Tumor-suppressor Pdcd4 inhibits transformation and invasion and is downregulated in cancers. So far, it has not been studied as to whether miRNAs, suppressing target expression by binding to the 3 0 -UTR, regulate Pdcd4 or invasion. The present study was conducted to investigate the regulation of Pdcd4, and invasion/intravasation, by miRNAs. A bioinformatics search revealed a conserved target-site for miR-21 within the Pdcd4-3 0 -UTR at 228-249 nt. In 10 colorectal cell lines, an inverse correlation of miR-21 and Pdcd4-protein was observed. Transfection of Colo206f-cells with miR-21 significantly suppressed a luciferase-reporter containing the Pdcd4-3 0 -UTR, whereas transfection of RKO with anti-miR-21 increased activity of this construct. This was abolished when a construct mutated at the miR-21/nt228-249 target site was used instead. Anti-miR-21-transfected RKO cells showed an increase of Pdcd4-protein and reduced invasion. Moreover, these cells showed reduced intra-vasation and lung metastasis in a chicken-embryo-metastasis assay. In contrast, overexpression of miR-21 in Colo206f significantly reduced Pdcd4-protein amounts and increased invasion, while Pdcd4-mRNA was unaltered. Resected normal/tumor tissues of 22 colorectal cancer patients demonstrated an inverse correlation between miR-21 and Pdcd4-protein. This is the first study to show that Pdcd4 is negatively regulated by miR-21. Furthermore, it is the first report to demonstrate that miR-21 induces invasion/intravasation/metastasis.

BACKGROUND.Programmed cell death 4 (Pdcd4) inhibits malignant transformation, and initial studies of Pdcd4 suggested the regulation of Pdcd4 localization by protein kinase B (Akt). However, supporting patient tissue data are missing, and the diagnostic/prognostic potential of Pdcd4 rarely has been studied. The objectives of the current were 1) to determine Pdcd4 as a diagnostic marker in the adenoma‐carcinoma sequence, 2) to support phosphorylated Akt (pAkt)‐mediated Pdcd4 regulation in vivo, and 3) to obtain the first prognostic evidence of Pdcd4 in colorectal cancer.METHODS.Tumor samples and normal tissues from 71 patients with colorectal cancer who were followed prospectively (median follow‐up, 36 months) and 42 adenomas were analyzed for Pdcd4, Akt, and pAkt in immunohistochemical and Western blot analyses.RESULTS.A significant reduction in Pdcd4 was observed between normal mucosa and adenomas and between adenomas and tumor samples (P < .01 and P < .01, respectively). Normal mucosa demonstrated strong nuclear Pdcd4, which was reduced significantly in adenomas (P < .01) and almost was lost in tumors (P < .01). pAkt was correlated inversely with Pdcd4 and with the transition of Pdcd4 from nucleus to cytoplasm (P < .01). Kaplan‐Meier analysis (using the Mantel‐Cox log‐rank test) indicated a significant correlation between the loss of total and nuclear Pdcd4 in tumors and overall survival (P < .05 and P < .02, respectively) and disease‐specific survival (P < .01 and P < .01, respectively). In multivariate analysis, loss of total or nuclear Pdcd4 was an independent predictor of disease‐specific or overall survival.CONCLUSIONS.To the authors' knowledge, this is the first study to demonstrate an independent prognostic impact of Pdcd4 and its expression pattern in colorectal cancer. Data from this study support the regulation of Pdcd4 localization by pAkt in vivo. Pdcd4 immunohistochemistry may be useful as a supportive diagnostic tool for the transition between normal, adenoma, and tumor tissues. Cancer 2007. Published 2007 by the American Cancer Society.

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