Axl-altered microRNAs regulate tumorigenicity and gefitinib resistance in lung cancer

The involvement of Axl kinase in non-small cell lung cancer''s (NSCLC) acquired resistance to tyrosine kinase inhibitors (TKIs) gefitinib or erlotinib has been identified recently, but the mechanism by which Axl contributes to TKI resistance is largely unknown. MicroRNAs (miRNAs) repress gene expression and their critical role in tumorigenesis has been implicated. To investigate the role of miRNAs in the Axl-mediated acquired gefitinib resistance, we examined the Axl-mediated miRNA changes in gefitinib-resistant lung cancers. A panel of Axl kinase-altered miRNAs was identified. In this study, we validate and report that miR-374a and miR-548b modulated by Axl have essential roles in cell cycle arrest, gefitinib-induced apoptosis, epithelial-to-mesenchymal transition, migration and tumorigenesis of gefitinib-resistant lung cancer cells in vitro and in vivo by targeting Wnt5a and CCNB1 genes, respectively. Of clinical significance, high expression of Axl and miR-374a and low expression of miR-548b are associated with poor disease-free survival postoperatively. These findings indicate that the modulation of specific miRNAs may provide a therapeutic target to treat or reverse gefitinib resistance in NSCLC with high expression of Axl in the future.     

MiR-34a/c-Dependent PDGFR-α/β Downregulation Inhibits Tumorigenesis and Enhances TRAIL-Induced Apoptosis in Lung Cancer

Lung cancer is the leading cause of cancer mortality in the world today. Although some advances in lung cancer therapy have been made, patient survival is still poor. MicroRNAs (miRNAs) can act as oncogenes or tumor-suppressor genes in human malignancy. The miR-34 family consists of tumor-suppressive miRNAs, and its reduced expression has been reported in various cancers, including non-small cell lung cancer (NSCLC). In this study, we found that miR-34a and miR-34c target platelet-derived growth factor receptor alpha and beta (PDGFR-α and PDGFR-β), cell surface tyrosine kinase receptors that induce proliferation, migration and invasion in cancer. MiR-34a and miR-34c were downregulated in lung tumors compared to normal tissues. Moreover, we identified an inverse correlation between PDGFR-α/β and miR-34a/c expression in lung tumor samples. Finally, miR-34a/c overexpression or downregulation of PDGFR-α/β by siRNAs, strongly augmented the response to TNF-related apoptosis inducing ligand (TRAIL) while reducing migratory and invasive capacity of NSCLC cells.     

NK92-CD16 cells are cytotoxic to non-small cell lung cancer cell lines that have acquired resistance to tyrosine kinase inhibitors

BackgroundTreatment with tyrosine kinase inhibitors (TKIs) has improved the outcomes for patients with non-small cell lung cancer (NSCLC) harboring targetable driver mutations. However, acquired resistance to TKIs invariably develops within approximately 1 year of treatment by various mechanisms, including gatekeeper mutations, alternative pathway activation and histological transformations. Because immunotherapy is an option for patients with drug-resistant cancers, we generated several TKI-resistant NSCLC cell lines in vitro, and then evaluated the cytotoxicity of NK92-CD16 cells to these resistant cells.Materials and MethodsTKI-resistant NSCLC cells (H3122CR1, H3122LR1, H3122CR1LR1, PC-9GR, PC-9ER, EBC-CR1 and EBC-CR2) were established from NCI-H3122 (EML4-ALK fusion), PC-9 (EGFR exon19 deletion) and EBC-1 (MET amplification) after continuous exposure to crizotinib, ceritinib, gefitinib, erlotinib and capmatinib. Expression of ligands for natural killer (NK) cell receptors and total EGFR were analyzed using flow cytometry. NK cytotoxicity and antibody-dependent cell-mediated cytotoxicity (ADCC) using anti-EGFR monoclonal antibody (mAb) cetuximab were measured using NK92-CD16 as effectors and detected using the ⁵¹Chromium-release assay.ResultsWe found that NK92-CD16 cells preferentially killed TKI-resistant NSCLC cells when compared with their parental NSCLC cells. Mechanistically, intracellular adhesion molecule 1 (ICAM-1) was up-regulated in the TKI-resistant NSCLC cells and patients’ tumors, and the ICAM-1 up-regulated cancer cells lines were less susceptible to NK cytotoxicity by blocking ICAM-1. Moreover, NK92-CD16 cell-induced cytotoxicity toward TKI-resistant NSCLC cells was enhanced in the presence of cetuximab, an EGFR-targeting mAb.ConclusionThese data suggest that combinational treatment with NK cell–based immunotherapy and cetuximab may be promising for patients with TKI-resistant NSCLC.     

miR-138-5p reverses gefitinib resistance in non-small cell lung cancer cells via negatively regulating G protein-coupled receptor 124

Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR TKIs) such as gefitinib are clinically effective treatments for non-small cell lung cancer (NSCLC) patients with EGFR activating mutations. However, therapeutic effect is ultimately limited by the development of acquired TKI resistance. MicroRNAs (miRNAs) represent a category of small non-coding RNAs commonly deregulated in human malignancies. The aim of this study was to investigate the role of miRNAs in gefitinib resistance. We established a gefitinib-resistant cell model (PC9GR) by continually exposing PC9 NSCLC cells to gefitinib for 6 months. MiRNA microarray screening revealed miR-138-5p showed the greatest downregulation in PC9GR cells. Re-expression of miR-138-5p was sufficient to sensitize PC9GR cells and another gefitinib-resistant NSCLC cell line, H1975, to gefitinib. Bioinformatics analysis and luciferase reporter assay showed that G protein-coupled receptor124 (GPR124) was a direct target of miR-138-5p. Experimental validation demonstrated that expression of GPR124 was suppressed by miR-138-5p on protein and mRNA levels in NSCLC cells. Furthermore, we observed an inverse correlation between the expression of miR-138-5p and GPR124 in lung adenocarcinoma specimens. Knockdown of GPR124 mimicked the effects of miR-138-5p on the sensitivity to gefitinib. Collectively, our results suggest that downregulation of miR-138-5p contributes to gefitinib resistance and that restoration of miR-138-5p or inhibition GPR124 might serve as potential therapeutic approach for overcoming NSCLC gefitinib resistance.     

MicroRNA-34A inhibits the growth,invasion and metastasis of gastric cancer by targeting PDGFR and MET expression

Within the family of RTKs (receptor tyrosine kinases), PDGFR (platelet-derived growth factor receptor) has been implicated in carcinogenesis and tumour development. miRNAs (microRNAs), which can target the mRNAs (messenger RNAs) of cancer-associated genes, are abnormally expressed in various cancers. In this study, our aim was to identify the miRNAs that target PDGFR-α/β and to study the functions of these miRNAs. miR-34a was predicted to target PDGFR, and luciferase reporter assays showed that miR-34a could directly target PDGFR. Meanwhile, we found that miR-34a was down-regulated in gastric cancer tissues and was associated with metastasis. Our findings showed that miR-34a could inhibit gastric cancer cell migration, invasion and proliferation, but these tumourigenic properties were only partially restored when PDGFR-α/β was overexpressed. In subsequent experiments, we found that the overexpression of both PDGFR and MET could completely restore the gastric cancer tumourigenic properties. Moreover, the cancer-associated cell signalling pathway was studied, and we found that miR-34a could inhibit Akt [PKB (protein kinase B)] phosphorylation, which was restored by the overexpression of both PDGFR and MET. In conclusion, miR-34a may act as a potential tumour suppressor in gastric cancer and is associated with the mechanisms of gastric cancer metastasis; miR-34a can inhibit gastric cancer tumourigenesis by targeting PDGFR and MET through the PI3K (phosphoinositide 3-kinase)/Akt pathway.     

MET Gene Amplification and MET Receptor Activation Are Not Sufficient to Predict Efficacy of Combined MET and EGFR Inhibitors in EGFR TKI-Resistant NSCLC Cells

Epidermal growth factor receptor (EGFR), member of the human epidermal growth factor receptor (HER) family, plays a critical role in regulating multiple cellular processes including proliferation, differentiation, cell migration and cell survival. Deregulation of the EGFR signaling has been found to be associated with the development of a variety of human malignancies including lung, breast, and ovarian cancers, making inhibition of EGFR the most promising molecular targeted therapy developed in the past decade against cancer. Human non small cell lung cancers (NSCLC) with activating mutations in the EGFR gene frequently experience significant tumor regression when treated with EGFR tyrosine kinase inhibitors (TKIs), although acquired resistance invariably develops. Resistance to TKI treatments has been associated to secondary mutations in the EGFR gene or to activation of additional bypass signaling pathways including the ones mediated by receptor tyrosine kinases, Fas receptor and NF-kB. In more than 30–40% of cases, however, the mechanisms underpinning drug-resistance are still unknown. The establishment of cellular and mouse models can facilitate the unveiling of mechanisms leading to drug-resistance and the development or validation of novel therapeutic strategies aimed at overcoming resistance and enhancing outcomes in NSCLC patients. Here we describe the establishment and characterization of EGFR TKI-resistant NSCLC cell lines and a pilot study on the effects of a combined MET and EGFR inhibitors treatment. The characterization of the erlotinib-resistant cell lines confirmed the association of EGFR TKI resistance with loss of EGFR gene amplification and/or AXL overexpression and/or MET gene amplification and MET receptor activation. These cellular models can be instrumental to further investigate the signaling pathways associated to EGFR TKI-resistance. Finally the drugs combination pilot study shows that MET gene amplification and MET receptor activation are not sufficient to predict a positive response of NSCLC cells to a cocktail of MET and EGFR inhibitors and highlights the importance of identifying more reliable biomarkers to predict the efficacy of treatments in NSCLC patients resistant to EGFR TKI.     

miRNA profiling in colorectal cancer highlights miR-1 involvement in MET-dependent proliferation

Altered expression of miRNAs is associated with development and progression of various human cancers by regulating the translation of oncogenes and tumor suppressor genes. In colorectal cancer, these regulators complement the Vogelstein multistep model of pathogenesis and have the potential of becoming a novel class of tumor biomarkers and therapeutic targets. Using quantitative real-time PCR, we measured the expression of 621 mature miRNAs in 40 colorectal cancers and their paired normal tissues and identified 23 significantly deregulated miRNAs. We subsequently evaluated their association with clinical characteristics of the samples and presence of alterations in the molecular markers of colorectal cancer progression. Expression levels of miR-31 were correlated with CA19-9 and miR-18a, miR-21, and miR-31 were associated with mutations in APC gene. To investigate the downstream regulation of the differentially expressed miRNAs identified, we integrated putative mRNA target predictions with the results of a meta-analysis of seven public gene expression datasets of normal and tumor samples of colorectal cancer patients. Many of the colorectal cancer deregulated miRNAs computationally mapped to targets involved in pathways related to progression. Here one promising candidate pair (miR-1 and MET) was studied and functionally validated. We show that miR-1 can have a tumor suppressor function in colorectal cancer by directly downregulating MET oncogene both at RNA and protein level and that reexpression of miR-1 leads to MET-driven reduction of cell proliferation and motility, identifying the miR-1 downmodulation as one of the events that could enhance colorectal cancer progression.     

p53/miR-30a-5p/ SOX4 feedback loop mediates cellular proliferation,apoptosis, and migration of non-small-cell lung cancer

Many microRNAs (miRNAs) play vital roles in the tumorigenesis and development of cancers. In this study, we aimed to identify the differentially expressed miRNAs and their specific mechanisms in non-small-cell lung cancer (NSCLC). Based on data from the GSE56036 database, miR-30a-5p expression was identified to be downregulated in NSCLC. Further investigations showed that overexpression of miR-30a-5p inhibited cell proliferation, migration, and promoted apoptosis in NSCLC. Increase of miR-30a-5p level could induce the increase of Bax protein level and decrease of Bcl-2 protein level. In addition, chromatin immunoprecipitation assays showed that miR-30a-5p expression was induced by binding of p53 to the promoter of MIR30A. Bioinformatics prediction indicated that miR-30a-5p targets SOX4, and western blot analysis indicated that overexpression of the miRNA decreases the SOX4 protein expression level, which in turn regulated the level of p53. Thus, this study provides evidence for the existence of a p53/miR-30a-5p/SOX4 feedback loop, which likely plays a key role in the regulation of proliferation, apoptosis, and migration in NSCLC, highlighting a new therapeutic target.     

Inhibition of Hedgehog signaling sensitizes NSCLC cells to standard therapies through modulation of EMT-regulating miRNAs

Background

Epidermal growth factor receptor- tyrosine kinase inhibitors (EGFR-TKIs) benefit Non-small cell lung cancer (NSCLC) patients, and an EGFR-TKIi erlotinib, is approved for patients with recurrent NSCLC. However, resistance to erlotinib is a major clinical problem. Earlier we have demonstrated the role of Hedgehog (Hh) signaling in Epithelial-to-Mesenchymal transition (EMT) of NSCLC cells, leading to increased proliferation and invasion. Here, we investigated the role of Hh signaling in erlotinib resistance of TGF-β1-induced NSCLC cells that are reminiscent of EMT cells.

Methods

Hh signaling was inhibited by specific siRNA and by GDC-0449, a small molecule antagonist of G protein coupled receptor smoothened in the Hh pathway. Not all NSCLC patients are likely to benefit from EGFR-TKIs and, therefore, cisplatin was used to further demonstrate a role of inhibition of Hh signaling in sensitization of resistant EMT cells. Specific pre- and anti-miRNA preparations were used to study the mechanistic involvement of miRNAs in drug resistance mechanism.

Results

siRNA-mediated inhibition as well as pharmacological inhibition of Hh signaling abrogated resistance of NSCLC cells to erlotinib and cisplatin. It also resulted in re-sensitization of TGF-β1-induced A549 (A549M) cells as well the mesenchymal phenotypic H1299 cells to erlotinib and cisplatin treatment with concomitant up-regulation of cancer stem cell (CSC) markers (Sox2, Nanog and EpCAM) and down-regulation of miR-200 and let-7 family miRNAs. Ectopic up-regulation of miRNAs, especially miR-200b and let-7c, significantly diminished the erlotinib resistance of A549M cells. Inhibition of Hh signaling by GDC-0449 in EMT cells resulted in the attenuation of CSC markers and up-regulation of miR-200b and let-7c, leading to sensitization of EMT cells to drug treatment, thus, confirming a connection between Hh signaling, miRNAs and drug resistance.

Conclusions

We demonstrate that Hh pathway, through EMT-induction, leads to reduced sensitivity to EGFR-TKIs in NSCLCs. Therefore, targeting Hh pathway may lead to the reversal of EMT phenotype and improve the therapeutic efficacy of EGFR-TKIs in NSCLC patients.

     

A panel of noncoding RNAs in non–small-cell lung cancer

Non–small-lung cancer (NSCLC) is the leading cause of cancer death. Early detection of NSCLC could pave the way for effective therapies. Analysis of molecular genetic biomarkers in biological fluids has been proposed as a useful tool for cancer diagnosis. Here, we aimed to develop a panel of noncoding RNAs (ncRNAs) in sputum for NSCLC early detection. Expression of 11 ncRNAs were analyzed by real–time polymerase chain reaction in sputum samples of 30 NSCLC patients and 30 sex- and age-matched cancer-free controls. Stability of endogenous microRNAs (miRNAs) in sputum was evaluated after 3 and 6 days at 4°C, 6 months, and 1 year at −80°C. Nine ncRNAs showed significant differences of their expression in sputum between NSCLC patients and controls. A logistic regression model with the best prediction was built based on miR-145, miR-126, and miR-7. The composite of the three miRNAs produced 90% sensitivity and specificity in distinguishing NSCLC patients from the controls. Results indicate that miRNAs could be useful biomarkers based on their stability under various storage conditions and maintain differential changes between cancer and control groups. Moreover, measurement of miRNAs in sputum could be a noninvasive approach for detection of lung cancer.     

miR-141 and miR-200c as Markers of Overall Survival in Early Stage Non-Small Cell Lung Cancer Adenocarcinoma

Background

Several treatments in non-small cell lung cancer (NSCLC) are histology-dependent, and the need for histology-related markers is increasing. MicroRNAs (miRNAs) are promising molecular markers in multiple cancers and show differences in expression depending on histological subtype. The miRNA family miR-200 has been associated with the regulation of epithelial-mesenchymal (EMT)/mesenchymal-epithelial transition (MET). EMT involves profound phenotypic changes that include the loss of cell-cell adhesion, the loss of cell polarity, and the acquisition of migratory and invasive properties that facilitates metastasis. A dual role for the miR-200 family in the prognosis of several tumors has been related to tumor cell origin. However, the prognostic role and function of miR-200 family in early-stage NSCLC adenocarcinoma and squamous cell carcinoma (SCC) have not been well established.

Methods

miRNA expression was determined using TaqMan assays in 155 tumors from resected NSCLC patients. Functional studies were conducted in three NSCLC cell lines: H23, A-549 and HCC-44.

Results

High miR-200c expression was associated with shorter overall survival (OS) in the entire cohort (p = 0.024). High miR-200c (p = 0.0004) and miR-141 (p = 0.009) expression correlated with shorter OS in adenocarcinoma – but not in SCC. In the multivariate analysis, a risk score based on miR-141 and miR-200c expression emerged as an independent prognostic factor for OS in the entire cohort (OR, 2.787; p = 0.033) and in adenocarcinoma patients (OR, 10.649; p = 0.002). Functional analyses showed that miR-200c, was related to mesenchymal-epithelial transition (MET) and affected cell migration and E-cadherin levels, while overexpression of miR-141 reduced KLF6 protein levels and produced an increase of secretion of VEGFA in vitro (H23, p = 0.04; A-549, p = 0.03; HCC-44, p = 0.02) and was associated with higher blood microvessel density in patient tumor samples (p<0.001).

Conclusion

High miR-141 and miR-200c expression are associated with shorter OS in NSCLC patients with adenocarcinoma through MET and angiogenesis.     

Identification of key microRNAs and hub genes in non-small-cell lung cancer using integrative bioinformatics and functional analyses

Non-small-cell lung cancer (NSCLC) is an extremely debilitating respiratory malignancy. However, the pathogenesis of NSCLC has not been fully clarified. The main objective of our study was to identify potential microRNAs (miRNAs) and their regulatory mechanism in NSCLC. Using a systematic review, two NSCLC-associated miRNA data sets (GSE102286 and GSE56036) were obtained from Gene Expression Omnibus, and the differentially expressed miRNAs (DE-miRNAs) were accessed by GEO2R. Survival analysis of candidate DE-miRNAs was conducted using the Kaplan-Meier plotter database. To further illustrate the roles of DE-miRNAs in NSCLC, their potential target genes were predicted by miRNet and were annotated by the Database for Annotation, Visualization and Integrated Discovery (DAVID) program. Moreover, the protein-protein interaction (PPI) and miRNA-hub gene regulatory network were established using the STRING database and Cytoscape software. The function of DE-miRNAs in NSCLC cells was evaluated by transwell assay. Compared with normal tissues, a total of eight DE-miRNAs was commonly changed in two data sets. The survival analysis showed that six miRNAs (miR-21-5p, miR-31-5p, miR-708-5p, miR-30a-5p, miR-451a, and miR-126-3p) were significantly correlated with overall survival. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that target genes of upregulated miRNAs were enriched in pathways in cancer, microRNAs in cancer and proteoglycans in cancer, while the target genes of downregulated miRNAs were mainly associated with pathways in cancer, the PI3K-Akt signaling pathway and HTLV-I infection. Based on the miRNA-hub gene network and expression analysis, PTEN, EGFR, STAT3, RHOA, VEGFA, TP53, CTNNB1, and KRAS were identified as potential target genes. Furthermore, all six miRNAs exhibited significant effects on NSCLC cell invasion. These findings indicate that six DE-miRNAs and their target genes may play important roles in the pathogenesis of NSCLC, which will provide novel information for NSCLC treatments.     

MiR-181a contributes gefitinib resistance in non-small cell lung cancer cells by targeting GAS7

Tyrosine kinase inhibitors (TKIs) exert potent therapeutic efficacy in non-small cell lung cancers (NSCLC) harboring epidermal growth factor receptor (EGFR) activating mutations. However, a major impediment for the effective treatment is the development of drug resistance. Some evidence supports a role for miRNAs in modulating NSCLC TKIs resistance. Here we show that miR-181a is significantly up-regulated in gefitinib-resistant cells compared with gefitinib-sensitive cells. Upregulation of miR-181a caused resistance of gefitinib, whereas downregulation of miR-181a sensitized NSCLC cells to gefitinib. Furthermore, the miR-181a plasma levels were significantly increased in acquired gefitinib resistant NSCLC patients compared with the plasma levels prior to gefitinib treatment in each patient. Bioinformatics analysis and luciferase reporter assay showed that growth arrest-specific 7 (GAS7) was a direct target gene of miR-181a. A significant inverse correlation between the expression of miR-181a and GAS7 was identified in NSCLC tissues. Downregulation of GAS7 expression could antagonize gefitinib re-sensitivity in PC9GR mediated by knockdown of miR-181a via AKT/ERK pathways and epithelial-to-mesenchymal transition markers. Additionally, GAS7 expression was downregulated in a large cohort of NSCLC patients, and a high mRNA level of GAS7 was associated with improved overall survival. Collectively, our findings provide a novel basis for using miR-181a/GAS7-based therapeutic strategies to reverse gefitinib resistance in NSCLC.     

The RON and MET oncogenes are co-expressed in human ovarian carcinomas and cooperate in activating invasiveness

RON is a member of the receptor tyrosine kinase gene family that includes the MET oncogene, whose germline mutations have been causally related to human tumorigenesis. In vitro, RON and MET receptors cross-talk, synergize in intracellular signaling, and cooperate in inducing morphogenic responses. Here we show that the RON and MET oncogenes were expressed in 55% and 56% of human ovarian carcinomas, respectively, and were significantly coexpressed in 42% (P < 0.001). In ovarian carcinoma samples and cell lines we did not find mutations in RON and MET gene kinase domain, nor coexpression of RON and MET receptor ligands (MSP and HGF, respectively). We show that motility and invasiveness of ovarian cancer cells coexpressing MET and RON receptors were elicited by HGF and, to a lesser extent, by MSP. More interestingly, invasion of both reconstituted basement membrane and collagen gel was greatly enhanced by the simultaneous addition of the two ligands. These data suggest that coexpression of the MET and RON receptors confer a selective advantage to ovarian cancer cells and might promote ovarian cancer progression.     

MicroRNA expression in ovarian carcinoma and its correlation with clinicopathological features

ABSTRACT: BACKGROUND: MicroRNA (miRNA) expression is known to be deregulated in ovarian carcinomas. However, limited data is available about the miRNA expression pattern for the benign or borderline ovarian tumors as well as differential miRNA expression pattern associated with histological types, grades or clinical stages in ovarian carcinomas. We defined patterns of microRNA expression in tissues from normal, benign, borderline, and malignant ovarian tumors and explored the relationship between frequently deregulated miRNAs and clinicopathologic findings, response to therapy, survival, and association with Her-2/neu status in ovarian carcinomas. METHODS: We measured the expression of nine miRNAs (miR-181d, miR-30a-3p, miR-30c, miR-30d, miR-30e-3p, miR-368, miR-370, miR-493-5p, miR-532-5p) in 171 formalin-fixed, paraffin-embedded ovarian tissue blocks as well as six normal human ovarian surface epithelial (HOSE) cell lines using Taqman-based real-time PCR assays. Her-2/neu overexpression was assessed in ovarian carcinomas (n = 109 cases) by immunohistochemistry analysis. RESULTS: Expression of four miRNAs (miR-30c, miR-30d, miR-30e-3p, miR-370) was significantly different between carcinomas and benign ovarian tissues as well as between carcinoma and borderline tissues. An additional three miRNAs (miR-181d, miR-30a-3p, miR-532-5p) were significantly different between borderline and carcinoma tissues. Expression of miR-532-5p was significantly lower in borderline than in benign tissues. Among ovarian carcinomas, expression of four miRNAs (miR-30a-3p, miR-30c, miR-30d, miR-30e-3p) was lowest in mucinous and highest in clear cell samples. Expression of miR-30a-3p was higher in well-differentiated compared to poorly differentiated tumors (P = 0.02), and expression of miR-370 was higher in stage I/II compared to stage III/IV samples (P = 0.03). In multivariate analyses, higher expression of miR-181d, miR-30c, miR-30d, and miR-30e-3p was associated with significantly better disease-free or overall survival. Finally, lower expression of miR-30c, miR-30d, miR-30e-3p and miR-532-5p was significantly associated with overexpression of Her-2/neu. CONCLUSIONS: Aberrant expression of miRNAs is common in ovarian tumor suggesting involvement of miRNA in ovarian tumorigenesis. They are associated with histology, clinical stage, survival and oncogene expression in ovarian carcinoma.     

MET-dependent cancer invasion may be preprogrammed by early alterations of p53-regulated feedforward loop and triggered by stromal cell-derived HGF

MET, a receptor protein tyrosine kinase activated by hepatocyte growth factor (HGF), is a crucial determinant of metastatic progression. Recently, we have identified p53 as an important regulator of MET-dependent cell motility and invasion. This regulation occurs via feedforward loop suppressing MET expression by miR-34-dependent and -independent mechanisms. Here, by using Dicer conditional knockout, we provide further evidence for microRNA-independent MET regulation by p53. Furthermore, we show that while MET levels increase immediately after p53 inactivation, mutant cells do not contain active phosphorylated MET and remain non-invasive for a long latency period at contrary to cell culture observations. Evaluation of mouse models of ovarian and prostate carcinogenesis indicates that formation of desmoplastic stroma, associated production of HGF by stromal cells and coinciding MET phosphorylation precede cancer invasion. Thus, initiation mutation of p53 is sufficient for preprogramming motile and invasive properties of epithelial cells, but the stromal reaction may represent a critical step for their manifestation during cancer progression.