GJB5 association with BRAF mutation and survival in cutaneous malignant melanoma

BACKGROUND

Gap junctional intercellular communication is crucial for epidermal cellular homeostasis. Inability to establish melanocyte-keratinocytes contacts and loss of intercellular junction's integrity may contribute to melanoma development. Connexins, laminins and desmocollins have been implicated in the control of melanoma growth, where their reduced expression has been reported in metastatic lesions.

OBJECTIVES

The aim of this study was to investigate Connexin 31.1 (GJB5) expression and identify any association with BRAF mutational status, melanoma patient prognosis and MAPK inhibitors (MAPKi) treatment.

MATERIAL AND METHODS

GJB5 expression was measured at RNA and protein level in melanoma clinical samples and established cell lines treated or not with BRAF and MEK inhibitors, as well as in cell lines which developed MAPK inhibitors resistance. Findings were further validated and confirmed by analysis of independent datasets.

RESULTS

Our analysis reveals significant downregulation of GJB5 expression in metastatic melanoma lesions compared to primary ones and in BRAF mutated versus BRAF wild-type melanomas. Likewise, GJB5 expression is significantly lower in BRAF^V600E compared with BRAF^WT cell lines and increases upon MAPKi treatment. MAPKi-resistant melanoma cells display a similar expression pattern compared to BRAF^WT cells, with increased GJB5 expression associated with morphological changes. Enhancement of BRAF^V600E expression in BRAF^WT melanoma cells significantly upregulates miR-335-5p expression with consequent downregulation of GJB5, one of its targets. Furthermore, overexpression of miR-335-5p in two BRAF^WT cell lines confirms specific GJB5 protein downregulation. RT-qPCR analysis also revealed upregulation of miR-335 in BRAF^V600E melanoma cells, which is significantly downregulated in cells resistant to MEK inhibitors. Our data were further validated using the TCGA-SKCM dataset, where BRAF mutations associate with increased miR-335 expression and inversely correlate with GJB5 expression. In clinical samples, GJB5 underexpression is also associated with patient overall worse survival, especially at early stages.

CONCLUSION

We identified a significant association between metastases / BRAF mutation and low GJB5 expression in melanoma. Our results identify a novel mechanism of Gap-junctional protein regulation, suggesting a prognostic role for GJB5 in cutaneous melanoma.

Polarization Selectivity in Vibrational Electron-Energy-Loss Spectroscopy

Orientation-dependent aloof-beam vibrational electron-energy-loss spectroscopy is carried out on uniaxial icosahedral B_{12}P_{2} submicron crystals. We demonstrate that the high sensitivity of the signal to the crystal orientation allows for an unambiguous determination of the symmetry of normal modes occurring at the Brillouin zone center of this anisotropic compound. The experimental results are assessed using first-principles quantum mechanical calculations (density functional theory) of the dielectric response of the specimen. The high spatial resolution inherent to this technique when implemented in the transmission electron microscope thus opens the door to nanoscale orientation-dependent vibrational spectroscopy.

First-Principles Vibrational Electron Energy Loss Spectroscopy of β-Guanine

A general approach to model vibrational electron energy loss spectra obtained using an electron beam positioned away from the specimen is presented. The energy-loss probability of the fast electron is evaluated using first-principles quantum mechanical calculations (density functional theory) of the dielectric response of the specimen. The validity of the method is assessed using recently measured anhydrous β-guanine, an important molecular solid used by animals to produce structural colors. The good agreement between theory and experiments lays the basis for a quantitative interpretation of this spectroscopy in complex systems.

Abstract 5710: COX-1 and COX-2 polymorphisms, NSAID use, and the risk of colorectal neoplasia

Introduction: Nonsteroidal anti-inflammatory drugs (NSAIDs) reduce risk of colorectal adenomas and cancer. NSAIDs, including aspirin, target the prostaglandin H synthases, COX-1 and COX-2, which convert arachidonic acid into prostaglandins. We examined tagSNPs and candidate polymorphisms in COX-1 and COX-2 in relation to colorectal neoplasia risk and potential interactions with NSAID use.

Methods: A linkage-disequilibrium (LD)-based tagSNP-selection algorithm (r2=0.90, MAF=4%) identified tagSNPs in PTGS1 (COX-1) and PTGS2 (COX-2) representative of common genetic variation in Europeans. Including candidate polymorphisms, we genotyped 18 SNPs in PTGS1 and 17 SNPs in PTGS2. SNPs were genotyped on the same Illumina platform in three independent study populations that capture the range of colorectal carcinogenesis by including adenoma and cancer cases. We investigated these SNPs in relation to the risk of colorectal neoplasia and potential interactions with NSAID use in three US population-based case-control studies of colon cancer (n=1424) vs. controls (n=1780), rectal cancer (n=583) vs. controls (n=775), and colorectal adenoma (n=485) vs. controls (n=578). For single SNP associations, multiple logistic regression analysis was used, adjusting for age, sex, center and restricted to Caucasians (>90% of all study populations). No correction was made for multiple testing.

Results: There were no main associations with PTGS1 tagSNPs or candidate polymorphisms (R8W, P17L and L237M) and colorectal neoplasia risk. Although not statistically significant, the L15-L16 deletion allele showed a trend towards increased risk for both colon and rectal cancer, consistent with the previously reported increased adenoma risk. In PTGS2, a rare 5′ tagSNP (rs4648250, −1877A>G, MAF=1%) was associated with a marginally decreased risk of both rectal (OR: 0.24, 95% CI: 0.05-1.08) and colon cancer (OR: 0.63, 95% CI: 0.36-1.10).

NSAID use is known to reduce the risk of colorectal neoplasia and all three studies have shown the same protective effect in previous analyses. Interactions between genotypes and NSAID use essentially fell into one of two general categories: a) Individuals with the variant allele lost the protective effect of NSAID use (PTGS1 rs10306110-G, rectal p-interaction=0.02, adenoma p-int=0.08; PTGS2 rs689466-G, rectal p-int=0.03, colon p-int=0.18; rs20424-G, colon p-int=0.05; rs689469-A, colon p-int=0.03, rectal p-int=0.09).); and b) Individuals with the variant allele showed stronger protection with by NSAIDs than individuals with the wildtype genotype (PTGS1 rs6478565-G, rs10306135-T, rs10306164-G, rectal p-int=0.01-0.02).

Conclusion: These data suggest that a rare 5′ SNP in PTGS2 may predict risk of colorectal cancer and provide further evidence that genetic variability in PTGS1 and PTGS2 may modify the protective association between NSAID and colorectal neoplasia risk, especially for rectal cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5710.

Abstract 934: Phospholipase A2A polymorphisms and risk of colorectal neoplasia

Introduction: Pancreatic phospholipase A2 (also known as PLA2G1B or PLA2A) catalyzes the release of fatty acids from dietary phospholipids for adsorption in the small intestine. Some of the polyunsaturated fatty acids removed from the intestinal lumen are precursors to eicosanoids, which are linked to inflammation, cell proliferation and colorectal carcinogenesis. We suspect that genetic variation at the PLA2A locus might affect colorectal neoplasia and thus we evaluated the association of PLA2A tagSNPs with colorectal neoplasia risk in three independent study populations capturing the range of colorectal carcinogenesis.

Methods: A linkage-disequilibrium (LD)-based tagSNP selection algorithm (r2=0.90, MAF=4%) identified 3 tagSNPs in PLA2A. We genotyped these SNPs on the same Illumina platform in 3 US population-based case-control studies of colon cancer (1424 cases/1780 controls), rectal cancer (583 cases/775 controls), and colorectal adenomas (485 cases/578 controls). LD was calculated among Caucasian controls for each study. For gene-level associations, we conducted principal components analysis (PCA) and haplotype analysis. Multiple logistic regression was used for single SNPs, adjusting for age, sex, and study center, restricted to Caucasians (>90% of all study populations).

Results: Two PLA2A variants were statistically significantly associated with reduced risk of rectal cancer (rs5637, 3702G>A Ser98Ser, p-trend = 0.03 and rs9657930, 1593C>T p-trend = 0.01, see table). Linkage disequilibrium between the SNPs was modest (r2<0.6). Principal component analysis was significant (p=0.02). No statistically significant associations were observed with colon cancer or colorectal polyps overall; however, there was significant heterogeneity by tumor site for polyps (p= 0.01).

Conclusion: The results suggest that genetic variability in PLA2A affects susceptibility to rectal but not colon cancer. Additional observational and functional follow-up studies are needed.Table.Selected tagSNPs in PLA2A and risk of rectal cancer, adjusted for age, sex, and study centerSNPGenotypeCasesControlsOR95%CIp (2df)p-trendrs56373702 G>AGG4285361.00..  Ser98SerGA1472150.850.661.08   AA8230.430.190.980.060.03         rs9657930CC4886141.00..  1593 C>TCT891480.750.561.00   TT3100.390.111.430.050.01         rs2070873GG4365741.00..  3027 G>TGT1391811.000.781.29   TT6190.420.171.060.150.36Principal component analysis p= 0.02

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 934.

Mitochondrial DNA variability modulates mRNA and intra-mitochondrial protein levels of HSP60 and HSP75: experimental evidence from cybrid lines

To explore possible relationships between mitochondrial DNA (mtDNA) polymorphism and the expression levels of stress-responder nuclear genes we assembled five cybrid cell lines by repopulating 143B.TK(-) cells, depleted of their own mtDNA (Rho(0) cells), with foreign mitochondria with different mtDNA sequences (lines H, J, T, U, X). We evaluated, at both basal and under heat stress conditions, gene expression (mRNA) and intra-mitochondrial protein levels of HSP60 and HSP75, two key components in cellular stress response. At basal conditions, the levels of HSP60 and HSP75 mRNA were lower in one cybrid (H) than in the others (p = 0.005 and p = 0.001, respectively). Under stress conditions, the H line over-expressed both genes, so that the inter-cybrid difference was abolished. Moreover, the HSP60 intra-mitochondrial protein levels differed among the cybrid lines (p = 0.001), with levels higher in H than in the other cybrid lines. On the whole, our results provide further experimental evidence that mtDNA variability influences the cell response to stressful conditions by modulating components involved in this response. Sentence summary of the article: the results reported in the present study provide important experimental evidence that in human cells mtDNA variability is able to influence the cellular response to heat stress by modulating both the transcription of genes involved in this response and their intra-mitochondrial protein levels.

Probing physical properties of confined fluids within individual nanobubbles

Spatially resolved electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM) has been used to investigate a He fluidic phase in nanobubbles embedded in a metallic Pd(90)Pt(10) matrix. Using the 1s-->2p excitation of the He atoms, maps of the He density and pressure in bubbles of different diameters have been realized, to provide an indication of the bubble formation mechanism. Detailed local variations of the He K-line characteristics have been measured and interpreted as modifications of the electromagnetic properties of the He atom close to a metallic interface, which affects a correct estimation of the densities within the smallest bubbles.

Frequency of potential therapeutic targets identified by immunohistochemistry (IHC) and DNA microarray (DMA) in tumors from patients who have progressed on multiple therapeutic agents

3071

An important question that arises when caring for patients referred for phase I clinical trials is, if one studied the patients’ tumors carefully enough, would there be targets in those patients’ tumors for which a therapeutic agent might already be available. Perhaps treating the patient with that therapeutic agent would be better than trying the phase I agent. To address that issue we have performed IHC assays for up to 13 targets (e.g. Her2/neu, ER, c-kit, etc.) as well as a two color Agilent oligonucleotide microarray with 17, 085 unique probes, on tumors from patients with advanced cancer who have exhausted conventional therapy and who were undergoing a procedure for a cancer related matter (e.g. obstruction, ascites, etc.). Ninety-one patients had excess tissue submitted from the procedure, immediately frozen and subjected to microarray analysis and had IHC performed on sections obtained from the paraffin blocks prepared as part of their standard surgical workup. IHC was considered positive if ≥ 30% of tumor cells were scored as +1 or greater staining. For microarray studies the gene expressions were called significantly increased or decreased if the fold change in expression relative to the nominal tissue of origin reference was significant at p≤0.001. For the 91 patients where frozen tumor was submitted 89 (98%) of them had RNA that was of excellent quality. The findings were a surprise in that IHC identified an average of 1.2 targets (for which a conventional therapeutic agent is available) per patient (range 0 - 4 targets). The DMA identified an average of 3.3 targets per patient (range 0 - 8 targets). Overall, a target was found for 89 (98%) of the patients. This data indicates that using IHC and DMA one can consistently find a potential target for which we have a therapeutic agent in patients’ tumors even thought they have progressed on prior therapies. This has implications for patients’ planning on participating in phase I clinical trials. It is important to conduct a prospective clinical trial to determine whether the targets discovered using IHC and DMA can be used to select therapy which will further benefit the patient who would otherwise be participating in a phase I clinical trial.

[Table: see text]

Electron energy loss spectroscopy measurement of the optical gaps on individual boron nitride single-walled and multiwalled nanotubes

Spatially resolved electron energy loss spectroscopy experiments have been performed in an electron microscope on several individual boron nitride (BN) single-, double-, and triple-walled nanotubes, whose diameters and number of shells have been carefully measured. In the low-loss region (from 2 to 50 eV) the spectra have been analyzed within the framework of the continuum dielectric theory, leading to the conclusion of a weak influence of out-of-plane contribution to the dielectric response of the tubes. The gap has been measured to be independent of the nanotubes geometry, and close to the in-plane gap value of hexagonal BN (5.8+/-0.2 eV).

Reduced blood vessel formation and tumor growth in alpha5-integrin-negative teratocarcinomas and embryoid bodies

Embryonic stem (ES) cells-wild-type, heterozygous, or null for alpha5-integrin-were injected ectopically into syngeneic mice to develop teratocarcinomas. alpha5-null-derived teratocarcinomas were significantly smaller than the wild-type or alpha5 heterozygous tumors. Histological analysis revealed the presence of tissues derived from all three germ layers, in all tumors. However, alpha5-null teratocarcinomas displayed less undifferentiated tissue than did the controls. Decreased proliferation and increased apoptosis were observed in the undifferentiated areas of the alpha5-null teratocarcinomas. The expression of extracellular matrix proteins, fibronectin and tenascin-C, and the basement membrane components, laminin, entactin/nidogen, and collagen IV, was similar in the different tumors, although the deposition of these molecules was more disorganized in alpha5-null teratocarcinomas. The absence of alpha5-integrin in the various tissues of the alpha5-null tumors was confirmed by immunohistochemistry. Many vessels, but not all, stained positively for alpha5-integrin, showing that they were host derived. Analysis of the area occupied by vessels revealed, on average, an 8-fold decrease in alpha5-null teratocarcinomas compared with control tumors. Staining for smooth muscle alpha-actin showed that pericytes and smooth muscle cells were recruited around the vessels in all tumors, suggesting similar vessel differentiation. Deposition of EIIIA and EIIIB and fibronectin around the vessels was observed in all tumors. The fact that some, although few, alpha5-integrin-negative vessels existed in alpha5-null tumors indicated that alpha5-/- ES cells could differentiate into endothelial cells. Endothelial cell differentiation and vessel formation were analyzed also in vitro. alpha5-null ES cells were differentiated into embryoid bodies, although they were delayed in growth and attachment. Differentiation into endothelial cells was achieved, but the organization into a complex vasculature was delayed compared with controls. We conclude that alpha5beta1-integrin plays a significant role in vessel formation both in ES cell cultures and in teratocarcinomas. Reduced vascularization likely contributed to the reduced proliferation and increased apoptosis observed in alpha5-null teratocarcinomas.

In vivo roles of integrins during leukocyte development and traffic: insights from the analysis of mice chimeric for alpha 5, alpha v, and alpha 4 integrins

Mice chimeric for integrins alpha(5), alpha(V), or alpha(4) were used to dissect the in vivo roles of these adhesion receptors during leukocyte development and traffic. No major defects were observed in the development of lymphocytes, monocytes, or granulocytes or in the traffic of lymphocytes to different lymphoid organs in the absence of alpha(5) or alpha(V) integrins. However, in agreement with previous reports, the absence of alpha(4) integrins produced major defects in development of lymphoid and myeloid lineages and a specific defect in homing of lymphocytes to Peyer's patches. In contrast, the alpha(4) integrin subunit is not essential for localization of T lymphocytes into intraepithelial and lamina propria compartments in the gut, whereas one of the partners of alpha(4), the beta(7) chain, has been shown to be essential. However, alpha(4)-deficient T lymphocytes cannot migrate properly during the inflammatory response induced by thioglycolate injection into the peritoneum. Finally, in vitro proliferation and activation of lymphocytes deficient for alpha(5), alpha(V), or alpha(4) integrins upon stimulation with different stimuli were similar to those seen in controls. These results show that integrins play distinct roles during in vivo leukocyte development and traffic.

Dystrophic muscle in mice chimeric for expression of alpha5 integrin

alpha5-deficient mice die early in embryogenesis (). To study the functions of alpha5 integrin later in mouse embryogenesis and during adult life we generated alpha5 -/-;+/+ chimeric mice. These animals contain alpha5-negative and positive cells randomly distributed. Analysis of the chimerism by glucose- 6-phosphate isomerase (GPI) assay revealed that alpha5 -/- cells contributed to all the tissues analyzed. High contributions were observed in the skeletal muscle. The perinatal survival of the mutant chimeras was lower than for the controls, however the subsequent life span of the survivors was only slightly reduced compared with controls (). Histological analysis of alpha5 -/-;+/+ mice from late embryogenesis to adult life revealed an alteration in the skeletal muscle structure resembling a typical muscle dystrophy. Giant fibers, increased numbers of nuclei per fiber with altered position and size, vacuoli and signs of muscle degeneration-regeneration were observed in head, thorax and limb muscles. Electron microscopy showed an increase in the number of mitochondria in some muscle fibers of the mutant mice. Increased apoptosis and immunoreactivity for tenascin-C were observed in mutant muscle fibers. All the alterations were already visible at late stages of embryogenesis. The number of altered muscle fibers varied in different animals and muscles and was often increased in high percentage chimeric animals. Differentiation of alpha5 -/- ES cells or myoblasts showed that in vitro differentiation into myotubes was achieved normally. However proper adhesion and survival of myoblasts on fibronectin was impaired. Our data suggest that a novel form of muscle dystrophy in mice is alpha5-integrin-dependent.

A test of the role of alpha5 integrin/fibronectin interactions in tumorigenesis

Published data show that reduction or loss of fibronectin or its receptor, alpha5beta1 integrin, occurs frequently in tumors and transformed cells. Furthermore, restoration of these adhesion proteins has been reported to reduce tumorigenesis. These results suggest that fibronectin/alpha5beta1 interactions may act to suppress tumor development or progression. To test this hypothesis in the context of spontaneous tumor formation, we have analyzed tumor development in mice genetically altered in the genes for fibronectin or alpha5 integrin. Our results show that heterozygosity for either does not lead to an increased incidence of tumors, alteration in tumor spectrum, or increased levels of metastasis, even when the fibronectin or alpha5 mutations are combined with mutations in the p53 tumor suppressor gene that lead to spontaneous tumor formation and could also cause loss of heterozygosity. Furthermore, loss of heterozygosity for alpha5 was not a common concomitant of tumorigenesis or metastasis. Finally, chimeric animals containing high proportions of alpha5-null cells did not show an increased incidence of tumors or a change in tumor progression. We conclude that, in the genetic backgrounds studied here, loss of fibronectin or alpha5beta1 integrin does not contribute to tumorigenesis or metastasis.

Growth, differentiation and survival of HC11 mammary epithelial cells: diverse effects of receptor tyrosine kinase-activating peptide growth factors

The HC11 mouse mammary epithelial cells are a useful in vitro model of mammary cell differentiation. When treated with the lactogenic hormones mix dexamethasone, insulin and prolactin (DIP) these cells synthesize the milk protein beta-casein. HC11 cells express receptor tyrosine kinases (RTK) of various subclasses. Here we present an analysis of the effect of their stimulation on growth, differentiation and survival. Growth conditions are an important part in the HC11 cell differentiation program. In order to respond optimally to DIP, cells must be grown to confluency in medium containing epidermal growth factor (EGF) plus insulin, at which stage the cells are defined as competent. During the growth phase all the peptide factors rested in this study: EGF, fibroblast growth factor (FGF)-2, insulin, IGF-I, platelet-derived growth factor (PDGF) and stem cell factor (SCF), stimulated MAP kinase (ERK2) activity and-DNA synthesis. However, not all factors were equivalent in promoting competency. Only FGF-2 replaced EGF during growth, while IGF-1 or SCF were able to substitute for insulin. PDGF replaced neither EGF nor insulin and was ineffective as a competence factor. The only peptide which could substitute for insulin in the lactogenic DIP mix and induce beta-casein synthesis was IGF-1, albeit at a high concentration. Competent cultures of HC11 cells maintained in serum-free medium in the presence of only dexamethasone and prolactin undergo apoptosis, which is prevented by the addition of either insulin, IGF-1, FGF-2, or EGF, but not PDGF or SCF. We conclude that in HC11 cells all peptide factors induce DNA synthesis but have distinct effects on differentiation and survival in HC11 cells.

NDF/heregulin activates MAP kinase and p70/p85 S6 kinase during proliferation or differentiation of mammary epithelial cells

Neu differentiation factors (NDF) are a novel family of polypeptide factors which activate sub-class I tyrosine kinase receptors. In all mammary epithelial cells analysed in this study, NDF activates the same signalling pathways while it induces different, cell-specific biological effects. In AU565 cells which are growth inhibited, as well as in T47D or HC11 cells which proliferate in response to NDF, the MAP kinase isoforms p44ERK1 and p42ERK2 and the p70/p85 S6 kinase are activated. NDF stimulates tyrosine phosphorylation and the in vitro kinase activity of ErbB-2. When PKC is activated by TPA, NDF is no longer able to activate ErbB-2 in T47D cells, leading to a blockage of cell proliferation. Activation of ErbB-2 by point mutation, or by monoclonal antibodies, also stimulates both the MAPK and the p70/p85 S6 kinase pathways. The same monoclonal antibodies can induce AU565 cell differentiation. In summary, during growth or differentiation of mammary epithelial cells, NDF stimulates several independent signalling pathways which can also be triggered by ErbB-2 stimulation alone. PKC activation blocks the biological effect induced by NDF through negative modulation of ErbB-2.

Neu differentiation factor/heregulin modulates growth and differentiation of HC11 mammary epithelial cells

The HC11 mouse mammary epithelial cell line has proven to be a valuable in vitro model to study the roles of peptide factors and hormones involved in the growth and differentiation of mammary cells. Treatment of HC11 cells with the lactogenic hormones, dexamethasone, insulin, and PRL (DIP), leads to cellular differentiation and production of the milk protein beta-casein. We have analyzed the effects of Neu differentiation factor (NDF)/heregulin, a newly described activating ligand for erbB-2 and other members of the epidermal growth factor (EGF) receptor family, on cell growth and the expression of milk proteins in HC11 cells. In these cells, NDF induces tyrosine phosphorylation of erbB-2 and erbB-3. Both NDF and EGF stimulate HC11 cell proliferation and promote the responsiveness of HC11 cells to lactogenic hormones. NDF induces the expression of a 22-kilodalton milk protein. This protein is up-regulated by other factors, including dexamethasone, EGF, and basic fibroblast growth factor, and is controlled in a manner distinct from that of beta-casein. Like EGF, NDF inhibits the DIP-induced expression of beta-casein at the level of transcription. The inhibition is due to the negative effect of NDF on the activation of mammary gland factor (MGF/Stat5), a member of the Stat family of transcription factors, which is essential for beta-casein gene expression.

Oestrogen and epidermal growth factor down-regulate erbB-2 oncogene protein expression in breast cancer cells by different mechanisms

Mitogen-induced mammary cell growth is often accompanied by decreased levels of expression of the p185erbB-2 protein. We have previously reported that oestrogen inhibits erbB-2 mRNA and protein expression in breast cancer cells, while epidermal growth factor (EGF) treatment has been shown to decrease p185erbB-2 levels in normal mouse mammary epithelial cells. In the present work, we studied the effect of oestrogen and EGF on erbB-2 expression in oestrogen-responsive breast cancer cells. We observed that both oestrogen and EGF comparably down-regulated p185erbB-2 levels, while stimulating growth of T47D and ZR75.1 cells. Oestrogens, but not EGF, concomitantly down-regulated erbB-2 mRNA. Run-on analysis showed a reduced erbB-2 transcription rate in the presence of oestrogens. Furthermore, the transcriptional activity of a 219 bp proximal fragment of the human erbB-2 promoter was repressed by oestrogens, whereas it was enhanced by EGF. EGF stimulated both tyrosine phosphorylation and autokinase activity of p185erbB-2 down-regulates p185erbB-2 at a post-translational level. Thus, two factors converging in terms of effects on cell growth, display divergent mechanisms of regulation of erbB-2 expression.

Laminin and tenascin assembly and expression regulate HC11 mouse mammary cell differentiation

HC11 is a normal mouse mammary epithelial cell line that requires certain growth factors, such as EGF or bFGF, to respond optimally to lactogenic hormones and produce the differentiation marker beta-casein. Growth in insulin (Ins) or PDGF does not produce cells competent to respond to lactogenic hormones. Here we show that competency for differentiation is due at least in part to the modulation of extracellular matrix components. In particular we have studied laminin and tenascin. EGF alters endogenous laminin assembly. In addition, promotion of competency can be partially mimicked by plating HC11 cells on the E8 laminin fragment, which is able to induce lactogenic responsiveness in cells grown in the absence of EGF or bFGF. The production and assembly of tenascin is also dependent upon the growth conditions of the HC11 cells. EGF- or bFGF-grown competent cells produce tenascin but do not assemble it at the extracellular matrix as efficiently as Ins- or PDGF-grown, non-competent cells. This alteration apparently leads to a change in the cellular microenvironment that supports beta-casein production. In addition, when competent cells are plated on dishes coated with tenascin, lactogenic hormone induction of beta-casein is inhibited. The data suggest that tenascin assembly and beta-casein production are opposing features of a coordinated differentiation program of HC11 cells.

erbB-2 expression in estrogen-receptor-positive breast-tumor cells is regulated by growth-modulatory reagents

It has previously been shown that, in the estrogen-receptor-positive breast-tumor cell lines T47D and ZR75.1, the erbB-2 protein and mRNA content are controlled negatively and positively by, respectively, estrogens and anti-estrogens. Since estrogens have a positive effect on cell proliferation, while anti-estrogens inhibit cell growth, the results suggested that there may be an inverse correlation between growth and erbB-2 expression. We have now examined this matter further. The effect of various growth-modulatory agents including estrogen (E2), progesterone (Pg), retinoic acid (RA), epidermal growth factor (EGF), insulin (Ins), prolactin (Prl), 12-O-tetradecanolyl-phorbol-13-acetate (TPA) and dibutyryl-3':5'-cyclic-AMP (cAMP) on c-erbB-2 promoter activity, RNA and protein expression have been examined. The growth stimulators E2 and EGF both reduced the level of erbB-2 protein. However, while E2 clearly repressed erbB-2 transcription, in the case of EGF, neither mRNA nor transcription were decreased. Of the agents which inhibit the growth of T47D and ZR75.1 cells--Pg, Prl, cAMP, RA and TPA--only Pg and cAMP caused an increase in the erbB-2 protein level. Pg and cAMP positively influenced c-erbB-2 promoter activity and RNA amount. TPA and RA also increased promoter activity but neither erbB-2 mRNA nor protein level was enhanced. The erbB-2 protein expression in cultures of T47D and ZR75.1 cells at different densities was also analyzed. Both the level of erbB-2 protein and c-erbB-2 promoter activity rose markedly in confluent cultures, suggesting a transcriptional mechanism of control. In conclusion, the data suggest that the effects of various agents on erbB-2 expression are complex and cannot be explained simply as reflecting the growth state of the cells.

Growth suppression of normal mammary epithelial cells by wild-type p53

p53 mutations are frequent in human breast cancer. In order to understand the role of p53 in the context of the accumulation of mutations in breast cancer, a model of non transformed mammary cells was sought. The HC11 cells are immortalized, non transformed rodent mammary epithelial cells which synthesize milk proteins following stimulation with lactogenic hormones. p53 protein was readily detected in HC11 protein extracts with the PAb421 antibody. Two mutations were identified in the p53 cDNA from HC11 cells: a missense mutation at codon 138, substituting Trp for Cys, and a microdeletion, codon 123 to 130, of exon 5. The latter results from an intronic mutation of the splice acceptor site at the intron 4/exon 5 junction. The mutations affect separate p53 alleles, and no wt allele was found. Wt p53 was introduced into HC11 cells by means of a retroviral vector, under the control of a Cd(++)-inducible promoter. In the presence of CdSO4 a dramatic growth inhibition was observed. A temperature-sensitive mutant p53 gene was also transfected into HC11 cells. This resulted in a marked inhibition of cells growth at 32 degrees C, when the p53 is in the wt conformation, while no effect was observed at 37 degrees C, when the mutant conformation is predominant. wt p53-mediated inhibition of monolayer growth does not involve induction of programmed cell death and does not activate de novo synthesis of differentiation-specific milk proteins. We conclude that mutations in the p53 gene likely played a role in their immortalization. The HC11 cells provide a model for assessing the cooperative action of other mutations in mammary tumorigenesis.

Growth suppression of normal mammary epithelial cells by wild-type p53

We examined the status of the p53 gene in the HC11 normal mammary epithelial cells. Two mutations were identified: a Cys to Trp change at codon 138 and a microdeletion of codon 123 to 130 resulting from mutation of the splice acceptor site. These two mutations were independent, and no wild-type p53 allele was found. Introduction of wt-p53 strongly inhibited growth in monolayer. Thus, the absence of wt-p53 can be sufficient for the immortalization of mammary cells.

Surface expression of erbB-2 protein is post-transcriptionally regulated in mammary epithelial cells by epidermal growth factor and by the culture density

The control of expression of the erbB-2 protein was examined in two mammary epithelial cells lines, HC11 and 31E. The erbB-2 protein content varied dramatically depending upon cell density and upon the presence of epidermal growth factor (EGF) in the culture medium. The changes in protein content were not due to variation in the erbB-2 mRNA level. Analysis of the metabolic turnover of the erbB-2 protein showed that its rate of degradation was two- to threefold higher in cells growing at low density than in cells confluent for 2 days. The addition of EGF to the culture medium caused an increase in the phosphoamino acid content and an increase in the turnover of the erbB-2 protein. Cell fractionation experiments were performed, and a shift in the cellular localization of the erbB-2 protein towards the lysosomal compartment in EGF-treated HC11 cells was found. This is reflected by an increase in the degradation rate of the erbB-2 protein. These findings suggest that in mammary epithelial cells the stability of the erbB-2 protein is an important regulatory control point in determining the level of the protein. The degradation rate is sensitive to cell confluency and is controlled by EGF receptor activity.

The int-2 gene product acts as a growth factor and substitutes for basic fibroblast growth factor in promoting the differentiation of a normal mouse mammary epithelial cell line

We have investigated the effect of basic fibroblast growth factor (bFGF) and the related int-2 gene on the growth, transformation, and differentiation of HC11 mouse mammary epithelial cells. We show that in HC11 cells infected with int-2 retroviral expression vectors, the int-2 protein can function as a bFGF-like growth factor in stimulating: (a) HC11 cell proliferation in monolayer, (b) anchorage-independent growth in soft agar, and (c) soft agar growth of the bFGF-responsive SW13 tumor cell line. These effects are observed irrespective of whether the int-2 protein is expressed in its wild-type form or is linked to a signal peptide. A candidate bFGF receptor, which is the product of the flg gene and which may recognize the int-2 protein, is expressed at high levels in HC11 cells. Following epidermal growth factor or bFGF priming and subsequent treatment with lactogenic hormones, all of the int-2 infected and the parental HC11 cells synthesize similar levels of beta-casein. However, the autocrine expression of int-2 in HC11 cells abrogates their requirement for either exogenous epidermal growth factor or bFGF priming. These data suggest that, in HC11 cells, the growth factor activity of the int-2 gene is indistinguishable from that of bFGF and does not interfere with the mammary cell differentiation program associated with lactogenesis.

Epidermal growth factor receptor, but not c-erbB-2, activation prevents lactogenic hormone induction of the beta-casein gene in mouse mammary epithelial cells

The HC11 cell line was isolated from mammary gland cells of pregnant mice. The cells displayed a normal phenotype and retained some characteristics of mammary epithelial cell differentiation. After treatment with the lactogenic hormones prolactin and glucocorticoids, the HC11 cells expressed the milk protein beta-casein. Various oncogenes were transfected and expressed in HC11 cells. The oncogenes were tested for their transformation ability and for their effects upon the differentiation of the HC11 cells. All of the oncogenes tested, including activated human Ha-ras, human transforming growth factor-alpha, activated rat neuT, and human c-erbB-2 activated by a point mutation in the transmembrane domain, caused transformation of the HC11 cells, as shown by tumor formation in nude mice. HC11 cells expressing the neuT and activated c-erbB-2 genes synthesized beta-casein in response to lactogenic hormones, whereas those expressing the Ha-ras or transforming growth factor-alpha oncogenes were no longer able to respond to the lactogenic hormones. This inhibition of beta-casein production occurs at the transcriptional level and in the transforming growth factor-alpha-transformed cells is due to an autocrine mechanism involving the activation of the epidermal growth factor receptor. This suggests that, although the c-erbB-2 and epidermal growth factor receptors are structurally quite similar, their activation has different effects upon mammary epithelial cell differentiation.

Inhibition of c-erbB-2 oncogene expression by estrogens in human breast cancer cells

The c-erbB-2 oncogene is thought to play a relevant role in the development and progression of mammary neoplasia. Using the human breast cancer cell lines T47D and MCF7, we found that the arrest of cell growth induced by a steroid-depleted medium was accompanied by a strong increase of c-erbB-2 mRNA and of the c-erbB-2-encoded p185 protein. The treatment of arrested cells with estrogens was found to resume cell proliferation and to inhibit dramatically c-erbB-2 expression at both mRNA and protein level. The regulation of c-erbB-2 expression was remarkably different from that observed for c-myc, which was strongly stimulated by estrogens, and ras, whose expression was unaffected all through the treatments. In addition, in the normal rat mammary gland undergoing development and differentiation during pregnancy and lactation, p185 expression was detected only in the functionally differentiated tissue. Altogether, our data indicate that the expression of c-erbB-2 is repressed during estrogen-induced proliferation and enhanced during growth arrest and/or differentiation of mammary cells.