Single-steep transformation of human breast epithelial cells by SV40 large T oncogene

Decreased autocrine EGFR signaling in metastatic breast cancer cells inhibits tumor growth in bone and mammary fat pad

Breast cancer metastasis to bone triggers a vicious cycle of tumor growth linked to osteolysis. Breast cancer cells and osteoblasts express the epidermal growth factor receptor (EGFR) and produce ErbB family ligands, suggesting participation of these growth factors in autocrine and paracrine signaling within the bone microenvironment. EGFR ligand expression was profiled in the bone metastatic MDA-MB-231 cells (MDA-231), and agonist-induced signaling was examined in both breast cancer and osteoblast-like cells. Both paracrine and autocrine EGFR signaling were inhibited with a neutralizing amphiregulin antibody, PAR34, whereas shRNA to the EGFR was used to specifically block autocrine signaling in MDA-231 cells. The impact of these was evaluated with proliferation, migration and gene expression assays. Breast cancer metastasis to bone was modeled in female athymic nude mice with intratibial inoculation of MDA-231 cells, and cancer cell-bone marrow co-cultures. EGFR knockdown, but not PAR34 treatment, decreased osteoclasts formed in vitro (p<0.01), reduced osteolytic lesion tumor volume (p<0.01), increased survivorship in vivo (p<0.001), and resulted in decreased MDA-231 growth in the fat pad (p<0.01). Fat pad shEGFR-MDA-231 tumors produced in nude mice had increased necrotic areas and decreased CD31-positive vasculature. shEGFR-MDA-231 cells also produced decreased levels of the proangiogenic molecules macrophage colony stimulating factor-1 (MCSF-1) and matrix metalloproteinase 9 (MMP9), both of which were decreased by EGFR inhibitors in a panel of EGFR-positive breast cancer cells. Thus, inhibiting autocrine EGFR signaling in breast cancer cells may provide a means for reducing paracrine factor production that facilitates microenvironment support in the bone and mammary gland.

PTHrP P3 promoter activity in breast cancer cell lines: role of Ets1 and CBP (CREB binding protein)

Parathyroid hormone-related protein (PTHrP) is produced by many tumors including breast cancer. We have reported that Ets1 factor activates P3 PTHrP promoter in our model of tumorigenic breast cancer cell and not in pre- or non-tumorigenic cell lines, thus contributing to an increased PTHrP production. In this study, gel retardation assays revealed that Etsl and its promoter binding site (EBS) specifically formed complexes whose abundance correlates with Ets1 levels in the three cell lines. Coexpression of Etsl and CBP induced a synergistic activation of the P3 promoter only in the tumorigenic cell line. This synergism required the integrity of the EBS and was abrogated by E1A. All breast cancer cell lines showed high basal concentrations of phosphorylated CREB. Moreover a CRE-like sequence was also required for Ets1/CBP synergy and, finally, CREB expression was found to enhance the PTHrP P3 promoter activity. Thus a multipartite complex of transcription factors and coactivators seems to regulate PTHrP transcription and contribute to the alterations that promote tumorigenic behavior in breast epithelial cells.

Transforming growth factor beta-1 and amphiregulin act in synergy to increase the production of urokinase-type plasminogen activator in transformed breast epithelial cells

Amphireguline (AR) is an epidermal growth factor (EGF)-related peptide that seems to play an important role in breast cancer progression. We have demonstrated recently that suppression of AR expression in transformed breast epithelial cells considerably reduced both size and neovascularization of tumors developed in nude mice. We show that the reduction of AR expression allowed to an important decrease of the levels of urokinase-type plasminogen activator (uPA) and transforming growth factor-beta1 (TGFbeta1). According to these data, exogenous AR (10(-10) M-10(-8) M) stimulated the production of uPA and TGFbeta1 in AR antisense-transfected A2-15 and A2-P17F25 cells. The addition of 2 x 10(-10) M TGFbeta1 into culture medium increased the level of uPA produced by AR-expressing parental cells but not by A2-15 and A2-P17F25 cell clones. Whereas AR alone stimulated uPA production to 200% of control, combined AR and TGFbeta1 treatment increased protease level in A2-15 and A2-P17F25 cells to 500-600% of control, demonstrating a synergism between TGFbeta1 and AR. This was accompanied by an important augmentation of the number of tumoral cells that invaded matrigel in vitro. The synergistic induction of uPA protein resulted of an early and transient augmentation of steady state mRNA level and was blocked in the presence of the MAP kinase kinase inhibitor PD098059, strongly suggesting that synergistic effect of AR and TGFbeta1 on uPA expression required MAPK pathway. This data demonstrates concerted action between AR and TGFbeta1 that may have profound effect on protease production and consequently on breast cancer progression.

Ets-1 activates parathyroid hormone-related protein gene expression in tumorigenic breast epithelial cells

Parathyroid hormone-related protein (PTHrP) is produced by many tumors not associated with humoral hypercalcemia, including breast cancers. In this study, we used three human immortalized mammary epithelial cell lines that differ in tumorigenicity and PTHrP expression. Using RT-PCR we investigated 5' and 3' alternative splicing of PTHrP transcripts and promoter usage in the lines. Increased levels of P3-derived transcripts and the 1-139 mRNA isoform were observed in the most tumorigenic cell line. Transient transfection experiments identified elements close to P3 promoter that appeared to account for a portion of differential PTHrP expression among the three cell lines. Using site-directed mutagenesis, a previously described Ets-1/Sp1 binding site upstream of P3 was determined to be crucial for full activity of this promoter. RT-PCR and western blot evaluation of Ets family member expression found that Ese-1 was present in all three lines, but that appreciable levels of Ets-1 protein were present exclusively in the most tumorigenic line. Cotransfection of Ets-1 expression vectors activated PTHrP reporter constructs in the most tumorigenic line but not in the other cell lines. These findings suggest a potential mechanism by which PTHrP transcription may be regulated as a consequence of events that promote tumorigenic behavior in breast epithelial cells.

Effects of simian virus 40 T-antigens on normal human mammary epithelial cells reveal evidence for spontaneous alterations in addition to loss of p16(INK4a) expression

Under standard culture conditions, normal human mammary epithelial cells (HMECs) divide a limited number of times before proliferation ceases in a growth-arrested state referred to as selection. Cells that have undergone spontaneous loss of p16(INK4a) expression due to hypermethylation of the p16(INK4a) CpG island emerge from selection and proliferate for an extended, but limited, period before senescence. Here we show, as expected, that selection was bypassed by expression of SV40 large T-antigen proteins containing an intact pRb-binding domain in preselection cells. These cells were immortalized with high efficiency (seven of nine separate cultures). Also as expected, postselection cells were immortalized by expression of the human papillomavirus-16 E6 oncoprotein (four of four cultures), which inactivates p53 protein. In contrast, we found that expression of SV40 large T-antigen protein, which also inactivates p53, was poorly maintained in postselection cultures due to its growth-suppressive effects; consequently, these cells became immortalized at low efficiency (one of 11 cultures). Reexpression of p16(INK4a) in postselection HMECs by the demethylating agent, 5-azacytidine, or transfection of a p16(INK4a) expression plasmid did not restore the ability of these cells to undergo SV40-induced transformation. Postselection HMECs are a widely used in vitro model system, but these observations indicate they have undergone changes in gene expression in addition to loss of p16(INK4a) expression.

An in vitro model of human breast carcinogenesis: epigenetic aspects

A review is given of 12 years of research on a human breast epithelial cell line, HMT-3522, which has undergone malignant transformation in vitro without being exposed to known carcinogenic agents. Epigenetic aspects of the malignant transformation have been considered and the results have been viewed in a clinical context. It has been concluded that the history and characteristics of the cell line resembles the comedocarcinoma of the human breast. It is hypothesized that progression from benign lesion to comedo in situ carcinoma and invasive carcinoma occurs if low levels of epidermal growth factor are prevailing in the microenvironment. Our data also suggest that breast cancer developed under high epidermal growth factor receptor activity is estrogen receptor negative, while suppression of epidermal growth factor receptor activity promotes estrogen responsive breast cancer.

Parathyroid hormone-related peptide stimulates proliferation of highly tumorigenic human SV40-immortalized breast epithelial cells

Parathyroid hormone-related protein (PTHrP) is the main mediator of humoral hypercalcemia of malignancy (HHM) and it is produced by many tumors, including breast cancers. Breast epithelial cells as well as breast cancer tumors and cell lines have been reported as expressing PTHrP and the PTH/PTHrP receptor, suggesting that PTHrP may act as an autocrine factor influencing proliferation or differentiation of these cell types. We investigated PTHrP gene expression, PTH/PTHrP receptor signaling, and PTHrP-induced mitogenesis in three immortalized human mammary epithelial cell lines that exhibit differential tumorigenicity. The most tumorigenic cells expressed the highest levels of PTHrP messenger RNA (mRNA) and protein. We used reverse-transcription polymerase chain reaction (RT-PCR) and immunoblotting to detect the PTH/PTHrP receptor transcripts and proteins in all of the three cell lines. Treatment with human PTHrP(1-34) [hPTHrP(1-34)] and hPTH(1-34) increased intracellular cyclic adenosine monophosphate (cAMP) but not free Ca2+ in the nontumorigenic line. These agonists increased both cAMP and free Ca2+ levels in the moderately tumorigenic line, but only increased free Ca2+ in the highly tumorigenic line. Application of the PTH/PTHrP receptor antagonist [Asn10,Leu11,D Trp12]PTHrP(7-34) or PTHrP antibodies reduced [3H]thymidine incorporation in a dose-dependent fashion in the highly tumorigenic cell line but did not affect the other lines. Thus, treatment with a PTH/PTHrP receptor antagonist reduced cell proliferation, suggesting that PTHrP signaling mediated by the phospholipase C (PLC) pathway stimulates proliferation of a highly tumorigenic immortalized breast epithelial cell line.

Establishment of a human polyclonal oral epithelial cell line

OBJECTIVE

To develop a human oral epithelial cell line to constitute a continuous source of cells readily available for human oral epithelial cell research.

STUDY DESIGN

Oral epithelial cells from a 30-week gestational, stillborn male fetus were grown in serum-free medium and transfected by lipid-mediation with the shuttle vector plasmid, pZ189, containing the T-antigen coding region and replication origin from the SV40 virus.

RESULTS

Resulting cultures produced foci of rapidly multiplying cells that failed to senesce, in contrast to controls. The transformed culture, designated GMSM-K, was polyclonal. The original culture possessed a normal human male karyotype, and the transformed line was largely hypotetraploid. Multiple clones, isolated from soft agar studies and low density plating, showed decreased doubling times. Electron microscopy and immunohistochemistry confirmed an epithelial phenotype. Cells did not generate tumors in nude mice.

CONCLUSION

Few human epithelial cell lines are available to investigators and most are tumor-derived. The nontumor-derived GMSM-K line has value as a resource for human oral epithelial cell research.

Antisense expression for amphiregulin suppresses tumorigenicity of a transformed human breast epithelial cell line

The epidermal growth factor (EFG) family of receptors and their respective ligands play a major role in breast cancer progression and are the targets of new therapeutic approaches. Following immortalization with SV40 T antigen of normal human breast epithelial cells, a transformed variant cell line (NS2T2A1) was selected for its increased tumorigenicity in nude mice. This cell line was shown to have a higher expression of EGF receptors (EGFR) and amphiregulin (AR) when compared to their normal counterparts or less aggressive transformed cells. Dual staining of EGFR and AR was observed in 50-60% of NS2T2A1 cells, while 30-40% cells expressed AR only. To explore the potential tumorigenic role of AR, a 1.1 kb AR cDNA in an antisense orientation was transfected in NS2T2A1 cells. Three clones, selected by hygromycin B, expressed AR antisense RNA (AR AS1, AR AS2 and AR AS3 cell lines) in which AR protein expression was reduced (ranging from about 50 to < 5%). The anchorage-independent growth of AR AS cell lines was reduced to levels ranging from 32.4-6.8% relative to the control cell line transfected with the vector alone. The clones expressing AR antisense RNA showed a reversion of the malignant phenotype when injected in nude mice, since a significant reduction of tumor intake was observed coincident with a significant tumor mass reduction (> 96%). Moreover, intra-tumoral vascularization decreased significantly in tumors derived from AR AS cells (26.7, 70.7 and 50.4% of control). These in vitro and in vivo data reveal the oncogenic nature of AR in transformed breast epithelial cells and imply a role for AR in tumor angiogenesis.

Role of epidermal-growth-factor receptor in tumor progression in transformed human mammary epithelial cells

The presence of epidermal-growth-factor receptors (EGFR) and of its ligands (TGFalpha and amphiregulin) in breast-cancer tissues suggests that they play a paracrine/autocrine role in tumor growth or progression. This hypothesis was tested on 3 cell lines, S2T2, NS2T2A and NS2T2A1. These epithelial cells are derived from a normal human breast-epithelial-cell culture transformed by SV40-T Ag, are of the same clonal origin, have respectively increasing levels of EGFR, TGFalpha, amphiregulin and of thymidine-kinase activity associated with increasing tumorigenic potential in nude mice (tumor intake and tumor volume). The monoclonal antibody MAb 425, which blocks ligands interaction with EGFR, reduced by more than 90% anchorage-independent growth of the most tumorigenic cells, NS2T2A1. Another anti-EGFR MAb, 528, reduced to 25% of controls the mean tumor mass after NS2T2A1 grafting in mice. Anti-sense RNA expression of EGFR in these cells confirmed the importance of this receptor in tumor progression, since it reduced significantly the tumor volume and tumor weight of NS2T2A1 cells to 16% of those in mock-transfected control cells.

Growth requirements and neoplastic transformation of two types of normal human breast epithelial cells derived from reduction mammoplasty

A chemically defined culture medium was developed to support the growth of two distinctly different types of normal human breast epithelial cells (HBEC) derived from reduction mammoplasty. Type I cells expressed luminal epithelial cell markers and were deficient in gap junctional intercellular communication (GJIC), whereas Type II cells expressed basal epithelial cell markers and were efficient in GJIC. In this study, we examined and compared the growth factor and hormone requirements of these two types of cells and a series of cell lines that were obtained by sequential transfection with SV40 DNA (extended lifespan, nontumorigenic), treatment with 5-bromodeoxyuridine (BrdU)/black light (immortal and weakly tumorigenic), and infection of a virus carrying the neu oncogene (highly tumorigenic). Growth of Type I cells was inhibited by withdrawing epidermal growth factor (EGF), hydrocortisone (HC), or insulin (INS) from the culture media, but was enhanced by fetal bovine serum (FBS) supplementation. Growth of Type II cells was inhibited by withdrawal of EGF, HC, or INS from the media, and was inhibited by FBS supplementation. Withdrawal of human transferrin (HT) or 17 beta-estradiol (E2) from the media did not alter the growth of Type I or Type II cells. SV40 transfected Type I cell lines still required EGF, HC, or INS for optimal growth. However, the highly tumorigenic cell line did not show a growth dependence on EGF, HC, or INS but did appear to require HT and 3,3',5-triiodo-D.L. thyronine (T3) for optimal growth. In addition, FBS stimulated the growth of these cell lines. Thus, this study shows that Type I HBEC are distinctly different from Type II HBEC in growth response to FBS and that neoplastically transformed Type I cells could become growth factor and hormone independent.

Defective interleukin six expression and responsiveness in human mammary cells transformed by an adeno 5/SV40 hybrid virus

Mammary epithelial cells (MECs) were isolated and cultured from mammary glands of healthy women undergoing reduction mammoplasty. Normal MECs were infected with the transforming hybrid virus adeno-5/SV40. Two transformed epithelial cell lines, M1 and M2, were obtained, characterised phenotypically and studied for the production of and the response to cytokines and growth regulators. In both cell lines, expression of the SV40 large T antigen was associated with loss of interleukin 6 (IL-6) production and responsiveness as well as with down-regulation of IL-8 and transforming growth factor (TGF)-alpha production. Both M1 and M2 cell lines were capable of forming colonies in semisolid media, but upon injection into severe combined immunodeficient (SCID) mice only M2 cells were tumorigenic. DNA synthesis in M1 cells was partially inhibited by serum or TNF-alpha and weakly stimulated by hydrocortisone (HC) and IL-8. In contrast, M2 cells were totally unresponsive to a variety of growth regulators. Both lines overexpressed the p53 protein at levels about 20-fold higher than those observed in primary MEC cultures, but no mutations of the p53 gene could be detected. The date confirm the view that the expression in human mammary cells of different oncogenes - including the SV40 T antigen - is frequently associated with alterations of cytokine production and responsiveness.

Biodistribution of iodine-125 tyramine transforming growth factor alpha antisense oligonucleotide in athymic mice with a human mammary tumour xenograft following intratumoral injection

The Watson-Crick base pairing rule provides the underlying principle for the antisense (AS) approach to inhibiting gene expression. Transforming growth factor alpha (TGFalpha) was the first growth factor to be associated with tumorigenesis, thus making the TGFalpha (mRNA) a potential target for AS therapy and offering the potential for monitoring of the progression of malignancy by non-invasive imaging with radiolabelled AS phosphodiester. Probe labelling and biodistribution were studied in the present report. A 23-mer oligonucleotide sequence was synthesized and grafted in 5' with a tyramine group which was further radioiodinated. The radiolabelled AS was injected intratumorally in mammary tumour-bearing BALB/c mice (3 weeks after inoculation of 7.10(6)NS2T2A mammary cells). Biodistribution was monitored by sequential scintigraphy and organ radioactivity after autopsy. The 5' tyramine group allowed specific and stable radiolabelling of the AS with 125I. The 125I AS oligonucleotide was rapidly cleared from the tumour by intestine and kidneys. Four hours after intratumoral injection, 6.5%+/-1.5% of the dose was retained in the tumour as non-degraded 125I AS. It is concluded that 5' tyraminylated AS provides information on the biodistribution of AS oligonucleotide following intratumoral injection. These data will contribute to the pharmacology of AS oligonucleotides which can be used for therapy.

Tumor viruses and endogenous retrotransposons in mammary tumorigenesis

Much of our knowledge about the intricate pathways and molecular mechanisms involved in the conversion of a normal mammary epithelial cell to malignancy derives from studies on mammary tumorigenesis induced by the retrovirus mouse mammary tumor virus. In addition, three DNA tumor viruses, simian virus 40, polyomavirus, and human papillomavirus, have been instrumental in dissecting the series of steps comprising neoplastic progression of mammary epithelium, particularly with cultured human breast cells. Endogenous transposons are analogous bioagents receiving increased attention recently. At least 10% of the cell genome consists of transposable elements, a growing number of which have been implicated in mutagenizing DNA in a variety of human tissues and disorders. Research efforts have therefore intensified to determine if endogenous elements such as retrotransposons participate in the development of breast cancer in animals and humans.

Recurrent cytogenetic alterations of prostate carcinoma and amplification of c-myc or epidermal growth factor receptor in subclones of immortalized PNT1 human prostate epithelial cell line

To develop an experimental prostate cancer model, we immortalized normal human prostate adult epithelial cells with SV40 large-T antigen. Two sublines were derived in culture, namely PNT1A and PNT1B. They retained the characteristics of prostate epithelial cells, but did not clone in soft agarose. PNT1A occasionally formed undifferentiated adenocarcinoma tumors in nude mice, but only in the presence of matrigel. PNT1A and PNT1B displayed common cytogenetic alterations: a 10q arm deletion, which is a recurrent alteration in prostate carcinoma, chromosome losses and a translocation involving chromosome 5. An extensive study of oncogenic alterations occurring in these cells showed that PNT1A displayed c-myc gene amplification, forming an hsr on chromosome 4, as well as gene amplification, forming an hsr on chromosome 4, as well as c-myc mRNA overexpression, with a faster doubling time (25 hr); moreover, it seemed less sensitive to EGF than PNT1B. PNT1B had a doubling time identical to that of normal cells (48 hr) but displayed EGF receptor gene amplification accompanied by an increased number of EGF binding sites and sensitivity to EGF. Because both cell lines displayed cytogenetic and oncogenic alterations found in prostate cancer, as well as differing malignant potentials, they represent an interesting model for studying the progression of prostate tumors.

Modulation of cell phenotype in human osteoblast-like cells by the simian virus 40

At present, the majority of in vitro research into bone metabolism is performed on either primary cultures of bone or osteosarcoma lines. A better model of the behaviour of normal bone cells would be a cell line derived from normal, adult bone that retained osteoblast-like characteristics. We infected a culture of bone cells from adult humans with simian virus 1613, a variant of the simian virus 40, and obtained 12 clones of variable morphology. The clones were maintained in culture for as long as 6 months. Population doubling times, synthesis of alkaline phosphatase and osteocalcin, secretion of mineral, morphology, and ability to withstand freezing were examined. SV/EC cell morphology varied from the polygonal, osteoblast-like to the bipolar, fibroblast-like. Population doubling times ranged from 0.55 to 2.8 days (compared with 3.9 days for the nontransformed human osteoblast-like cells). Synthesis of alkaline phosphatase varied but was less than that by the human osteoblast-like cells. With the exception of clone 11, all of the transformed clones synthesised mineral in vitro under mineralising conditions. Four clones showed increased synthesis of alkaline phosphatase and increased population doubling times after passaging. All of the clones were successfully frozen and thawed, but, unlike normal human osteoblast-like cells, none responded to stimulation with parathyroid hormone.(ABSTRACT TRUNCATED AT 250 WORDS)

Loss of chromosome 3p arm differentiating tumorigenic from non-tumorigenic cells derived from the same SV40-transformed human mammary epithelial cells

After immortalization of human normal mammary epithelial cells by replication-defective SV40 genome integration, 2 cultures were developed independently. Both had the same integration site, in band 9q21, but rapidly diverged karyotypically. After a few passages, one, designated SC2T2, exhibited near-diploid (a) and the other, designated SL2T2, near-tetraploid (b) karyotypes. The simplest formulas were 44, X, -X, der(3;22) (q10;q10), der(4) t(4;9)(q34;q12), +8, +9, add(13)(p1), der(19) t(8;19)(q21;p13.3), add(22)(p1) for karyotype (a) and 93, XXXX, add(1)(q12), add(11)(q13), +20 for karyotype (b). A number of alterations were further acquired with passages. Both cell cultures were tumorigenic, but their efficiency of grafting in nude mice largely differed: it was low for SL2T2 and high for SC2T2 cultures. All cultures of the xenografted tumors, obtained from either SL2T2 or SC2T2, exhibited the same clonal anomalies as those characterizing karyotype (a). It was concluded that only cells with karyotype (a) were tumorigenic, and that the difference in the tumorigenic potential of cultures SC2T2 and SL2T2 was related to their richness in cells with this karyotype. The comparison of the various karyotypes, together with data obtained in other cell types transformed by SV40, suggests that the acquisition of tumorigenicity in S2T2 mammary epithelial cells may be related to the loss of chromosome 3p arm.

Growth factor requirement, oncogene expression and TP53 mutations of a tumorigenic and a non-tumorigenic subline of the human breast carcinoma cell line, HMT-3909

From a human breast carcinoma cell line, HMT-3909, a tumorigenic and a non-tumorigenic subline have previously been described. Cells of both sublines have been characterised as carcinoma cells. In the present work we examined whether differences in growth factor requirements or oncogene expression may explain the difference in tumorigenicity. We found that exogenous growth factor dependence discriminated between the two sublines. No alterations in oncogenes or tumour suppressor genes were demonstrated that could explain the differences in tumorigenicity. The lower growth factor requirement and the higher growth rate of the tumorigenic subline indicates that, in these cells, growth potential may determine the outcome of the tumorigenicity assay.

EGF modulation of the ras-related rhoB gene expression in human breast-cancer cell lines

The mRNA levels of the ras-related human rhoA, rhoB and rhoC genes were studied in human breast-cancer cell lines (HBCal), and in normal and immortalized mammary epithelial cells (HMEC) by Northern blot analysis and in situ hybridization. In contrast to the ubiquitous rhoA and rhoC gene expression, dramatic variations in the mRNA level of the rhoB gene were evidenced. The rhoB mRNA level appeared to be inversely correlated to the amounts of the epidermal-growth-factor(EGF) receptors in these cells. The rhoB transcripts were detected at high levels in ZR75-1, MCF7, HSL 53, HSL 59, HSL 90, T47D and SKBR3 HBCal, at hardly detectable levels in BT 20, MDA-MB 231 and H466B HBCal and at intermediate levels in normal and immortalized breast epithelial cells. Rapid and transient induction of the rhoB transcription was observed after EGF treatment in serum-deprived MDA-MB231, T47D and immortalized epithelial cells. In contrast, no modulation of rhoB expression by EGF could be objectified in the MCF7 and ZR75-1 cell lines. Yet a normal function of EGF receptors was evidenced, since the immediate early gene c-fos was rapidly induced, suggesting a constitutive expression of rhoB in these cell lines bypassing the regulation by EGF. In human mammary epithelial cells, rhoB mRNA is rapidly and transiently induced with EGF concentrations known to stimulate cell proliferation. This suggests that the rhoB product might be involved in a cascade that initiates or promotes cell proliferation, and plays an important role in EGF-stimulated growth of breast normal and cancer cells.

Analysis of proviral integration in human mammary epithelial cell lines immortalized by retroviral infection with a temperature-sensitive SV40 T-antigen construct

A panel of eight conditionally immortal lines derived by infection of human breast epithelial cells with an amphotropic retrovirus transducing a ts mutant of SV40 large T-antigen was analyzed with respect to individual retroviral integration patterns. Each line contained multiple integration sites which were clonal and stable over extended passage. Similar integration patterns were observed between individual lines arising separately from the same stock of pre-immortal cells, suggesting a common progenitor. Retroviral integration analysis of pre-immortal cells at different stages of pre-crisis growth showed changes indicative of a progressive transition from polyclonality to clonality as the cells approached crisis. Each of the immortal lines contained a sub-set of the integration sites of their pre-immortal progenitors, with individual combinations and copy numbers of sites. Since all the cell lines appeared to originate from single foci in separate flasks, it is likely that each set arose from a common clone of pre-immortal cells as the result of separate genetic events. There was no evidence from this analysis to suggest that specific integration sites played any part either in the selection of pre-crisis clones or in the subsequent establishment of immortal lines.

Transformation and immortalization of Leydig cells from the Sprague-Dawley rat by an early genetic region of simian virus 40 DNA

Two transformed cell lines of rat Leydig cells were established by transfection of primary cells with the transforming region of simian virus (SV40) DNA. Normal adult Leydig cells are non-proliferating cells and cease to grow after the first trypsinization for cell culturing. The cell lines, NWL2 and NWL15, continued to proliferate and subsequently needed subculturing every 2 weeks (split ratio 1:2). No crisis was observed after 35 passages for 18 months. Nile red staining showed the presence of lipid droplets in both normal and transformed cells, although the transformed cells had 2-3-fold higher amounts than the normal cells. The integration of T-antigen DNA has taken place in at least 2 and 1 sites in NWL2 and NWL15, respectively. Both cell lines expressed T-antigen mRNA. The cell lines expressed luteinizing hormone receptor (LH-R) (a Leydig cell-specific gene), insulin-like growth factor-I, insulin-like growth factor-I receptor (IGF-I-R) and insulin-like growth factor binding protein-2 (IGFBP-2) genes. The amounts of transcripts of LH-R were lower in the transformed cells as compared to the normal cells. The IGF-I-R mRNA levels were comparable to those of the normal Leydig cells. NWL2 and NWL15 cells also expressed IGF-I mRNA although to a lesser extent than the normal Leydig cells. IGFBP-2 mRNA levels were much higher in both the transformed cell lines than in the normal Leydig cells. The transformed cells were evaluated for the expression of P450scc, which catalyzes the conversion of cholesterol to pregnenolone.(ABSTRACT TRUNCATED AT 250 WORDS)

Malignant progression of SV40-immortalised human milk epithelial cells

A human breast epithelial cell line (Hu-MI), established by microinjecting SV40 DNA into human milk epithelial cells, exhibits the phenotype of luminal epithelial cells and is neither clonogenic nor tumorigenic. From this cell line we have selected two sublines, HuMI-T and HuMI-TTul, reflecting different stages of spontaneous transformation. HuMI-T cells grow anchorage-independently, but do not induce tumours in nude mice. HuMI-TTul cells are clonogenic as well as tumorigenic. Cells from both lines exhibit polymorphic structural and numerical chromosome aberrations. Immortalisation of normal luminal epithelial cells from human mammary gland with SV40 DNA alone may thus cause random genetic changes eventually resulting in tumorigenic cell lines. Since Hu-MI, HuMI-T and HuMI-TTul represent some of the consecutive stages taking place during cellular transformation, they are particularly suited as a novel in vitro model system to study progression of human breast cancer.