MiRNA-155 and colorectal cancer, the role of real time PCR in laboratory diagnosis

We were very interested to read the article published by Liu et al1 regarding the involvement of microRNA-155 (miR155) on the invasion ability of colon-rectal cancer (CRC) cells. The authors have designed an in vitro approach with SW-480 cell lines that proves an active role of miR- 155 in β-catenin overexpression. This mechanism should be connected with the cancer cell invasion rate1. CRC is a modern-day health problem in developed countries and is the third most commonly diagnosed tumor and the fourth leading cause of cancer death in the world. Its early clinical diagnosis is based on colonoscopy after a positive fecal occult blood test2-5. The subsequent laboratory diagnosis considers histological-histochemical exams and molecular procedures in order to discover the mutations of CRC oncogenes such as BRAF6. Although this analytical approach has resulted as being extremely useful for a precise and sensitive diagnosis of CRC in loco, it has often proved to be incapable of forecasting the invasion attitude of an initial neoplastic lesion, with consequent uncertainty in the disease prognosis2. The linkage between miR-155, β-catenin, and cancer has been evaluated for different tumors. β-catenin is a subunit of a protein complex acting as a signal transducer (Wnt signaling) that has a role in different cell functions, for example, embryogenesis. Its overexpression is associated with many types of cancers, e.g., breast, lung, and CRC. One cause of this mechanism is an increase in the cellular cytoplasm of miR-155. This is a single-stranded non-coding RNA (ncRNA) which contains approximately 19-25 nt developed from hairpin precursor molecules containing 70-120 nt (Figure 1). As described by Liu et al1, upregulating the expression of miR-155 in CRC SW-40 cells promotes the distant cell invasion and consequently the tumor metastasis. This preliminary work could be interesting in the CRC diagnosis and understanding of cancer pathogenesis, in particular, we have focalized three main points: (a) it can provide ideas for new protocols in the CRC personalized treatment, for example by blocking the expression of miR-155 and the tumoral activity of Wnt/β-catenin system; (b) it suggest a clinically validate laboratory assay for a precise quantification of the miR-155 level in tissue for tumor detection factor, but also as a signal of prognosis outcome. Amongst currently available techniques for profiling miR- 155, described by Liu et al1, as well as other authors7 (Table I), the most frequently used is the quantitative Real-time PCR (qRT-PCR).