MicroRNA-133b is regulated by TAp63 while no gene mutation is present in colorectal cancer

Downregulation of miR-133b has been reported in multiple types of malignancies including colorectal cancer (CRC). We previously confirmed that TAp63 actively translates microRNA-133b (miR-133b) transcripts. While the presence of miRNA mutations have frequently been described in CRC, most CRCs do not show any variation in the miR-133b coding sequence. Therefore, it is important to elucidate the relationship between TAp63 and miR-133b, and identify other mediators of miR-133b downregulation in CRC. The expression of TAp63 was detected by RT-qPCR, western blotting, immunohistochemistry (IHC) and densitometric analysis using Image-Pro Plus 6.0 software in 38 CRC and corresponding non-cancerous tissues (NCTs). The expression of mature miR-133b was determined by RT-qPCR, in situ hybridization (ISH) and densitometric analysis using Image-Pro Plus 6.0 software. The DNA from 38 CRC tissues and NCTs were screened for miR-133b mutations through sequence analysis. Compared with the NCTs, TAp63 mRNA expression was significantly lower in 21 (55.27%) tumor tissues. Compared with the NCTs, the miR-133b expression level was significantly lower in 31 (81.58%) tumor tissues. The expression of miR-133b was found to be positively correlated with TAp63. Loss of TAp63 and miR-133b was associated with an increased likelihood of metastatic events. The area under the ROC curve (AUC) of TAp63 for CRC was 0.623 [95% confidence interval (CI), 0.497-0.748; P=0.046], with 73.7% sensitivity and 50% specificity, respectively. The AUC of miR-133b for CRC was 0.857 (95% CI, 0.774-0.940; P<0.0001), with 78.9% sensitivity and 81.6% specificity, respectively. The combined AUC of TAp63 and miR-133b for CRC was 0.881 (95% CI, 0.805-0.956; P<0.0001), with 89.5% sensitivity and 71.1% specificity, respectively. Point mutations within the seed region of miR-133b were found in 1 patient, but the point mutation did not impact the secondary structure of the pre-miR-133b. Therefore, downregulation of TAp63 may be one reason for the dysregulation of miR-133b in CRC. The expression analysis of TAp63 and miR-133b revealed that they may be used as valuable prognostic biomarkers for CRC.