**8. Role of MicroRNA in colorectal cancer development**

MiRNAs have been shown to play an important role in colorectal cancer oncogenesis, progression, angiogenesis, invasion and metastasis (Lee, et al, 2007, Huang, et al, 2008 & Liu, et al, 2011). Esquela-Kerscher & Slack in their review have suggested that the dysregulation of miRNA genes that target mRNAs for tumour suppressor or oncogenes can influence tumourigensis (Esquela-Kerscher, et al, 2006). The miRNA expression profiling studies on colonic tumour and adjacent normal tissue have identified several differentially expressed miRNAs in cancerous tissue. Table 1 summarizes the relatively over-expressed and underexpressed miRNAs studied in CRC tissue from different studies. Studies focussing on the functional and mechanistic involvement of miRNAs in colon cancers have reported that selected groups of distinct miRNAs are commonly and concurrently upregulated or downregulated in colon cancer tissues and are often associated with distinct cytogenetic abnormalities (Xi, et al, 2006, Schepeler, et al, 2008 & Schetter, et al, 2008). Table 3 shows the summary of dysregulated miRNAs in colorectal tumour tissue compared to adjacent normal colonic mucosa. Over expressed or under expressed miRNAs identified by two or more studies are underlined and the miRNAs with conflicting expression levels in different studies are identified in Bold.


10ng 100 ng 250ng

Method PCR Hybridization Deep Sequencing

Time Required < 24 hours 24-48 hours >1 week

Throughput Medium-high High Ultra-high

**MicroRNA-Array** 

Low-medium for Pool Profiling

Relative and absolute

miRNAs

MiRNAs have been shown to play an important role in colorectal cancer oncogenesis, progression, angiogenesis, invasion and metastasis (Lee, et al, 2007, Huang, et al, 2008 & Liu, et al, 2011). Esquela-Kerscher & Slack in their review have suggested that the dysregulation of miRNA genes that target mRNAs for tumour suppressor or oncogenes can influence tumourigensis (Esquela-Kerscher, et al, 2006). The miRNA expression profiling studies on colonic tumour and adjacent normal tissue have identified several differentially expressed miRNAs in cancerous tissue. Table 1 summarizes the relatively over-expressed and underexpressed miRNAs studied in CRC tissue from different studies. Studies focussing on the functional and mechanistic involvement of miRNAs in colon cancers have reported that selected groups of distinct miRNAs are commonly and concurrently upregulated or downregulated in colon cancer tissues and are often associated with distinct cytogenetic abnormalities (Xi, et al, 2006, Schepeler, et al, 2008 & Schetter, et al, 2008). Table 3 shows the summary of dysregulated miRNAs in colorectal tumour tissue compared to adjacent normal colonic mucosa. Over expressed or under expressed miRNAs identified by two or more studies are underlined and the miRNAs with conflicting expression levels in different

quantification of

**MicroRNA-Sequencing** 

High

Relative quantification of known miRNAs. Identification of novel miRNA sequences.

**Upregulated miRNAs in CRC** 

**tissue** 

**Detection Systems MicroRNA QRT-PCR** 

Cost Low-medium for Pool

Utility Relative and absolute

studies are identified in Bold.

**Studies Downredulated miRNAs in CRC tissue** 

miR-200b

 miR-26a, miR-102, miR-143, miR-145,

Michael, et al, 2003 let-7, **miR-16**, miR-24,

Initial RNA Concentration

Table 2.

**Expression Profiling** 

Profiling. Even lower for custom designed individual assays.

quantification of

**8. Role of MicroRNA in colorectal cancer development** 

miRNAs


Table 3.

**Tissue Type** 

Whole

Plasma RNA

Table 4.

Plasma Pu, et al, 2010

2011

2010

Ng, et al, 2009

Huang, et al ,

adenoma could be more informative and accurate.

Cheng , et al,

MicroRNAs are Novel Biomarkers for Detection of Colorectal Cancer 9

**MiRNAs** 

**Diagnostic Accuracy** 

89.1

84.7\*

81.4\*

71

**Specificity %** 

**Sensitivity %** 

miR-221 86 41

miR-141 66.7 80.8

miR-17-3p 64 70 miR-92 89 70

62.2\*

64.9\*

miR-29 69

miR-92a 84

**Studies Participants Target** 

CRC (n=103)

Controls (n=37)

CRC I-IV (n=102)

Controls (n=48)

CRC (n=90)

Controls (n=40)

CRC (n=100)

Adenomas\* (n=37)

Controls (n=59)

are detecting cancer-related but not tissue specific miRNAs. Another explanation of the findings is that the detection of miRNAs released into the circulation originates in immune cells which occur as a result of a systemic immune response generated by the tumour causing abnormal proliferation of colonic cells (Dong, et al, 2011). This might also explain the finding of commonly dysregulated miRNAs in patients with CRC and Ulcerative Colitis (Pekow, et al, 2011). Furthermore, studies to date have focused on measuring the circulating levels of either single miRNAs or a subset of the known miRNAs. Due to the above reasons, a single miRNA based detection strategy would be rather ineffective whereas a CRC tissue specific expression signature generated from plasma or serum of patients with CRC and

The recent discovery of exosome mediated transport of cancer related miRNAs into the circulation, has shifted the focus of miRNA studies towards the isolation of tissue specific circulating exosomes and their encompassed miRNAs. Exosomes are membrane bound small vesicles (20 to 100 nm in diameter) of endocytic origin and are released by a variety of cells in both healthy and disease conditions (Théry, et al, 2002 & Keller, et al, 2006). Exosomes correspond to the internal vesicles of multivesicular bodies (MVBs) and are released in the extracellular environment upon fusion of MVBs with the plasma membrane, (Théry, et al, 2002 & Cocucci, et al, 2009). Since exosome formation includes two inward budding processes, exosomes maintain the same topological orientation as the cell, with membrane proteins on the outside and some cytosol on the inside. Exosomes contain

The topical orientation of exosomal membrane may help in identification of their source by using surface antigen directed antibodies e.g. anti-MHCII. One drawback of this isolation method is that unless all the exosomes contain the specific surface antigen used for the

cytoplasmic proteins, miRNAs and mRNA transcripts (Valadi, et al, 2007).
