Interaction of the rabies virus P protein with the LC8 dynein light chain.

The rabies virus P protein is involved in viral transcription and replication but its precise function is not clear. We investigated the role of P (CVS strain) by searching for cellular partners by using a two-hybrid screening of a PC12 cDNA library. We isolated a cDNA encoding a 10-kDa dynein light chain (LC8). LC8 is a component of cytoplasmic dynein involved in the minus end-directed movement of organelles along microtubules. We confirmed that this molecule interacts with P by coimmunoprecipitation in infected cells and in cells transfected with a plasmid encoding P protein. LC8 was also detected in virus particles. Series of deletions from the N- and C-terminal ends of P protein were used to map the LC8-binding domain to the central part of P (residues 138 to 172). These results are relevant to speculate that dynein may be involved in the axonal transport of rabies virus along microtubules through neuron cells.

Mapping of monoclonal antibody epitopes of the rabies virus P protein.

Thirty-six monoclonal antibodies (MAbs) specific for the rabies virus P phosphoprotein were obtained from mice immunized with recombinant P (PV strain) produced in E. coli. All MAbs reacted against the corresponding rabies virus protein by ELISA and by Western blot analysis and revealed the presence of cytoplasmic inclusions in rabies virus infected cells. The epitopes of seven MAbs were mapped by testing their reactivity with protein fragments expressed from deletion mutants in transfected cells. Western blotting, immunoprecipitation and immunofluorescence assays were performed. These MAbs recognized epitopes in different domains of the P protein: 60% were directed against a region lying between residues 83-172 suggesting a major antigenic determinant of the rabies virus P protein in this region. Most of the antigenic sites appeared to be composed of linear epitopes. These MAbs will be useful as tools to dissect structural and functional properties of the rabies virus P protein.

Identification of amino acids controlling the low-pH-induced conformational change of rabies virus glycoprotein.

The glycoprotein (G) of rabies virus assumes at least three different conformations: the native state detected at the viral surface above pH 7, the activated state involved in the first step of the fusion process, and the fusion-inactive conformation (I). A new category of monoclonal antibodies (MAbs) which recognized specifically the I conformation at the viral surface has recently been described. These MAbs (17A4 and 29EC2) became neutralizing when the virus was preincubated at acidic pH to induce the conformational change toward the I state of G. Mutants escaping neutralization were then selected. In this study, we have investigated the fusion and the low-pH-induced fusion inactivation properties of these mutants. All of these mutants have fusion properties similar to those of the CVS parental strain, but five mutants (E282K, M44I, M44V, V392G, and M396T) were considerably slowed in their conformational change leading to the I state. These mutants allow us to define regions that control this conformational change. These results also reinforce the idea that structural transition toward the I state is irrelevant to the fusion process. Other mutations in amino acids 10, 13, and 15 are probably located in the epitopes of selecting MAbs. Furthermore, in electron microscopy, we observed a hexagonal lattice of glycoproteins at the viral surface of mutants M44I and V392G as well as strong cooperativity in the conformational change toward the I state. This finding demonstrates the existence of lateral interactions between the spikes of a rhabdovirus.

Monoclonal antibodies which recognize the acidic configuration of the rabies glycoprotein at the surface of the virion can be neutralizing.

Around 15% of our anti-glycoprotein monoclonal antibodies (MAbs) failed to neutralize the infectivity of the rabies virus during a 1-hr incubation at room temperature. In previous studies, we have demonstrated that it is possible to induce a massive conformational change of the glycoprotein population by incubating the virus at acidic pH. The conformational change is reversible and consequently viral infectivity is not affected by transient exposure at acidic pH. The proportion of glycoproteins in acidic or neutral configuration depends on the pH which means that even at neutral pH some glycoproteins transiently adopt the acidic configuration and vice versa. Here we report that some of our nonneutralizing MAbs recognize the acidic form of the glycoprotein at the virion surface. After incubation of the virus at pH 6.4, most glycoproteins are in the acidic configuration. Further 1-hr incubation with these MAbs at the same pH resulted in more immunoglobulins being attached to the virus and consequently neutralization was induced. It was also possible to induce neutralization with the same MAbs by incubation at neutral pH for a longer period or at a higher temperature. Mutants resistant to neutralization by these MAbs could be selected. Mutations confering resistance to neutralization were not localized in previously described antigenic sites and did not modify these sites at distance. They had no effect on the pathogenic power of the virus. Either they are situated in the epitope or they modify the epitope, so that it is no longer recognized by the antibody on the acidic configuration of the protein. Alternatively, these mutations may stabilize the protein in its neutral configuration. In addition, these experiments confirm our previous finding that neutralization requires the fixation of a large number of immunoglobulins on the virus, irrespective of the region of the protein recognized by the antibody.

Differential influence of stromal fibroblasts from different breast tissues on human breast tumour cell growth in nude mice.

The influence of human stromal fibroblasts cultured from normal, non-malignant and malignant breast tissues on in vivo growth of human breast tumour cells was studied. Earlier appearance and increased incidence were observed when low cell inocula of breast MDA-MB 231 tumour cells were coinjected with fibroblasts from either normal or non-malignant mammary tissue. However, at higher cell inoculations the appearance of MDA-MB tumours was delayed while the incidence was reduced. Coinjected fibroblasts derived from breast tumours did not modify MDA-MB tumour growth. The tumourigenic MCF-7 and non-tumourigenic NPM14-T4/9 breast cell lines were not affected by the presence of normal breast fibroblasts. These results indicate that fibroblasts can influence the behavior of tumour cells in vivo but the effects depend on the type and the proportions of coinoculated cells.

Mechanisms of rabies virus neutralization.

The number of immunoglobulins necessary to neutralize rabies virus (CVS strain) was estimated using IgG and IgM monoclonal antibodies (MAb) specific to the three antigenic sites of the glycoprotein. It was estimated that below 130 IgG or 30 IgM bound per virions, infectivity was totally preserved. Neutralization occurred for an average of 1 or 2 IgG for 3 spikes and 1 IgM for 9 to 10 spikes on the virus surface. Saturation was obtained for 1 to 3 IgG per spike, depending on the antibody, and 1 IgM for 4 to 5 spikes. This result was confirmed by electron microscopy. Neutralization-resisting mutants which continued to fix the selecting MAb in ELISA were also investigated. In two cases, the lack of neutralization was due to the fact that the maximum number of immunoglobulins bound per virion was below the neutralizing dose. In one case, however, the mutant was able to fix the same number of IgG as the parental strain and was not neutralized, even at saturation. The capacity of the antibodies to reduce the attachment of the virus onto BSR cells was also examined. Every intermediate between no inhibition of the attachment and inhibition by a factor of 20 was found; even in this last case, inhibition of attachment was insufficient to explain the extent of neutralization. No correlation was found between the antigenic site recognized by the antibody and the level of inhibition. IgM inhibited attachment more than IgG and one IgG2b antibody did not inhibit attachment at all. The fusion of virions saturated with this antibody with artificial liposomes was totally inhibited, either specifically or because virus-antibody complexes did not attached to the liposomes.

New stable butyrate derivatives alter proliferation and differentiation in human mammary cells.

Two new butyric esters which were devised to extend the half-life of n-butyric acid in vivo, were used to study their effects on a number of phenotypic characteristics including cell morphology, cell proliferation, colony formation, cell-surface antigen and estrogen receptor expression in 3 normal immortalized cell lines and 2 carcinoma cell lines derived from the human mammary gland. When treated with butyric esters, human mammary cells acquired numerous cytoplasmic granules and vacuoles, reminiscent of secretory functions, and increased in volume. Modulation of the expression of membrane-associated antigens recognized by the monoclonal antibodies (MAbs) 115D8, 140C1 and 125B5 was also observed. Furthermore, butyrate derivatives inhibited the proliferation of all the cell lines tested and the colony-forming capacity of those that grew in soft agar. The inhibitory effects were, however, reversible upon removal of butyric esters from the culture medium. In the human breast carcinoma cell line, MCF-7, in which the cytostatic effects of butyric esters were the most pronounced, cells accumulated in the G0/G1 phase of the cell cycle. This cell line was the only one to contain estrogen receptors which decreased in number when treated with butyric esters without any modification in their binding affinity. Moreover, the stimulatory effects of estrogen on MCF-7 cell proliferation were antagonized by butyric esters. Our results demonstrate that many of the proliferative and differentiation changes previously reported for n-butyrates in tumor cells are similarly produced by the new stable butyrate derivatives in normal and malignant human mammary cell lines.

Fetal myofibroblast-like cells isolated from post-radiation fibrosis in human breast cancer.

Cells were isolated from post-radiation fibrosis biopsies of patients with recurrent breast carcinoma. These cells were identified as fibroblasts and compared with fibroblasts from normal breast tissues for their proliferative activities, chromosome number and for the presence of various components of the extracellular matrix and cytoskeleton. The proliferative activity of the fibrosis-derived fibroblasts did not significantly differ from that of normal breast fibroblasts. Both cell types required serum to grow and did not form colonies in soft agar. Cells from 2 of the 3 fibroses analyzed displayed aneuploid karyotypes with multiple structural abnormalities. All of the fibroblastic cells produced types I, III and V collagen, fibronectin and vimentin. However, in contrast to normal breast fibroblasts, fibrosis-derived cells produced high amounts of oncofetal fibronectin. In addition, fibrosis of fibroblasts also expressed the alpha-actin isoform which is specific for smooth-muscle cells. These results suggest that post-radiation fibrosis in malignant breast contains atypical fibroblasts with fetal and myofibroblastic characteristics.

Primary cultures of human benign mastopathies and mammary carcinomas; growth factor requirements.

Primary cultures of non malignant human breast tissues, benign mastopathies and breast carcinoma were performed in defined culture conditions. Epithelial cells from these primary cultures were characterized for mammary epithelial cell specific markers, for in vitro cell proliferation, for steroid receptors and hormone sensitivity (estradiol, progesterone and prolactin) and for EGF sensitivity. We show that although some mastopathies have estradiol and progesterone receptors, they did not respond to hormone treatment. Human prolactin had no effect on the proliferation of one mastopathy but stimulates the cell growth of another fibrocystic mastopathy. EGF was capable of stimulating the three types of primary cultures. As regards growth characteristics, steroid hormone receptors and prolactin sensitivity, phenotypes of mastopathy cells differ from each other; some are similar to non malignant cells, whereas others are comparable to tumor cells.

Steroid hormone receptors and tumorigenicity of sublines from breast tumor metastatic MDA-MB 231 cell line.

Ten cell sublines the MDA-MB 231 human breast cell line were analyzed for their phenotypic diversity: morphology, karyotype, growth rate, clonogenicity in semisolid medium, tumorigenicity in nude mice, number and affinity of nuclear receptors for oestradiol, progesterone and glucocorticoids. Karyotypic analysis showed different aneuploidies from 50 to 120 chromosomes and variable chromosomal rearrangements in the analyzed subclones. All except two of the ten subclones were tumorigenic when injected subcutaneously or intraperitoneally into nude mice. Although the parental cell line has no receptor, all except two of the tested subclones contained various amounts of high affinity oestradiol and progesterone receptors ranging from 3,000 to 33,000 per cell. Seven subclones contained either high affinity oestradiol or progesterone receptors in nuclei. The diversity found in different subclones derived from one breast carcinoma cell line might represent variabilities acquired and selected continuously in culture.

A study of gastrointestinal cancer-associated antigen (GICA) in human fetal organs.

The gastrointestinal cancer-associated antigen (GICA) characterized by 1116 NS 19-9 monoclonal antibody was studied in human fetal organs by immunohistology and immunofixation on nitrocellulose sheets. It was found in all the gastrointestinal tracts of fetuses and newborns. Other fetal organs, except biliary and pancreatic ducts, were negative. Immunohistological data and enzymatic studies led us to conclude that GICA is predominantly a mucin-type glycoprotein in fetal organs.