Transcriptional regulation of the tumor suppressor FHL2 by p53 in human kidney and liver cells.

Four and a Half LIM protein 2 (FHL2) is a LIM domain only protein that is able to form various protein complexes and regulate gene transcription. Recent findings showed that FHL2 is a potential tumor suppressor gene that was down-regulated in hepatocellular carcinoma (HCC). Moreover, FHL2 can bind to and activate the TP53 promoter in hepatic cells. In this study, the activity of the two promoters of FHL2, 1a and 1b, were determined in the human embryonic kidney cell line HEK293 and the activation of these two promoters by p53 was investigated. Our results showed that the 1b promoter has a higher activity than the 1a promoter in HEK 293 cells but the 1a promoter is more responsive to the activation by p53 when compared with the 1b promoter. The regulation of FHL2 by p53 was further confirmed in liver cells by the overexpression of p53 in Hep3B cells and the knockdown of p53 in HepG2 cells. Combining promoter activity results of truncated mutants and predictions by bioinformatics tools, a putative p53 binding site was found in the exon 1a of FHL2 from +213 to +232. The binding between the p53 protein and the putative p53 binding site was then validated by the ChIP assay. Furthermore, the expression of FHL2 and TP53 were down-regulated in majority of HCC tumour samples (n = 41) and significantly correlated (P = 0.026). Finally, we found that the somatic mutation 747 (G→T), a hot spot mutation of the TP53 gene, is potentially associated with a higher expression of FHL2 in HCC tumour samples. Taken together, this is the first in-depth study about the transcriptional regulation of FHL2 by p53.

Identification of FHL2-regulated genes in liver by microarray and bioinformatics analysis.

FHL2 is a LIM domain protein that is able to form various protein complexes and regulate gene transcription. Recent findings showed that FHL2 is a potential tumor suppressor gene that was down-regulated in hepatocellular carcinoma. In the present study, microarray profiling of gene expression was performed to identify the genes regulated by FHL2 in mouse livers. The differentially expressed genes were further analyzed by bioinformatics tools including DAVID, KEGG, and STRING. Our data illustrate that FHL2 affects genes involved in various functions including signal transduction, responses to external stimulus, cancer-related pathways, cardiovascular function and regulation of actin cytoskeleton. Moreover, a network of differentially expressed genes identified in this study and known FHL2-interacting proteins was constructed. Then, genes identified by bioinformatics tools and most functional relevant to FHL2 were selected for further validation. Finally, the differential expression of Ar, Id3, Inhbe, Alas1, Bcl6, Pparδ, Angptl4, and Erbb4 were confirmed by quantitative real-time PCR. In summary, we have established a database of genes that are potentially regulated by FHL2 and these genes should be future targets for the elucidation of functional roles of FHL2.

Effect of avian influenza A H5N1 infection on the expression of microRNA-141 in human respiratory epithelial cells.

BACKGROUND: Avian influenza remains a serious threat to human health. The consequence of human infection varies markedly among different subtypes of avian influenza viruses. In addition to viral factors, the difference in host cellular response is likely to play a critical role. This study aims at elucidating how avian influenza infection perturbs the host's miRNA regulatory pathways that may lead to adverse pathological events, such as cytokine storm, using the miRNA microarray approach. RESULTS: The results showed that dysregulation of miRNA expression was mainly observed in highly pathogenic avian influenza A H5N1 infection. We found that miR-21*, miR-100*, miR-141, miR-574-3p, miR-1274a and miR1274b were differentially expressed in response to influenza A virus infection. Interestingly, we demonstrated that miR-141, which was more highly induced by H5N1 than by H1N1 (p < 0.05), had an ability to suppress the expression of a cytokine - transforming growth factor (TGF)-ß2. This was supported by the observation that the inhibitory effect could be reversed by antagomiR-141. CONCLUSIONS: Since TGF-ß2 is an important cytokine that can act as both an immunosuppressive agent and a potent proinflammatory molecule through its ability to attract and regulate inflammatory molecules, and previous report showed that only seasonal influenza H1N1 (but not the other avian influenza subtypes) could induce a persistent expression of TGF-ß2, we speculate that the modulation of TGF-ß2 expression by different influenza subtypes via miR-141 might be a critical step for determining the outcome of either normal or excessive inflammation progression.

p63 regulates cell proliferation and cell cycle progression­associated genes in stromal cells of giant cell tumor of the bone.

Giant cell tumor of bone (GCT) is a destructive neoplasm of uncertain etiology that affects the epiphyseal ends of long bones in young adults. GCT stromal cells (GCTSCs) are the primary neoplastic cells of this tumor and are the only proliferating cell component in long-term culture, which recruits osteoclast-like giant cells that eventually mediate bone destruction. The oncogenesis of GCT and factors driving the neoplastic stromal cells to proliferate extensively and pause at an early differentiation stage of pre-osteoblast lineage remain unknown. Overexpression of p63 was observed in GCTSCs and there is growing evidence that p63 is involved in oncogenesis through different mechanisms. This study aimed to understand the specific role of p63 in cell proliferation and oncogenesis of GCTSCs. We confirmed p63 expression in the mononuclear cells in GCT by immunohistochemical staining. By real-time PCR analysis, we showed a higher level (>15­fold) of TAp63 expression in GCTSCs compared to that in mesenchymal stem cells. Furthermore, we observed that knockdown of the p63 gene by siRNA transfection greatly reduced cell proliferation and induced cell cycle arrest at S phase in GCTSCs. We found that the mRNA expression of CDC2 and CDC25C was substantially suppressed by p63 knockdown at 24-72 h. Moreover, p63 was found to be recruited on the regulatory regions of CDC2 and CDC25C, which contain p53-responsive elements. In summary, our data suggest that p63 regulates GCTSC proliferation by binding to the CDC2 and CDC25C p53-REs, which may inhibit the p53 tumor suppressor activity and contribute to GCT tumorigenesis.

The LIM-only protein FHL2 regulates interleukin-6 expression through p38 MAPK mediated NF-κB pathway in muscle cells.

Interleukin 6 (IL-6) is pleiotropic cytokine playing an important role in inflammatory response. Other than classical immune tissues, IL-6 is also produced in muscle cells under specific conditions. Four-and-a-half LIM-only protein 2 (FHL2) is preferentially expressed in skeletal and cardiac muscle cells compared to other tissues indicating it has an important role in skeletal muscle and cardiovascular system. In this report, the regulation of IL-6 by FHL2 in muscle cells was investigated. We demonstrated that FHL2 overexpression increased IL-6 mRNA level and its protein secretion in skeletal myoblasts. In contrast, the IL-6 secretion was significantly decreased after FHL2-knockdown by siRNA in response to TNFα stimulation. We further showed that FHL2-mediated induction of IL-6 was regulated by the activation of IL-6 promoter through stimulating NF-κB and p38 MAPK signaling pathway. Our results further illustrated the molecular mechanisms of IL-6 production, which provides new insights in the roles of FHL2 in post-injury inflammation or cytoprotection of muscle cells.

The G1613A mutation in the HBV genome affects HBeAg expression and viral replication through altered core promoter activity.

Infection of hepatitis B virus (HBV) causes acute and chronic hepatitis and is closely associated with the development of cirrhosis and hepatocellular carcinoma (HCC). Previously, we demonstrated that the G1613A mutation in the HBV negative regulatory element (NRE) is a hotspot mutation in HCC patients. In this study, we further investigated the functional consequences of this mutation in the context of the full length HBV genome and its replication. We showed that the G1613A mutation significantly suppresses the secretion of e antigen (HBeAg) and enhances the synthesis of viral DNA, which is in consistence to our clinical result that the G1613A mutation associates with high viral load in chronic HBV carriers. To further investigate the molecular mechanism of the mutation, we performed the electrophoretic mobility shift assay with the recombinant RFX1 protein, a trans-activator that was shown to interact with the NRE of HBV. Intriguingly, RFX1 binds to the G1613A mutant with higher affinity than the wild-type sequence, indicating that the mutation possesses the trans-activating effect to the core promoter via NRE. The trans-activating effect was further validated by the enhancement of the core promoter activity after overexpression of RFX1 in liver cell line. In summary, our results suggest the functional consequences of the hotspot G1613A mutation found in HBV. We also provide a possible molecular mechanism of this hotspot mutation to the increased viral load of HBV carriers, which increases the risk to HCC.

Characterization of human FHL2 transcript variants and gene expression regulation in hepatocellular carcinoma.

The four-and-a-half LIM protein 2 (FHL2) was originally identified to be expressed abundantly in the heart, as well as in a wide range of tissues demonstrated in various studies. The human FHL2 gene expresses different transcripts which are known to differ only in the 5'UTR region. However, little is known about the functional role of the different variants and the mechanism of gene regulation. In the present study, we characterized the different alternative spliced transcripts of FHL2 by in silico analysis and RT-PCR analysis. A novel transcript variant was identified. The FHL2 gene produces transcripts by different 5' exons, which may be responsible for tissue-specific regulation. To study the mechanism of FHL2 gene regulation, the potential promoter region was investigated. We have identified a functional promoter region upstream of the transcription start site. Deletion mutation analysis of 5' flanking region showed that the fragment from -138 to +292 bp have positive regulatory effect. We identified the binding sites of Pax-5/ZF5 in this region and found that Pax-5 and ZF5 expression in HCC samples had a significant positive correlation with FHL2 expression, suggesting a possible role for these transcription factors in the regulation of FHL2 expression.