Australasian Science 11-5

32 | JUNE 2016

MM

ore than 25 years ago at the University of Zurich, Roger Parish and his colleagues

identified a protein on the surface of mouse fibroblast cells that dramatically

changed the normal behaviour of the cells. Generally, when fibroblast cells collide

they change their direction of movement and retract from one another. Loss of

this contact inhibition helps to drive invasion in cancer.

The fibroblasts displayed normal contact inhibition when the protein was blocked with a

monoclonal antibody. However, the cells completely lost contact inhibition when the protein was

not blocked.

This protein, named p37, is located on the surface of the bacterium Mycoplasma hyorhinis,

where it forms a complex with two other proteins located in the outer membrane of the

bacterium. The three proteins constitute a high-affinity transport system that the mycoplasma

cells employ to take up molecules such as nutrients.

Mycoplasmas are minute bacteria that lack a cell wall. Several species cause inflammatory

diseases in humans. M. pneumonia, for example, causes atypical pneumonia while M. genitalium

gives rise to pelvic inflammatory diseases. M. hyorhinisis often present in the respiratory tract of

young pigs and causes severe arthritis when they experience stress or a concomitant infection.

Evidence began to accumulate that p37, and hence M. hyorhinis, was associated with cancer. In

2001, for example, a research group from Peking University Cancer Hospital and Institute

observed mycoplasma infections in human cancer tissues. They reported that 56% of gastric

carcinomas, 55.1% of colon carcinomas and 45.5% of other carcinomas (oesophagus, lung, breast

and glioma) were infected with M. hyorhinis,and the p37 protein was identified. In 2014 the

Peking University team reported that M. hyorhinisinfection correlated with metastasis, and

predicted poor survival of gastric cancer patients.

But what is the evidence that infectious bacteria like M. hyorhiniscan cause cancer?

AMBER GOMERSALL & ROGER PARISH

A bacterial protein can trigger inflammation and facilitate the

progression of cancer.

Microscopy imaging of metastatic cancer cells.Credit: drimafilm/adobe

The Bacteria that

Promote Cancer