Improving the reproducibility of the MCF-7 cell proliferation assay for the detection of xenoestrogens

The MCF-7 cell proliferation assay is potentially a simple and highly reproducible tool for the identification of estrogenic compounds. However, its widespread use has been complicated by the lack of a standardised protocol, resulting in considerable inter-laboratory variability. We have explored the sources of variability both in relation to cell lines and test regimens and report on optimised procedures for the identification of estrogenic agents. Two supposedly identical MCF-7 parent cell lines (designated UCL and SOP), and the BUS subline were cultured according to an existing protocol, and responses to 17-estradiol (E2) assessed. Despite yielding almost identical EC50 values, the proliferative response varied widely between cell lines from 0.98-fold over controls (UCL) to 8.9-fold (BUS) indicating major differences between them. The underlying causes may be genetic, and to assess this we used comparative genomic hybridisation (CGH), a technique which allows the detection of DNA sequence copy number changes on a genome-wide scale. Although numerous similarities existed between the different cell lines, the least oestrogen-responsive line (MCF-7/UCL) exhibited the greatest number of cytogenetic changes, many of which were not seen in MCF-7/SOP cells. We suggest that care must be taken, therefore, when choosing a cell line for MCF-7 cell-based experiments. Selecting the MCF-7/SOP line for further work, we carried out a thorough and systematic optimisation of the MCF-7 cell proliferation assay, finding that a 72-h period in oestrogen-free medium before treatment strongly influenced the cells response to E2. With 1 nM E2, proliferation increased from 1.5-fold to 6.5-fold relative to vehicle-treated controls, a response similar to that seen with MCF-7/BUS cells in the E-SCREEN protocol devised by Soto et al. With parent MCF-7 cells, other laboratories have reported only 4.5-fold increases as maximal. Here we present evidence that the choice of cell line and culture conditions are crucial in determining test outcomes, and once chosen and adhered to the assay yields reproducible results.

Acquisition of neuroendocrine characteristics by prostate tumor cells is reversible: implications for prostate cancer progression

Neuroendocrine (NE) cells occur as scattered foci within prostatic adenocarcinoma, similar to their distribution within ductal epithelial cells of the normal prostate. However, the density of NE cells is often greater in prostate carcinomas than in normal tissue, and the frequency of NE cells correlates with tumor grade, loss of androgen sensitivity, autocrine/paracrine activity, and poor prognosis. Although NE cells are nonmitotic, proliferating cells are found in direct proximity to them, suggesting that NE cells provide paracrine stimuli for surrounding carcinoma cells. In vitro, differentiation of the LNCaP and PC3M prostatic tumor cell lines to a NE phenotype can be induced by dibutyryl cyclic AMP (cAMP), suggesting that physiological agents that increase intracellular concentrations of cAMP might regulate NE differentiation in vivo. Indeed, we demonstrate in this report that LNCaP cells acquire NE characteristics in response to treatment with physiological and pharmacological agents that elevate intracellular cAMP, agents such as epinephrine, isoproterenol, forskolin, and dibutyryl cAMP. The androgen-independent LNCaP-derived cell line C4-2 also responded to these agents, indicating that cells representing later stages of tumor progression are also capable of differentiation. The NE phenotype in this study was monitored by the appearance of dense core granules in the cytoplasm, the extension of neuron-like processes, loss of mitogenic activity, and expression of the NE markers neuron-specific enolase, parathyroid hormone-related peptide, neurotensin, serotonin, and chromogranin A. However, contrary to previous reports, we observed rapid loss of the NE phenotype in both LNCaP and C4-2 cells upon withdrawal of inducing agents. Withdrawal also resulted in a rapid, dramatic increase in tyrosine kinase and mitogen-activated protein kinase activities, suggesting that activation of these intracellular signaling enzymes may be important for reentry into the cell cycle. Together, these results indicate that chronic cAMP-mediated signaling is required to block proliferation of prostate tumor cells and to induce NE differentiation.

Nascent transcript-binding protein of the pea chloroplast transcriptionally active chromosome

This study describes the nascent RNA-binding protein of the pea chloroplast transcriptional complex. The protein has been identified by photoaffinity labelling of the transcriptionally active chromosome (TAC) which utilizes the endogenous plastid DNA as template. UV irradiation of lysed chloroplast or the isolated TAC under conditions optimized for transcription photocross-links nascent radiolabelled transcripts (up to 250 nucleotides in length) to a 48 kDa protein. The photoaffinity labelling of the transcript-binding protein is dependent on UV irradiation, is maximal after about 30 min of irradiation, and is completely dependent on transcriptional activity; no cross-linkage has been observed with pre-synthesized RNA. Cross-linkage is influenced by salts and inhibitors in accordance with their effects on transcription. The photoconjugate is composed of protein and RNA moieties, and can be hydrolysed by several proteases. However, the cross-linked transcript is protected from nucleases until the protein is removed. Manganese enhances photoaffinity labelling of the transcript-binding protein, and this is paralleled by an increase in total transcriptional activity of TAC. This protein was isolated by 2-dimensional polyacrylamide gel electrophoresis and the sequence of 15 amino acid residues at the amino terminus was determined. The nascent transcript-binding protein appears to be involved in the transcription of all three classes of chloroplast genes. We also found a polypeptide of identical molecular weight to get cross-linked to nascent transcripts in chloroplasts isolated from other legumes such as Cicer arietenum, Vigna radiata and Phaseolus vulgaris, and monocots like Zea mays, Oryza sativa and Pennisetum americanum.

Dual phosphorylation and autophosphorylation in mitogen-activated protein (MAP) kinase activation

p42mapk [mitogen activated protein (MAP) kinase; extracellular signal-regulated protein kinase (ERK)] is a serine/threonine-specific protein kinase that is activated by dual tyrosine and threonine phosphorylation in response to diverse agonists. Both the tyrosine and threonine phosphorylations are necessary for full enzymic activity. A MAP kinase activator recently purified and cloned has been shown to be a protein kinase (MAP kinase kinase) that is able to induce the dual phosphorylation of MAP kinase on both the regulatory tyrosine and threonine sites in vitro. In the present paper we have utilized MAP kinase mutants altered in the sites of regulatory phosphorylation to show, both in vivo and in vitro, that phosphorylation of the tyrosine and the threonine can occur independently of one another, with no required order of phosphorylation. We also utilized kinase-defective variants of MAP kinase with mutations in either the ATP-binding loop or the catalytic loop, and obtained data suggesting that the activity or structure of the catalytic loop of MAP kinase plays an important role in its own dual phosphorylation.

Two distinct transcriptional activities of pea (Pisum sativum) chloroplasts share immunochemically related functional polypeptides

An RNA polymerase activity has been purified from pea (Pisum sativum) chloroplast extracts with a distinct transcriptional specificity for a chloroplast messenger gene. This activity (ms-RNA pol) differs from the pea RNA polymerase preparation reported by Sun, Shapiro, Wu & Tewari [(1986) Plant Mol. Biol. 6, 429-439], which specifically transcribes only the rRNA gene (rb-RNA pol). The specificity of transcription has been assessed by the synthesis in vitro of discrete transcripts of predicted sizes using cloned promoter regions of the chloroplast psbA and 16 S rRNA genes. The ms-RNA pol preparation, with polypeptides ranging in apparent molecular mass from 22 to 180 kDa, correctly initiates transcription from recombinant plasmids containing the psbA promoter and does not support 16 S rRNA promoter-directed transcription. The two activities differ also in their response to Mn2+ ions. To investigate whether the two transcriptional activities share common functional polypeptides, monoclonal antibodies were developed against the rb-RNA pol preparation. Three clones were selected on the basis of their ability to inhibit transcription in vitro of the 16 S rRNA gene by rb-RNA pol. The antibodies from these clones independently recognized three polypeptides with molecular masses of 27, 90 and 95 kDa on immunoblots. Antibodies cross-reacting with the 90 kDa polypeptide completely eliminated the specific retardation of an end-labelled 16 S rRNA promoter fragment in a mobility-shift assay, whereas the antibodies against the 95 kDa polypeptide resulted in the formation of a ternary complex (enzyme-DNA-antibody). The antibodies cross-reacting with the 27 kDa polypeptide, however, did not alter the mobility of the retarded DNA-enzyme complex on the gel. These antibodies also inhibited transcription in vitro of the psbA gene by ms-RNA pol and recognized polypeptides of identical molecular masses in the ms-RNA pol. These results show that the three polypeptides are functional components of the chloroplast transcriptional complex and appear to be involved in the transcription of both rRNA and mRNA genes. Transcriptional specificity is probably conferred by ancillary transcription factor(s) which remain to be identified.

Parathyroid hormone related protein in hypercalcaemia of Hodgkin's disease

The role of parathyroid hormone related protein (PTHRP) as a humoral mediator of hypercalcaemia was investigated in a patient with lymphocyte depleted Hodgkin's disease during an episode of hypercalcaemia, using an immunohistochemical staining technique for PTHRP on the tumour tissue and an immunoradiometric (IRMA) assay for PTHRP1-86 on the patient's plasma. The plasma PTHRP was less than 0.23 pmol/l in the range found in normocalcaemic controls, and the immunohistochemical staining was not positive for protein. PTHRP did not have a role in the pathogenesis of hypercalcaemia in this patient.

Identification of the template binding polypeptide in the pea chloroplast transcriptional complex

We have identified the template-binding polypeptide in the pea chloroplast transcriptional complex by photoaffinity labelling. This polypeptide has an apparent molecular weight of about 150 kDa and binds to both, chloroplast ribosomal (16S rRNA) and messenger (psbA) promoters. The 16S rRNA and psbA promoters were amplified from chloroplast DNA by the polymerase chain reaction and labelled with a photoactive analogue of TTP, 5-bromodeoxy UTP, as well as with alpha-32P-dCTP. Using the filter-binding assay, the conditions for binding of the RNA polymerase complex to chloroplast promoters were optimized. The polypeptide directly interacting with the template was photo-crosslinked to it and resolved by denaturing gel electrophoresis. The photoaffinity labelling of the 150 kDa polypeptide was dependent on photoactivation by UV irradiation, and the presence of chloroplast promoters. Competition experiments showed that the protein formed a strong interaction with the plastid promoters which could not be displaced by lambda-phage DNA or synthetic polynucleotides. The photo-crosslinked and nuclease-treated promoter-polypeptide complex was resistant to further digestion with DNase and RNase, but could be hydrolyzed by Proteinase K. Binding of the promoters by the 150 kDa polypeptide could not be surpressed by transcription inhibitors like rifampicin and alpha-amanitin. However, heparin (0.001%) inhibited the formation of the enzyme-promoter complex, and interfered with the photoaffinity labelling of the 150 kDa polypeptide. The extent of photoaffinity labelling of 150 kDa polypeptide exhibits some degree of correlation to total transcriptional activity under various salt concentrations. The results demonstrate that the 150 kDa polypeptide is a functional template binding polypeptide of the pea chloroplast transcription complex.

Photoaffinity labelling of the pea chloroplast transcriptional complex by nascent RNA in vitro

We have used photoaffinity labelling to examine the chloroplast RNA polymerase components which come into contact with nascent transcripts during the in vitro transcription of plastid DNA. The transcripts were synthesized in the presence of a photoactive analogue (4-thio UTP) and alpha-32P-ATP, using enriched pea chloroplast RNA polymerase preparation and a recombinant plasmid containing the plastid 16S rRNA promoter. Brief irradiation of the transcriptional complex crosslinked the photoactive nascent RNA to proximal proteins. Labelling of the transcriptional complex was dependent on 4-thio UTP and template DNA. Two polypeptides of 51 and 54 kDa were consistently crosslinked to the nascent transcripts; about 60% of the total radioactivity of the crosslinked RNA was associated with these polypeptides. In some experiments, two additional polypeptides of 38 and 75 kDa were also found to be associated with about 13% and 17% of the total crosslinked RNA radioactivity, respectively. The UV-crosslinked transcriptional complexes were stable to either DNase or S1 nuclease hydrolysis but partially sensitive to RNase T1. Insensitivity of the complex to hydrolysis with RNase H suggested that the nascent transcripts were not crosslinked to the template. The complexes could also be hydrolysed by proteinase K and thermolysin. No crosslinkage was observed when labelled RNA molecules containing 4-thio UMP residues were added after synthesis to the polymerase preparation. This suggested that the method identified only those polypeptides which came into close contact with the transcript during its synthesis. Antibodies raised against the RNA-protein complex confirmed the presence of the polypeptides in the chloroplast RNA polymerase preparation on Western blots. Preincubation of these antibodies with the chloroplast RNA polymerase inhibited plastid DNA transcription. These data showed that the transcript-binding polypeptides were functional components of the chloroplast transcriptional complex.

Early clinical pathologists. 4: John Hunter (1728-1793)

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Breast conserving surgery in the management of in situ breast carcinoma

In a retrospective review of 73 patients with in situ breast carcinoma seen in the Combined Breast Clinic at the Royal Marsden and St. George's Hospitals between 1969 and 1988, 20 (27%) were found to have in situ lobular and 53 (73%) in situ intraduct carcinoma. Of 19 patients with in situ lobular carcinoma treated by breast conserving surgery alone there were three (16%) recurrences of in situ lobular carcinoma and one (5%) of infiltrating carcinoma after a mean follow-up period of 65.8 months. Of 53 patients with in situ intraduct carcinoma, 37 were treated by breast conserving surgery alone and in this group there were 14 (38%) recurrences, of which seven (19%) were in situ intraduct and seven (19%) were infiltrating carcinoma, after a mean follow-up of 96.5 months. Following successful salvage there were no breast cancer related deaths in either group.

Enhanced anti-tumour activity of carmustine (BCNU) with tumour necrosis factor in vitro and in vivo

The effects on experimental melanoma of a combination of recombinant human tumour necrosis factor alpha (rhTNF alpha) and carmustine (BCNU) were studied in vitro and in vivo. In vitro, BCNU alone was cytotoxic to murine B16 melanoma cells, and at all concentrations of BCNU this toxicity was increased by the addition of TNF. In vivo, BCNU and TNF, when given separately, caused tumour growth delay of B16 melanoma and of human melanoma xenografts in immune-deprived mice. The combination of TNF at low dose 2.5 x 10(5) U kg-1 = 122 ng kg-1) with BCNU (35 mg kg-1) resulted in significant growth delay (compared with either drug alone) in B16 melanoma (P = 0.005). There was no significant increase in toxicity as assessed by weight loss and peripheral blood counts. Experiments with human melanoma xenografts yielded similar results (P = 0.001) but only at higher doses of TNF (1 x 10(6) U kg-1 = 489 ng kg-1). The enhancement of BCNU cytotoxicity by TNF may be important if it can be translated into patients with melanoma. A randomised study is now underway to investigate the clinical potential of this observation.

Chemotherapy for malignant melanoma: combinations and high doses produce more responses without survival benefit

In a consecutive series of studies, 164 patients with symptomatic and/or visceral metastatic malignant melanoma were treated with single agent vindesine, high dose melphalan with autologous bone marrow transplantation (AMBT), high dose BCNU with ABMT or the BOLD (bleomycin, vincristine, CCNU and DTIC) combination. The high dose treatments and the combination chemotherapy resulted in significantly higher response rates but no prolongation of survival. Factors associated with longer survival included the absence of visceral metastases, the absence of bulky disease and good performance status. For all treatments, life table estimates of survival at 1 and 2 years were only 10% and 4% respectively.

Infused vincristine and adriamycin with high dose methylprednisolone (VAMP) in advanced previously treated multiple myeloma patients

Forty-five patients with relapsed or refractory multiple myeloma received continuous infusions of vincristine (0.4 mg total dose daily for 4 days) and adriamycin (9 mg m-2 daily for 4 days) with a high dose of methylprednisolone (1 g m-2 i.v. or p.o. daily by 1 h infusion), the VAMP regimen. Sixteen (36%) responded, with a median duration of remission of 11 months and median survival of 20 months. Major toxicities encountered were infective and cardiovascular. Two smaller groups of myeloma patients were treated with high dose methylprednisolone (HDMP) alone, or VAMP plus weekly low dose cyclophosphamide (Cyclo-VAMP). HDMP produced short responses in 25% of patients with less toxicity than VAMP. Cyclo-VAMP was used in a highly selected group of patients who had previously responded to high dose melphalan. It was well tolerated and produced responses in 61% of this group.