RUNX3 mRNA Expression Research Articles

Lack of RUNX3 regulation in human gastric cancer

It has been proposed that the transcription factor RUNX3 is the product of a gastric tumour suppressor gene. We examined RUNX3 expression in gastric biopsies from 105 patients with different histological presentations. Surprisingly, immunohistochemical staining detected RUNX3 protein expression only in infiltrating leukocytes but not in the gastric epithelium. Using laser capture microdissection and quantitative reverse transcription-polymerase chain reaction, we confirmed that the level of RUNX3 mRNA expression in the gastric epithelium was very low and was influenced neither by H. pylori infection nor by neoplastic transformation. Instead, RUNX3 was highly expressed in the gastric stroma and the level of expression correlated with the magnitude of H. pylori-induced gastric inflammation. The low level of RUNX3 expression in gastric epithelium and the absence of downregulation in gastric cancer do not support the hypothesis that RUNX3 functions as a gastric tumour suppressor gene.

RUNX3 Is Frequently Inactivated by Dual Mechanisms of Protein Mislocalization and Promoter Hypermethylation in Breast Cancer

A tumor suppressor function has been attributed to RUNX3, a member of the RUNX family of transcription factors. Here, we examined alterations in the expression of three members, RUNX1, RUNX2, and RUNX3, and their interacting partner, CBF-beta, in breast cancer. Among them, RUNX3 was consistently underexpressed in breast cancer cell lines and primary tumors. Fifty percent of the breast cancer cell lines (n = 19) showed hypermethylation at the promoter region and displayed significantly lower levels of RUNX3 mRNA expression (P < 0.0001) and protein (P < 0.001). In primary Singaporean breast cancers, 9 of 44 specimens showed undetectable levels of RUNX3 by immunohistochemistry. In 35 of 44 tumors, however, low levels of RUNX3 protein were present. Remarkably, in each case, protein was mislocalized to the cytoplasm. In primary tumors, hypermethylation of RUNX3 was observed in 23 of 44 cases (52%) and was undetectable in matched adjacent normal breast epithelium. Mislocalization of the protein, with or without methylation, seems to account for RUNX3 inactivation in the vast majority of the tumors. In in vitro and in vivo assays, RUNX3 behaved as a growth suppressor in breast cancer cells. Stable expression of RUNX3 in MDA-MB-231 breast cancer cells led to a more cuboidal phenotype, significantly reduced invasiveness in Matrigel invasion assays, and suppressed tumor formation in immunodeficient mice. This study provides biological and mechanistic insights into RUNX3 as the key member of the family that plays a role in breast cancer. Frequent protein mislocalization and methylation could render RUNX3 a valuable marker for early detection and risk assessment.

Luteinizing Hormone-Induced RUNX1 Regulates the Expression of Genes in Granulosa Cells of Rat Periovulatory Follicles

The LH surge induces specific transcription factors that regulate the expression of a myriad of genes in periovulatory follicles to bring about ovulation and luteinization. The present study determined 1) the localization of RUNX1, a nuclear transcription factor, 2) regulation of Runx1 mRNA expression, and 3) its potential function in rat ovaries. Up-regulation of mRNA and protein for RUNX1 is detected in preovulatory follicles after human chorionic gonadotropin (hCG) injection in gonadotropin-treated immature rats as well as after the LH surge in cycling animals by in situ hybridization and immunohistochemical and Western blot analyses. The regulation of Runx1 mRNA expression was investigated in vitro using granulosa cells from rat preovulatory ovaries. Treatments with hCG, forskolin, or phorbol 12 myristate 13-acetate stimulated Runx1 mRNA expression. The effects of hCG were reduced by inhibitors of protein kinase A, MAPK kinase, or p38 kinase, indicating that Runx1 expression is regulated by the LH-initiated activation of these signaling mediators. In addition, hCG-induced Runx1 mRNA expression was inhibited by a progesterone receptor antagonist and an epidermal growth factor receptor tyrosine kinase inhibitor, whereas amphiregulin stimulated Runx1 mRNA expression, demonstrating that the expression is mediated by the activation of the progesterone receptor and epidermal growth factor receptor. Finally, knockdown of Runx1 mRNA by small interfering RNA decreased progesterone secretion and reduced levels of mRNA for Cyp11a1, Hapln1, Mt1a, and Rgc32. The hormonally regulated expression of Runx1 in periovulatory follicles, its involvement in progesterone production, and regulation of preovulatory gene expression suggest important roles of RUNX1 in the periovulatory process.

Spreading of methylation within RUNX3 CpG island in gastric cancer

RUNX3 is a novel tumor suppressor gene that is frequently silenced by promoter hypermethylation in gastric cancer. The methylation status of multiple regions within the RUNX3 promoter CpG island (3,478 bp) was examined in gastric cancer cell lines, primary gastric cancers and non-neoplastic gastric mucosa to clarify how methylation spreads within the CpG island. The critical regions for RUNX3 silencing were evaluated by analysis of cell lines. The most 5' region of the CpG island was methylated in 90% (9/10) of gastric cancer cell lines, 96% (43/45) of primary gastric cancers and in 96% (43/45) of non-neoplastic gastric mucosa. The frequencies of methylation were less near the transcription start site and were 40% (4/10) in cell lines, 53% (24/45) in primary gastric cancers and 11% (5/45) in non-neoplastic gastric mucosa, where methylation was proven to be critical for gene silencing. Thus, hypermethylation initially occurs at the most 5' region of the RUNX3 CpG island and spreads to the transcription start site before ultimately shutting down RUNX3 mRNA expression. The detection of hypermethylation at multiple regions within the RUNX3 CpG island may be useful in the diagnosis and risk assessment of gastric cancer.

The Transcription Factors RUNX1/AML1 and RUNX3/AML2 Protect Bcr-Abl-Transformed B-Cells from Imatinib Induced Apoptosis.

The Abl-tyrosine kinase inhibitor Imatinib efficiently targets the Bcr-Abl kinase and produces major cytogenetic responses in most patients with chronic phase CML. In contrast, patients with advanced stage CML or Ph+ ALL frequently become refractory to Imatinib treatment. Resistance arises predominantly from point mutations in the Abl-kinase region, Bcr-Abl amplification or clonal evolution due to secondary genetic aberrations. To screen for genes contributing to clonal evolution, we have employed retroviral insertional mutagenesis in a murine CML/ALL model to identify potential candidate genes leading to Imatinib resistance. We found proviral insertions near the RUNX3/AML2 promoter in Imatinib resistant leukemic clones, leading to upregulation of RUNX3 mRNA expression. To analyze the effects of high RUNX3 levels on Imatinib response, we expressed RUNX3 in a Bcr-Abl-transformed murine pre-B-cell line. Significantly, whereas there was no effect on Imatinib-mediated proliferation inhibition, the cells displayed a marked reduction of apoptosis. A RUNX3R193A mutant carrying a mutation in the DNA-binding domain of RUNX3 did not protect from apoptosis, indicating that transcriptional regulation by RUNX3 was required to induce the anti-apoptotic effects. To allow for a controlled activation of RUNX transcriptional activity and to extend our analysis to other members of the RUNX family of transcription factors, we constructed 4-OH-tamoxifen (TAM) inducible RUNX3/AML2- and RUNX1/AML1-Estrogen receptor (ER) fusion proteins. These fusion proteins readily translocated from the cytoplasm into the nucleus and activated a RUNX-dependent TCRß-luciferase construct upon addition of TAM. Using these constructs, we could demonstrate that activation of RUNX3 as well as RUNX1 protected Bcr-Abl-transformed Ba/F3 cells from Imatinib-induced apoptosis. Furthermore, we found that RUNX1 mRNA levels were significantly upregulated in patients with Ph+ ALL upon resistance development. Taken together, our data indicate that elevated RUNX3 or RUNX1 levels may contribute to Imatinib resistance in Bcr-Abl expressing leukemic cells.

Downregulation of tumor suppressor Runx genes in malignant cutaneous melanoma

7531 Background: Frequent genomic alterations of the 6p and 1p chromosomal regions have been demonstrated in cutaneous melanoma and are thought to be sites of candidate tumor suppressor genes. Two transcription factors with proposed tumor suppressor activity, Runx2 and Runx3, map to 6p21 and 1p36 chromosomal loci, respectively. Runx genes play important regulatory roles in tissue development and tumor progression. We hypothesized that Runx2 and Runx3 expression will be altered during melanoma progression. Methods: Eleven established human metastatic melanoma cell lines, a normal melanocyte cell line, and 27 paraffin-embedded lymph node metastases from stage III melanoma patients were assessed. Runx2 and Runx3 mRNA expression was assessed by quantitative real-time RT-PCR. RNA was extracted and purified from cell lines and paraffin-embedded tissues. Runx2 and Runx3 mRNA expression levels were measured relative to a housekeeping gene to ensure RNA integrity and compared to the mRNA levels detected in normal melanocytes. Results: Runx2 and Runx3 were differentially expressed among the 11 melanoma lines and 27 tumor specimens. For both the Runx2 and Runx3 genes, the mean mRNA expression was significantly over 1000-fold decreased in 11 of 11 (100%, p<0.001) lines compared to melanocytes, and in 11 of 11 (100%, p<0.001) lines over 100-fold compared to melanocytes, respectively. Mean mRNA levels of Runx2 and Runx3 in melanoma tumors had a 1.4- and 6-fold decrease, respectively, in expression compared to normal controls (p< 0.01 and p< 0.0001). Conclusions: These preliminary studies are the first report of Runx2 and Runx3 transcription factor downregulation in metastatic melanoma. These two Runx genes are candidate tumor suppressor genes and may play important roles in melanoma tumor development and progression. No significant financial relationships to disclose.

Decreased expression and frequent allelic inactivation of the RUNX3 gene at 1p36 in human hepatocellular carcinoma

Alteration in transforming growth factor-beta signaling pathway is one of the main causes of hepatocellular carcinoma (HCC). The human runt-related transcription factor 3 gene (RUNX3) is an important component of this pathway. RUNX3 locus 1p36 is commonly deleted in a variety of human cancers, including HCC. Therefore, we examined genetic and epigenetic alterations of RUNX3 in human HCC. Five HCC cell lines and 41 patients with HCC were investigated in this study. We examined the expression of RUNX3 mRNA, methylation status of RUNX3 promoter region, loss of heterozygosity (LOH) at 1p36, and mutation analysis. These results were compared with clinicopathological data. Promoter hypermethylation was detected in four (80%) of five HCC cell lines and 31 (75.6%) of 41 HCC tissues, confirmed by sequence of bisulfite-treated DNA. LOH was detected in 14 (37.8%) of 37 HCC. By comparison with clinicopathological data, hypermethylation was more common in hepatitis C virus antibody and formation of capsule-positive cases, and decrease of expression was correlated strongly with advanced stage and LOH-detected cases. Hypermethylation and LOH appear to be common mechanisms for inactivation of RUNX3 in HCC. Therefore, RUNX3 may be an important tumor suppressor gene related to hepatocarcinogenesis.

Frequent loss of RUNX3 gene expression in human bile duct and pancreatic cancer cell lines.

RUNX3, a Runt domain transcription factor involved in TGF-beta signaling, is a candidate tumor-suppressor gene localized in 1p36, a region commonly deleted in a wide variety of human tumors, including those of the stomach, bile duct, and pancreas. Recently, frequent inactivation of RUNX3 has been demonstrated in human gastric carcinomas. In this study, to examine the involvement of RUNX3 abnormalities in tumorigenesis of bile duct as well as pancreatic cancers, we investigated not only the expression but also methylation status of RUNX3 in 10 human bile duct and 12 pancreatic cancer cell lines. Seven (70%) of the bile duct and nine (75%) of the pancreatic cancer cell lines exhibited no expression of RUNX3 by both Northern blot analysis and the reverse transcriptase polymerase chain reaction. All of the 16 cell lines that did not express RUNX3 also showed methylation of the promoter CpG island of the gene, whereas the six cell lines that showed RUNX3 expression were not methylated or only partially methylated in the RUNX3 promoter region. Moreover, treatment with the methylation inhibitor 5'-aza-2'-deoxycitidine activated RUNX3 mRNA expression in all of 16 cancer cell lines that originally lacked RUNX3 expression. Finally, hemizygous deletion of RUNX3, as detected by fluorescence in situ hybridization, was found in 15 of the 16 cancer cell lines that lacked RUNX3 expression. These data suggest that the inactivation of RUNX3 plays an important role in bile duct and pancreatic carcinogenesis, and that methylation is a common mechanism by which the gene is inactivated.

Erythrophagocytosis by leukemic blasts in AML-M5a with t(8;16)(q13;p13) chromosome abnormality

Valproic acid (VPA) exhibits important pharmacological properties but has been reported to trigger side effects, notably on the hematological system. We previously reported that VPA affects hematopoietic homeostasis by inhibiting erythroid differentiation and promoting myeloid and megakaryocyte differentiation. Here, we analyzed the effect of VPA on regulatory factors involved in erythro-megakaryocytic differentiation pathways, including transcription factors and microRNAs (miRs). We demonstrate that VPA inhibited erythroid differentiation in erythropoietin (Epo)-stimulated TF1 leukemia cells and CD34+/hematopoietic stem cells (HSCs) and in aclacinomycin-(Acla)-treated K562 cells. Mir-144/451 gene expression was decreased in all erythroid and megakaryocyte models in correlation with GATA-1 inhibition. In Epo-stimulated CD34+/HSCs, VPA induced the expression of the ETS family transcription factors PU.1, ETS-1, GABP-α, Fli-1 and GATA-2, which are all known to be negative regulators of erythropoiesis, while it promoted the megakaryocytic pathway. PU.1 and ETS-1 expression were induced in correlation with miR-155 inhibition; however, the GATA-1/PU.1 interaction was promoted. Using megakaryoblastic Meg-01 cells, we demonstrated that VPA induced megakaryocyte morphological features and CD61 expression. GATA-2 and miR-27a expression were increased in correlation with a decrease in RUNX1 mRNA expression, suggesting megakaryocyte differentiation. Finally, by using valpromide and the Class I HDACi MS-275, we validated that the well-described HDACi activity of VPA is not required in the inhibitory effect on erythropoiesis. Overall, this report shows that VPA modulates the erythro-megakaryocytic differentiation program through regulatory micro-networks involving GATA and ETS transcription factors and miRNAs, notably the GATA-1/miR-144/451 axis.

Inhibition of the growth and metastasis of human colon cancer by restoration of RUNX3 expression in cancer cells

Recent studies demonstrated an epigenetic inactivation of the runt-related transcription factor 3 (RUNX3) gene in human colon cancer. However, it remains unclear whether RUNX3 is tumor suppressive in colon cancer and, if so, the underlying molecular mechanisms of this activity are still unknown. In the present study, we sought to determine the level of RUNX3 expression in human colon tumor specimens and used an animal model of colon cancer to determine the impact of RUNX3 expression on tumor growth and metastasis. First, we analyzed RUNX3 expression in 83 human colon tumor specimens using immunohistochemical, reverse transcriptase-polymerase chain reaction, and Western blot analysis. RUNX3 mRNA and protein expression levels were consistently lower in tumor tissue specimens than in matched normal colon tissue specimens. Also, restoration of RUNX3 expression in colon cancer cells using gene transfer inhibited colon tumor growth and metastasis in our animal model, which was consistent with inhibition of colon tumor growth in vitro. Collectively, our clinical and experimental data support the notion that RUNX3 is a tumor suppressor in human colon cancer.