Bacteria—agents of cancer

According to a recent estimate from the American Cancer Society, 20% of cancer cases worldwide are caused by pathogens. At the same time, the influence of bacterial infection on tumorigenesis remains poorly understood, although recent studies have provided intriguing evidence that p37, a protein expressed by the bacterium Mycoplasma hyorhinis can boost the invasiveness of skin and prostate cancer cells.

Namiki et al. have now followed up on these findings by investigating the effects of infecting the benign human prostate-derived cell line BPH-1 with two species of Mycoplasma, M. hyorhinis and M. genitalium. In their recent article from PLoS ONE, they show that by 19 weeks after infection, both bacterial species induced increased capacity for migration, invasion and colony formation—all signs of malignant transformation. Infection also leads to increased karyotypic instability, with infected cells exhibiting markedly increased polysomy. Uninfected BPH-1 cells failed to form tumors in nude mice; however, cells that were subject to prolonged infection with M. hyorhinis or M. genitalium, respectively, formed tumors in 63 and 43% of mice after inoculation.

BPH-1 is an immortalized cell line, and infection of a nongenetically manipulated fibroblast cell line (CCL-123) with mycoplasma failed to yield malignant cells, suggesting that the presence of viral genes or proteins may be necessary for bacterially induced transformation. However, as infection with nonpathogenic viruses is a widespread phenomenon among humans worldwide, the authors suggest that the conditions that enable such transformation may be fairly commonplace.

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Original research paper
Namiki K et al. Persistent exposure to mycoplasma induces malignant transformation of human prostate cells. PLoS ONE 2009; 4: e6872.