Reversal of P-glycoprotein-associated multidrug resistance by ivermectin

P-Glycoprotein (P-gp) causes a multidrug resistance (MDR) phenotype in tumour cells. In some cancers, the expression of P-gp has been correlated with low clinical response to chemotherapy and survival of patients. Previous studies have shown that certain lipophilic drugs bind to P-gp and reverse the MDR phenotype of tumour cells. In this study, we extend that list of compounds and present evidence for the capacity of a potent and clinically safe anthelmintic, ivermectin (IVM), as an MDR-reversing drug. Using a highly drug-resistant human cell line, we compared IVM with other MDR-reversing agents and showed that IVM is 4- and 9-fold more potent than cyclosporin A and verapamil, respectively. The capacity of IVM to inhibit iodoaryl-azidoprazosin photolabeling of P-gp is consistent with direct binding to P-gp. Studies showed that [3H]IVM binding to membranes from resistant cells is specific and saturable with KD and Bmax values of 10.6 nM and 19.8 pmol/mg, respectively. However, while cyclosporin A or vinblastine inhibited [3H]IVM binding to membranes from drug-resistant but not drug-sensitive cells, neither verapamil nor colchicine had any effect. Furthermore, both IVM and cyclosporin A and, to a lesser extent, verapamil also inhibited [3H]vinblastine binding to membranes from drug-resistant cells. Drug transport studies showed that [3H]IVM is a substrate for the P-gp drug efflux pump. However, it was transported less efficiently by P-gp than [3H]vinblastine. Moreover, only cyclosporin A was effective in potentiating the accumulation of [3H]IVM in drug-resistant cells. Taken together, the high efficiency of MDR reversal by IVM combined with its low toxicity are consistent with the properties of an ideal MDR-reversing agent.

N-ethylmaleimide increases P-glycoprotein photoaffinity labeling with iodoaryl-azidoprazosin in multidrug resistant cells

P-glycoprotein (P-gp) mediates a multidrug resistance (MDR) phenotype in tumor cell lines selected with lipophilic cytotoxic drugs. Transport studies using purified P-glycoprotein reconstituted into defined liposomes have shown energy-dependent drug efflux of structurally dissimilar drugs. In this report, we have examined the effects of N-ethylmaleimide, a potent inhibitor of the P-gp ATPase, on P-gp drug binding in intact MDR cells and in plasma membranes. Our results show that short term treatment of MDR cells with 1-50 microM N-ethylmaleimide led to a concentration dependent increase in P-gp photoaffinity labeling with iodoaryl-azidoparazosin (IAAP). In addition, N-ethylmaleimide increases [3H] vinblastine accumu-lation in drug-resistant but not in sensitive cells. Comparison of IAAP photolabeled P-gp from intact cells with or without N-ethylmaleimide treatment did not show differences in the pattern of IAAP photolabeled peptides. Thus, the observed increase in P-gp photolabeling with IAAP in N-ethylmaleimide treated cells is not due to photolabeling at different sites. Incubation of MDR cells with [14C] N-ethylmaleimide showed that P-gp is directly modified at several Cysteine residues, as found from a complete proteolytic digestion of [14C] Nethylmaleimide labeled P-gp. The comparison of V8 staphylococcus aureas peptides from [14C] Nethylmaleimide or IAAP modified P-gp showed some peptides to co-migrate on SDS PAGE. However, modification of plasma membranes from drug resistant cells treated with N-ethylmaleimide did not show a dose-dependent increase in P-gp photolabeling with IAAP as seen with intact MDR cells. Interestingly, N-ethylmaleimide increases P-gp phosphorylation by inhibiting the turnover of Pgp phosphates. However, inhibition of P-gp phosphorylation with calyculin A did not show an increase in P-gp photolabeling in MDR cells. Taken together, the results of this study suggest that N-ethylmaleimide potentiates P-gp photolabeling with IAAP by inhibiting P-gp ATPase thereby increasing the local concentration of IAAP in intact MDR cells. Furthermore, inhibition of P-gp ATPase by N-ethylmaleimide does not lead to conformational changes that affects P-gp drug binding.

Sensitization to doxorubicin resistance in breast cancer cell lines by tamoxifen and megestrol acetate

Acquired drug resistance is a major factor in the failure of doxorubicin-based chemotherapy in breast cancer. We determined the ability of megestrol acetate and/or tamoxifen to reverse doxorubicin drug resistance in a doxorubicin-resistant breast cancer line (the human MCF-7/ADR). The cytotoxicity of doxorubicin, megestrol acetate, and/or tamoxifen was determined in the sensitive and resistant cell lines utilizing the sulphorhodamine B assay. Tamoxifen alone produced an IC50 (concentration resulting in 50% inhibition of control growth) of 10.6 microM, whereas megestrol acetate alone resulted in an IC50 of 48.7 microM in the MCF-7/ADR cell line. The IC50 of doxorubicin in MCF-7/ADR was 1.9 microM. Neither megestrol acetate alone nor tamoxifen alone at 1 or 5 microM altered the IC50 of doxorubicin. However, the combination of tamoxifen (1 or 5 microM) and megestrol acetate (1 or 5 microM) synergistically sensitized MCF-7/ADR cells. Additionally, megestrol acetate and tamoxifen inhibited iodoarylazidoprazosin binding to P-glycoprotein, and, in their presence, there was an increased doxorubicin accumulation in the MCF-7/ADR cells. Furthermore, the combination of tamoxifen and megestrol acetate had much less effect on the cytotoxicity of doxorubicin in MCF-7 wild-type cells. Clinically achievable concentrations of tamoxifen and megestrol acetate can largely sensitize MCF-7/ADR to doxorubicin. The combination of these three drugs in a clinical trial may be informative.

BIBW22 BS, potent multidrug resistance-reversing agent, binds directly to P-glycoprotein and accumulates in drug-resistant cells

The expression of P-glycoprotein (P-gp) in tumor cells causes a multidrug resistance (MDR) phenotype. P-gp has been shown to mediate the transport of structurally dissimilar drugs across the cell membrane in an energy-dependent manner. In this report, we show that BIBW22 BS, a phenylpteridine analog, reverses the MDR phenotype of CEM human lymphoma cells in a dose-dependent fashion. Using a photoactive analog of BIBW22 BS {[3H]azido-4-[N-(2-hydroxy-2-methylpropyl)-ethanolamino]-2, 7-bis(cis-2,6-dimethyl-morpholino)-6-phenylpteridine}, we show the photoaffinity labeling of a 170-kDa protein in drug-resistant cells immunoprecipitated with P-gp-specific monoclonal antibodies. The photolabeling of P-gp by [3H]azido-BIBW22 BS was specific and saturable. Furthermore, BIBW22 BS, vinblastine, and verapamil, but not colchicine, inhibited the photolabeling of P-gp by [3H]azido-BIBW22 BS. Drug binding studies showed that membranes from MDR cells bound more BIBW22 BS than parental drug-sensitive cells, and this binding was inhibited with vinblastine and, to a lesser extent, with uridine. However, drug transport studies demonstrated that BIBW22 BS is not a substrate for P-gp efflux pump. Interestingly, BIBW22 BS was shown to accumulate more in resistant cells. Also, BIBW22 BS accumulation in drug-sensitive and -resistant cells was not energy dependent. These results are in contrast with the observed decrease in accumulation or enhanced efflux of [3H]vinblastine seen in the same MDR cells. A comparison of [3H]azido-BIBW22 BS or [3H]azidopine photolabeled P-gp by Cleveland mapping with Staphylococcus aureus V8 protease showed differences in the photolabeled peptides. Taken together, the results of this study show that BIBW22 BS is a potent MDR-reversing agent that binds directly to P-gp but is not effluxed from drug-resistant cells.

Fetal ultrasound imaging and the production of authoritative knowledge in Greece

In Greece repetitive and intensive fetal scanning is now a universal feature of prenatal care. This article examines some of the ways in which pregnant women and obstetricians experience the intensive use of fetal ultrasound in a small city in eastern Greece. Based on observations and interviews conducted in a public hospital, it is argued that fetal imaging plays a privileged role in the production of authoritative knowledge around pregnancy for both doctors and women. The authority of the technology rests primarily on its ability to create a straightforward sense of reality and visual pleasure. These qualities lead women to actively demand fetal scanning, which helps them to feel the reality of their pregnancies, reassures them of fetal health, and provides a pleasurable sense of contact with, and knowledge about, the fetus. Doctors freely offer multiple scans to attract women to the public hospital, to practice "modern" obstetrics, and to negotiate among themselves for control over the management of pregnant women.

p-Azidosalicyl-5-amino-6-phenoxybenzimidazole photolabels the N-terminal 63-103 amino acids of Haemonchus contortus beta-tubulin 1

Benzimidazoles (BZ) are broad spectrum anthelmintics thought to exert their effects by interacting with and disrupting the functions of microtubules. However, direct biochemical evidence for binding between BZ and tubulin has not been shown nor is it known what sequences in tubulin interact with BZ. In this study, a photoactive analogue of 2-acetamido-5-(3-aminophenoxy)benzimidaz ole that has biological activity similar to other benzimidazoles was synthesized and used to photoaffinity label cell lysates from the parasitic nematode of sheep Haemonchus contortus. The photoactive analogue, 2-acetamido-5-[3-(4-azido-3-125I-salicyl amido)phenoxy]benzimida zol e or 125I-ASA-BZ, was shown to photolabel a 54-kDa protein that was specifically immunoprecipitated with anti-tubulin monoclonal antibodies. Tubulin photoaffinity labeling by 125I-ASA-BZ was also inhibited with molar excess of various BZ analogues and colchicine. Interestingly, 125I-ASA-BZ photoaffinity-labeled the beta- and not the alpha-subunits of tubulin. Proteolytic digestion of 125I-ASA-BZ-labeled tubulin with Staphylococcus aureus V8 proteinase revealed one major peptide with an apparent molecular mass of 3.5 kDa. Exhaustive digestion of 125I-ASA-BZ-labeled beta-tubulin with trypsin resulted in two fractions containing radioactive peptides. Protein sequencing of the high performance liquid chromatography-purified tryptic ASA-BZ-photolabeled peptides identified the N-terminal 63-77 and 78-103 sequences as the BZ binding domain.

Abortion policy and practice in Greece

Despite its illegality until recently, abortion is estimated to have been responsible for almost half of the sharp postwar decline in the Greek birth rate. This article examines abortion as a part of a Greek contraceptive culture which has taken shape during the postwar period both in response, and in resistance to, a variety of macro- and micropolitical institutions and forces. During much of this period, pronatalist policies and discourses of both state and church combined to foreclose most medical contraceptive alternatives. In contrast, illegal abortion was a relatively safe, medicalized procedure widely practiced by doctors. Even after being legalized in 1980, female medical contraceptive methods continue to be rejected by the great majority of Greek women, and abortion and male methods of birth control remain the principal means of controlling fertility. The article focuses on the specific abortion practices and meanings of three generations of married women living in the city of Rhodes, capital of the Dodecanese Province of Greece's Eastern Aegean, and explores the ways in which they have been shaped by, and reflect, local cultural understandings of the body, health, sexuality, morality, motherhood and childhood, as well as micropolitical relations within the family.

Identification of a sister gene to P-glycoprotein

The P-glycoproteins (Pgps) are a small family of transport proteins associated with the multidrug resistance phenotype of cell lines selected for growth in cytotoxic drugs. Utilizing low stringency screening, we have identified a novel gene closely related to the Pgps expressed in the pig and other mammalian liver which we have called Sister of P-glycoprotein (spgp). Sequence of this gene shows it to be a member of the ATP-binding cassette family of transporters and the gene most closely related to Pgp identified to date. The function of spgp is not known, but it can be recognized by at least one Pgp mAb, C219. This cross-reactivity has implications for expression studies in tissues and tumors utilizing this and other Pgp antibodies.

Benzimidazoles, potent anti-mitotic drugs: substrates for the P-glycoprotein transporter in multidrug-resistant cells

P-glycoprotein is though to mediate the energy-dependent efflux of many structurally and functionally unrelated lipophilic compounds. Presently, the molecular mechanism underlying the binding and efflux of drugs by P-glycoprotein is not well understood. However, it has been suggested that two planar benzene ring structures and a cationic charge are commonly found in many drugs that interact with P-glycoprotein. The benzimidazoles (BZs) are potent anti-tumour, anti-fungal and anti-parasitic agents, whose mode of action is thought to result from their inhibition of microtubule functions. Although other classes of microtubule inhibitors, such as colchicine and vinblastine, have been studied extensively with respect to their interaction and efflux by P-glycoprotein, the BZ group of drugs has not been characterized. In this study, we have characterized the interaction of BZ with multidrug-resistant cells and found that resistant cells accumulated substantially less BZ compared with drug-sensitive cells. Furthermore, BZ was more toxic to sensitive than to drug-resistant cells, suggesting that BZ is likely to be a substrate for the P-glycoprotein drug efflux pump. In addition, we used a photoactive analogue of BZ ([125I]ASA-BZ) to demonstrate a direct binding between BZ and P-glycoprotein. Results showing that a molar excess of vinblastine, unmodified BZ, verapamil and rhodamine 123, but not colchicine, inhibited the photoaffinity labelling of P-glycoprotein by [125I]ASA-BZ confirmed the binding specificity of BZ to P-glycoprotein. Protease digestion of [125I]ASA-BZ photoaffinity labelled P-glycoprotein yielded two peptides that were similar to those obtained with other P-glycoprotein-associated drugs, e.g. azidopine and iodoaryl azidoprazosin. Taken together, these results demonstrate a direct and specific interaction between P-glycoprotein and BZ in a manner that is probably similar to other previously characterized P-glycoprotein-associated drugs.

Characterization of rhodamine 123 binding to P-glycoprotein in human multidrug-resistant cells

The overexpression of P-glycoprotein is currently believed to be responsible for the enhanced efflux or decreased influx of cytotoxic drugs across the cell membrane in drug-resistant cells. P-glycoprotein has been proposed to mediate the efflux of a large number of structurally and functionally unrelated drugs. Although it has been suggested that P-glycoprotein binds directly to many lipophilic cations, it remains unclear whether one or more sites in P-glycoprotein mediate its broad substrate specificity. In this report, a photoactive derivative of rhodamine 123 (Rh123) [125I-azidosalicylic acid (ASA)-Rh123] was synthesized and used in a photoaffinity labeling assay to demonstrate, for the first time, direct and specific binding to P-glycoprotein. The photoaffinity labeling of P-glycoprotein by ASA-Rh123 was specifically inhibited in the presence of vinblastine and verapamil but not in the presence of colchicine. Surprisingly, ASA-Rh123 photoaffinity labeled a 6-kDa V8 peptide in P-glycoprotein that was previously shown to be photoaffinity labeled by another multidrug resistance-associated drug, [125I]iodoarylazidoprazosin. Photoaffinity labeling of mitochondria from drug-sensitive or -resistant cells with 125I-ASA-Rh123 did not reveal significant differences in the mitochondrial proteins from sensitive or resistant cells. Interestingly, however, 125I-ASA-Rh123 did photolabel a 66-kDa protein in mitochondria that was not detected in plasma membrane preparations with this assay. Taken together, our results demonstrate for the first time that Rh123 binds specifically to P-glycoprotein and that its binding site may be shared by other multidrug resistance-associated drugs.

Effects of nonionic detergents on P-glycoprotein drug binding and reversal of multidrug resistance

Multidrug-resistant cells are thought to maintain low intracellular cytotoxic drug concentration though the active efflux of drugs across the cell membrane. It is presently believed that P-glycoprotein mediates this energy-dependent drug efflux by interacting directly with various lipophilic compounds. In this report, we have used [3H]azidopine in a photoaffinity labeling assay to study the effect of detergents and denaturing agents on P-glycoprotein drug binding in intact cells. Nonionic detergents such as Triton X-100 or Nonidet P-40 at very low concentrations were found to completely abolish azidopine photolabeling to P-glycoprotein and are able to reverse the multidrug resistance phenotype. In contrast, high concentrations of the denaturing agent urea or the zwitterionic detergent 1-[(3-cholamidopropyl)dimethylamino]-1-propanesulfonate did not inhibit azidopine photolabeling to P-glycoprotein. A comparison between verapamil and Triton X-100 revealed that the latter was more effective in inhibiting azidopine photolabeling to P-glycoprotein while verapamil was more effective in potentiating [3H]vinblastine accumulation in drug-resistant cells. Drug transport studies showed that [3H]Triton X-100 accumulated in both drug-sensitive and -resistant cells, and its accumulation was not modulated by excess vinblastine, verapamil, or colchicine. Taken together, these findings suggest that low concentrations of Triton X-100 reverse the multidrug resistance phenotype by inhibiting P-glycoprotein drug binding. In addition, it is also suggested that the site(s) of P-glycoprotein drug binding is localized to sequences found within the lipid bilayer.

Body fat distribution in men and women of the Hispanic health and nutrition examination survey of the United States: associations with behavioural variables

Body fat distribution is a biological risk factor for cardiovascular disease and diabetes. There are known genetic factors influencing body fat distribution, but variation in this characteristic is also attributable to human behavioural and socioeconomic variables such as social class. Björntorp has proposed that these associations may be due to a series of physiological responses to psychosocial stress, most prominently chronic stimulation of the adrenal-cortical system. This system is known to affect body fat distribution. Elsewhere we have shown that general socioeconomic status is related to body fat distribution in men and women of the Hispanic Health and Nutrition Examination Survey (HHANES) of the United States. In this paper we explore the relationship with those behavioural variables available from the HHANES which could hypothetically serve as indicators of psychosocial stress: smoking, drinking and depression. For both sexes in all Hispanic ethnic groups except Puerto Rican men, as socioeconomic status declined, subcutaneous fat became more centrally distributed. This relationship continued to be significant after controlling for the behavioural variables. A positive relationship was also found between smoking and central body fat distribution which was independent of socioeconomic status. This relationship was statistically significant for all subsamples except Cuban-American women. No consistent relationships were found between body fat distribution, drinking and depression. The data support the hypothesis that body fat distribution may be linked to the social stress of low socioeconomic status, independent of the behavioural factors tested.

Topology of P-glycoprotein as determined by epitope mapping of MRK-16 monoclonal antibody

There is growing evidence for the direct role of P-glycoprotein mediating multidrug resistance in tumor cells. P-glycoprotein is thought to function as an energy-dependent drug efflux pump. The monoclonal antibody MRK-16 binds to an external domain of P-glycoprotein and partially inhibits drug efflux in multidrug-resistant cells. As an approach toward elucidating the mechanism by which MRK-16 affects drug transport, we undertook the definition of the precise binding site of this antibody. In this study we have mapped the epitope of MRK-16 monoclonal antibody to a resolution of a single amino acid using a series of overlapping synthetic peptides. We demonstrate that MRK-16 recognizes only the class I isoform (MDR1) of human P-glycoprotein and that its epitope encompasses at least two (first and fourth) of the six predicted extracellular peptide loops. These results suggest that the epitope of MRK-16 is discontinuous and that the sequences involved which are separated by about 625 amino acids in the linear sequence must be spatially situated in close proximity in the native protein. Based on these results, we present a model for transmembrane alpha-helical packing of P-glycoprotein in the lipid bilayer. This may have implications for understanding the function of P-glycoprotein in drug transport.

Toremifene resistance in a rat mammary tumour model

The effect of Toremifene on cell growth in vitro was tested on the R3230AC rat mammary adenocarcinoma as model. Toremifene differed from Tamoxifen in that it did not induce resistance; some cross-resistance was observed in Tamoxifen tolerant tumour cell lines. Toremifene does not influence P-glycoprotein expression in this model and at the levels studied.

Molecular and biological characterization of cottontail rabbit papillomavirus variant DNA sequences integrated in the VX7 carcinoma

The transplantable VX7 carcinoma was derived from a tumor induced by a recoverable strain of cottontail rabbit papillomavirus (CRPV) able to replicate in domestic rabbits. Low levels of late viral gene expression have been retained through serial propagation in rabbits. We have cloned and characterized the three major types of CRPV sequences integrated in this tumor, a genome-length 8-kb DNA molecule and two rearranged 9- and 3.8-kb molecules. The VX7 8-kb DNA displays only a few differences in its restriction map, when compared to the wild-type (wt) CRPV DNA. The VX7 9- and 3.8-kb DNAs derive from the VX7 8-kb DNA since they share the same restriction site polymorphism. The VX7 9-kb DNA contains a duplication of the E6 open reading frame. The VX7 3.8-kb DNA results from the deletion of most of the E region and the insertion, between the borders of the deletion, of 174-nucleotide-long segment of the long control region potentially driving the expression of a truncated L2 protein. Both VX7 9- and 3.8-kb species potentially allow the expression of abnormal E6 fusion proteins. Nineteen point mutations were detected in the 3.8-kb DNA, compared to the wt CRPV DNA. None of these molecules were able to induce warts in domestic rabbits, in contrast to wt CRPV DNA. Furthermore, when cloned VX7 DNAs were inoculated together with wt CRPV DNA, none of the VX7 CRPV sequences, as identifiable by their specific restriction enzyme cleavage patterns, could be detected in the resulting warts. This suggests that CRPV sequences integrated in the VX7 carcinoma are no longer able to replicate as episomes, which might be a prerequisite for the production of warts.

Modulation of ATP and drug binding by monoclonal antibodies against P-glycoprotein

The role of P-glycoprotein in mediating the drug-resistance phenotype in multidrug resistant cells is now well documented. It is thought to function as an energy-dependent drug-efflux pump of broad specificity. Structurally, P-glycoprotein is an internally duplicated molecule containing two large multi-spanning transmembrane domains and two cytoplasmic ATP binding domains. In this report we demonstrate that monoclonal antibodies C219, C494, and C32 directed against short linear regions of the P-glycoprotein molecule inhibit ATP binding to P-glycoprotein in vitro. We also provide direct evidence that both predicted ATP-binding domains bind ATP and that there is co-operativity between the two sites. In addition, the capacity of P-glycoprotein to bind the calcium channel blocker, azidopine, is inhibited differentially by the antibodies. These observations are the first evidence linking specific perturbations of the P-glycoprotein molecule with ATP and drug binding.

R-verapamil decreases anti-estrogen resistance in a breast cancer model

Drug resistance eventually limits the effectiveness of antiestrogens in breast cancer treatment. Pharmacological reversal of this refractoriness has been attempted with R-Verapamil, a well tolerated calcium channel blocker. This drug significantly decreased the incidence of lung foci after intravenous seeding of the R3230AC rat adenocarcinoma; this effect was correlated with reduction in the expression of P-glycoprotein. The simultaneous administration of antiestrogens with a non-toxic enantiomer of Verapamil was beneficial in the tumour model investigated.

Sex-dependent and independent expression of the P-glycoprotein isoforms in Chinese hamster

P-glycoprotein (Pgp) is a small family of membrane proteins which belongs to a superfamily of energy-dependent membrane transport proteins identified in phylogenetically distant species, from bacteria to man. Among mammalian species, some of the Pgp isoforms can mediate multidrug resistance by acting as an energy-dependent drug efflux pump. However, the physiologic functions of the Pgp isoforms have not been defined. In this study we examined the expression of the three hamster Pgp isoforms in normal hamster tissues, by using isoform-specific monoclonal antibodies in a competitive immunohistochemical assay. We showed that each Pgp isoform is predominantly expressed in a small, distinct group of differentiated cells, where it is likely to function in specific secretory pathways. The expression of the Pgp isoforms appears to be tightly regulated and, at least in some cells, under complex hormonal control. Furthermore, there is a striking sex difference in Pgp content of the adrenal cortex. These findings are important for the ultimate understanding of the normal physiologic roles of the Pgp gene family members.

Identification of a membrane glycoprotein overexpressed in murine lymphoma sublines resistant to cis-diamminedichloroplatinum(II)

A series of murine thymic lymphoma cell sublines was selected in vitro for resistance to cis-diamminedichloroplatinum(II) (CDDP). The level of CDDP resistance correlated with reduced drug accumulation in these cells. A rabbit antiserum was raised against the plasma membrane of a CDDP-resistant subline and used in Western blot analyses. Increased expression of a surface antigen of approximately 200 kDa was observed and found to correlate with the degree of resistance. Further biochemical and immunological studies demonstrated that this is a plasma membrane glycoprotein. However, it is different from the multidrug resistance-associated P-glycoprotein with a molecular weight of about 170,000. We have called this unique CDDP resistance-associated membrane protein CPR-200.

Detection of P-glycoprotein isoforms by gene-specific monoclonal antibodies

P-glycoprotein is a highly conserved membrane protein shown to be overexpressed in many multidrug-resistant tumor cell lines. P-glycoprotein is encoded by a small gene family in mammalian cells. Class I and II isoforms cause multidrug resistance, whereas class III does not. In this report, we have characterized three P-glycoprotein-specific monoclonal antibodies (mAbs) by high-resolution epitope mapping with a series of hexapeptides. mAb C494 is gene specific, binding to a sequence present only in the class I isoform of hamster and human. The mAb C32 recognizes a sequence conserved in hamster class I and II isoforms but not in class III isoforms. In contrast, the mAb C219 recognizes a highly conserved amino acid sequence found in all P-glycoprotein isoforms characterized to date. These mAbs were used to reveal differential expression and specific localization of the three P-glycoprotein isoforms in hamster tissues by immunohistochemical staining and competition with epitope-specific peptides. Colonic epithelial cells expressed predominantly the class I isoform in a polarized manner, adrenal cortical cells expressed predominantly the class II isoform, whereas a small percentage of skeletal muscle fibers expressed the class III isoform of P-glycoprotein. These findings suggest that the P-glycoprotein isoforms have distinct physiological roles associated with specialized cell functions.

Neurofilament phosphorylation in cultured bovine adrenal chromaffin cells is stimulated by phorbol ester

Primary cultures of bovine adrenal chromaffin cells contain neurofilament proteins that are hypophosphorylated. When the cells were grown in medium containing 32Pi and 0.1 microM 12-O-tetradecanoyl-phorbol 13-acetate (TPA), 32P-labelling of the three neurofilament subunits was increased 6- to 20-fold relative to controls, the highest level of stimulation occurring for the mid-sized subunit. Addition of the protease inhibitor leupeptin to the growth medium had no effect on TPA-stimulated phosphorylation. The increased 32P incorporation was accompanied by a marked reduction in the gel electrophoretic mobilities of the two largest subunits. The augmented phosphorylation was observed 10 min after addition of TPA to a concentration of 0.1 microM or after 1 h of incubation in the presence of 0.01 microM TPA. One-dimensional peptide mapping and phosphoamino acid analysis indicated that TPA stimulated the phosphorylation of seryl residues at new sites in the mid-sized subunit. All of the latter subunit contained in the cytoskeletal fraction of chromaffin cells was converted to a more highly phosphorylated state after the cells were grown in the presence of TPA for 1 h.

[Cleft lip and palate in Campeche Mayas]

It has been suggested that among American Indians, as in some genetically-related Asiatic ethnic groups, incidence of cleft lip and/or cleft palate is higher than among people of Caucasian extraction. Such hypothesis, plus growing demand for services observed at a center for the surgery of cleft lip and cleft palate in Campeche state, led the authors to undertake research among the Maya residents of that region. However, neither careful review of case histories nor field research performed in several Indian communities could confirm the hypothesis of a higher incidence among this ethnic community.

Electrophoretic analysis of P-glycoproteins produced by mouse J774.2 and Chinese hamster ovary multidrug-resistant cells

P-glycoprotein (P-gp) plays a fundamental role in multidrug resistance. The quantity of P-gp relates to the degree of drug resistance. A comparison was made between P-gps in mouse and hamster cell lines in both Laemmli and modified Fairbanks gel systems. Both proteins are derived from precursors of similar size that undergo differential N-linked glycosylation. The electrophoretic mobility and the amount of P-gp are remarkably dependent on the conditions of analysis. Notably, boiling P-gp before Laemmli gel electrophoresis decreases its mobility by an amount that is equivalent to approximately equal to 15 kDa and results in an apparent diminution in the amount of protein. The latter effect can give a false impression concerning the quantity of P-gp in cells.

Hypophosphorylated neurofilament subunits in the cytoskeletal and soluble fractions of cultured bovine adrenal chromaffin cells

The neurofilament proteins in cultured bovine adrenal chromaffin cells are in a hypophosphorylated state, as determined by the co-migration of the 160,000 and 210,000 molecular weight subunits with in vitro dephosphorylated bovine brain subunits on sodium dodecyl sulfate polyacrylamide gels. In addition, chromaffin cells were not stained by anti-heavy neurofilament subunit that binds only to phosphorylated epitopes. Pulse-labeling with 32Pi in the presence and absence of the protein synthesis inhibitor emetine indicated that some neurofilament protein phosphorylation occurred co-translationally and/or immediately after synthesis of the proteins. Pulse-chase experiments showed that the three neurofilament proteins rapidly attained their maximal phosphorylation levels, as multiple forms of either of the respective subunits were not seen after a one hour chase. We found that Triton X-100-soluble forms of high molecular weight neurofilament and middle molecular weight neurofilament subunits were present in chromaffin cells, and they also co-migrated with standard neurofilament proteins dephosphorylated in vitro. However, there were differences between the phosphopeptide maps of cytoskeleton-associated and soluble middle molecular weight neurofilament subunit, suggesting that the localization of phosphate moieties rather than extent of phosphorylation influences the association of the subunit with neurofilaments. Double immunofluorescence staining of cell cultures with antibody to the 70,000 molecular weight subunit and with anti-vimentin showed that chromaffin cells do not express vimentin.

Chemical modification of charged amino acid moieties alters the electrophoretic mobilities of neurofilament subunits on SDS/polyacrylamide gels

The increase in the mobilities of neurofilament subunits on SDS-PAGE after dephosphorylation was reversed upon boiling in urea or trifluoroacetylation of lysine epsilon-amino groups. Trifluoroacetylation of native and dephosphorylated neurofilaments also resulted in an overall increase in the phosphorylation of the three subunits by the catalytic subunit of cyclic-AMP-dependent protein kinase. The gel-electrophoretic mobility of neurofilament subunits was also shown to be influenced by carboxylic amino acid residues, as neutralization of these moieties by glycinamidation increased the mobilities of all three subunits on SDS-PAGE. Neurofilament subunits that were both glycinamidated and dephosphorylated had apparent molecular masses of approximately 60 kDa, 112 kDa and 138 kDa. The major sites of these changes in the two largest subunits were shown to be the carboxy-terminal tail domains, which are known to contain high percentages of glutamate. Since interspecies differences in the apparent molecular masses of neurofilament subunits were shown to persist after glycinamidation and dephosphorylation, they appear to be due to differences in polypeptide chain length, rather than glutamate content.

Dephosphorylation of neurofilaments by exogenous phosphatases has no effect on reassembly of subunits

Exhaustive in vitro dephosphorylation of porcine neurofilaments (NFs) by alkaline or acid phosphatase did not cause a dissociation of the 210-kD (NF-H), 160-kD (NF-M), or 70-kD (NF-L) subunits and had no effect on the reassembly of NFs from urea or guanidine solution. Electron microscopy revealed that the NFs reassembled from isolated or dephosphorylated subunits had similar morphologies. Phosphatase treatment caused significant increases in the mobilities of NF-M and NF-H on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, suggesting that the subunits underwent marked conformational changes after dephosphorylation. Chemical phosphate analysis showed that as isolated NF-H, NF-M, and NF-L contained about 22, 11, and 3 mol phosphate/mol polypeptide, respectively. The corresponding values for the three subunits from alkaline phosphatase-treated NFs were about 8, 6, and 2 mol phosphate/mol polypeptide, respectively. These results indicate the occurrence of a class of phosphate moieties that is not accessible to exogenous phosphatases.

Neurofilament proteins in cultured chromaffin cells

Antibodies were raised against the 200-kd, 145-kd, and 68-kd subunits of a rat neurofilament preparation. Immunoblots showed that each antibody was specific for its antigen and that it did not cross-react with any of the two other neurofilament polypeptides. Use of the three antibody preparations to stain bovine chromaffin cells in culture by the indirect immunofluorescence technique indicated that the three neurofilament polypeptides are present in chromaffin cells maintained in culture for 3 or 7 days. The three anti-neurofilament antibodies labelled the cells in a similar pattern: very thin filaments specifically localized around the nucleus were observed whereas neurites and growth cones, developed by cultured chromaffin cells, were generally not stained. Some fibroblasts were present in our cultures but they were never stained by any of the neurofilament antibodies. This indicated that the antibodies used do not react with vimentin, the major intermediate filament protein found in fibroblasts. The three neurofilament antibodies were also used to immunoprecipitate specifically three proteins of molecular weights 210 kd, 160 kd, 70 kd from solubilized extracts of cultured chromaffin cells that were radiolabelled with [35S]methionine. These proteins correspond in molecular weight to the neurofilament triplet found in bovine brain. Finally, the presence of neurofilaments in freshly isolated chromaffin cells was tested by immunoblotting using the 68-kd antibody. A 70-kd protein was specifically stained by this antibody, suggesting that neurofilaments are not only present in cultured chromaffin cells but also in the adrenal gland in vivo. It is concluded from these results that chromaffin cells contain completely assembled neurofilaments. This additional neuronal property again illustrates that chromaffin cells are closely related to neurons and therefore represent an attractive model system for the study of functional aspects of adrenergic neurons.

Physical state and transcription of the cottontail rabbit papillomavirus genome in warts and transplantable VX2 and VX7 carcinomas of domestic rabbits

The physical state and the transcription of the genome of cottontail rabbit papillomavirus (CRPV) in non-virus-producing warts and in the VX2 and VX7 transplantable carcinomas of domestic rabbits were compared. The CRPV DNA present in VX2 and VX7 carcinomas (10 to 20 and 100 to 200 genome equivalents per diploid cell, respectively) was found to be entirely integrated into the cellular DNA, most probably as head-to-tail tandem repeats, in contrast to warts, in which viral DNA (10 to 100 copies per diploid cell) was found only as free, mainly monomeric, molecules. In the VX7 tumor, ca. 50% of the viral DNA molecules were found to be longer than one genome length, indicating that viral DNA rearrangements had occurred. A major viral transcript of 1,250 bases was detected in warts and in VX2 and VX7 carcinomas. Complementary sequences were localized within the E region, the putative transforming region inferred from the nucleotide sequence of the CRPV genome (I. Giri, O. Danos, and M. Yaniv, manuscript in preparation). Analysis of heteroduplexes formed between single-stranded CRPV DNA and polyadenylated RNAs from the VX2 tumor showed that the 1,250-base RNA resulted from the splicing of the sequences corresponding to the open reading frame E6 to those corresponding to the 3' third of E2. A second viral transcript, measuring 2,000 bases, was detected in warts and, in lesser amounts than the 1,250-base species, in VX2 carcinoma, and a 2,100-base RNA was found in VX7 carcinoma. Complementary sequences to these messengers were localized to the same part of the genome as the 1,250-base species and to a contiguous fragment situated upstream. Heteroduplex analysis showed that the 2,000-base species from VX2 carcinoma resulted from the splicing of the sequences corresponding to E6 and E7 to those corresponding to the 3' third of E2. The sequences spliced out upon the maturation of the two messengers of VX2 carcinoma correspond to E1, the two-thirds of E2, and most of E4. Additional transcripts were found in VX7 carcinoma, a major 3,100-base species transcribed from the E region, and several minor species, measuring from 2,400 bases, which all hybridize with a subgenomic fragment contained in the L region encoding the viral capsid polypeptides. This could account for the antiviral antibodies found in animals bearing the VX7 carcinoma.

Polyoma virus mutants as probes of variety among mouse embryonal carcinoma cell lines

Embryonal carcinoma (EC) cells are resistant to infection with polyoma virus and become permissive when allowed to differentiate. Polyoma host-range (PyEC) mutants have been selected on two embryonal carcinoma cell lines, PCC4 and F9, which differ in their differentiation potential, both in vitro and in vivo. Since PyEC mutants selected on one line failed to develop, or developed only poorly on the other, we used these two classes of mutants as probes towards several EC lines which differed in their origin and differentiation properties. From their susceptibility to either mutant, and from the effect of temperature upon the efficiency of infection, we inferred a classification of these teratocarcinoma cell lines, which is an agreement with a previous one based upon metabolic coupling. We also discussed results indicating that different EC cell lines might present steps in the process of cell determination at the embryonic level.