PTHrP increases xenograft growth and promotes integrin alpha6beta4 expression and Akt activation in colon cancer

Parathyroid hormone-related protein (PTHrP) is expressed by human colon cancer tissue and cell lines. Expression of PTHrP and phosphatidylinositol 3-kinase (PI3-K) pathway components correlates with the severity of colon carcinoma. Here we observed a positive effect of endogenous PTHrP on LoVo (human colon cancer) cell proliferation, migration, invasion, integrin alpha6 and beta4 expression, and p-Akt levels. There was a direct correlation between PTHrP expression and anchorage-independent cell growth. PTHrP significantly increased xenograft growth; tumors from PTHrP-overexpressing cells showed increased expression of integrins alpha6 and beta4, and PI3-K pathway components. The higher expression of PTHrP in human colon cancer adenocarcinoma vs. normal colonic mucosa was accompanied by increased integrin alpha6 and beta4 levels. Elevated PTHrP expression in colon cancer may thus upregulate integrin alpha6beta4 expression, with consequent PI3-K activation. Targeting PTHrP might result in effective inhibition of tumor growth, migration, and invasion.     

Role of transforming growth factor beta 1 in induction of colon carcinoma differentiation by hexamethylene bisacetamide

The differentiation agent hexamethylene bisacetamide (HMBA) increased expression of transforming growth factor beta 1 (TGF beta 1) mRNA in HT29 colon carcinoma cells. The increase was evident after 24 h and was maintained at levels 4-5-fold the control levels for at least 5-13 days. No increase in expression of TGF beta 2 or TGF alpha mRNA was observed. Both TGF beta 1 and HMBA induced loss of expression of a cell surface malignancy marker on HT29 cells, and both decreased cell growth in serum-free medium. Exogenously applied TGF beta 1 mimicked the growth-arresting effect of HMBA on three surgically resected moderately differentiated colon carcinomas in serum-free primary culture. Both TGF beta 1 and HMBA increased the tumor growth fraction in a second group of three more aggressive colon carcinomas, while neither agent had any measurable growth-modulating activity on two other colon carcinomas. The induction of TGF beta 1 mRNA by HMBA along with the parallel biological effects of HMBA and exogenously applied TGF beta 1 on resected carcinomas and on HT29 cells suggest that the effects of HMBA on colon carcinoma cells may be mediated in part by induction of TGF beta 1.     

Activated K-ras is involved in regulation of integrin expression in human colon carcinoma cells

Integrins participate in controlling proliferation and migration. Therefore, changes in integrin expression might be responsible for unrestrained proliferation and invasiveness of tumor cells. Alterations of integrin subunit expression have been observed in human colon carcinoma, especially loss or reduction of the alpha5 subunit, which was observed consistently. The mechanisms responsible for reduction of alpha5 expression and alteration of expression of other integrins are not fully understood. Circumstantial evidence from previous investigations points to an involvement of activated ras oncogenes in repression of integrin expression. The K-ras protooncogene is activated by point mutation in 50% of human colon carcinomas. Thus, we choose an antisense approach for specific inactivation of activated K-ras in the human colon carcinoma cell line SW 480 in order to test whether activated K-ras contributes to changes in integrin expression on colon carcinoma cells. Cell surface expression of the alpha1 and the alpha5 subunit was increased in K-ras antisense transfected clones, cell surface expression of the alpha3 subunit and the alphav subunit was decreased. This shows, in a human system, that activated K-ras is involved in diminishing cell surface expression of the alpha1beta1 collagen/laminin receptor and the alpha5beta1 fibronectin receptor, both of which are implicated in maintenance of a non-transformed phenotype. Moreover, activated K-ras contributes to increased cell surface expression of the alpha3beta1 laminin/collagen/fibronectin receptor and the alphavbeta5 vitronectin receptor, which might play a role in metastatic behavior of tumor cells.     

Characterization of GRO alpha, beta and gamma expression in human colonic tumours: potential significance of cytokine involvement.

The GRO genes, isolated from transformed fibroblasts, belong to a superfamily of genes such as platelet factor 4 and neutrophil activating peptide/IL-8. Three related GRO genes are described which are closely linked on chromosome 4: GRO alpha, GRO beta, and GRO gamma: GRO beta and GRO gamma share 90 and 86% sequence homology with GRO alpha. The GRO alpha gene product shares homology with, and is melanocyte growth stimulatory activity (MGSA). The MGSA/GRO alpha has potent chemotactic, growth regulatory and transformative functions. The function of GRO beta and gamma is unknown. Expression of GRO alpha is well characterized in vitro; studies in actual human tissues are not reported. We chose to determine the specific expression of GRO alpha, beta and gamma in both normal and transformed human colonic tissues and to assess the role of exogenous cytokines on their induction. Tissues from ten patients with colonic neoplasia were obtained at the time of colectomy. All specimens underwent Northern analysis for GRO gene expression, comparing normal colonic mucosa with neoplastic mucosa. Differential GRO alpha, beta and gamma expressions were determined by polymerase chain reaction (PCR). GRO alpha expression was evaluated in the tumour specimens compared with normal, while there was constitutive expression of GRO gamma in both normal and neoplastic colonic mucosa. Expression of GRO beta was minimal in all tissue specimens. In addition, HT29 colon carcinoma cells stimulated with IL-1 beta and TNF alpha demonstrated induction of GRO alpha and IL-8. Thus, GRO alpha is differently elevated in in vivo colon carcinoma specimens. GRO gamma was constitutively expressed in colonic tissues; GRO beta was not similarly expressed.     

Altered surface expression and increased turnover of the alpha6beta4 integrin in an undifferentiated carcinoma

The integrin alpha6beta4, predominantly expressed on tissues of epithelial origin, is known to be variably expressed on carcinomas. The biochemical changes resulting in altered expression during tumor progression are unknown. We have analyzed the expression of alpha6beta4 in a multi-step mouse model of skin carcinogenesis representing normal keratinocyte, benign papilloma and malignant undifferentiated carcinoma. All cell lines expressed the alpha6 integrin exclusively as the alpha6beta4 integrin heterodimer. Analysis of this integrin by flow cytometry and immunoprecipitation of surface labeled proteins revealed that the undifferentiated carcinoma cells have an approximately 75% reduction in surface expression of the integrin as compared with the keratinocyte and papilloma cell lines. The alpha6beta4 integrin which remains expressed on the carcinoma cells is diffusely distributed in the membrane and has an approximately 2.5-fold increased biological turnover as compared with normal keratinocytes. The decreased biological half-life and the loss of polarized expression of alpha6beta4 on the carcinoma cells suggests an altered functional role for the alpha6beta4 integrin on carcinoma cells during tumor progression. These factors may contribute to the known supression of hemidesmosome structures and the increased migration phenotype associated with some epithelial carcinomas.     

Insulin-like growth factor-I receptor, E-cadherin and alpha v integrin form a dynamic complex under the control of alpha-catenin

Dynamic crosstalk between cell adhesion molecules, extracellular matrix and soluble informative factors is essential for cancer cell migration and invasion. Here, we investigated the mechanisms by which the E-cadherin/catenin complex and alpha v integrin can modulate insulin-like growth factor-I (IGF-I)-induced cell migration. Human colon mucosa, human colon cancer cell lines, HT29-D4 and HCT-8 derivatives that differ in their expression of alpha-catenin, were used as models. Interactions between E-cadherin, alpha v integrin and IGF-I receptor (IGF-IR) were analyzed by coimmunoprecipitation and immunolocalization experiments. The impact of these interactions on cell mobility was determined by haptotaxis assays. We report that alpha v integrin, E-cadherin and IGF-IR form a ternary complex in both cultured cancer cells and human normal colonic mucosa. alpha-Catenin regulates the scaffolding of this complex. IGF-IR ligation by IGF-I induces the disruption of the complex and the relocalization of alpha v integrin from cell-cell contacts to focal contact sites. This perturbation is correlated with the observed increase in cell migration. These results suggest that regulation of the alpha v integrin/E-cadherin/IGF-IR scaffolding is essential for the modulation of cell mobility. Its alteration could be of major importance to sustain alterations in cell adhesion that occur during cancer cell invasion and metastasis.     

The alpha v beta 6 integrin induces gelatinase B secretion in colon cancer cells

In human cancers, the co-operative role between cell-adhesion receptors and proteases capable of degrading matrix barriers remains poorly understood. We have previously reported that the epithelium-restricted integrin alpha(v)beta6 becomes highly expressed in colon cancer compared with normal mucosa and that heterologous expression of alpha(v)beta6 in colon cancer cells is associated with enhanced cell growth. Herein, we report that alpha(v)beta6 expression in colon cancer cells leads to a relative increase in secretion of the matrix metalloproteinase gelatinase B over its respective inhibitor and that this secretion parallels the level of cell-surface beta6 expression. The alpha(v)beta6-mediated gelatinase B secretion is associated with increased proteolysis of denatured collagen at the cell surface, and inactivation of gelatinase B in beta6-expressing tumour cells inhibits cell spreading and proliferation within 3-dimensional collagen matrices. Our findings suggest that alpha(v)beta6-mediated gelatinase B secretion is important in the progression of human colon cancer.     

Matrilysin 1 influences colon carcinoma cell migration by cleavage of the laminin-5 beta3 chain

Matrilysin 1 [matrix metalloproteinase 7 (MMP7)] is one of the most important metalloproteinases expressed in human tissues. This enzyme is generally not expressed by normal differentiated epithelial colon cells, but has been shown to be up-regulated in human colon adenomas and adenocarcinomas. Little is known about the role of MMP7 in cell invasion and its involvement in proteolytic processes. By searching the ligands of MMP7 in the colonic carcinoma cells HT29, we identified laminin-5/laminin-332 (LN5) as a specific target for MMP7 enzymatic activity. LN5, composed of alpha3, beta3, and gamma2 chains, is an important component of epithelial basement membranes where it induces firm adhesion and hemidesmosome formation. In this study, we show that LN5 and MMP7 are coexpressed in HT29 cells as well as in HT29 xenograft tumors and human colorectal adenocarcinomas. We provide evidence that human LN5 is a ligand for MMP7 and that a specific cleavage occurs in its beta3 chain, giving rise to a carboxyl-terminal beta3 chain fragment of 90 kDa. We have identified the MMP7 cleavage site at position Ala(515)-Ile(516) in the beta3 chain. Videomicroscopic analysis of HT29 cells plated on LN5 substrates reveals that the MMP7-processed LN5 significantly enhances cell motility. Moreover, the delayed migration of HT29 cells obtained after specific inhibition of MMP7 reinforces the hypothesis supporting its involvement in cell migration. Altogether, our results show that MMP7 is likely to play a crucial role in the regulation of carcinoma cell migration by targeting specific proteolytic processing of the LN5 beta3 chain.     

结肠癌HT29细胞的相关分子表达及与多药耐药的相关性

目的:探讨结肠癌HT29细胞的相关分子表达及与多药耐药的相关性。方法:选择人结肠癌HT29细胞株进行三维培养,采用RT-PCR与免疫组化检测整合素ανβ的表达情况,同时在三维培养和整合素ανβ3阻断型抗体加入条件下对细胞的多药化疗耐药性进行检测。结果:结肠癌HT29细胞在三维培养24h后,部分聚集成由数个细胞组成的细胞团,电镜观察多细胞球球体呈较规则的致密的球形结构,多细胞球球体模型构建成功。结肠癌HT29细胞多细胞球球体中整合素ανβ3基因的表达比一般平面培养细胞高,整合素β3蛋白、整合素αν主要定位于胞浆,在多细胞球球体中表达明显高于普通平面培养细胞。HT29细胞多细胞球球体+整合素ανβ3抗体组在5-氟尿嘧啶和奥沙利铂作用后48h的细胞凋亡率为0.31±0.04,细胞坏死率为0.52±0.02;而HT29细胞多细胞球球体组的细胞凋亡率与坏死率分别为0.14±0.03和0.21±0.03,对比差异明显(P<0.05)。结论:结肠癌HT29多细胞球球体中的整合素ανβ3在基因与蛋白水平都呈现表达升高的趋势,可能是细胞多药耐药产生的重要原因。     

Integrin receptors and ECM proteins involved in preferential adhesion of colon carcinoma cells to lung cells

To assess the putative role of extracellular matrix (ECM) proteins on lung cells interacting with integrin receptors on colon carcinoma cells, an in vitro adhesion assay was used to investigate these factors. Tumor necrosis factor (TNF)-alpha treatment of fetal lung cell line MRC 9, upregulated expression of ECM proteins and also supported enhanced adhesion of PTC colon carcinoma cells. Antibodies to ECM proteins significantly blocked this enhanced adhesion of PTC cells. Similarly, antibody blocking of beta1 and beta2 integrin receptors on PTC cells revealed the integrin receptors involved in this enhanced adhesion. beta1 integrin receptors like alpha2beta1, alpha4beta1 and alpha5beta1 on PTC cells were found interacting with their ECM ligands like fibronectin and laminin on TNF-alpha stimulated MRC 9 cells. Interestingly, PTC cells were found to constitutively express alphaLbeta2, which is normally expressed by leukocytes. The data from the present study indicates that expression of multiple beta1 and beta2 integrins by colon carcinoma cells putatively allows these cells to successfully adhere to secondary sites like lungs.     

Increased levels of phorbin, c-myc, and ornithine decarboxylase RNAs in human colon cancer.

Our previous work on protein kinase C (PKC) and colon cancer has shown altered levels of PKC activity in human colon tumors, as well as activation of PKC by colon tumor promoters such as bile acids. To understand further the role of PKC in colon carcinogenesis, we analyzed the expression of phorbin, a gene induced by PKC activation, in a series of different stages of human colon tumors. As shown by northern blot analyses of poly (A)+ RNA, higher levels of phorbin RNA were seen in 26 colon tumor samples than in their adjacent normal colonic mucosa. There also appeared to be a correlation between the abundance of phorbin RNA in the tumors and the extent of invasion (tumor-to-normal tissue phorbin RNA ratio = 4.2, 8.0, and 11.9 for Dukes' A, B, and C, respectively). Phorbin RNA was also abundant in a human colon cancer line (HT29). We also examined the expression of other mitogen-responsive genes (c-myc, ODC, and beta-actin) in a set of 19 colon tumor samples. All tumors displayed significant (mean 3.8-fold) increases in the level of c-myc RNA compared with their adjacent normal colonic mucosa. About 47% and 16% of these tumor samples also showed increased levels of ODC (mean 3.1-fold) and beta-actin (mean 1.6-fold) RNA, respectively. The increased levels of c-myc, ODC, and beta-actin RNA did not correlate with the extent of tumor invasion. Taken together, these results demonstrate that human colon tumors usually display increased levels of both phorbin and c-myc RNAs. The marked increases in phorbin RNA suggest that this could serve as a useful biomarker in studies on human colon cancer.     

Integrin alpha v beta 6 mediates the potential for colon cancer cells to colonize in and metastasize to the liver

Integrin alpha v beta 6 (alpha v beta 6) is correlated with colon cancer progression. To detect the effects of alpha v beta 6 on liver metastasis, the specificity of alpha v beta 6 against the monoclonal antibody (mAb) 2G2 was examined by immunoprecipitation. Integrin alpha v beta 6-immunoreactivity (IR) in liver metastasis tissues (63 cases) and colon carcinoma (358 cases) were examined. These results showed that alpha v beta 6 was specifically recognized by the mAb 2G2, and that rates of alpha v beta 6 positivity in liver metastatic tissues (71.4%, 45/63) were higher than that for primary colon cancer (34.0%, 122/358) (P < 0.01). Patients who were alpha v beta 6-positive had higher liver metastasis rates (17%, 21/122) than those who were alpha v beta 6-negative (only 3%, 7/236) (P < 0.01). To examine the underlying mechanisms associated with alpha v beta 6 regulating colonic metastasis in the liver, experimental liver metastasis (intrasplenic injection of HT29 transfectants) and liver colonization assays (direct injection of WiDr transfectants into the liver) in nude mice were performed; these demonstrated that alpha v beta 6 contributed to the promotion of the metastatic potential and the survival of cancer cells in the liver. Matrix metalloproteinase-9 (MMP-9) levels in the cultures of both HT29 and WiDr cells were detected by the Biotrak MMP-9 activity assay system and gelatin zymography assay, and showed that suppression of alpha v beta 6-IR inhibited MMP-9 activity and secretion. Transwell migration assay in vitro also showed that alpha v beta 6 promoted migration on fibronectin for HT29/WiDr mock compared with HT29/WiDr antisense beta 6 transfects (P < 0.01). We concluded that alpha v beta 6 may mediate the potential for colon cancer cells to colonize in and metastasize to the liver. The mechanisms that alpha v beta 6 may be involved in include the promotion of MMP-9 secretion, the enhancement of migration on fibronectin, and the survival of cancer cells in the liver.     

The alpha6beta4 integrin maintains the survival of human breast carcinoma cells in vivo

The alpha6beta4 integrin has been widely implicated in carcinoma function in vitro; however, in vivo data are scarce. To determine the importance of alpha6beta4 in tumor progression, a SUM-159 breast carcinoma cell line that is essentially devoid of alpha6beta4 expression was generated using an RNA interference strategy. Loss of alpha6beta4 expression inhibits colony formation in soft agar assays, suggesting a vital role for alpha6beta4 in survival signaling and anchorage-independent growth. Orthotopic injection of the beta4-deficient cell line into the mammary fat pad of immunocompromised mice yielded significantly fewer and smaller tumors than the control cell line, revealing a role for the alpha6beta4 integrin in tumor formation. Under conditions that mimicked the in vivo environment, decreased expression of the alpha6beta4 integrin led to enhanced apoptosis as determined by the percentage of Annexin V-FITC+, PI- cells and the presence of caspase-3 cleavage products. Recombinant vascular endothelial growth factor (VEGF) significantly inhibited the cell death observed in the beta4-deficient cell line, demonstrating the importance of VEGF expression in this survival pathway. Furthermore, loss of alpha6beta4 expression leads to enhanced apoptosis and reduced expression of VEGF in breast carcinoma cells in vivo. Importantly, the specificity of alpha6beta4 in both the in vitro and in vivo assays showed that reexpression of the beta4 subunit into the beta4-deficient cell line could rescue the functional phenotype. Taken together, these data implicate the alpha6beta4 integrin in tumor formation by regulating tumor cell survival in a VEGF-dependent manner.     

Differential regulation of c-myc and transforming growth factor-alpha messenger RNA expression in poorly differentiated and well-differentiated colon carcinoma cells during the establishment of a quiescent state

A previous report from this laboratory indicated that a transformed fibroblast cell line up-regulated c-myc by as much as 14-fold as cultures approached saturating densities, whereas the untransformed counterparts displayed little alteration in c-myc expression (Cancer Res., 49: 2320, 1989). The results suggested a mechanism for the growth advantage of the transformed cells at postconfluent densities. Similarly, the present results indicate that regulation of c-myc expression during establishment of a quiescent state markedly differed in poorly differentiated versus well-differentiated human colon carcinoma cells. While c-myc expression increased 2- to 3-fold during this period in the poorly differentiated cells, expression levels for this protooncogene showed little variation in the well-differentiated cells. There was, however, no correlation between degree of differentiation and c-myc mRNA levels in growing cultures (i.e., cells in late log phase). Another proliferation-associated mRNA, transforming growth factor alpha (TGF-alpha), was also differentially regulated in the two groups of colon carcinoma cells as cultures approached quiescence. Further, addition of exogenous growth-stimulatory factors (epidermal growth factor plus insulin plus transferrin) to quiescent, well-differentiated cells resulted in an up-regulation of TGF-alpha mRNA levels by 9-fold over a 24-h period. In contrast, poorly differentiated cells displayed little alteration in TGF-alpha mRNA levels under similar conditions. The results suggest that inappropriate kinetic regulation of c-myc and TGF-alpha mRNAs at quiescence may be related to the growth factor independence of the poorly differentiated colon carcinoma cells. Furthermore, altered temporal regulation of c-myc and TGF-alpha expression appears to be more relevant to differentiation status in human colon carcinoma cells than are absolute expression levels.     

A novel mechanism for integrin-mediated ras activation in breast carcinoma cells: the alpha6beta4 integrin regulates ErbB2 translation and transactivates epidermal growth factor receptor/ErbB2 signaling

ErbB2 (HER2, Neu) and Ras play key roles in tumor invasion and metastasis. We identified a novel mechanism by which integrin alpha(6)beta(4) regulates ErbB2 expression, Ras activation, and the invasion of breast carcinoma cells. Here we show that integrin alpha(6)beta(4) regulates Ras activity especially in serum-depleted condition. Down-regulation of beta(4) integrin by beta(4) short hairpin RNA (shRNA) decreased Ras activity and carcinoma invasion whereas reexpression of this integrin restored Ras activity. ErbB2, a binding partner of epidermal growth factor receptor (EGFR), and EGFR modulated Ras activity, and integrin alpha(6)beta(4) regulated phospho-EGFR level without affecting EGFR expression. We also found that integrin alpha(6)beta(4) is involved in ErbB2 expression. Depletion of beta(4) by shRNA reduced ErbB2 protein level without affecting ErbB2 mRNA level and reexpression of beta(4) increased ErbB2 protein level. Reduction of eukaryotic initiation factor 4E, a rate-limiting factor for cap-dependent translation, decreased ErbB2 protein level, and beta(4) shRNA cells exhibited a shift in ErbB2 mRNA to light polysomes compared with control cells. These results show that integrin alpha(6)beta(4) regulates ErbB2 through translational control. In summary, we propose a novel mechanism for ErbB2 up-regulation and Ras activation in serum-depleted breast cancer cells; integrin alpha(6)beta(4) regulates the expression of ErbB2 and the subsequent phosphorylation of EGFR and activation of Ras. These findings provide a mechanism that substantiates the reported role of alpha(6)beta(4) in carcinoma invasion.     

The alpha 3 beta 1 integrin is associated with mammary carcinoma cell metastasis, invasion, and gelatinase B (MMP-9) activity

The alpha 3 beta 1 integrin is elevated in several types of metastatic tumor and has been associated with increased migration and invasion. Our analysis of a series of mammary carcinomas of different histotypes and their corresponding metastases demonstrated significantly increased expression of alpha 3 beta 1 in the tumor metastases. We therefore studied alpha 3 beta 1 expression of several human breast carcinoma cell lines and its association with the invasive phenotype. The MDA-MB-231 cell line expressed high levels of the beta1, alpha 2, alpha 3, alpha 5, and alpha 6 integrin subunits along with moderate levels of the alpha v beta 3 integrin. This line was highly migratory and the most invasive using a chemo-invasion assay. In contrast, the other lines tested, MDA-MB-145, MCF-7, and SK-BR-3, showed lower migratory and invasive activity and reduced alpha 3 integrin subunit expression. Metalloproteases capable of degrading collagen IV are necessary for the invasive process. RT-PCR showed that MDA-MB-231 cells expressed MMP-9, but not MMP-2, gelatinase/collagenase IV. Gelatin zymography demonstrated that invading MDA-MB-231 cells released high levels of MMP-9 gelatinase activity. A direct role for this gelatinase in MDA-MB-231 cell invasion was confirmed by inhibition of invasion using the metalloprotease inhibitor Batimastat. Treatment of MDA-MB-231 cells with a function-blocking anti-alpha 3 antibody strongly inhibited migration and invasion. This correlated with a marked reduction in MMP-9 activity produced by MDA-MB-231 cells, suggesting a role for alpha 3 beta 1 ligand binding in cell signaling and regulation of extracellular matrix degradation.