Bacterium Actively Drives CRC Tumor Growth

Colorectal cancer (CRC) is a leading cause of cancer-related death. The recognition that microbial agents can contribute to the development of CRC raises hope for improving CRC diagnosis and treatment by incorporating both microbial and patient characteristics into clinical strategies.

It has been known for some time that people infected with the Streptococcus gallolyticus subspecies gallolyticus (Sgg) are more likely to have colorectal cancer (CRC), and is the second most common cause of cancer in women. However, it was unknown whether Sgg actively promotes CRC or whether it simply grows comfortably in the environment provided by CRC tumor cells.

Scientists at Texas A&M Health Science Center (Houston, TX, USA) and colleagues performed several studies using cultured human colorectal cells, mice with CRC, and tissue from human tumors. They used various techniques including using cultured bacterial cell lines, human colon cancer cell lines, cell proliferation assays, adherence and internalization assays, Western blot assays. They also performed quantitative reverse transcription polymerase chain reaction (RT-qPCR) to compare relative expression of cyclin D1 and cytokines in a Viia 7 Real Time PCR System. Flow cytometry analysis of samples was done using a LSRII flow cytometer.

The investigators demonstrated that Sgg promotes human colon cancer cell proliferation in a manner that depends on cell context, bacterial growth phase and direct contact between bacteria and colon cancer cells. In addition, they observed increased level of β-catenin, c-Myc and proliferating cell nuclear antigen (PCNA) in colon cancer cells following incubation with Sgg. The team tested tumor samples from people with colon cancer, they found 74% had Sgg bacteria in them, and 26% had very high levels of it. They also showed that Sgg is present in the majority of CRC patients and is preferentially associated with tumor compared to normal tissues obtained from CRC patients.

The authors concluded that overall, their findings strongly suggest that Sgg plays an active role in CRC development in humans. In the future, the precise mechanisms of its tumor-promoting activity could potentially be exploited to develop new strategies to diagnose, prevent, and treat CRC. The study was published on July 13, 2017, in the journal Public Library of Science Pathogens.

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