Characterization of the promoter for the mouse alpha 3 integrin gene

Transcription factor hlh-2/E/Daughterless drives expression of α integrin ina-1 during DTC migration in C. elegans

Integrins are involved in a vast number of cell behaviors due to their roles in adhesion and signaling. The regulation of integrin expression is of particular interest as a mechanism to drive developmental events and for the role of altered integrin expression profiles in cancer. Dynamic regulation of the expression of integrin receptors is required for the migration of the distal tip cell (DTC) during gonadogenesis in Caenorhabditis elegans. α integrin ina-1 is required for DTC motility, yet is up-regulated by an unknown mechanism. Analysis of the promoter for α integrin ina-1 identified two E-box sequences that are required for ina-1 expression in the DTC. Knockdown of transcription factor hlh-2, an established E-box binding partner and ortholog of E/Daughterless, prevented expression of a transcriptional fusion of the ina-1 promoter to RFP and blocked DTC migration. Similarly, knockdown of hlh-2 also prevented expression of a translational fusion of the genomic ina-1 gene to GFP while blocking DTC migration. Knockdown of HLH-2 binding partner MIG-24 also reduced ina-1 expression and DTC migration. Overall, these results show that the transcription factor hlh-2 is required for up-regulation of ina-1 at the onset of DTC migration.

Slug/SNAI2 regulates cell proliferation and invasiveness of metastatic prostate cancer cell lines

Many metastatic cancers recapitulate the epithelial-to-mesenchymal transition (EMT) resulting in enhanced cell motility and invasiveness. The EMT is regulated by several transcription factors, including the zinc finger protein SNAI2, also named Slug, which appears to exert additional functions during development and cancer progression. We have studied the function of SNAI2 in prostate cancer cells. Quantitative RT-PCR analysis showed strong SNAI2 expression particularly in the PC-3 and PC3-16 prostate carcinoma cell lines. Knockdown of SNAI2 by specific siRNA induced changes in EMT markers and inhibited invasion of both cell lines into a matrigel matrix. SNAI2 siRNA-treated cells did not tolerate detachment from the culture plates, likely at least in part due to downregulation of integrin alpha6beta4. SNAI2 knockdown disturbed the microtubular and actin cytoskeletons, especially severely in PC-3 cells, resulting in grossly enlarged, flattened, and sometimes multinuclear cells. Knockdown also decreased cell proliferation, with a prominent G0/G1 arrest in PC3-16. Together, our data imply that SNAI2 exerts strong effects on the cytoskeleton and adhesion of those prostate cancer cells that express it and is necessary for their proliferation and invasiveness.

Snail regulates cell survival and inhibits cellular senescence in human metastatic prostate cancer cell lines

The epithelial-mesenchymal transition (EMT) is regarded as an important step in cancer metastasis. Snail, a master regulator of EMT, has been recently proposed to act additionally as a cell survival factor and inducer of motility. We have investigated the function of Snail (SNAI1) in prostate cancer cells by downregulating its expression via short (21-mer) interfering RNA (siRNA) and measuring the consequences on EMT markers, cell viability, death, cell cycle, senescence, attachment, and invasivity. Of eight carcinoma cell lines, the prostate carcinoma cell lines LNCaP and PC-3 showed the highest and moderate expression of SNAI1 mRNA, respectively, as measured by quantitative RT-PCR. Long-term knockdown of Snail induced a severe decline in cell numbers in LNCaP and PC-3 and caspase activity was accordingly enhanced in both cell lines. In addition, suppression of Snail expression induced senescence in LNCaP cells. SNAI1-siRNA-treated cells did not tolerate detachment from the extracellular matrix, probably due to downregulation of integrin α6. Expression of E-cadherin, vimentin, and fibronectin was also affected. Invasiveness of PC-3 cells was not significantly diminished by Snail knockdown. Our data suggest that Snail acts primarily as a survival factor and inhibitor of cellular senescence in prostate cancer cell lines. We therefore propose that Snail can act as early driver of prostate cancer progression.

Identification and characterization of alternative promoters of zebrafish Rtn-4/Nogo genes in cultured cells and zebrafish embryos

In mammals, the Nogo family consists of Nogo-A, Nogo-B and Nogo-C. However, there are three Rtn-4/Nogo-related transcripts were identified in zebrafish. In addition to the common C-terminal region, the N-terminal regions of Rtn4-n/Nogo-C1, Rtn4-m/Nogo-C2 and Rtn4-l/Nogo-B, respectively, contain 9, 25 and 132 amino acid residues. In this study, we isolated the 5'-upstream region of each gene from a BAC clone and demonstrated that the putative promoter regions, P1-P3, are functional in cultured cells and zebrafish embryos. A transgenic zebrafish Tg(Nogo-B:GFP) line was generated using P1 promoter region to drive green fluorescent protein (GFP) expression through Tol2-mediated transgenesis. This line recapitulates the endogenous expression pattern of Rtn4-l/Nogo-B mRNA in the brain, brachial arches, eyes, muscle, liver and intestines. In contrast, GFP expressions by P2 and P3 promoters were localized to skeletal muscles of zebrafish embryos. Several GATA and E-box motifs are found in these promoter regions. Using morpholino knockdown experiments, GATA4 and GATA6 were involved in the control of P1 promoter activity in the liver and intestine, while Myf5 and MyoD for the control of P1 and P3 promoter activities in muscles. These data demonstrate that zebrafish Rtn4/Nogo transcripts might be generated by coupling mechanisms of alternative first exons and alternative promoter usage.

Laminin-511, inducer of hair growth, is down-regulated and its suppressor in hair growth, laminin-332 up-regulated in chemotherapy-induced alopecia

BACKGROUND

Chemotherapy-induced alopecia (CIA) has a devastating cosmetic effect, especially in the young. Recent data indicate that two major basement membrane components (laminin-332 and -511) of the skin have opposing effects on hair growth.

OBJECTIVE

In this study, we examined the role and localization of laminin-332 and -511 in CIA.

METHODS

We examined the expression of laminin-332 and -511 during the dystrophic catagen form of CIA induced in C57BL/6 mice by cyclophosphamide (CYP) treatment.

RESULTS

Our data indicate that both laminin-332 and its receptor alpha 6 beta 4 integrin are up-regulated (both quantitatively and spatially) after mid to late dystrophic catagen around the outer root sheath (ORS) in the lower third of hair follicles in CIA. This up-regulation also occurs at the transcriptional level. In contrast, laminin-511 is down-regulated after mid dystrophic catagen at the protein level, with transcriptional inactivation of laminin-511 occurring transiently at the early dystrophic catagen stage in both epidermal and ORS keratinocytes. Laminin-511 expression correlates with expression of alpha 3 integrin in CIA and we also demonstrate that laminin-511 can up-regulate the activity of the alpha 3 integrin promoter in cultured keratinocytes. Injection of a laminin-511 rich protein extract, but not recombinant laminin-332, in the back skin of mice delays hair loss in CYP-induced CIA.

CONCLUSIONS

We propose that abrupt hair loss in CIA is, at least in part, caused by down-regulation of laminin-511 and up-regulation of laminin-332 at the transcriptional and translational levels.

Enhanced expression of trophinin promotes invasive and metastatic potential of human gallbladder cancer cells

PURPOSE

To study effects of trophinin on the metastatic potential of human gallbladder cancer cells and its potential mechanism.

MATERIALS AND METHODS

Expression of trophinin in the highly metastatic GBC-SDH(i) cells was investigated by real time RT-PCR and western blot. Recombinant expression plasmid vector of the human trophinin gene was constructed and transfected into GBC-SD cells. Effects of trophinin on the invasion of GBC-SD cells were investigated by adhesion assay and invasion assay in vitro. The siRNA was used to down-regulate the expression of trophinin. Some genes related to the invasion and metastasis of cancer were determined by real time RT-PCR and western blot. The pulmonary metastasis regulated by trophinin was determined in the nude mice.

RESULTS

Overexpression of trophinin in GBC-SDH(i) cells was confirmed compared with its parental counterparts. Up-regulation of trophinin enhanced the in vitro invasion in the GBC-SD/TRO cells. The enhancement was associated with increasing integrin alpha3, MMP-7, MMP-9, and Ets-1 expression. The results were further demonstrated by RNA interference experiment in vitro. In in vivo study, we also demonstrated that trophinin-transfected gallbladder cancer cells had more pulmonary metastases than the vector-transfected one or its parental counterparts.

CONCLUSION

Overexpression of trophinin leads to a more invasive phenotype and metastatic potential in human gallbladder cancer, at least in part, through regulating integrin alpha3, MMP-7, MMP-9, and Ets-1 expression.

Identification of the functional role of AF1Q in the progression of breast cancer

A novel highly metastatic MDA-MB-231HM cells, derived from MDA-MB-231, was established in our institute. RT-PCR, real-time PCR and Western blot showed that AF1Q gene was differentially expressed between highly metastatic MDA-MB-231HM cells and its parental MDA-MB-231 cells. However, its molecular mechanisms in breast cancer metastasis remain to be characterized. To investigate the effects of AF1Q on the progression of human breast cancer cells, in the present study, recombinant expression plasmid vectors of the human AF1Q gene was transfected into MDA-MB-231 cells. We demonstrated that AF1Q overexpression enhanced the in vitro proliferation and invasive potential of breast cancer cells. Focused microarray analyses showed that 22 genes were differentially expressed between AF1Q transfected cells and its parental counterparts. Integrin alpha3, accompanied by up-regulation of Ets-1 and MMP-2, significantly enhanced the in vitro invasive potential of human breast cancer cells mediated by AF1Q. Estrogen-responsive ring finger protein gene (EFP), also played a role in the enhancement of in vitro proliferation of human breast cancer cells mediated by AF1Q, accompanied by down-regulation of 14-3-3delta. The association was ERalpha independent. These results were further demonstrated by RNA interference (RNAi) experiment in vitro. In in vivo study, we also demonstrated that AF1Q transfected breast cancer cells grew much faster and had more pulmonary metastases than vector-transfected or its parental counterparts. On the contrary, AF1Q knockdown cells grew slower and had less pulmonary metastasis. Similar effects of AF1Q on integrin alpha3, Ets-1, MMP-2, EFP, and 14-3-3delta expression observed in vitro studies were also found in the in vivo study. Taken together, these results provide functional evidences that overexpression of AF1Q leads to a more progression in human breast cancer, at least in part, through regulating the integrin alpha3, Ets-1, MMP-2, EFP, and 14-3-3delta expression.

Slug regulates integrin expression and cell proliferation in human epidermal keratinocytes

The human epidermis is a self-renewing epithelial tissue composed of several layers of keratinocytes. Within the epidermis there exists a complex array of cell adhesion structures, and many of the cellular events within the epidermis (differentiation, proliferation, and migration) require that these adhesion structures be remodeled. The link between cell adhesion, proliferation, and differentiation within the epidermis is well established, and in particular, there is strong evidence to link the process of terminal differentiation to integrin adhesion molecule expression and function. In this paper, we have analyzed the role of a transcriptional repressor called Slug in the regulation of adhesion molecule expression and function in epidermal keratinocytes. We report that activation of Slug, which is expressed predominantly in the basal layer of the epidermis, results in down-regulation of a number of cell adhesion molecules, including E-cadherin, and several integrins, including alpha3, beta1, and beta4. We demonstrate that Slug binds to the alpha3 promoter and that repression of alpha3 transcription by Slug is dependent on an E-box sequence within the promoter. This reduction in integrin expression is reflected in decreased cell adhesion to fibronectin and laminin-5. Despite the reduction in integrin expression and function, we do not observe any increase in differentiation. We do, however, find that activation of Slug results in a significant reduction in keratinocyte proliferation.

Collagen binding alpha2beta1 and alpha1beta1 integrins play contrasting roles in regulation of Ets-1 expression in human liver myofibroblasts

Activation of hepatic stellate cells from quiescence to myofibroblast-like cells (MFBs) is a pivotal event in hepatic fibrogenesis. Plastic-cultured stellate cells (an established in vitro model of the activated phenotype) recultured on Matrigel revert to quiescence. In the present study we analyzed the molecular mechanism underlying this process, focusing on the effect of collagen receptors alpha(2)beta(1) and alpha(1)beta(1) integrin signaling on the expression of Ets-1 transcription factor and its target gene MMP1 in cultured human MFBs. Cells grown in 3-dimensional (3D) substrates (Matrigel) or collagen type I gel) markedly upregulated Ets-1 and MMP1 messages, in comparison to cells cultured on plastic. A similar effect but less intense was mimicked by stimulation of alpha(2)beta(1) or blocking of alpha(1)beta(1) integrin in cells grown on plastic. We observed increased expression of MMP1 transcripts with parallel changes in MMP1 promoter activity, and in mRNA and protein levels of upstream transcription factors Ets-1 and c-Jun. Interference with alpha(2)beta(1) and alpha(1)beta(1) integrin function in cells cultured in a 3D collagen substrate resulted in an even greater effect. Morphologically, stimulation of alpha(2)beta(1) integrin resulted in formation of multicellular networks, probably by facilitation of cell migration. Thus, we report the novel observation that in cultured human MFBs reverting to quiescence, the expression of transcription factor Ets-1 and its downstream target MMP1 can be modulated by changes in the microenvironment, which are mediated, at least in part, by the balance between collagen receptor integrin alpha(2)beta(1) and alpha(1)beta(1) activities.

Characterization of the promoter for the alpha3 integrin gene in various tumor cell lines: roles of the Ets- and Sp-family of transcription factors

The alpha3beta1 integrin is an adhesion receptor for extracellular matrix proteins, including laminin isoforms, and plays crucial roles in the organization of epithelial and endothelial tissues. The aberrant expression of this adhesion molecule on tumor cells is associated with their invasive and metastatic potentials. In the present study, we analyzed the elements essential for alpha3 integrin gene expression in various tumor cell lines with different tissue origins by luciferase assay. An approximately 0.3 kb fragment of the 5'-flanking region of the mouse alpha3 integrin gene (-260/+84, relative to the major transcription start site) showed strong promoter activity in all six examined tumor cell lines. However, we found that these cell lines could be divided into two groups according to the level of dependency on the putative Ets-transcription factor binding motif located at -133. This motif was previously shown to be crucial for alpha3 integrin expression in MKN1 gastric carcinoma cells. The gene expression in one group of cell lines was upregulated mainly by the Ets motif, whereas that in the other group was less dependent on the Ets motif. We then postulated that additional regulatory elements were responsible for the expression of alpha3 integrin, and found that a GC-rich motif at -69 was another important element. An electrophoretic mobility shift assay using specific antibodies and a Western blot analysis of nuclear proteins revealed that the Sp3-transcription factor bound to this GC-rich motif. These results suggest that the Sp3 and Ets transcription factors cooperatively regulate alpha3 integrin gene expression and that the contribution of each element depends on the type of tumor cells.

Transforming growth factor-beta1 upregulates transcription of alpha3 integrin gene in hepatocellular carcinoma cells via Ets-transcription factor-binding motif in the promoter region

The invasive and metastatic potentials of hepatocellular carcinoma (HCC) are positively correlated with the expression level of alpha3beta1 integrin, a high-affinity adhesion receptor for laminin isoforms. Transforming growth factor (TGF)-beta1 stimulates non-invasive HCC cells to acquire invasive phenotypes in association with the enhanced expression of alpha3 integrin. In this study, we investigated the molecular mechanism underlying the upregulation of alpha3beta1 integrin by TGF-beta1 in non-invasive HepG2 HCC cells. The treatment of HepG2 cells with TGF-beta1 induced the expression of alpha3 integrin and potentiated these cells to adhere to laminin-5 and to migrate through laminin-5-coated membranes. The promoter activity was measured by luciferase assay with a series of deletion constructs of the 5'-flanking region of the mouse alpha3 integrin gene, and the results showed that the -260/-119 region (relative to the major transcription start site) contained elements responsive to TGF-beta1 stimulation. The introduction of mutations into the putative consensus binding sequence for the Ets-family of transcription factors located at -133 greatly decreased the promoter activity responding to TGF-beta1 stimulation. The nuclear proteins extracted from TGF-beta1-stimulated HepG2 cells yielded a larger amount of DNA-nuclear protein complexes than did those extracted from unstimulated cells, as determined by an electrophoretic mobility shift assay using an oligonucleotide containing the Ets-site as a probe. These results suggest that TGF-beta1 stimulates HepG2 cells to express a higher level of alpha3 integrin by transcriptional upregulation via Ets transcription factors and to exhibit a more invasive phenotype.

Homeobox D10 Induces Phenotypic Reversion of Breast Tumor Cells in a Three-Dimensional Culture Model

Homeobox (Hox) genes are master regulatory genes that direct organogenesis and maintain differentiated tissue function. We previously reported that HoxD10 helps to maintain a quiescent, differentiated phenotype in endothelial cells by suppressing expression of genes involved in remodeling the extracellular matrix and cell migration. Here we investigated whether HoxD10 could also promote or maintain a differentiated phenotype in epithelial cells. We observed that HoxD10 expression is progressively reduced in epithelial cells as malignancy increases in both breast and endometrial tumors. Retroviral gene transfer to restore expression of HoxD10 in the malignant breast tumor cells MDA-MB-231 significantly impaired migration, and when these cells were cultured in a three-dimensional laminin-rich basement membrane (3DlrBM) model, they formed polarized, acinar structures. This phenotypic reversion was accompanied by decreased alpha3 integrin expression and reduced proliferation. Importantly, expression of HoxD10 in the MDA-MB-231 cells inhibited their ability to form tumors in mouse xenografts. Taken together, our results suggest that HoxD10 has tumor-suppressive functions for mammary epithelial cells.

Identification and characterization of the promoter for the gene encoding human tripeptidyl-peptidase II

Tripeptidyl-peptidase II (TPP II) is a ubiquitously expressed exopeptidase. The expression of this enzyme is increased, e.g. in some tumor cells, but the regulation of the expression of the gene has not been investigated previously. The gene encoding human TPP II (TPP2) is 82 kb and consists of 30 exons. An 8 kb NcoI fragment covering the 5'-flanking region of the TPP2 gene, including the initiation codon, was cloned into a luciferase-containing reporter vector. Human embryonic kidney cells (HEK-293 cells) and murine fibroblasts (NIH3T3 cells) were transiently transfected with the construct. Through sequential deletions and analysis of short PCR-fragments, the promoter could be localized to a 215 bp fragment upstream of the initiation codon. This region is GC-rich, lacks a TATA-box and contains two inverted CCAAT-boxes and a GC-box. Electrophoretic mobility shift assays showed that nuclear proteins bind to the promoter fragment. The 85 bp 5'-end of the promoter fragment is essential for transcriptional activation. Out of this a 44 bp fragment suffices to compete with binding of nuclear proteins to the 215 bp fragment. Supershift assays demonstrated that the CCAAT-binding factor (CBF; NF-Y) is involved in the formation of a complex with the 215 bp fragment. Although Sp1 binds to the promoter fragment in vitro, it was found to bind to the 3'-end of the 215 bp fragment which is not essential for transcription. The potential role of Sp1 in transcription of TPP2 therefore remains to be established.

p51/p63 Controls Subunit α3 of the Major Epidermis Integrin Anchoring the Stem Cells to the Niche

p51/p63, a member of the tumor suppressor p53 gene family, is crucial for skin development. We describe here identification of ITGA3 encoding integrin alpha(3) as a target of its trans-activating function, proposing that p51/p63 allows epidermal stem cells to express laminin receptor alpha(3)beta(1) for anchorage to the basement membrane. When activated by genotoxic stress or overexpressed ectopically in non-adherent cells, p51/p63 transduced a phenotype to attach to extracellular matrices, which was accompanied by expression of ITGA3. Motifs matching the p53-binding consensus sequence were located in a scattered form in intron 1 of human ITGA3, and served as p51/p63-responsive elements in reporter assays. In addition to the trans-activating ability of the TA isoform, we detected a positive effect of the DeltaN isoform on ITGA3. The high level alpha(3) production in human keratinocyte stem cells diminished upon elimination of p51/p63 by small interfering RNA or by Ca(2+)-induced differentiation. Furthermore, a chromatin immunoprecipitation experiment indicated a physical interaction of p51/p63 with intron 1 of ITGA3. This study provides a molecular basis for the standing hypothesis that p51/p63 is essential for epidermal-mesenchymal interactions.

Adhesion of gastric carcinoma cells to peritoneum mediated by alpha3beta1 integrin (VLA-3)

The interaction between gastric carcinoma cells and the peritoneal lining is a key step in peritoneal dissemination. In this study, we examined the roles of the beta1 family of integrin receptors in the adhesion of such cells to the peritoneum. The adhesion of several gastric carcinoma cell lines to peritonea excised from mice was inhibited most by an anti-alpha3 integrin antibody and to a lesser extent by an anti-alpha2 integrin antibody. In the peritoneal implantation of NUGC-4 human gastric carcinoma cells in athymic mice, treatment of the cells with anti-alpha2 or anti-alpha3 integrin antibody reduced the number of disseminated nodules; suppression by the anti-alpha3 integrin antibody was stronger than that by the anti-alpha2 integrin antibody. The cDNAs to human alpha2 and alpha3 integrins were introduced into K562 leukemic cells, which were positive for the integrin beta1 subunit but negative for the alpha2 or alpha3 subunit. The alpha3 integrin-transfected cells adhered to excised peritoneum and to a monolayer of peritoneal mesothelial cells more firmly than did the alpha2 integrin-transfected cells or the mock transfectant. Reverse transcription-PCR was used to analyze the expression of laminin-5 and laminin-10/11, which have been reported to serve as high-affinity ligands for alpha3beta1 integrin. mRNA for these laminin isoforms was found in mesothelial cells from the diaphragm and parietal peritoneum. These results strongly suggest that alpha3beta1 integrin plays an essential role in mediating the initial attachment of cancer cells to the peritoneum, leading to the formation of peritoneal metastasis.

Physiological and Pathological Roles of α3β1 Integrin

Alpha3beta1 integrin has been considered to be a mysterious adhesion molecule due to the pleiotropy in its ligand-binding specificity. However, recent studies have identified laminin isoforms as high-affinity ligands for this integrin, and demonstrated that alpha3beta1 integrin plays a number of essential roles in development and differentiation, mainly by mediating the establishment and maintenance of epithelial tissues. Furthermore, alpha3beta1 integrin is also implicated in many other biological phenomena, including cell growth and apoptosis, angiogenesis and neural functions. This integrin receptor forms complexes with various other membrane proteins, such as the transmembrane-4 superfamily proteins (tetraspanins), cytoskeletal proteins and signaling molecules. Recently, lines of evidence have been reported showing that complex formation regulates integrin functions in cell adhesion and migration, signal transduction across cell membranes, and cytoskeletal organization. In addition to these roles in physiological processes, alpha3beta1 integrin performs crucial functions in various pathological processes, especially in wound healing, tumor invasion and metastasis, and infection by pathogenic microorganisms.

Disabled-1-regulated adhesion of migrating neurons to radial glial fiber contributes to neuronal positioning during early corticogenesis

Disabled-1 regulates laminar organization in the developing mammalian brain. Although mutation of the disabled-1 gene in scrambler mice results in abnormalities in neuronal positioning, migratory behavior linked to Disabled-1 signaling is not completely understood. Here we show that newborn neurons in the scrambler cortex remain attached to the process of their parental radial glia during the entire course of radial migration, whereas wild-type neurons detach from the glial fiber in the later stage of migration. This abnormal neuronal-glial adhesion is highly linked to the positional abnormality of scrambler neurons and depends intrinsically on Disabled-1 Tyr220 and Tyr232, potential phosphorylation sites during corticogenesis. Importantly, phosphorylation at those sites regulates alpha3 integrin levels, which is critical for the timely detachment of migrating neurons from radial glia. Altogether, these results outline the molecular mechanism by which Disabled-1 signaling controls the adhesive property of neurons to radial glia, thereby maintaining proper neuronal positioning during corticogenesis.