-lymphotropic virus and other similar retroviruses), but influenza is not such a virus (also influenza has an RNA genome, not a DNA genome).

 

[Ygggdrasil]

Yes I do. On page 16 of this paper, it states: "Taken together, putative integrations of bacterial DNA in human tissues, including tumors, can be detected with nextgeneration sequencing. Such integrations were detected 210 x more frequently in tumor samples than normal samples"

I am quite skeptical of that paper. Various artifacts can be created in the generation sequencing libraries as well as their computational analysis. Given the rarity of events analyzed and reports of contamination in NGS data, I would not believe the author's claim without verification by an independent method. Furthermore, even if the authors were to show that the transfer of bacterial DNA into the human genome were real, they still lack data linking these genetic transfer events to cancer (e.g. it may just be that cancer cells are more susceptible to such transfer and not that the transfer events contribute to cancer).

That said, there is other work linking bacterial infections to cancer, though likely through other mechanisms than that proposed by the PLoS Comp Biol paper. The Trends in Microbiology paper linked by @SemM is a good source as H. pylori is probably the most well studied example of a link between bacteria and cancer. Recent work published in Science also seems to suggest that bacteria could play an important role in colon cancer. So, this is definitely still very much an active area of research, where much of the information will still be speculative and preliminary.