In vitro modelling of epithelial and stromal interactions in non-malignant and malignant prostates

To study the effects of stromal epithelial cell interactions on prostate cancer metastasis, we have used primary human prostatic stromal cells derived from malignant and non-malignant tissues and established epithelial cell lines from normal (PNT1a and PNT2-C2) and tumour (PC-3, DU145 and LNCaP) origins. The effects of stromal cells on epithelial cell growth were studied in direct and indirect (using culture inserts) co-culture and by exposure to stromal cell-conditioned medium (assessed by MTT assay). The influence of stromal cells on epithelial cell invasion was measured using matrigel invasion chambers and on epithelial cell motility using time lapse microscopy. Results indicated that epithelial cell line growth was similarly unaffected or inhibited by stromal cells derived from malignant (n = 8) or non-malignant tissue (n = 8). In contrast, PNT2-C2 and PC-3 cells were found to be the least and the most invasive and motile epithelia respectively. Stromal cultures enhanced the invasion of both epithelial cells, but no differences were observed between the use of malignant and non-malignant tissues. All stromal cultures modestly stimulated PNT2-C2 motility but displayed a greater stimulation of PC-3 cell motility, while stromal cells derived from malignant tissue stimulated PNT2-C2 and PC-3 cell motility more than stromal cultures from non-malignant tissues.

Allelic imbalance within the E-cadherin gene is an infrequent event in prostate carcinogenesis

By exploiting two single nucleotide polymorphisms (SNPs) located within the E-cadherin gene, at 16q22, we have determined the frequency of allelic imbalance at this proposed tumor suppressor locus in a series of human prostatic carcinoma DNA samples. Whereas results with seven highly polymorphic microsatellite markers flanking the E-cadherin locus confirmed the existence of three separate loci on chromosome 16, at which allelic imbalance increased with increasing loss of tumor cell differentiation, no allelic imbalance within the E-cadherin gene was detected either by single-strand conformational polymorphism analysis or by direct sequencing. We conclude that the loss of E-cadherin function observed in prostate cancer is not a result of allelic deletion. Genes Chromosomes Cancer 27:104-109, 2000.

FGF7/KGF triggers cell transformation and invasion on immortalised human prostatic epithelial PNT1A cells

Fibroblast growth factor 7 (FGF7/KGF) is synthesized exclusively by fibroblasts in normal tissues; it acts as a potent mitogen on epithelial cells, through interaction with the FGF7-specific receptor FGFR2/IIIb. To examine the importance of this growth factor both to prostate physiology and to prostate-cancer progression, we have tested the exogenous effect of FGF7. Thus, by mimicking the paracrine pathway (on proliferation, growth in soft agar and invasion) on the human prostatic epithelial cell line PNT1A positively checked for FGFR2/IIIb expression, FGF7 significantly enhanced cell proliferation at an optimal concentration of 7.5 x 10(-11) M, but no significant invasion or growth in soft agar were observed. To confirm FGF7 properties on human prostatic epithelial cells, we constitutively expressed FGF7 by transfecting PNT1A cells with FGF7-cDNA. The FGF7-transfected clones, PNT1A/ FGF7-T5 and PNT1A/FGF7-T6, were stable and expressed FGF7. Analysis of the FGF7-autocrine loop on the non-tumorigenic epithelial cells PNT1A showed acquired invasive potential in in vitro extracellular-matrix migration assays, specifically inhibited by an FGF7-neutralizing antibody, and over-expressed factors implicated in the migration process: the metalloproteinase MMP-1 and the plasminogen activator uPA. Taken together, these results demonstrate a role for FGF7 in triggering invasion of human prostatic epithelial cells. Furthermore, these FGF7-transfected clones exhibited functional and physiological differences from the original PNT1A cell line: anchorage-independent growth, growth in serum-free media and increased proliferation. These data confirm the oncogenic function of FGF7 in prostate progression potentially acting through paracrine and/or autocrine regulatory pathways.

FGF7/KGF triggers cell transformation and invasion on immortalised human prostatic epithelial PNT1A cells

Fibroblast growth factor 7 (FGF7/KGF) is synthesized exclusively by fibroblasts in normal tissues; it acts as a potent mitogen on epithelial cells, through interaction with the FGF7-specific receptor FGFR2/IIIb. To examine the importance of this growth factor both to prostate physiology and to prostate-cancer progression, we have tested the exogenous effect of FGF7. Thus, by mimicking the paracrine pathway (on proliferation, growth in soft agar and invasion) on the human prostatic epithelial cell line PNT1A positively checked for FGFR2/IIIb expression, FGF7 significantly enhanced cell proliferation at an optimal concentration of 7.5 x 10(-11) M, but no significant invasion or growth in soft agar were observed. To confirm FGF7 properties on human prostatic epithelial cells, we constitutively expressed FGF7 by transfecting PNT1A cells with FGF7-cDNA. The FGF7-transfected clones, PNT1A/ FGF7-T5 and PNT1A/FGF7-T6, were stable and expressed FGF7. Analysis of the FGF7-autocrine loop on the non-tumorigenic epithelial cells PNT1A showed acquired invasive potential in in vitro extracellular-matrix migration assays, specifically inhibited by an FGF7-neutralizing antibody, and over-expressed factors implicated in the migration process: the metalloproteinase MMP-1 and the plasminogen activator uPA. Taken together, these results demonstrate a role for FGF7 in triggering invasion of human prostatic epithelial cells. Furthermore, these FGF7-transfected clones exhibited functional and physiological differences from the original PNT1A cell line: anchorage-independent growth, growth in serum-free media and increased proliferation. These data confirm the oncogenic function of FGF7 in prostate progression potentially acting through paracrine and/or autocrine regulatory pathways.

BCL10 is rarely mutated in human prostate carcinoma, small-cell lung cancer, head and neck tumours, renal carcinoma and sarcomas. MPT Collaborators, St George's Hospital Collaborators

We have used single-strand conformation polymorphism (SSCP) analysis to screen for mutations in the BCL10 gene in 81 primary prostate carcinomas, 20 squamous cell cancers of the head and neck, 15 small-cell lung cancer cell lines, 24 renal carcinoma cell lines and 13 sarcoma cell lines. We failed to find evidence of somatically acquired mutations of the BCL10 gene suggesting that BCL10 does not play a major role in the development of these malignancies.

Expression, crystallization and preliminary X-ray analysis of the E2 transactivation domain from papillomavirus type 16

The N-terminal transactivation domain of the E2 protein from human papillomavirus type 16 has been crystallized by vapour diffusion. Crystals belong to the space group P3121 (or P3221) with unit-cell dimensions a = b = 54.3, c = 155.5 A. There is one molecule per asymmetric unit with a solvent content of 55%. Crystals diffract to at least 2.5 A resolution and complete X-ray data to 3.4 A have been collected on a conventional laboratory source. This 201 amino-acid domain of the E2 protein has been shown to interact functionally with both the HPV E1 protein and at least three cellular transcription factors, to fulfil its role in the control of viral transcription and replication. A knowledge of the structural basis of these multiple interactions should lead to a fuller understanding of the mechanism of action of this key regulator of the HPV life cycle.

Expression patterns of the human papillomavirus type 16 transcription factor E2 in low- and high-grade cervical intraepithelial neoplasia

Specific antibodies against the C-terminus of E2, produced by affinity purification of polyclonal antisera, have been used to identify the cellular populations which express the HPV 16 E2 transcription factor, in a series of formalin-fixed, paraffin-embedded cervical tissues. Cases were selected for both the presence of HPV 16 DNA (confirmed by multiple gene-specific PCR detections) and the presence of multiple grades of cervical intraepithelial neoplasia (CIN). The data indicate that E2 expression is highest in CIN I and in koilocytic lesions. Lower expression was observed in CIN II and little in CIN III lesions. In contrast, there was some restoration of E2 expression in invasive carcinomas, although the intracellular distribution was much more diffuse. The location of E2 expression to the superficial layers of the cervical epithelium, as well as the occurrence of some basal expression in CIN I, suggests that antibodies against HPV 16 E2 could be a useful adjunct to standard histological techniques for the detection of 'at-risk' patients as part of a cervical screening programme.

Predisposing gene for early-onset prostate cancer, localized on chromosome 1q42.2-43

There is genetic predisposition associated with >=10% of all cancer of the prostate (CaP). By means of a genomewide search on a selection of 47 French and German families, parametric and nonparametric linkage (NPL) analysis allowed identification of a locus, on chromosome 1q42.2-43, carrying a putative predisposing gene for CaP (PCaP). The primary localization was confirmed with several markers, by use of three different genetic models. We obtained a maximum two-point LOD score of 2.7 with marker D1S2785. Multipoint parametric and NPL analysis yielded maximum HLOD and NPL scores of 2.2 and 3.1, respectively, with an associated P value of . 001. Homogeneity analysis with multipoint LOD scores gave an estimate of the proportion of families with linkage to this locus of 50%, with a likelihood ratio of 157/1 in favor of heterogeneity. Furthermore, the 9/47 families with early-onset CaP at age <60 years gave multipoint LOD and NPL scores of 3.31 and 3.32, respectively, with P = .001.

Characterization of the interactions of human papillomavirus type 16 E6 with p53 and E6-associated protein in insect and human cells

Human papillomavirus (HPV) 16 E6 induces the degradation of the tumour suppressor protein p53 by the ubiquitin-dependent proteolysis pathway. In vitro, this process involves the formation of a trimolecular complex between E6, p53 and a cellular protein E6-associated protein (E6-AP). However, an analysis of their potential interactions in vivo has not been carried out. We have established a model for the expression and analysis of the interactions of these three proteins in insect cells, a eukaryotic system where potentially crucial modifications of the proteins will occur. In baculovirus-infected cells the degradation of p53 can occur. However, p53 is only degraded early in the infectious cycle due to a lack of ATP at later times. Consequently, substantial quantities of material can be produced in this system for further analysis. Evidence is also provided that, in vivo, E6 can interact with p53 in the absence of E6-AP and that E6-AP can interact with p53 in the absence of E6. Furthermore, analysis of the subcellular localization of the proteins using both biochemical fractionation and indirect immunofluorescence suggests that the degradation of p53 occurs in the perinuclear region of the cell.

Precise microdissection of human prostate cancers reveals genotypic heterogeneity

To determine the incidence of genetic heterogeneity in primary prostate cancer, we have microdissected 125 tumor and mesenchymal foci from 18 patient biopsies and analyzed the DNA for loss of heterozygosity using PCR microsatellite markers. In 100% of patients with genetic lesions on chromosome 8p, there was evidence for intratumoral genetic heterogeneity. There was also a low but significant incidence of loss of heterozygosity in mesenchymal tissue. Our results show that phenotypically similar tumor foci can have different genotypes and provide evidence for the multifocality of tumor development in the prostate.

Androgens are not a direct requirement for the proliferation of human prostatic epithelium in vitro

The androgen receptor pathway is known to be a key regulator of growth in the normal and pathological prostate. However, the precise mechanisms of this signaling pathway with respect to the different cellular compartments of the prostate remain largely unknown. We have used a primary culture system to grow human prostatic epithelial cells of normal, benign, tumor and metastatic origin, as well as immortalized human prostatic epithelial cell lines, to demonstrate the absence of a direct or indirect effect of androgens on cellular proliferation in vitro. In parallel to this observed androgen independence for growth, all cell systems lost significant expression of androgen receptor, prostate-specific antigen and prostatic acid phosphatase. Since the androgen receptor is expressed in the epithelium in situ, our results suggest that the androgen effect on epithelial cells may be one of prostatic differentiation rather than proliferation, and that the androgen receptor/growth factor pathway acts through mesenchymal-epithelial interactions.

Molecular analysis of the interaction between HPV type 16 E6 and human E6-associated protein

The complex formed between the human papillomavirus type 16 E6 protein and human E6-associated protein, which combine to ubiquitylate and degrade p53, has been studied by chemical crosslinking. Analysis of the interactions of proteins purified from Escherichia coli as well as proteins expressed in insect cells indicates that, while E6 has the capacity to form dimers, E6 and E6-associated protein interact as two monomers to form a heterologous dimer.

Constitutive expression of FGF2/bFGF in non-tumorigenic human prostatic epithelial cells results in the acquisition of a partial neoplastic phenotype

Fibroblast growth factor 2 (FGF2), also known as basic fibroblast growth factor (bFGF), belongs to the FGF family, which consists of at least 9 closely related members. FGF2 is a potent mitogen for fibroblasts derived from normal prostate and, to a lesser extent, for prostatic epithelial cells. Its role in the physiology of the normal prostate seems to be limited to stromal cells, whereas in prostate cancer FGF2 may also have an autocrine/paracrine effect on epithelial cells. In order to better understand the effects of FGF2 on the prostatic epithelium, especially its role in the progression of prostate cancer by establishing an autocrine-stimulation loop, we transfected FGF2 cDNA into a human prostatic epithelial cell line, PNT1A, immortalized with SV40 large-T antigen. This cell line is non-tumorigenic and expresses a high-affinity FGF2 receptor, FGFR1/flg. We characterized 3 independent FGF2-transfected clones and found that the establishment of an FGF2 autocrine loop on these cells led to (i) serum-independent growth, (ii) increased proliferation and (iii) anchorage-independent growth. Such results argue in favor of the possible action of FGF2 on progression of prostate cancer via an FGF2 autocrine loop on epithelial cells.

Analysis of prostate tissue DNA for the presence of human papillomavirus by polymerase chain reaction, cloning, and automated sequencing

We have analysed the DNA from 24 prostate tissue biopsies, spanning a range of Gleason grading from benign to grade 5 and mixed randomly with cervical cancer samples of known human papillomavirus (HPV) status, for the prevalence of HPV DNA, in a double-blind study to ensure complete objectivity. Polymerase chain reactions (PCR) were performed using general E1 open reading frame primers for HPV under low stringency conditions, in addition to reactions containing primers specific for HPV16, E2, and E6 open reading frames under higher, more stringent PCR conditions. The presence of cellular DNA was verified by the use of primers for hypoxanthine guanine phosphoribosyl transferase. DNA bands were not detected in the prostate biopsies using the HPV16-specific primers under high-stringency PCR conditions, however a predominant band in the 400 bp region was observed in 15 of the prostate biopsies using the general primers and the low annealing temperature of 40 degrees C. This fragment was excised and cloned into the pT7 blue vector and the sequence of the insert determined. Although the cloned sequences initiated and terminated with the two authentic PCR primers, they did not contain a significant HPV-related open reading frame. Our results indicate that HPV type 16 and closely related types, as detected by the general primer pair, are unlikely initiators of prostate carcinogenesis within our population.

Co-ordinated changes in expression of cell adhesion molecules in prostate cancer

The expressions of E-cadherin, the integrin subunits beta 1, beta 2, beta 3, CD44 and alpha-catenin were studied in parallel by immunohistochemistry in a series of 40 prostate biopsies comprising one normal, 11 benign prostatic hyperplasia (BPH), and 28 prostatic adenocarcinomas. As reported by others, there was a consistent loss of E-cadherin expression with increasing tumour grade and de-differentiation. However, a significant proportion of losses occurred at earlier grades than previously reported. The parallel nature of this study showed, for the first time in human prostate carcinoma, a reciprocal expression pattern of E-cadherin and beta 1 integrin in the higher grades of prostate cancer. A reciprocal expression pattern was also found for E-cadherin and CD44 between moderately and poorly differentiated tumours. alpha-Catenin expression was downregulated only in those cells which had previously lost E-cadherin expression, and beta 2 and beta 3 integrin were rarely expressed in prostate tumours. A loss of expression of the luminal epithelial specific keratins CK8 and CK18 was also observed in advanced stage, poorly differentiated carcinomas.

Differences in serological IgA responses to recombinant baculovirus-derived human papillomavirus E2 protein in the natural history of cervical neoplasia

Infection with certain types of human papillomavirus (HPV) presents a high risk for the subsequent development of cervical intraepithelial neoplasia (CIN) and cervical carcinoma. Immunological mechanisms are likely to play a role in control of cervical HPV lesions. The HPV E2 protein has roles in virus replication and transcription, and loss of E2 functions may be associated with progression of cervical neoplasia. Accordingly, it is of interest to monitor immune responses to the E2 protein, and previous studies have reported associations between serological reactivity to E2 peptide antigens and cervical neoplasia. In order to investigate serological responses to native, full-length E2 protein, we expressed HPV-16 E2 proteins with and without an N-terminal polyhistidine tag using the baculovirus system. Purified HPV-16 E2 protein was used to develop enzyme-linked immunosorbent assays to detect serological IgG and IgA responses in cervical neoplasia patients and controls. We found that serum IgA levels against the E2 protein were elevated in CIN patients relative to normal control subjects but were not elevated in cervical cancer patients. Moreover, there appeared to be a gradient of response within cervical neoplasia such that the highest antibody levels were seen in lower grades of neoplasia up to CIN 2, whereas lower levels were observed in CIN 3 and still lower levels in cervical carcinoma. These findings suggest that the IgA antibody response to E2 may associate with stage and progression in cervical neoplasia.

A microdissection approach to detect molecular markers during progression of prostate cancer

To investigate the underlying mechanisms of carcinogenesis, we have developed a technique to determine the frequency of genetic changes in prostatic carcinoma tissue. We have demonstrated that at a ratio of between 1:4 and 1:9 mutant-normal alleles, the signal from a mutant TP53 allele is not apparent after polymerase chain reaction (PCR) amplification and further direct sequencing or single-strand conformation polymorphism (SSCP) analysis. To bypass this problem, which is inherent in the heterogeneity of the prostate tissue and of the tumour, we selected areas of graded prostate tumours (Gleason score) from cryosectioned preparations and microdissected these cells (20-100 cells). After anionic resin removal of proteins, PCR amplification of TP53 gene exons 5/6 and SSCP analysis, an abnormal SSCP band shift was observed in suspected tumour cells, compared with microdissected stromal cells used as an internal control, while (1) a crude preparation of tissue DNA carrying the tumour did not show any abnormality and (2) immunostaining by a set of monoclonal antibodies against TP53 protein remained negative. Nucleotide sequence analysis of the different bands confirmed the presence of a mutation in the TP53 gene exon 6 position 13,336 in an abnormal band for one specimen, while no mutation was detected in the normal SSCP band. By targeting recognised tumour cells we can find DNA mutations which are undetectable using the standard technique of whole-tissue DNA extraction, particularly in a heterogeneous tumour such as carcinoma of the prostate.

Characterization of human papillomavirus type 16 E2 protein and subdomains expressed in insect cells

The E2 open reading frame of human papillomavirus type 16 (HPV-16) encodes a DNA-binding protein which modulates papillomavirus transcription and replication. To investigate the biological and biochemical properties of the HPV-16 E2 protein, we have constructed recombinant baculoviruses which express the full-length molecule and individual N- and C-terminal domains in Sf21 insect cells. In this system the full-length E2 protein was phosphorylated and targeted to the insect cell nucleus. A 93 amino acid C-terminal fragment encompassing the DNA binding and dimerization functions of E2 was also translocated to the nucleus but was not modified by phosphorylation. The E2 N-terminal protein accumulated in the insect cell cytoplasm but was not efficiently phosphorylated. The formation of heterodimers between full-length and N-terminally truncated E2 species was observed when Sf21 cells were co-infected with recombinant viruses and when homodimers were mixed in vitro, suggesting that the dimer interface is not sufficiently stable to prevent subunit exchange in vivo. Both homo- and heterodimeric E2 species were able to bind specifically and in any combination to tandem E2 binding sites from the HPV-16 regulatory region. Furthermore, the HPV-16 E2 protein bound to DNA exhibited a distinct susceptibility profile to pronase digestion, potentially contrasting with that reported for BPV-1 E2. These observations suggest that significant structural and functional differences may exist between the BPV/HPV E2 proteins and have implications for understanding E2-dependent regulation of transcription and replication.

A polymerase chain reaction (PCR) investigation of oral verrucae which contain HPV types 2 and 57 by in situ hybridization

The polymerase chain reaction (PCR) and direct DNA sequencing have been used to identify strain variants of HPV types 2a/57 in formalin-fixed sections of human oral verrucae, where the virus had previously been detected by both immunofluorescence and in situ hybridization. By employing type-specific and type-common PCR primers we show that these lesions contain a mixture of viral DNAs which vary by up to 27% in DNA sequence, in a region where the variation between HPV types 2a and 57 is only 4%. The extra discriminatory power of fluorescent sequencing indicates that the lesions may also contain wild-type HPV2a/57 DNA which could provide a helper function for defective viral DNA molecules or indicate a mosaic origin for the lesions.

Human papillomavirus DNA and TP53 mutations in lung cancers from butchers

To investigate whether the high frequency of human papillomavirus infection in butchers may be linked to their higher than average incidence of lung cancer, we have examined lung cancers from 40 butchers and 26 controls for the presence of DNA from both HPV type 7, which is found almost uniquely in hand warts from butchers and fishermen, and for those HPV types associated with laryngeal and genital cancers. No HPV 7, and only a low frequency of HPV DNA was found, suggesting that HPV infection does not make an important contribution to the elevated levels of lung cancer in meat handlers. In addition, the frequency of p53 mutation was shown to be slightly lower than previously reported in lung cancers.

Kinetic and equilibrium binding studies of the human papillomavirus type-16 transcription regulatory protein E2 interacting with core enhancer elements

The human papillomaviruses (HPVs) are a family of DNA viruses which cause benign tumours of the skin and mucosa that infrequently progress to malignant carcinoma. The E2 open reading frame of HPV is thought to encode a papillomavirus-specific transcription factor which also has a role in viral replication. The E2 proteins of all papillomaviruses studied to date have been shown to bind specifically to the common conserved sequence ACC(N)6GGT found at multiple locations in their genomes. In the case of HPV-16, a 'high risk' genital papillomavirus, the E2 protein is thought to negatively regulate expression of the major viral transforming genes E6 and E7, which have been directly implicated in the oncogenic process. However, little information exists concerning the relative or absolute affinities of the native HPV-16 protein for its palindromic recognition sequences; moreover, interpretation of any transcription or replication phenomena attributed to this protein is more complicated in the absence of such data. Here we describe the overexpression, purification and characterisation of the C-terminal 89 amino acids of the protein encompassing the DNA binding/dimerisation domain. We show that the recombinant protein purified from E.coli by a combination of non-group-specific chromatography steps retains high biological activity and is able to bind to all sites in the HPV-16 genome with high affinity (approximately 8 x 10(-11) M). In addition, kinetic studies show that the E2-DNA complexes are very stable, with half-lives ranging from 2.15 to greater than 240 min, and that nucleotides internal and external to the conserved palindrome appear to influence stability.

Immunocytochemical comparison of cultured normal epithelial prostatic cells with prostatic tissue sections

By analyzing a culture system of human prostatic epithelial cells (HPEC) and human prostatic fibroblasts (HPF) for expression of several determinants by immunocytochemistry, we have shown that long-term cultures are able to preserve the phenotypic characteristics of the normal tissue from which they are derived. The cytoskeletal elements, prostate-specific proteins, and steroid receptor profiles were compared to those of prostatic epithelium and stroma in situ. When cultured in low serum and low calcium medium, the adult HPEC grew as two layers of cells, the upper one of which retained the differentiation characteristics observed in the luminal fraction of normal prostatic epithelium. This cell type is the likely origin of prostatic neoplasia, with expression of CK8, 18, and 19 but not CK14. Androgen receptors, prostatic-specific antigen, and prostatic acid phosphatase are also expressed in vitro but at lower level than in situ. The lower cell layer expressed most of the same determinants but at a much lower level, suggestive of a stem-cell type. The HPF cultured in RPMI serum supplemented media retained the stromal pattern of the cells observed in situ. Culture systems which conserve the characteristics of their normal counterparts in vivo should provide useful models for studying in vitro genetic and epigenetic factors associated with differentiation and proliferation, but also with tumorigenic progression in the prostatic gland.

Butchers' warts: no evidence for person to person transmission of HPV7

The distribution of warts due to HPV7 in workers in six abattoirs and 103 retail and wholesale butcheries has been studied to determine whether the high prevalence of HPV7 in the meat trade is the result of enhanced person to person transmission, or whether it is a ubiquitous virus which is activated by an unknown factor in meat. Warts were detected in 164 of 486 men. Scrapings were taken from 156 men, and HPV DNA was found in 112 samples, 74 of which contained HPV7. HPV7 was found in 36 workplaces, and there was no evidence of clustering of cases, as would be expected if person to person transmission was occurring in the workplace. This suggests that HPV7 is widely distributed in the community, but only causes clinical disease under specific conditions. We suggest that some unknown factor in meat enhances viral replication.