Metastasis-association of the rat ortholog of the human epithelial glycoprotein antigen EGP314

Ping-Pong-Tumor and Host in Pancreatic Cancer Progression

Metastasis is the main cause of high pancreatic cancer (PaCa) mortality and trials dampening PaCa mortality rates are not satisfying. Tumor progression is driven by the crosstalk between tumor cells, predominantly cancer-initiating cells (CIC), and surrounding cells and tissues as well as distant organs, where tumor-derived extracellular vesicles (TEX) are of major importance. A strong stroma reaction, recruitment of immunosuppressive leukocytes, perineural invasion, and early spread toward the peritoneal cavity, liver, and lung are shared with several epithelial cell-derived cancer, but are most prominent in PaCa. Here, we report on the state of knowledge on the PaCIC markers Tspan8, alpha6beta4, CD44v6, CXCR4, LRP5/6, LRG5, claudin7, EpCAM, and CD133, which all, but at different steps, are engaged in the metastatic cascade, frequently via PaCIC-TEX. This includes the contribution of PaCIC markers to TEX biogenesis, targeting, and uptake. We then discuss PaCa-selective features, where feedback loops between stromal elements and tumor cells, including distorted transcription, signal transduction, and metabolic shifts, establish vicious circles. For the latter particularly pancreatic stellate cells (PSC) are responsible, furnishing PaCa to cope with poor angiogenesis-promoted hypoxia by metabolic shifts and direct nutrient transfer via vesicles. Furthermore, nerves including Schwann cells deliver a large range of tumor cell attracting factors and Schwann cells additionally support PaCa cell survival by signaling receptor binding. PSC, tumor-associated macrophages, and components of the dysplastic stroma contribute to perineural invasion with signaling pathway activation including the cholinergic system. Last, PaCa aggressiveness is strongly assisted by the immune system. Although rich in immune cells, only immunosuppressive cells and factors are recovered in proximity to tumor cells and hamper effector immune cells entering the tumor stroma. Besides a paucity of immunostimulatory factors and receptors, immunosuppressive cytokines, myeloid-derived suppressor cells, regulatory T-cells, and M2 macrophages as well as PSC actively inhibit effector cell activation. This accounts for NK cells of the non-adaptive and cytotoxic T-cells of the adaptive immune system. We anticipate further deciphering the molecular background of these recently unraveled intermingled phenomena may turn most lethal PaCa into a curatively treatable disease.

EPCAM mutation update: Variants associated with congenital tufting enteropathy and Lynch syndrome

The epithelial cell adhesion molecule gene (EPCAM, previously known as TACSTD1 or TROP1) encodes a membrane‐bound protein that is localized to the basolateral membrane of epithelial cells and is overexpressed in some tumors. Biallelic mutations in EPCAM cause congenital tufting enteropathy (CTE), which is a rare chronic diarrheal disorder presenting in infancy. Monoallelic deletions of the 3′ end of EPCAM that silence the downstream gene, MSH2, cause a form of Lynch syndrome, which is a cancer predisposition syndrome associated with loss of DNA mismatch repair. Here, we report 13 novel EPCAM mutations from 17 CTE patients from two separate centers, review EPCAM mutations associated with CTE and Lynch syndrome, and structurally model pathogenic missense mutations. Statistical analyses indicate that the c.499dupC (previously reported as c.498insC) frameshift mutation was associated with more severe treatment regimens and greater mortality in CTE, whereas the c.556‐14A>G and c.491+1G>A splice site mutations were not correlated with treatments or outcomes significantly different than random simulation. These findings suggest that genotype–phenotype correlations may be useful in contributing to management decisions of CTE patients. Depending on the type and nature of EPCAM mutation, one of two unrelated diseases may occur, CTE or Lynch syndrome.

Functional polymorphisms in CD166/ALCAM gene associated with increased risk for breast cancer in a Chinese population

Activated Leukocyte Cell Adhesion Molecules (ALCAM, also called CD166, MEMD) are cell surface immunoglobulins that are considered to be prognostic markers for breast cancer. CD166/ALCAM has gained increasing attention because of its significant association with tumor progression and the metastatic spread of breast cancer. Two polymorphisms have been identified in the CD166/ALCAM gene: 5'UTR C/T (rs6437585) and 3'UTR A/G (rs11559013). We analyzed the genotypes of 1033 individuals with breast cancer, and 1116 controls; odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using logistic regression. The effects and functions of polymorphisms were examined using luciferase gene expression assays and real-time PCR analyses. Our data demonstrated that individuals with the rs6437585 CT + TT genotype had an OR of 1.38 (95% CI, 1.11-1.72) for developing breast cancer, compared to those with the CC genotype. The T allele increased the risk of breast cancer in a dose-dependent manner (P (trend) < 0.001). However, there were no significant differences found between cases and controls at the rs11559013 A/G site. Additional experiments that we performed, which focused on reporter gene expression driven by CD166/ALCAM promoters, demonstrated that the presence of an rs6437585 T allele led to greater transcriptional activity than the rs6437585 C allele. This was consistent with the increased cancer risk that we observed in our case-control analysis.

Profile of estrogen-responsive genes in an estrogen-specific mammary gland outgrowth model

Both ovarian and pituitary hormones are required for the pubertal development of the mouse mammary gland. Estradiol directs ductal elongation and branching, while progesterone leads to tertiary branching and alveolar development. The purpose of this investigation was to identify estrogen-responsive genes associated with pubertal ductal growth in the mouse mammary gland in the absence of other ovarian hormones and at different stages of development. We hypothesized that the estrogen-induced genes and their associated functions at early stages of ductal elongation would be distinct from those induced after significant ductal elongation had occurred. Therefore, ovariectomized prepubertal mice were exposed to 17beta-estradiol from two to 28 days, and mammary gland global gene expression analyzed by microarray analysis at various times during this period. We found that: (a) gene expression changes in our estrogen-only model mimic those changes that occur in normal pubertal development in intact mice, (b) both distinct and overlapping gene profiles were observed at varying extents of ductal elongation, and (c) cell proliferation, the immune response, and metabolism/catabolism were the most common functional categories associated with mammary ductal growth. Particularly striking was the novel observation that genes active during carbohydrate metabolism were rapidly and robustly decreased in response to estradiol. Lastly, we identified mammary estradiol-responsive genes that are also co-expressed with estrogen receptor alpha in human breast cancer. In conclusion, our genomic data support the physiological observation that estradiol is one of the primary hormonal signals driving ductal elongation during pubertal mammary development.

The epithelial cell adhesion molecule EpCAM is required for epithelial morphogenesis and integrity during zebrafish epiboly and skin development

The aberrant expression of the transmembrane protein EpCAM is associated with tumor progression, affecting different cellular processes such as cell–cell adhesion, migration, proliferation, differentiation, signaling, and invasion. However, the in vivo function of EpCAM still remains elusive due to the lack of genetic loss-of-function studies. Here, we describe epcam (tacstd) null mutants in zebrafish. Maternal-zygotic mutants display compromised basal protrusive activity and epithelial morphogenesis in cells of the enveloping layer (EVL) during epiboly. In partial redundancy with E-cadherin (Ecad), EpCAM made by EVL cells is further required for cell–cell adhesion within the EVL and, possibly, for proper attachment of underlying deep cells to the inner surface of the EVL, thereby also affecting deep cell epiboly movements. During later development, EpCAM per se becomes indispensable for epithelial integrity within the periderm of the skin, secondarily leading to disrupted morphology of the underlying basal epidermis and moderate hyper-proliferation of skin cells. On the molecular level, EVL cells of epcam mutant embryos display reduced levels of membranous Ecad, accompanied by an enrichment of tight junction proteins and a basal extension of apical junction complexes (AJCs). Our data suggest that EpCAM acts as a partner of E-cadherin to control adhesiveness and integrity as well as plasticity and morphogenesis within simple epithelia. In addition, EpCAM is required for the interaction of the epithelia with underlying cell layers.

EpCAM is a well-established marker for carcinomas of epithelial origin and a potential target for immunotherapy. In vitro analyses have implicated EpCAM in a plethora of different cellular processes, such as adhesion, motility, proliferation, differentiation, and signaling. Strikingly, depending on the context, EpCAM displayed rather opposite effects, either promoting or attenuating cell–cell adhesion versus cell migration and tissue invasion, a phenomenon described as the “double-face” of EpCAM. However, the in vivo relevance of its different effects remained largely unclear. Here, we present the first genetic analysis of EpCAM function in vivo, based on loss-of-function mutants in the zebrafish. As it is in mammals, zebrafish EpCAM is expressed in simple epithelia. Mutant embryos display defects both in epithelial morphogenesis and in epithelial integrity. Reduced epithelial morphogenesis is accompanied, and possibly caused, by an extension of apical junctional complexes and compromised basal protrusive activity. Furthermore, mutant epithelia display alterations in the relative abundance of adherence junction versus tight junction components. In addition, EpCAM tightly cooperates with E-cadherin and has a previously unrecognized trans effect on the morphogenesis and integrity of underlying cell layers. Cell differentiation and proliferation in EpCAM mutants are not, or only secondarily, affected. During later development and adulthood, EpCAM is largely dispensable, reinforcing its suitability as a target for anti-carcinoma immunotherapy with minimal side effects.

Claudin-7 regulates EpCAM-mediated functions in tumor progression

EpCAM has been described as a therapeutically relevant tumor marker. We noted an interaction between EpCAM and the tight junction protein claudin-7 and here explored the nature of this interaction and its effect on EpCAM-mediated functions. The interaction between EpCAM and claudin-7 was defined in HEK293 cells transfected with rat claudin-7 and EpCAM cDNA. Deletions of the epidermal growth factor-like and the thyroglobin repeat domains of EpCAM or the cytoplasmic domain of EpCAM or claudin-7 did not prevent the EpCAM-claudin-7 association. A chimeric EpCAM molecule with an exchange of the cytoplasmic and transmembrane domains and an EpCAM molecule with point mutations in an AxxxG motif in the transmembrane region do not associate with claudin-7. HEK cells and the rat pancreatic tumor line BSp73AS, transfected with (mutated) EpCAM and claudin-7 cDNA, revealed that the association of both molecules severely alters the functional activity of EpCAM. Claudin-7-associated EpCAM is recruited into tetraspanin-enriched membrane microdomains (TEM). The TEM-located claudin-7-EpCAM complex supports proliferation accompanied by sustained extracellular signal-regulated kinase-1/2 phosphorylation, up-regulation of antiapoptotic proteins, and drug resistance, but not EpCAM-mediated cell-cell adhesion. Enhanced motility may be supported by colocalization of claudin-7 with actin bundles, which is only seen in EpCAM-claudin-7-expressing cells. The EpCAM-claudin-7 complex strongly promotes tumorigenicity, accelerates tumor growth, and supports ascites production and thymic metastasis formation. High expression of the tumor marker EpCAM is frequently associated with poor prognosis, which could well rely on the EpCAM-claudin-7 association that prohibits EpCAM-mediated cell-cell adhesion but promotes migration, proliferation, apoptosis resistance, and tumorigenicity.

A genome-wide expression analysis identifies a network of EpCAM-induced cell cycle regulators

Expression of the epithelial cell adhesion molecule EpCAM is upregulated in a variety of carcinomas. This antigen is therefore explored in tumour diagnosis, and clinical trials have been initiated to examine EpCAM-based therapies. Notably, the possible intracellular effects and signalling pathways triggered by EpCAM-specific antibodies are unknown. Here, we show treatment of the mouse lung carcinoma cell line A2C12, of the human lung carcinoma cell line A549 and the human colorectal cell line Caco-2 with the monoclonal EpCAM antibody G8.8 to cause dose dependently an increase in cell proliferation, as determined by the MTS and the 5′-bromo-2′-deoxyuridine (BrdU) labelling assay. Furthermore, a genome-wide approach identified networks of regulated genes, most notably cell cycle regulators, upon treatment with an EpCAM-specific antibody. Indeed, changes in the expression of cell cycle regulators agreed well with the BrdU labelling data, and an analysis of differentially expressed genes revealed the processes with the strongest over-representation of modulated genes, for example, cell cycle, cell death, cellular growth and proliferation, and cancer. These data suggest that EpCAM is involved in signal transduction triggering several intracellular signalling pathways. Knowing EpCAM signalling pathways might lead to a reassessment of EpCAM-based therapies.

Decreased expression of Ep-CAM protein is significantly associated with the progression and prognosis of oral squamous cell carcinomas in Taiwan

BACKGROUND

The epithelial cell adhesion molecule (Ep-CAM) is involved in cell signaling, migration, proliferation, cell-cycle regulation, and cancer metastasis.

METHODS

This study used an immunohistochemical technique to examine the expression of Ep-CAM protein in 84 specimens of oral squamous cell carcinoma (OSCC), 98 specimens of oral epithelial dysplasia (OED, 31 mild, 41 moderate, and 26 severe OED cases), and 15 specimens of normal oral mucosa (NOM).

RESULTS

We found that the mean Ep-CAM labeling indices (LIs) decreased significantly from NOM (80 +/- 18%) and mild OED (76 +/- 14%) through moderate OED (66 +/- 22%) and severe OED (55 +/- 20%) to OSCC samples (46 +/- 16%, P < 0.001). A significant correlation was found between the lower mean Ep-CAM LI and OSCCs with larger tumor size (P = 0.003), positive lymph node metastasis (P = 0.022), more advanced clinical stages (P < 0.001), cancer recurrence (P = 0.021), or extracapsular spread of lymph node (P = 0.015). However, only Ep-CAM LI < 50% (P < 0.0001) was identified as an independent unfavorable prognosis factor by multivariate analyses with Cox proportional hazard regression model. Kaplan-Meier curve showed that OSCC patients with an Ep-CAM LI < 50% had a significantly poorer cumulative survival than those with an Ep-CAM LI > or = 50% (P < 0.00001, log-rank test).

CONCLUSIONS

We conclude that the decreased expression of Ep-CAM protein is an early event in oral carcinogenesis. The Ep-CAM LI in OSCC samples can predict the progression of OSCCs and the survival of OSCC patients.

A complex of EpCAM, claudin-7, CD44 variant isoforms, and tetraspanins promotes colorectal cancer progression

High expression of EpCAM and the tetraspanin CO-029 has been associated with colorectal cancer progression. However, opposing results have been reported on CD44 variant isoform v6 (CD44v6) expression. We recently noted in rat gastrointestinal tumors that EpCAM, claudin-7, CO-029, and CD44v6 were frequently coexpressed and could form a complex. This finding suggested the possibly that the complex, rather than the individual molecules, could support tumor progression. The expression of EpCAM, claudin-7, CO-029, and CD44v6 expression was evaluated in colorectal cancer (n = 104), liver metastasis (n = 66), and tumor-free colon and liver tissue. Coexpression and complex formation of the molecules was correlated with clinical variables and apoptosis resistance. EpCAM, claudin-7, CO-029, and CD44v6 expression was up-regulated in colon cancer and liver metastasis. Expression of the four molecules did not correlate with tumor staging and grading. However, coexpression inversely correlated with disease-free survival. Coexpression was accompanied by complex formation and recruitment into tetraspanin-enriched membrane microdomains (TEM). Claudin-7 contributes to complex formation inasmuch as in the absence of claudin-7, EpCAM hardly associates with CO-029 and CD44v6 and is not recruited into TEMs. Notably, colorectal cancer lines that expressed the EpCAM/claudin-7/CO-029/CD44v6 complex displayed a higher degree of apoptosis resistance than lines devoid of any one of the four molecules. Expression of EpCAM, claudin-7, CO-029, and CD44v6 by themselves cannot be considered as prognostic markers in colorectal cancer. However, claudin-7-associated EpCAM is recruited into TEM and forms a complex with CO-029 and CD44v6 that facilitates metastasis formation.

Epithelial cell adhesion molecule: more than a carcinoma marker and adhesion molecule

The epithelial cell adhesion molecule (EpCAM, CD326) is a glycoprotein of approximately 40 kd that was originally identified as a marker for carcinoma, attributable to its high expression on rapidly proliferating tumors of epithelial origin. Normal epithelia express EpCAM at a variable but generally lower level than carcinoma cells. In early studies, EpCAM was proposed to be a cell-cell adhesion molecule. However, recent insights revealed a more versatile role for EpCAM that is not limited only to cell adhesion but includes diverse processes such as signaling, cell migration, proliferation, and differentiation. Cell surface expression of EpCAM may actually prevent cell-cell adhesion. Here, we provide a comprehensive review of the current knowledge on EpCAM biology in relation to other cell adhesion molecules. We discuss the implications of the newly identified functions of EpCAM in view of its prognostic relevance in carcinoma, inflammatory pathophysiology, and tissue development and regeneration as well as its role in normal epithelial homeostasis.

Overexpression of the small transmembrane and glycosylated protein SMAGP supports metastasis formation of a rat pancreatic adenocarcinoma line

Small cell transmembrane and glycosylated protein (SMAGP) was recently identified in the metastasizing rat pancreatic adenocarcinoma line BSp73ASML. SMAGP, an evolutionary conserved transmembrane protein, is expressed on lateral epithelial cell membranes. SMAGP expression was restricted to or was upregulated in several metastasizing as compared to nonmetastasizing human and rat tumor lines. In contrast to nontransformed tissue, SMAGP was mainly expressed in the cytoplasm, as has already been described for high-grade human colorectal cancer. This raised the question on the impact of SMAGP on tumor progression. To answer the question, metastasis formation was evaluated in the nonmetastasizing rat pancreatic adenocarcinoma subline BSp73AS (AS), which was stably transfected with SMAGP cDNA (AS-SMAGP). Cytoplasmic SMAGP expression promoted cell agglomeration, but inhibited tumor cell proliferation, adhesion to and migration toward vitronectin and matrigel invasion, which was accompanied by a failure of actin reorganization. AS-SMAGP clones strongly promoted metastasis formation by dislodgment of normal tissue; 82% of rats developed lymph node metastasis as compared to 22% of rats receiving AS or mock-cDNA-transfected AS cells. The incidence of lung metastasis was increased from 6% in AS to 98% in AS-SMAGP tumor-bearing rats. Thus, SMAGP strongly promotes tumor progression. This likely is due to redistribution from the plasma membrane into the cytoplasm. SMAGP redistribution does not only facilitate tumor cell detachment from neighboring cells and the extracellular matrix, but obviously contributes actively by a not yet defined mechanism to tumor cell agglomeration and capillary plugging.

EGP-314 is expressed differentially in three brain zones at an early time in an experimentally induced ischemia rat model

Gene expression in frontal, occipital, and hippocampal regions of rat brains at 15 min of ischemic injury was studied in a rat model by producing focal cerebral ischemia through middle cerebral artery (MCA) occlusion without reperfusion. Catalase, epithelial glycoprotein (EGP-314), cytochrome C oxidase-subunit 1, ribosomal L31 protein, and ceruloplasmin were found to be differentially expressed. Specific primers were designed to study this newly reported brain EGP-314, a cellular adhesion molecule involved in cell-cell and cell-extracellular matrix interactions and related with cytoskeletal organization, differentiation, and proliferation. In the frontal and occipital lobes, EGP-314 expression was low in control and ischemic conditions and increased in sham injured conditions, whereas in the hippocampal region its expression was induced only by ischemia. In situ hybridization and immunohistochemistry revealed that EGP-314 mRNA and the protein were present in the ischemic hippocampus pyramidal neurons. DNA fragmentation was demonstrated by TUNEL and LM-PCR analysis in hippocampus region. TUNEL positive pyramidal neurons were observed at 15 min of ischemia. DNA ladder was found at 12 and 15 min of ischemia.

Biological role of Ep-CAM in the physical interaction between epithelial cells and lymphocytes in intestinal epithelium

The mucosal epithelium including intestinal epithelial cells (IECs) and intraepithelial lymphocytes (IELs) provide a first line of defense in the gastrointestinal tract. However, limited information is currently available concerning the nature of the physical interaction molecule that interconnects IECs and IELs. Among the several monoclonal antibodies (mAbs) generated by immunizing porcine IECs, mAb (5-15-1) was shown to strongly react with IELs in addition to IECs. MALDI-TOF-MS and tandem MS analysis suggested that the antigen belongs to a family of human homophilic epithelial cell adhesion molecule (Ep-CAM). The amino acid sequence of porcine Ep-CAM showed 82.8%, 78.1%, and 76.8% homology compared to human, mouse, and rat Ep-CAM. Moreover, 5-15-1 specifically reacted with transfectant of porcine Ep-CAM. These data suggest that the Ep-CAM may act as a physical homophilic interaction molecule between IELs and IECs at the mucosal epithelium for providing immunological barrier as a first line of defense against mucosal infection.

SMAGP, a new small trans-membrane glycoprotein altered in cancer

Using the Affymetrix array technology, we previously identified an EST strongly expressed in several metastatic cell lines. In the present study, we cloned the corresponding cDNA that encodes a new glycoprotein composed of 97 amino acids and containing a trans-membrane domain. Therefore, we named it SMAGP for Small trans-Membrane And Glycosylated Protein. SMAGP is strongly conserved during evolution. It is expressed by normal epithelia of various organs, the protein being notably localized to the lateral face of the plasma membrane of cohesive well-polarized epithelial cells. In addition, SMAGP contains binding domains for the protein 4.1 and the PDZ domain of MAGUK proteins. Similar protein features are observed in several cell-surface proteins involved via ternary complexes in intercellular processes leading to cytoskeleton assembly as well as intracellular signalling. Thus, SMAGP might similarly be involved in a scaffolding protein complex, and therefore participate in the epithelium organization or in subsequent functions. Immunohistochemical data obtained using human breast, colon and lung cancer samples sustain this hypothesis since they showed that, in both primary tumours and metastases, reduced expression and/or cytoplasmic redistribution of SMAGP is superimposable with low histological tumour differentiation features, namely a lack of epithelial cell polarity and disorganized tissue phenotype.

CD44 variant isoforms associate with tetraspanins and EpCAM

The metastasizing subline of the rat pancreatic adenocarcinoma BSp73 expresses a set of membrane molecules, the combination of which has not been detected on non-metastasizing tumor lines. Hence, it became of interest whether these molecules function independently or may associate and exert specialized functions as membrane complexes. Separation of CD44v4-v7 containing membrane complexes in mild detergent revealed an association with the alpha3 integrin, annexin I, EpCAM, and the tetraspanins D6.1A and CD9. EpCAM and the tetraspanins associate selectively with CD44 variant (CD44v), but not with the CD44 standard (CD44s) isoform. The complexes are found in glycolipid-enriched membrane (GEM) microdomains, which are dissolved by stringent detergents, but the complexes are not destroyed by methyl-beta-cyclodextrin (MbetaCD) treatment, which implies that complex formation does not depend on a lipid-rich microenvironment. However, a complex-associated impact on cell-matrix and cell-cell adhesion as well as on resistance towards apoptosis essentially depended on the location in GEMs. Thus, CD44v-specific functions may well be brought about by complex formation of CD44v with EpCAM, the tetraspanins, and the alpha3 integrin. Because CD44v4-v7-EpCAM complex-specific functions strictly depended on the GEM localization, linker or signal-transducing molecules associating with the complex are likely located in GEMs.

Gene expression analysis in Interleukin-12-induced suppression of mouse mammary carcinoma

Interleukin-12 (IL-12) has potent antitumor activities via natural killer cells and cytotoxic T lymphocytes. However, the molecular mechanisms whereby IL-12 induces tumoricidal activities are poorly understood. Here, we report the genome-wide analysis of gene expression in a primary murine mammary carcinoma model that resembles human breast cancer, following the therapeutic application of recombinant IL-12, which restricted tumor growth and metastasis. IL-12 was able to curtail neovascularization in the tumor as well as enhance the number of tumor-infiltrating lymphocytes. Comprehensive examination of global gene expression revealed IL-12-induced molecular changes associated with tumor regression and reduced lung metastasis, thus providing a high-resolution snapshot of a host response against a developing malignancy and a rich source of potential targets for therapeutic intervention of breast cancer.

The association of the tetraspanin D6.1A with the alpha6beta4 integrin supports cell motility and liver metastasis formation

The metastatic subline of a rat pancreatic adenocarcinoma differs from the non-metastasizing subline by overexpression of 5 membrane molecules: CD44 variant isoforms, EpCAM, the tetraspanin D6.1A, an uPAR-related molecule and, as described here, the alpha6beta4 integrin. An antibody-defined molecule was identified by mass spectrometry and cloning as alpha6beta4 integrin. Transfection-induced expression of alpha6beta4 in the non-metastasizing subline did not support migration on laminin 5 or tumor progression. However, when the non-metastasizing subline was doubly transfected to express alpha6beta4 and the D6.1A tetraspanin, intraperitoneally injected tumor cells frequently formed liver metastasis. For the following reasons we assume that metastasis formation is supported by an interaction between alpha6beta4 and D6.1A. (i) The 2 molecules can associate and co-localize. (ii) Co-localization is strengthened by PKC stimulation. (iii) PKC stimulation, which induces a migratory phenotype, leads to a redistribution of alpha6beta4/D6.1A complexes. In resting cells, the molecules co-localize at the trail of the cell; during PKC stimulation they become transiently internalized and are (re-)expressed in the leading lamella. Thus, in the appropriate milieu, i.e. intraperitoneally, alpha6beta4 changes from an adhesion-supporting towards a migration-supporting molecule by its association with a tetraspanin. The findings provide a convincing experimental explanation for the repeatedly described involvement of alpha6beta4 in tumor progression.