The four and a half LIM-only protein 2 regulates liver homeostasis and contributes to carcinogenesis

Overexpression of FHL1 suppresses papillary thyroid cancer proliferation and progression via inhibiting Wnt/β-catenin pathway

PURPOSE

The four and a half LIM domain protein 1 (FHL1) has been found to act as a tumor suppressor in several cancers. However, the clinical and functional significance, as well as underlying molecular mechanisms of FHL1 in papillary thyroid cancer (PTC) are largely unknown.

METHODS

Bioinformatics analyses, qRT-PCR and Western blotting were used to investigate the expression of FHL1 in PTC. Cell proliferation was measured using CCK8, Edu, colony formation, and flow cytometry assays. Cell migration and invasion were examined by wound healing and Transwell assays. qRT-PCR, Western blot, immunofluorescence and Top/Fop reporter assays were performed to assess the underlying mechanisms.

RESULTS

FHL1 expression was significantly downregulated in PTC. FHL1 downregulation negatively correlated with stage, T classification, and N classification of the patients. The downregulation of FHL1 is associated with poor prognosis. Overexpression of FHL1 inhibited PTC cells' proliferation, invasion, migration and Wnt/β-catenin pathway activity. LiCl partially restored the inhibitory effects of FHL1 on aggressive phenotypes and Wnt/β-catenin pathway activity of PTC cells.

CONCLUSION

FHL1 is downregulated in PTC and its expression is associated with better clinical outcomes for patients with the disease. FHL1 acts as a tumor suppressor via, at least partially, suppressing Wnt/β-catenin pathway.

MiR-3682-3p promotes esophageal cancer progression by targeting FHL1 and activating the Wnt/β-catenin signaling pathway

BACKGROUND

Esophageal cancer (EC) is highly ranked among all cancers in terms of its incidence and mortality rates. MicroRNAs (miRNAs) are considered to play key regulatory parts in EC. Multiple research studies have indicated the involvement of miR-3682-3p and four and a half LIM domain protein 1 (FHL1) in the achievement of tumors. The aim of this research was to clarify the significance of these genes and their possible molecular mechanism in EC.

METHODS

Data from a database and the tissue microarray were made to analyze the expression and clinical significance of miR-3682-3p or FHL1 in EC. Reverse transcription quantitative PCR and Western blotting were used to detect the expression levels of miR-3682-3p and FHL1 in EC cells. CCK8, EdU, wound healing, Transwell, flow cytometry, and Western blotting assays were performed to ascertain the biological roles of miR-3682-3p and FHL1 in EC cells. To confirm the impact of miR-3682-3p in vivo, a subcutaneous tumor model was created in nude mice. The direct interaction between miR-3682-3p and FHL1 was demonstrated through a luciferase assay, and the western blotting technique was employed to assess the levels of crucial proteins within the Wnt/β-catenin pathway.

RESULTS

The noticeable increase in the expression of miR-3682-3p and the decrease in the expression of FHL1 were observed, which correlated with a negative impact on the patients' overall survival. Upregulation of miR-3682-3p expression promoted the growth and metastasis of EC, while overexpression of FHL1 partially reversed these effects. Finally, miR-3682-3p motivates the Wnt/β-catenin signal transduction by directly targeting FHL1.

CONCLUSION

MiR-3682-3p along the FHL1 axis activated the Wnt/β-catenin signaling pathway and thus promoted EC malignancy.

The roles of FHL2 in cancer

LIM domain protein 2, also known as LIM protein FHL2, is a member of the LIM-only family. Due to its LIM domain protein characteristics, FHL2 is capable of interacting with various proteins and plays a crucial role in regulating gene expression, cell growth, and signal transduction in muscle and cardiac tissue. In recent years, mounting evidence has indicated that the FHLs protein family is closely associated with the development and occurrence of human tumors. On the one hand, FHL2 acts as a tumor suppressor by down-regulating in tumor tissue and effectively inhibiting tumor development by limiting cell proliferation. On the other hand, FHL2 serves as an oncoprotein by up-regulating in tumor tissue and binding to multiple transcription factors to suppress cell apoptosis, stimulate cell proliferation and migration, and promote tumor progression. Therefore, FHL2 is considered a double-edged sword in tumors with independent and complex functions. This article reviews the role of FHL2 in tumor occurrence and development, discusses FHL2 interaction with other proteins and transcription factors, and its involvement in multiple cell signaling pathways. Finally, the clinical significance of FHL2 as a potential target in tumor therapy is examined.

High FHL2 mRNA expression and its prognostic value in lung cancer

BACKGROUND

Lung cancer is the most frequent cancer globally with a high number of cancer-related deaths. The 4-and-a-half LIM domain protein 2 (FHL2) is an oncogenic gene, which promotes the proliferation, invasion, and metastasis of cancer cells. In this study, we aimed to demonstrate that lung cancer patients with high FHL2 expression have worse overall survival (OS) and relapse-free survival (RFS).

METHODS

TCGA was used to study FHL2 mRNA expression. Nomograms were used to predict the relationship between FHL2 expression levels and survival. The qRT-PCR was used to detect the FHL2 expression in lung cancer cells. In vitro experiments including CCK-8 assay, wound healing, and Transwell assay were performed.

RESULTS

This study comprised RNA-Seq gene expression data and clinical features for 1018 lung cancer patients. FHL2 was found to be overexpressed in lung cancer tissues. FHL2 demonstrated moderate diagnostic ability for lung cancer (AUC = 0.857). Kaplan-Meier curves and Cox regression analysis revealed the higher FHL2 expression with the poorer OS and RFS (P < 0.001). The nomogram results indicated that FHL2 could be used to predict the survival of lung cancer patients. GSEA analysis results show that high expression of FHL2 is related to glycolysis and unfolded protein reflection. FHL2 was highly expressed in lung cancer cells and related to their proliferation, migration, and invasion ability.

CONCLUSIONS

The high expression level of FHL2 in lung cancer can be used as an independent predictor of prognosis in clinical practice.

How (Epi)Genetic Regulation of the LIM-Domain Protein FHL2 Impacts Multifactorial Disease

Susceptibility to complex pathological conditions such as obesity, type 2 diabetes and cardiovascular disease is highly variable among individuals and arises from specific changes in gene expression in combination with external factors. The regulation of gene expression is determined by genetic variation (SNPs) and epigenetic marks that are influenced by environmental factors. Aging is a major risk factor for many multifactorial diseases and is increasingly associated with changes in DNA methylation, leading to differences in gene expression. Four and a half LIM domains 2 (FHL2) is a key regulator of intracellular signal transduction pathways and the FHL2 gene is consistently found as one of the top hyper-methylated genes upon aging. Remarkably, FHL2 expression increases with methylation. This was demonstrated in relevant metabolic tissues: white adipose tissue, pancreatic β-cells, and skeletal muscle. In this review, we provide an overview of the current knowledge on regulation of FHL2 by genetic variation and epigenetic DNA modification, and the potential consequences for age-related complex multifactorial diseases.

FHL3 Contributes to EMT and Chemotherapy Resistance Through Up-Regulation of Slug and Activation of TGFβ/Smad-Independent Pathways in Gastric Cancer

BACKGROUND

Gastric cancer presents high risk of metastasis and chemotherapy resistance. Hence, it is important to understand the mechanisms of gastric cancer distant metastasis and chemotherapeutic resistance. Our previous study has revealed Four and a Half LIM Domains 3 (FHL3) plays as a binding partner of Glycogen Synthase Kinase 3 Beta (GSK3β), promoted tumor metastasis in pancreatic cancer. However, the role of FHL3 in gastric cancer still remains unclear.

METHODS

TCGA database and clinical samples are used for exploring the role of FHL3 in disease progression and prognosis. Oxaliplatin (OHP) resistance cell lines were established to study the role of FHL3 in chemotherapy resistance. The experiments about cell proliferation, apoptosis, and metastasis were performed to measure the chemotherapy effects of sh-FHL3 on gastric cancer cell lines and in vivo. That FHL3 changed the EMT phenotype was verified by western blot. Finally, we explored the mechanism of FHL3-mediated EMT and chemotherapy resistance.

RESULTS

mRNA and protein level of FHL3 were significantly up-regulated in gastric cancer tissues when compared with adjacent tissue. FHL3 higher expression is always accompanied with higher TNM stage and worse overall survival. FHL3 over-expressed could lead to OHP resistance. Knockdown of FHL3 slightly inhibited the cell growth, while it obviously sensitized the chemotherapy in vivo and in vitro. In addition, down-regulation of FHL3 increased the mesenchymal markers, such as Slug, Snail, Twist Family BHLH Transcription Factor 1 (Twist1), and Vimentin, while it decreased the epithelial marker E-cadherin. Cell and animal experiments also proved that down-regulation of FHL3 can decrease cancer cell metastasis. For mechanism study, FHL3 knockdown down-regulated the expression level of Mitogen-Activated Protein Kinase (MAPK)/Extracellular Regulated Protein Kinase (ERK) pathway and Transforming Growth Factor-β (TGFβ)/Phosphatidylinositol 3-Kinase (PI3K)/protein kinase B(Akt)/GSK3β-(Ring Finger Protein 146) RNF146/ubiquitin pathway. FHL3 competitively bonded the ubiquitin complex (Slug/GSK3β/RNF146) with Slug and inhibited ubiquitination of Slug. Mesenchymal phenotype cells hold higher level of Multidrug Resistance Gene1 (MDR1), and the FHL3 knockdown reverts the MDR1 in this type cell.

CONCLUSION

FHL3 high expression contributed to EMT and chemotherapy resistance via MAPK, and PI3K pathways were activated. FHL3 competitively bonded the ubiquitin complex with Slug, resulting in the up-regulation of Slug and leading to metastasis of gastric cancer.

Four-And-A-Half LIM-Domain Protein 2 (FHL2) Deficiency Aggravates Cholestatic Liver Injury

Cholestasis occurs in different clinical circumstances and leads to severe hepatic disorders. The four-and-a-half LIM-domain protein 2 (FHL2) is a scaffolding protein that modulates multiple signal transduction pathways in a tissue- and cell context-specific manner. In this study, we aimed to gain insight into the function of FHL2 in cholestatic liver injury. FHL2 expression was significantly increased in the bile duct ligation (BDL) model in mice. In Fhl2-deficient (Fhl2-ko) mice, BDL caused a more severe portal and parenchymal inflammation, extended portal fibrosis, higher serum transaminase levels, and higher pro-inflammatory and pro-fibrogenic gene expression compared to wild type (wt) mice. FHL2 depletion in HepG2 cells with siRNA resulted in a higher expression of the bile acid transporter Na⁺-taurocholate cotransporting polypeptide (NTCP) gene. Furthermore, FHL2-depleted HepG2 cells showed higher expression of markers for oxidative stress, lower B-cell lymphoma 2 (Bcl2) expression, and higher Bcl2-associated X protein (BAX) expression after stimulation with deoxycholic acid (DCA). In hepatic stellate cells (HSCs), FHL2 depletion caused an increased expression of TGF-β and several pro-fibrogenic matrix metalloproteinases. In summary, our study shows that deficiency in FHL2 aggravates cholestatic liver injury and suggests FHL2-mediated effects on bile acid metabolisms and HSCs as potential mechanisms for pronounced hepatocellular injury and fibrosis.

Role of FHL2 in digestive system malignancies

FHL2 is a scaffold protein that regulates signal transduction and gene transcription, and it has typical structural features of FHL proteins. Each FHL protein contains four half-LIM domains, and different LIM domains can bind to different proteins, which can activate or inhibit the activities of transcription factors such as P53 and serum response factors, and then influences the development of tumors. Previous studies have found that FHL2 has a complex biological role in tumorigenesis, and may promote or suppress tumor development in different types of tumors. In this article, we review the role of FHL2 in digestive system malignancies.

miR-340-FHL2 axis inhibits cell growth and metastasis in ovarian cancer

Although increasing evidence indicated that deregulation of microRNAs (miRNAs) contributed to tumor initiation and progression, but little is known about the biological role of miR-340 in ovarian cancer (OC). In this study, we found that miR-340 expression was downregulated in OC tissues compared with its expression in normal ovarian epithelium and endometrium, and treatment with 5-aza-2′-deoxycytidine (5-Aza-dC) or trichostatin A (TSA) increased miR-340 expression in OC cells. In addition, ectopic miR-340 expression inhibited OC cell growth and metastasis in vitro and in vivo. Four and a half LIM domains protein 2 (FHL2) was confirmed as a direct target of miR-340 and silencing FHL2 mimicked the effects of miR-340 in OC cells. Further mechanistic study showed that miR-340 inhibited the Wnt/β-catenin pathway by targeting FHL2, as well as downstream cell cycle and epithelial-to-mesenchymal transition (EMT) signals in OC cells. Moreover, the greatest association between miR-340 and FHL2 was found in 481 ovarian serous cystadenocarcinoma tissues via pan-cancer analysis. Finally, we revealed that lower miR-340 or higher FHL2 was associated with poor OC patient outcomes. Our findings indicate that the miR-340-FHL2 axis regulates Wnt/β-catenin signaling and is involved in tumorigenesis in OC. Therefore, manipulating the expression of miR-340 or its target genes is a potential strategy in OC therapy.

FHL2 interacts with iASPP and impacts the biological functions of leukemia cells

iASPP is an inhibitory member of apoptosis-stimulating proteins of p53 (ASPP) family, which inhibits p53-dependent apoptosis. iASPP was highly expressed in acute leukemia, inhibited leukemia cells apoptosis and promoted leukemogenesis. In order to clarify its mechanism, a yeast two-hybrid screen was performed and FHL2 was identified for the first time as one of the binding proteins of iASPP. FHL2 was highly expressed in K562 and Kasumi-1 cells. FHL2 and iASPP interacted with each other and co-localized in both nucleus and cytoplasm. Either FHL2 or iASPP silenced could reduce cell proliferation, induce cell cycle arrest at G0/G1 phase, and increase cell apoptosis. Western blot analysis showed that the level of p21 and p27 increased, CDK4, E2F1, Cyclin E and anti-apoptotic proteins Bcl-2 and Bcl-xL reduced. Interestingly, when FHL2 was knocked down, the protein expression level of iASPP also decreased. Similarly, the expression of FHL2 would reduce when iASPP was silenced. These results indicated that FHL2 might be a novel potential target for acute myelocytic leukemia treatment.

Distinct role of nuclear receptor corepressor 1 regulated de novo fatty acids synthesis in liver regeneration and hepatocarcinogenesis in mice

It is urgent that the means to improve liver regeneration (LR) be found, while mitigating the concurrent risk of hepatocarcinogenesis (HCG). Nuclear receptor corepressor 1 (NCoR1) is a co-repressor of nuclear receptors, which regulates the expression level of metabolic genes; however, little is known about its potential contribution for LR and HCG. Here, we found that liver-specific NCoR1 knockout in mice (NCoR1^Δhep ) dramatically enhances LR after partial hepatectomy and, surprisingly, blocks the process of diethylnitrosamine (DEN)-induced HCG. Both RNA-sequencing and metabolic assay results revealed improved expression of Fasn and Acc2 in NCoR1^Δhep mice, suggesting the critical role of de novo fatty acid synthesis (FAS) in LR. Continual enhanced de novo FAS in NCoR1^Δhep mice resulted in overwhelmed adenosine triphosphate ATP and nicotinamide adenine dinucleotide phosphate (NADPH) consumption and increased mitochondrial reactive oxygen species production, which subsequently attenuated HCG through inducing apoptosis of hepatocytes at an early stage after DEN administration.

CONCLUSION

NCoR1 functions as a negative modulator for hepatic de novo FAS and mitochondria energy adaptation, playing distinct roles in regeneration or carcinogenesis. (Hepatology 2018;67:1071-1087).

FHL2 interacts with EGFR to promote glioblastoma growth

Four-and-a-half LIM protein2 (FHL2) is a member of the LIM-only protein family, which plays a critical role in tumorigenesis. We previously reported that FHL2 is upregulated and plays an oncogenic role in glioblastoma (GBM), the most common and aggressive brain tumor. GBM is also marked by amplification of the epidermal growth factor receptor (EGFR) gene and its mutations, of which EGFRvIII is the most common and functionally significant. Here we report that FHL2 physically interacts with the wild-type EGFR and its mutated EGFRvIII form in GBM cells. Expression of FHL2 caused increased EGFR and EGFRvIII protein levels and this was due to an increase in protein stability rather than an increase in EGFR mRNA expression. In contrast, FHL2 knockdown using RNA interference reduced EGFR and EGFRvIII protein expression and the phosphorylation levels of EGFR and AKT. Consistent with these features, EGFR expression was significantly lower in mouse FHL2-null astrocytes, where reintroduction of FHL2 was able to restore EGFR levels. Using established GBM cell lines and patient-derived neurosphere lines, FHL2 silencing markedly induced cell apoptosis in EGFRvIII-positive cells. Targeting FHL2 significantly prevented EGFRvIII-positive GBM tumor growth in vivo. FHL2 expression also positively correlated with EGFR expression in GBM samples from patients. Taken together, our results demonstrate that FHL2 interacts with EGFR and EGFRvIII to increase their levels and this promotes glioma growth, representing a novel mechanism that may be therapeutically targetable.

Autophagy Induced FHL2 Upregulation Promotes IL-6 Production by Activating the NF-κB Pathway in Mouse Aortic Endothelial Cells after Exposure to PM2.5

Epidemiological and clinical studies have increasingly shown that fine particulate matter (PM2.5) is associated with cardiovascular morbidity and mortality, which share the common feature of PM2.5-induced vascular inflammation; however, the underlying mechanisms of how PM2.5 triggers increased inflammatory response in vascular endothelial cells are not well understood. After treating mouse aortic endothelial cells (MAECs) with different concentrations of PM2.5, we assessed interleukin (IL)-6 and four and a half LIM domains 2 (FHL2) expression in cell supernatant by enzyme-linked immunosorbent assay and Western blot, respectively, as well as activation of nuclear factor (NF)-κB and immune-response signaling pathways. Additionally, changes in pathway activation, IL-6 expression, and autophagy were evaluated under PM2.5 exposure, following FHL2 knockdown with small interfering RNA. Our results indicated that PM2.5 exposure induced FHL2 expression and IL-6 secretion, as well as activation of pathways associated with immune response. Additionally, following FHL2 knockdown, the activation of NF-κB-related pathways and IL-6 secretion was inhibited under PM2.5 exposure, although the Akt- and p38-signaling pathways were not affected. Furthermore, PM2.5 exposure induced autophagy, whereas autophagy inhibition eventually inhibited PM2.5-induced FHL2 expression. These findings suggested a novel link between autophagy induced FHL2 upregulation and IL-6 production in MAECs under PM2.5 exposure.

LIM-Only Protein FHL2 Is a Negative Regulator of Transforming Growth Factor β1 Expression

Transforming growth factor β1 (TGF-β1) is a master cytokine in many biological processes, including tissue homeostasis, epithelial-to-mesenchymal transition, and wound repair. Here, we report that four and a half LIM-only protein 2 (FHL2) is a critical regulator of TGF-β1 expression. Devoid of a DNA-binding domain, FHL2 is a transcriptional cofactor that plays the role of coactivator or corepressor, depending on the cell and promoter contexts. We detected association of FHL2 with the TGF-β1 promoter, which showed higher activity in Fhl2^-/- cells than in wild-type (WT) cells in a reporter assay. Overexpression of FHL2 abrogates the activation of the TGF-β1 promoter, whereas the upregulation of TGF-β1 gene transcription correlates with reduced occupancy of FHL2 on the promoter. Moreover, ablation of FHL2 facilitates recruitment of RNA polymerase II on the TGF-β1 promoter, suggesting that FHL2 may be involved in chromatin remodeling in the control of TGF-β1 gene transcription. Enhanced expression of TGF-β1 mRNA and cytokine was evidenced in the livers of Fhl2^-/- mice. We tested the in vivo impact of Fhl2 loss on hepatic fibrogenesis that involves TGF-β1 activation. Fhl2^-/- mice developed more severe fibrosis than their WT counterparts. These results demonstrate the repressive function of FHL2 on TGF-β1 expression and contribute to the understanding of the TGF-β-mediated fibrogenic response.

Deficiency of multidrug resistance 2 contributes to cell transformation through oxidative stress

Multidrug resistance 2 (Mdr2), also called adenosine triphosphate-binding cassette B4 (ABCB4), is the transporter of phosphatidylcholine (PC) at the canalicular membrane of mouse hepatocytes, which plays an essential role for bile formation. Mutations in human homologue MDR3 are associated with several liver diseases. Knockout of Mdr2 results in hepatic inflammation, liver fibrosis and hepatocellular carcinoma (HCC). Whereas the pathogenesis in Mdr2 (-/-) mice has been largely attributed to the toxicity of bile acids due to the absence of PC in the bile, the question of whether Mdr2 deficiency per se perturbs biological functions in the cell has been poorly addressed. As Mdr2 is expressed in many cell types, we used mouse embryonic fibroblasts (MEF) derived from Mdr2 (-/-) embryos to show that deficiency of Mdr2 increases reactive oxygen species accumulation, lipid peroxidation and DNA damage. We found that Mdr2 (-/-) MEFs undergo spontaneous transformation and that Mdr2 (-/-) mice are more susceptible to chemical carcinogen-induced intestinal tumorigenesis. Microarray analysis in Mdr2-/- MEFs and cap analysis of gene expression in Mdr2 (-/-) HCCs revealed extensively deregulated genes involved in oxidation reduction, fatty acid metabolism and lipid biosynthesis. Our findings imply a close link between Mdr2 (-/-) -associated tumorigenesis and perturbation of these biological processes and suggest potential extrahepatic functions of Mdr2/MDR3.

LIM-only protein FHL2 critically determines survival and radioresistance of pancreatic cancer cells

Numerous factors determine the current poor prognosis of pancreatic ductal adenocarcinoma (PDAC). One of the greatest challenges to overcome is treatment resistance. Among a large repertoire of intrinsic resistance mechanisms, integrin-mediated cell adhesion to extracellular matrix (ECM) has been identified to be fundamental. Coalesced in focal adhesion complexes, integrins, receptor tyrosine kinases, protein kinases and adapter proteins mediate prosurvival signaling. Four and a half LIM domains protein 2 (FHL2) is one of these adapter proteins, which operates through protein-protein interactions and shows tumor-specific expression. Based on this, we investigated FHL2 expression in PDAC specimens and three-dimensionally grown cell lines and how FHL2 mechanistically contributes to cell survival, cell cycling and radiation resistance. PDAC exhibited a significantly increased and heterogeneous FHL2 expression. Upon FHL2 depletion, pancreatic cancer cell lines showed significantly decreased cell survival, proliferation and radioresistance as well as enhanced apoptosis and MEK/ERK signaling and cyclin D1, E, A and B1 expression were strongly induced. Targeting of FHL2 and MEK1 was similarly effective than FHL2 depletion alone, suggesting MEK1 as a downstream signaling mediator of FHL2. Taken together, our results provide evidence for the importance of the focal adhesion protein FHL2 in pancreatic cancer cell survival, proliferation and radiosensitivity.

Enhanced FHL2 and TGF-β1 Expression Is Associated With Invasive Growth and Poor Survival in Malignant Melanomas

OBJECTIVES

This study examines the expression and the role of four-and-a-half LIM domains protein 2 (FHL2) and transforming growth factor β1 (TGF-β1) in human malignant melanoma. It is determined whether both proteins influence melanoma survival time.

METHODS

We analyzed the immunohistochemical staining intensities of FHL2 and TGF-β1 in normal skin and in 50 malignant melanomas with different mutation status (BRAF-V600E, NRAS codon 61 mutation, and wild type). Survival data were available for 45 cases.

RESULTS

In melanocytes of nonneoplastic human skin, FHL2 expression was absent. In contrast, 38 (76%) of 50 melanomas showed strong cytoplasmic and partly nuclear FHL2 expression. At the invasion front, cytoplasmic TGF-β1 staining was observed in 32 (64%) of 50 melanomas, and a correlation of FHL2 and TGF-β1 staining intensities was detectable. In follow-up analyses, enhanced FHL2 and TGF-β1 staining intensities in the tumor invasion front were associated with poor survival.

CONCLUSIONS

Enhanced FHL2 and TGF-β1 expression is correlated with poor survival in human malignant melanoma. Protumorigenic effects of autocrine TGF-β1 secretion might be exerted by induction of FHL2 expression in melanoma cells. Since melanomas treated with targeted therapies often do not show sufficient response rates, inhibition of FHL2 and/or TGF-β1 might be a promising therapeutic approach.

Tumoral expression of nuclear cofactor FHL2 is associated with lymphatic metastasis in sporadic but not in HNPCC-associated colorectal cancer

BACKGROUND

Four and a half LIM domain protein-2 (FHL2) is part of the focal adhesion structures modulating cell motility. FHL2 may translocate into the nucleus serving as a transcriptional cofactor binding several transcription factors. Overexpression of FHL2 has been linked to cancer progression in various neoplasias. The aim of the present study was to determine, whether FHL2's function as nuclear cofactor plays a prognostic role in invading tumor cells of sporadic and HNPCC-associated colorectal cancer (CRC).

DESIGN

Immunohistochemical staining intensity of nuclear FHL2 was quantified by Remmele score analysing 47 sporadic and 42 HNPCC-associated colorectal cancers. Analysis was restricted to carcinoma cells of the tumoral invasion front.

RESULTS

Confocal microscopy detected nuclear expression of FHL2 in colon cancer cells and absence of nuclear FHL2 signal in normal colon enterocytes. In colon cancer, nuclear FHL2 expression was predominantly observed in low-differentiated, often mucinous tumor areas. 42.55% of sporadic and 54.76% of HNPCC-associated CRC showed enhanced (Remmele score 6-12) nuclear FHL2 expression in the carcinoma cells of the tumoral advancing edge. Enhanced nuclear FHL2 expression was significantly linked to lymphatic metastasis in sporadic CRC (p=0.0197) and almost reached significance in HNPCC-associated CRC (p=0.0545). In contrast, nuclear FHL2 expression was neither associated with hematogenic metastasis in sporadic (p=0.7087) nor in HNPCC-associated colorectal cancer (p=0.3007).

CONCLUSIONS

We recently demonstrated that enhanced nuclear FHL2 expression in tumor stroma of sporadic colon cancer is associated with lymphatic metastasis. The results of the present study indicate a synergistic effect of nuclear cofactor FHL2 in tumor cells as well as in peritumoral stroma cells promoting lymphatic metastasis in sporadic CRC. As HNPCC-associated tumors did not show a significant association between tumoral nuclear FHL2 expression and lymphatic metastasis we speculate, that the intensive lymphocytic immune response in HNPCC precludes a direct contact of tumor cells and stromal cells resulting in reduced lymphatic spread.

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.

LIM-only protein FHL2 activates NF-κB signaling in the control of liver regeneration and hepatocarcinogenesis

Four-and-a-half LIM-only protein 2 (FHL2) is an important mediator in many signaling pathways. In this study, we analyzed the functions of FHL2 in nuclear factor κB (NF-κB) signaling in the liver. We show that FHL2 enhanced tumor necrosis factor (TNF) receptor-associated factor 6 (TRAF6) activity in transcriptional activation of NF-κB targets by stabilizing the protein. TRAF6 is a binding partner of FHL2 and an important component of the Toll-like receptor-NF-κB pathway. Knockdown of FHL2 in 293-hTLR4/MD2-CD14 cells impaired lipopolysaccharide (LPS)-induced NF-κB activity, which regulates expression of inflammatory cytokines. Indeed, FHL2(-/-) macrophages showed significantly reduced production of TNF and interleukin 6 (IL-6) following LPS stimulation. TNF and IL-6 are the key cytokines that prime liver regeneration after hepatic injury. Following partial hepatectomy, FHL2(-/-) mice exhibited diminished induction of TNF and IL-6 and delayed hepatocyte regeneration. In the liver, NF-κB signaling orchestrates inflammatory cross talk between hepatocytes and hepatic immune cells that promote chemical hepatocarcinogenesis. We found that deficiency of FHL2 reduced susceptibility to diethylnitrosamine-induced hepatocarcinogenesis, correlating with the activator function of FHL2 in NF-κB signaling. Our findings demonstrate FHL2 as a positive regulator of NF-κB activity in liver regeneration and carcinogenesis and highlight the importance of FHL2 in both hepatocytes and hepatic immune cells.

Identification and analysis of expressed genes using a cDNA library from rat thymus during regeneration following cyclophosphamide-induced T cell depletion

Understanding the mechanisms of thymus regeneration is necessary for designing strategies to enhance host immunity when immune function is suppressed due to T cell depletion. In this study, expressed sequence tag (EST) analysis was performed following generation of a regenerating thymus cDNA library to identify genes expressed in thymus regeneration. A total of 1,000 ESTs were analyzed, of which 770 (77%) matched to known genes, 178 matched to unknown genes (17.8%) and 52 (5.2%) did not match any known sequences. The ESTs matched to known genes were grouped into eight functional categories: gene/protein synthesis (28%), metabolism (24%), cell signaling and communication (17%), cell structure and motility (6%), cell/organism defense and homeostasis (6%), cell division (3%), cell death/apoptosis (2%), and unclassified genes (14%). Based on the data of RT-PCR analysis, the expression of TLP, E2IG2, pincher, Paip2, TGF-β1, 4-1BB and laminin α3 genes was increased during thymus regeneration. These results provide extensive molecular information, for the first time, on thymus regeneration indicating that the regenerating thymus cDNA library may be a useful source for identifying various genes expressed during thymus regeneration.

Deficiency in four and one half LIM domain protein 2 (FHL2) aggravates liver fibrosis in mice

BACKGROUND

Four and one half LIM domain protein 2 (FHL2) has been reported to be a key regulator in many cellular processes being associated with fibrogenesis such as cell migration and contraction. Moreover, hepatic FHL2 is involved in regulation pathways mediating proliferation and cell death machineries. We here investigated the role of FHL2 in the setting of experimental and clinical liver fibrosis.

METHODS

FHL2(-/-) and wild type (wt) mice were challenged with CCl(4). Fibrotic response was assessed by quantitative real time PCR (qRT-PCR) of fibrotic marker genes, measurement of hydroxyproline content and histological methods. Murine FHL2(-/-) and hepatic stellate cells (HSC) were isolated and investigated via immunofluorescence. Human fibrotic and normal liver samples were analysed immunohistochemically using antibodies directed against FHL2.

RESULTS

FHL2(-/-) mice displayed aggravated liver fibrosis compared to wt mice. However, immunofluorescence revealed no significant morphological changes in cultured FHL2(-/-) and wt myofibroblasts (MFB). In human liver samples, FHL2 was strongly expressed both in the nucleus and cytoplasm in MFB of fibrotic livers. In contrast, FHL2 expression was absent in normal liver tissue.

CONCLUSIONS

Deficiency of FHL2 results in aggravation of murine liver fibrosis. In human liver samples, FHL2 is expressed in activated HSCs and portal fibroblasts in human fibrotic livers, pointing to a central role of FHL2 for human hepatic fibrogenesis as well.