Abstract 1136: p53-induced miR-15a/16-1 and AP4 form a double-negative feedback loop to regulate epithelial-mesenchymal transition and metastasis in colorectal cancer

The transcription factor AP4 mediates epithelial-mesenchymal transition (EMT) in colorectal cancer (CRC) but its control in this setting is not fully understood. Here we report the definition of a double-negative feedback loop involving AP4 and miR-15a/16-1 that regulates EMT and metastatic progression. In CRC cells, AP4 was downregulated by DNA damage in a p53-dependent manner. AP4 downregulation by p53 was mediated indirectly by the tumor suppressive microRNAs miR-15a and miR-16-1, which targeted the 3′-UTR of AP4 mRNA, induced mesenchymal-epithelial transition (MET) and inhibited CRC cell migration and invasion. The downregulation of AP4 was necessary for MET induction by miR-15a/16-1. In tumor xenoplants, ectopic miR-15a/16-1 suppressed formation of lung metastases. Furthermore, AP4 directly suppressed expression of miR-15a/16-1. In clinical specimens of colorectal cancer, miR-15a levels inversely correlated with AP4 protein levels shown previously to correlate with distant metastasis and poor survival. In summary, our results define a double-negative feedback loop involving miR-15a/16-1 and AP4 that stabilizes epithelial and mesenchymal states, respectively, that may determine metastatic prowess.

Citation Format: Lei Shi, Rene Jackstadt, Helge Siemens, Huihui Li, Thomas Kirchner, Heiko Hermeking. p53-induced miR-15a/16-1 and AP4 form a double-negative feedback loop to regulate epithelial-mesenchymal transition and metastasis in colorectal cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1136. doi:10.1158/1538-7445.AM2014-1136

Repression of c-Kit by p53 is mediated by miR-34 and is associated with reduced chemoresistance, migration and stemness

The c-Kit receptor tyrosine kinase is commonly over-expressed in different types of cancer. p53 activation is known to result in the down-regulation of c-Kit. However, the underlying mechanism has remained unknown. Here, we show that the p53-induced miR-34 microRNA family mediates repression of c-Kit by p53 via a conserved seed-matching sequence in the c-Kit 3'-UTR. Ectopic miR-34a resulted in a decrease in Erk signaling and transformation, which was dependent on the down-regulation of c-Kit expression. Furthermore, ectopic expression of c-Kit conferred resistance of colorectal cancer (CRC) cells to treatment with 5-fluorouracil (5-FU), whereas ectopic miR-34a sensitized the cells to 5-FU. After stimulation with c-Kit ligand/stem cell factor (SCF) Colo320 CRC cells displayed increased migration/invasion, whereas ectopic miR-34a inhibited SCF-induced migration/invasion. Activation of a conditional c-Kit allele induced several stemness markers in DLD-1 CRC cells. In primary CRC samples elevated c-Kit expression also showed a positive correlation with markers of stemness, such as Lgr5, CD44, OLFM4, BMI-1 and β-catenin. On the contrary, activation of a conditional miR-34a allele in DLD-1 cells diminished the expression of c-Kit and several stemness markers (CD44, Lgr5 and BMI-1) and suppressed sphere formation. MiR-34a also suppressed enhanced sphere-formation after exposure to SCF. Taken together, our data establish c-Kit as a new direct target of miR-34 and demonstrate that this regulation interferes with several c-Kit-mediated effects on cancer cells. Therefore, this regulation may be potentially relevant for future diagnostic and therapeutic approaches.

p53-induced miR-15a/16-1 and AP4 form a double-negative feedback loop to regulate epithelial-mesenchymal transition and metastasis in colorectal cancer

The transcription factor AP4 mediates epithelial-mesenchymal transition (EMT) in colorectal cancer but its control in this setting is not fully understood. Here, we report the definition of a double-negative feedback loop involving AP4 and miR-15a/16-1 that regulates EMT and metastatic progression. In colorectal cancer cells, AP4 was downregulated by DNA damage in a p53-dependent manner. AP4 downregulation by p53 was mediated indirectly by the tumor-suppressive microRNAs miR-15a and miR-16-1, which targeted the 3' untranslated region (3'-UTR) of AP4 mRNA, induced mesenchymal-epithelial transition (MET), and inhibited colorectal cancer cell migration and invasion. The downregulation of AP4 was necessary for induction of MET and cell cycle arrest by miR-15a/16-1. In tumor xenoplants, ectopic miR-15a/16-1 suppressed formation of lung metastases. Furthermore, AP4 directly suppressed expression of miR-15a/16-1. In clinical specimens of colorectal cancer, miR-15a levels inversely correlated with AP4 protein levels shown previously to correlate with distant metastasis and poor survival. In summary, our results define a double-negative feedback loop involving miR-15a/16-1 and AP4 that stabilizes epithelial and mesenchymal states, respectively, which may determine metastatic prowess.

Detection of miR-34a promoter methylation in combination with elevated expression of c-Met and β-catenin predicts distant metastasis of colon cancer

PURPOSE

Here, we determined whether epigenetic inactivation of miR-34a and miR-34b/c genes may serve as a prognostic marker for distant metastases in colon cancer.

EXPERIMENTAL DESIGN

Using a case-control study design of 94 primary colon cancer samples with and without liver metastases, we determined CpG methylation frequencies of miR-34a and miR-34b/c promoters, expression of miR-34a, and its targets c-Met, Snail, and β-catenin and their prognostic value.

RESULTS

miR-34a methylation was detected in 45.1% (n = 42 of 93) of the samples and strongly associated with metastases to the liver (P = 0.003) and lymph nodes (P = 0.006). miR-34b/c methylation was detected in 91.9% of the samples (n = 79/86). A significant inverse correlation between miR-34a methylation and expression of mature miR-34a (P = 0.018) was detected. Decreased miR-34a expression was associated with upregulation of c-Met, Snail, and β-catenin protein levels (P = 0.031, 0.132, and 0.004), which were associated with distant metastases (P = 0.001, 0.017, and 0.005). In a confounder-adjusted multivariate regression model miR-34a methylation, high c-Met and β-catenin levels provided the most significant prognostic information about metastases to the liver (P = 0.014, 0.031, and 0.058) and matched pairs showed a higher prevalence of these risk factors in the samples with distant spread (P = 0.029). Finally, we obtained statistical evidence indicating that the simultaneous detection of these three markers has the highest prognostic value.

CONCLUSIONS

Silencing of miR-34a and upregulation of c-Met, Snail, and β-catenin expression is associated with liver metastases of colon cancer. Detection of miR-34a silencing in resected primary colon cancer may be of prognostic value, especially in combination with detection of c-Met and β-catenin expression.

miR-34 and SNAIL form a double-negative feedback loop to regulate epithelial-mesenchymal transitions

Recently, the inhibition of epithelial-mesenchymal-transition (EMT) by p53 has been described as a new mode of tumor suppression which presumably prevents metastasis. Here we report that activation of p53 down-regulates the EMT-inducing transcription factor SNAIL via induction of the miR-34a/b/c genes. Suppression of miR-34a/b/c caused up-regulation of SNAIL and cells displayed EMT markers and related features, as enhanced migration and invasion.  Ectopic miR-34a induced mesenchymal-epithelial-transition (MET) and down-regulation of SNAIL, which was mediated by a conserved miR-34a/b/c seed-matching sequence in the SNAIL 3'-UTR. miR-34a also down-regulated SLUG and ZEB1, as well as the stemness factors BMI1, CD44, CD133, OLFM4 and c-MYC. Conversely, the transcription factors SNAIL and ZEB1 bound to E-boxes in the miR-34a/b/c promoters, thereby repressing miR-34a and miR-34b/c expression. Since ectopic miR-34a prevented TGF-β-induced EMT, the repression of miR-34 genes by SNAIL and related factors is part of the EMT program. In conclusion, the frequent inactivation of p53 and/or miR-34a/b/c found in cancer may shift the equilibrium of these reciprocal regulations towards the mesenchymal state and thereby lock cells in a metastatic state.

Influence of induction of HSP70 on the cytotoxicity of oxazaphosphorine compounds and cisplatin

Induction of HSP70 and thermotolerance may also decrease the cytotoxicity of cytostatic agents or their combination with hyperthermia in clinically used thermochemotherapy. HSP70 and thermotolerance were induced by hyperthermia (42 degrees C, 1 h) in two human tumor cell lines in vitro and in vivo. The influence of thermotolerance on the cytotoxicity of CDDP and the oxazaphosphorine compounds Mafo and Ifo and their combination with hyperthermia (42 degrees C or 43 degrees C, 1 h) were studied. The results show that neither thermotolerance nor HSP70 affects the tumor cell sensitivity to CDDP or oxazaphosphorine compounds. However, the additive effect of hyperthermia and CDDP was found to be attenuated in thermotolerant cells. The cytotoxicity of oxazaphosphorine compounds combined with hyperthermia was not altered after preheating, suggesting a different mechanism may be responsible for the drug-hyperthermia interaction of CDDP and oxazaphosphorine compounds. There were no differences between in vitro and in vivo results suggesting mechanisms at the cellular level being responsible for the influence of thermotolerance on drug- and drug-hyperthermia action.