Involvement of activator protein 1 complexes in the epithelium-specific activation of the laminin gamma2-chain gene promoter by hepatocyte growth factor (scatter factor)

Laminin Beta 2 Is Localized at the Sites of Blood-Brain Barrier and Its Disruption Is Associated With Increased Vascular Permeability, Histochemical, and Transcriptomic Study

Heterotrimeric extracellular matrix proteins laminins are mostly deposited at basal membranes and are important in repair and neoplasia. Here, we localize laminin beta 2 (LAMB2) at the sites of blood-brain barrier (BBB). Microvasculature (MV) of normal brain is endowed with complete LAMB2 coverage. In contrast, its cognate protein laminin beta 1 (LAMB1) is absent in MV of normal brain but emerges at the sprouting tip of a growing vessels. Similarly, vascular proliferation in high-grade gliomas (HGG) is accompanied by marked overexpression of LAMB1, whereas LAMB2 shows deficient deposition. We find that many brain pathologies with presence of post-gadolinium enhancement (PGE) on magnetic resonance imaging (MRI) show disruption of LAMB2 vascular ensheathment. Inhibition of vascular endothelial growth factor signaling in HGG blocks angiogenesis, suppresses PGE in HGG, prevents expression of LAMB1, and restores LAMB2 vascular coverage. Analysis of single-cell RNA sequencing (scRNA-seq) databases shows that in quiescent brain LAMB2 is predominantly expressed by BBB-associated pericytes (PCs) and endothelial cells (ECs), whereas neither cell types produce LAMB1. In contrast, in HGG, both LAMB1 and 2 are overexpressed by endothelial precursor cells, a phenotypically unique immature group, specific to proliferating hyperplastic MV.

The mechanism of BUD13 m6A methylation mediated MBNL1-phosphorylation by CDK12 regulating the vasculogenic mimicry in glioblastoma cells

Vasculogenic mimicry (VM) is an endothelium-independent tumor microcirculation that provides adequate blood supply for tumor growth. The presence of VM greatly hinders the treatment of glioblastoma (GBM) with anti-angiogenic drugs. Therefore, targeting VM formation may be a feasible therapeutic strategy for GBM. The research aimed to evaluate the roles of BUD13, CDK12, MBNL1 in regulating VM formation of GBM. BUD13 and CDK12 were upregulated and MBNL1 was downregulated in GBM tissues and cells. Knockdown of BUD13, CDK12, or overexpression of MBNL1 inhibited GBM VM formation. METTL3 enhanced the stability of BUD13 mRNA and upregulated its expression through m6A methylation. BUD13 enhanced the stability of CDK12 mRNA and upregulated its expression. CDK12 phosphorylated MBNL1, thereby regulating VM formation of GBM. The simultaneous knockdown of BUD13, CDK12, and overexpression of MBNL1 reduced the volume of subcutaneously transplanted tumors in nude mice and prolonged the survival period. Thus, the BUD13/CDK12/MBNL1 axis plays a crucial role in regulating VM formation of GBM and provides a potential target for GBM therapy.

Upregulation of LAMB1 via ERK/c-Jun Axis Promotes Gastric Cancer Growth and Motility

Gastric cancer is the fifth most common cancer worldwide with a poor survival rate. Therefore, it is important to identify predictive and prognostic biomarkers of gastric cancer. Laminin subunit beta 1 (LAMB1) is involved in attachment, migration, and organization during development, and its elevated expression has been associated with several cancers. However, the role and mechanism of LAMB1 in gastric cancer remains unknown. Here, we determined that LAMB1 is upregulated in gastric cancer tissues and contributes to cell growth and motility. Using a public database, we showed that LAMB1 expression was significantly upregulated in gastric cancer compared to normal tissues. LAMB1 was also found to be associated with poor prognosis in patients with gastric cancer. Overexpression of LAMB1 elevated cell proliferation, invasion, and migration; however, knockdown of LAMB1 decreased these effects in gastric cancer cells. U0126, an extracellular signal-regulated kinase (ERK) inhibitor, regulated the expression of LAMB1 in gastric cancer cells. Additionally, we showed that c-Jun directly binds to the LAMB1 promoter as a transcription factor and regulates its gene expression via the ERK pathway in gastric cancer cells. Therefore, our study indicates that LAMB1 promotes cell growth and motility via the ERK/c-Jun axis and is a potential biomarker and therapeutic target of gastric cancer.

Identification of TNF-α-responsive promoters and enhancers in the intestinal epithelial cell model Caco-2

The Caco-2 cell line is one of the most important in vitro models for enterocytes, and is used to study drug absorption and disease, including inflammatory bowel disease and cancer. In order to use the model optimally, it is necessary to map its functional entities. In this study, we have generated genome-wide maps of active transcription start sites (TSSs), and active enhancers in Caco-2 cells with or without tumour necrosis factor (TNF)-α stimulation to mimic an inflammatory state. We found 520 promoters that significantly changed their usage level upon TNF-α stimulation; of these, 52% are not annotated. A subset of these has the potential to confer change in protein function due to protein domain exclusion. Moreover, we locate 890 transcribed enhancer candidates, where ∼50% are changing in usage after TNF-α stimulation. These enhancers share motif enrichments with similarly responding gene promoters. As a case example, we characterize an enhancer regulating the laminin-5 γ2-chain (LAMC2) gene by nuclear factor (NF)-κB binding. This report is the first to present comprehensive TSS and enhancer maps over Caco-2 cells, and highlights many novel inflammation-specific promoters and enhancers.

Abnormal Wnt and PI3Kinase signaling in the malformed intestine of lama5 deficient mice

Laminins are major constituents of basement membranes and are essential for tissue homeostasis. Laminin-511 is highly expressed in the intestine and its absence causes severe malformation of the intestine and embryonic lethality. To understand the mechanistic role of laminin-511 in tissue homeostasis, we used RNA profiling of embryonic intestinal tissue of lama5 knockout mice and identified a lama5 specific gene expression signature. By combining cell culture experiments with mediated knockdown approaches, we provide a mechanistic link between laminin α5 gene deficiency and the physiological phenotype. We show that laminin α5 plays a crucial role in both epithelial and mesenchymal cell behavior by inhibiting Wnt and activating PI3K signaling. We conclude that conflicting signals are elicited in the absence of lama5, which alter cell adhesion, migration as well as epithelial and muscle differentiation. Conversely, adhesion to laminin-511 may serve as a potent regulator of known interconnected PI3K/Akt and Wnt signaling pathways. Thus deregulated adhesion to laminin-511 may be instrumental in diseases such as human pathologies of the gut where laminin-511 is abnormally expressed as it is shown here.

Autocrine transforming growth factor-{beta}1 activation mediated by integrin {alpha}V{beta}3 regulates transcriptional expression of laminin-332 in Madin-Darby canine kidney epithelial cells

Laminin (LM)-332 is an extracellular matrix protein that plays a structural role in normal tissues and is also important in facilitating recovery of epithelia from injury. We have shown that expression of LM-332 is up-regulated during renal epithelial regeneration after ischemic injury, but the molecular signals that control expression are unknown. Here, we demonstrate that in Madin-Darby canine kidney (MDCK) epithelial cells LM-332 expression occurs only in subconfluent cultures and is turned-off after a polarized epithelium has formed. Addition of active transforming growth factor (TGF)-β1 to confluent MDCK monolayers is sufficient to induce transcription of the LM α3 gene and LM-332 protein expression via the TGF-β type I receptor (TβR-I) and the Smad2-Smad4 complex. Significantly, we show that expression of LM-332 in MDCK cells is an autocrine response to endogenous TGF-β1 secretion and activation mediated by integrin αVβ3 because neutralizing antibodies block LM-332 production in subconfluent cells. In confluent cells, latent TGF-β1 is secreted apically, whereas TβR-I and integrin αVβ3 are localized basolaterally. Disruption of the epithelial barrier by mechanical injury activates TGF-β1, leading to LM-332 expression. Together, our data suggest a novel mechanism for triggering the production of LM-332 after epithelial injury.

The role of the basement membrane as a modulator of intestinal epithelial-mesenchymal interactions

Intestinal development is a process of continuous dynamic bidirectional crosstalk between epithelial and underlying mesenchymal cells. This crosstalk is mediated by well-dissected signaling pathways. Another crucial actor in the epithelio-mesenchymal interactions is the stromal microenvironment, which is composed of extracellular matrix molecules. Among them, the basement membrane (BM) molecules are secreted by the epithelium and mesenchyme in a complementary manner. These molecules signal back to the cells via the integrins or other specific receptors. In this review, we mainly focus on the BM molecules, particularly laminins. The major BM molecules are organized in a complex molecular network, which is highly variable among organs. Cell culture, coculture, and grafting models have been of great interest in understanding the importance of these molecules. Mouse gene ablation of laminin chains are interesting models, which often lead to embryonic death and are frequently accompanied by compensatory processes. Overall, the BM molecules have a crucial role in the careful maintenance of intestinal homeostasis.

Divergent mechanisms underlie Smad4-mediated positive regulation of the three genes encoding the basement membrane component laminin-332 (laminin-5)

BACKGROUND

Functional inactivation of the tumor suppressor Smad4 in colorectal and pancreatic carcinogenesis occurs coincident with the transition to invasive growth. Breaking the basement membrane (BM) barrier, a prerequisite for invasive growth, can be due to tumor induced proteolytic tissue remodeling or to reduced synthesis of BM molecules by incipient tumor cells. Laminin-332 (laminin-5), a heterotrimeric BM component composed of alpha 3-, beta 3- and gamma 2-chains, has recently been identified as a target structure of Smad4 and represents the first example for expression control of an essential BM component by a tumor and invasion suppressor. Biochemically Smad4 is a transmitter of signals of the TGFbeta superfamily of cytokines. We have reported previously, that Smad4 functions as a positive transcriptional regulator of constitutive and of TGFbeta-induced transcription of all three genes encoding Laminin-332, LAMA3, LAMB3 and LAMC2.

METHODS

Promoter-reporter constructs harboring 4 kb upstream regions, each of the three genes encoding Laminin-322 as well as deletion and mutations constructs were established. Promoter activities and TGFbeta induction were assayed through transient transfections in Smad4-negative human cancer cells and their stable Smad4-positive derivatives. Functionally relevant binding sites were subsequently confirmed through chromatin immunoprecipitation.

RESULTS

Herein, we report that Smad4 mediates transcriptional regulation through three different mechanisms, namely through Smad4 binding to a functional SBE site exclusively in the LAMA3 promoter, Smad4 binding to AP1 (and Sp1) sites presumably via interaction with AP1 family components and lastly a Smad4 impact on transcription of AP1 factors. Whereas Smad4 is essential for positive regulation of all three genes, the molecular mechanisms are significantly divergent between the LAMA3 promoter as compared to the LAMB3 and LAMC2 promoters.

CONCLUSION

We hypothesize that this divergence in modular regulation of the three promoters may lay the ground for uncoupled regulation of Laminin-332 in Smad4-deficient tumor cells in response to stromally expressed cytokines acting on budding tumor cells.

Mesenchymal cells contribute to the synthesis and deposition of the laminin-5 gamma2 chain in the invasive front of oral squamous cell carcinoma

Tumour progression in oral squamous cell carcinoma (OSCC) is associated with a reorganisation of extracellular matrix. Laminin-5 (Ln-5) plays an important role for tumour migration and shows an increased expression in areas of direct tumour/stroma interactions. We have previously shown stromal spot like Ln-5/gamma2 chain deposits distant from the basement membrane region. In this study we have analysed which cell type is responsible for Ln-5/gamma2 chain synthesis in situ. Furthermore, we studied its spatial relation to TGF-beta1 as well as the Ln-5 modulating enzymes matrix metalloproteinase (MMP) 2, membrane type-1 (MT1-) MMP and bone morphogenetic protein (BMP-) 1 by different techniques including triple immunofluorescence labelling and in situ hybridisation in OSCC. We found that the stromal spot-like Ln-5 deposits occurred in the invasive front in the vicinity of mesenchymal cells and vessel structures. In particular, not only carcinoma cells but also mesenchymal cells were shown to express the Ln-5/gamma2 chain mRNA. Moreover, stromal Ln-5 deposits showed a spatial association with TGF-beta1 as well as with MT1-MMP and BMP-1. Based on these findings we suggest that mesenchymal cells contribute to the promotion of tumour cell migration as well as vessel formation in OSCC by providing and organising promigratory Ln-5 fragments.

Quantitative analysis of laminin 5 gene expression in human keratinocytes

To examine the expression of laminin 5 genes (LAMA3, LAMB3, and LAMC2) encoding the three polypeptide chains alpha3, beta3, and gamma2, respectively, in human keratinocytes, we developed novel quantitative polymerase chain reaction (PCR) methods utilizing Thermus aquaticus DNA polymerase, specific primers, and fluorescein-labeled probes with the ABI PRISM 7700 sequence detector system. Gene expression levels of LAMA3, LAMB3, and LAMC2 and glyceraldehyde-3-phosphate dehydrogenase were quantitated reproducibly and sensitively in the range from 1 x 10(2) to 1 x 10(8) gene copies. Basal gene expression level of LAMB3 was about one-tenth of that of LAMA3 or LAMC2 in human keratinocytes, although there was no clear difference among immunoprecipitated protein levels of alpha3, beta3, and gamma2 synthesized in radio-labeled keratinocytes. Human serum augmented gene expressions of LAMA3, LAMB3, and LAMC2 in human keratinocytes to almost the same extent, and this was associated with an increase of the laminin 5 protein content measured by a specific sandwich enzyme-linked immunosorbent assay. These results demonstrate that the absolute mRNA levels generated from the laminin 5 genes do not determine the translated protein levels of the laminin 5 chains in keratinocytes, and indicate that the expression of the laminin 5 genes may be controlled by common regulation mechanisms.

Laminin-5 in epithelial tumour invasion

Laminin-5 (LN-5), consisting of alpha3-, beta3-, and gamma2-chains, is a component of the cell adhesion complex containing hemidesmosomes and anchoring fibrils. This protein is a major constituent of the extracellular matrix and has recently proved to be an invasion marker for epithelial cells in many immunohistochemical surveys, indicating that it is frequently expressed in the invading edges of epithelial tumour cells. Additionally, intracellular accumulation of monomeric gamma2-chains has been widely observed in the invasive carcinoma cells, but its mechanism was not entirely understood. Epithelial carcinoma cells prefer to adhere onto the LN-5-rich basement membranes using the specific integrins as receptors. Induction of cell migration is an important function of LN-5 and the enhanced activity is observed in its truncated form after proteolytic shedding of the N-terminal fragments of gamma2-chains. This processing was demonstrated to be mediated mainly by several kinds of matrix metalloproteinases. The degraded fragments of gamma2-chains, released from invading carcinomas, can be immunodetected in biological fluids and potentially utilized in the clinical diagnosis of various epithelial cancers. Here, we summarize the previous clinical investigations of LN-5 in epithelial tumour progression, and also discuss what it can regulate in the cell physiological events.

Converging signals synergistically activate the LAMC2 promoter and lead to accumulation of the laminin gamma 2 chain in human colon carcinoma cells

The trimeric extracellular matrix molecule laminin-5 and its constituent chains (alpha 3, beta 3, gamma 2) are normally not detectable intracellularly in intestinal epithelial cells but the laminin gamma 2 chain can be detected in cancer cells at the invasive front of a subset of colon carcinomas. These cells are subjected to cytokines such as transforming growth factor beta 1 (TGF-beta 1) and hepatocyte growth factor (HGF), produced by the tumour cells or by the surrounding stromal cells. The purpose of the present work was to investigate whether TGF-beta 1 and HGF, known to stimulate the LAMC2 gene encoding the laminin gamma 2 chain, might synergize to activate the LAMC2 promoter, and to identify the promoter elements involved. We find evidence for synergy between TGF-beta and HGF with respect to laminin gamma 2 chain expression and promoter activation and demonstrate that this requires the 5' activator protein-1 (AP-1) element of the promoter and an additional upstream element which is also responsive to co-expression of the Smad3 protein from the TGF-beta signalling pathway. The transcripts encoding the other laminin-5 chains are not synergistically activated by HGF and TGF-beta. Thus the synergistic activation of the LAMC2 gene is mediated via different cis-elements and results in an overproduction of the laminin gamma 2 chain relative to the other laminin-5 constituent chains. This difference may explain why laminin gamma 2 chains accumulate in the cells at the invasive front of colon carcinomas.

Activation time course of activator protein-1 and effect of proline dithiocarbamate during ischemia-reperfusion in rat skeletal muscle

Activator protein 1 (AP-1) is thought to play an important role in the expression of genes expressed in response to ischemia-reperfusion injury. In this report, the activation of AP-1 in rat skeletal muscle during reperfusion after a 4-hour ischemic period was studied. AP-1 activation displayed a biphasic pattern, showing peak activities at 1 hour after perfusion and from 4 hours to 12 hours after perfusion. Inhibition of AP-1 activation was investigated using a potent nuclear factor kappa B inhibitor, proline dithiocarbamate (Pro-DTC). AP-1 binding activity at 1 hour of reperfusion was significantly reduced (29.0 +/- 10.1% SEM; p < 0.05) after intravenous administration of Pro-DTC (n = 7 animals in each group). Further elucidation of the role of AP-1 is warranted in hopes of developing strategies to reduce the deleterious effects of ischemia-reperfusion injury.

Identification of downstream target genes of latent membrane protein 1 in nasopharyngeal carcinoma cells by suppression subtractive hybridization

Nasopharyngeal carcinoma (NPC) is a common cancer in Southern China and is closely associated with infection of Epstein-Barr virus (EBV). The EBV encoded latent membrane protein 1 (LMP1) is frequently detected in NPC and may play a role in its pathogenesis. Previous studies have shown that LMP1 transformed rodent fibroblasts and altered growth properties in B cells and epithelial cells. However, the pathological role of LMP1 in NPC cells is still poorly understood. In order to investigate the downstream target genes of LMP1 in NPC cells, suppression subtractive hybridization was used to clone and identify the genes differentially expressed in a LMP1 expressing NPC cell line, CNE-2. Two subtractive cDNA libraries were constructed: one enriched for the genes upregulated by LMP1 and one was for the genes downregulated by LMP1. A total of 192 clones were screened by reverse Northern blotting. Fourteen of them were confirmed to be overexpressed while eight of them were suppressed. The upregulation of integrin alpha6, laminin 5gamma2, TAP1 and downregulation of p54nrb, RACK1 and p66Shc were further confirmed in three sets of LMP1 expressing NPC cell lines. The expression profiles of differentially expressed genes identified in this study suggest a role of LMP1 in promotion of cell survival and facilitation of tumor invasion.