BACKGROUND: MicroRNAs (miRNAs) are involved in carcinogenesis and tumor 
progression by regulating post-transcriptional gene expression. However, the 
miRNA-mRNA regulatory network is far from being fully understood. The objective 
of this study is to identify the colorectal cancer (CRC) specific miRNAs and 
their target mRNAs using a multi-step approach.
RESULTS: A multi-step approach combining microarray miRNA and mRNA expression 
profile and bioinformatics analysis was adopted to identify the CRC specific 
miRNA-mRNA regulatory network. First, 32 differentially expressed miRNAs and 
2916 mRNAs from CRC samples and their corresponding normal epithelial tissues 
were identified by miRNA and mRNA microarray, respectively. Secondly, 22 
dysregulated miRNAs and their 58 target mRNAs (72 miRNA-mRNA pairs) were 
identified by a combination of Pearson's correlation analysis and prediction by 
databases TargetScan and miRanda. Bioinformatics analysis revealed that these 
miRNA-mRNAs pairs were involved in Wnt signaling pathway. Additionally, 6 
up-regulated miRNAs (mir-21, mir-223, mir-224, mir-29a, mir-29b, and mir-27a) 
and 4 down-regulated predicted target mRNAs (SFRP1, SFRP2, RNF138, and KLF4) 
were selected to validate the expression level and their anti-correlationship in 
an extended cohort of CRC patients by qRT-PCR. Except for mir-27a, the 
differential expression and their anti-correlationship were proven. Finally, a 
transfection assay was performed to validate a regulatory relationship between 
mir-29a and KLF4 at both RNA and protein levels.
CONCLUSIONS: Seventy-two miRNA-mRNA pairs combined by 22 dysregulated miRNAs and 
their 58 target mRNAs identified by the multi-step approach appear to be 
involved in CRC tumorigenesis. The results in our study were worthwhile to 
further investigation via a functional study to fully understand the underlying 
regulatory mechanisms of miRNA in CRC.