microRNAs (miRNAs) are noncoding small RNAs that regulate gene expression at the translational level by mainly interacting with 39 UTRs of their target mRNAs. Archived formalin-fixed paraffin-embedded (FFPE) specimens represent excellent resources for biomarker discovery. Currently there is a lack of systematic analysis on the stability of miRNAs and optimized conditions for expression analysis using FFPE samples. In this study, the expression of miRNAs from FFPE samples was analyzed using highthroughput locked nucleic acid-based miRNA arrays. The effect of formalin fixation on the stability of miRNAs was also investigated using miRNA real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis. The stability of miRNAs of archived colorectal cancer FFPE specimens was characterized with samples dating back up to 10 yr. Our results showed that the expression profiles of miRNAs were in good correlation between 1 mg of fresh frozen and 1-5 mg of FFPE samples (correlation coefficient R 2 = 0.86-0.89). Different formalin fixation times did not change the stability of miRNAs based on real-time qRT-PCR analysis. There are no significant differences of representative miRNA expression among 40 colorectal cancer FFPE specimens. This study provides a foundation for miRNA investigation using FFPE samples in cancer and other types of diseases.

In this study, our high throughput microRNA (miRNA) expression analysis revealed that the expression of miR-140 was associated with chemosensitivity in osteosarcoma tumor xenografts. Tumor cells ectopically transfected with miR-140 were more resistant to methotrexate (MTX) and 5-fluorouracil (5-FU). Overexpression of miR-140 inhibited cell proliferation in both osteosarcoma U-2 OS (wt-p53) and colon cancer HCT 116 (wt-p53) cell lines, but less so in osteosarcoma MG63 (mut-p53) and colon cancer HCT 116 (null-p53) cell lines. miR-140 induced p53 and p21 expression accompanied with G1 and G2 phase arrest only in cell lines containing wild type of p53. Histone deacetylase 4 (HDAC4) was confirmed to be one of the important targets of miR-140. The expression of endogenous miR-140 was significantly elevated in CD133+hiCD44+hi colon cancer stem-like cells which exhibit slow proliferating rate and chemoresistance. Blocking endogenous miR-140 by locked nucleic acid (LNA) modified anti-miR partially sensitized resistant colon cancer stem-like cells to 5-FU treatment. Taken together, our findings indicate that miR-140 is involved in the chemoresistance by reduced cell proliferation via G1 and G2 phase arrest mediated in part, through the suppression of HDAC4. miR-140 might be a candidate target to develop novel therapeutic strategy to overcome drug resistance.

Purpose: The purpose of this study is to investigate the molecular mechanism of miR-192 in colon cancer. Experimental Design: Human colon cancer cell lines with different p53 status were used as our model system to study the effect of miR-192 on cell proliferation, cell cycle control, and mechanism of regulation. Results: Our results show that one of the key miR-192 target genes is dihydrofolate reductase (DHFR). miR-192 affects cellular proliferation through the p53-miRNA circuit. Western immunoblot analyses indicated that the expression of DHFR was significantly decreased by miR-192. Further investigation revealed that such suppression was due to translational arrest rather than mRNA degradation. More profound inhibition of cellular proliferation was observed by ectopic expression of miR-192 in colon cancer cell lines containing wild-type p53 than cells containing mutant p53. Thus, the effect of miR-192 on cellular proliferation is mainly p53 dependent. Overexpression of miR-192 triggered both G 1 and G 2 arrest in HCT-116 (wt-p53) cells but not in HCT-116 (null-p53) cells. The cell cycle checkpoint control genes p53 and p21were highly overexpressed in cells that overexpressed miR-192. Endogenous miR-192 expression was increased in HCT-116 (wt-p53) and RKO (wt-p53) cells treated with methotrexate, which caused an induction of p53 expression. Chromatin immunoprecipitation-quantitative reverse transcription-PCR analysis revealed that the p53 protein interacted with the miR-192 promoter sequence. Conclusion: These results indicate that miR-192 may be another miRNA candidate that is involved in the p53 tumor suppressor network with significant effect on cell cycle control and cell proliferation.