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Murine epidermal Langerhans cells (LC) synthesize and express E-cadherin, a homophilic adhesion molecule that mediates adhesion of LC to keratinocytes in vitro. To determine if E-cadherin expression is characteristic of LC or is a feature of all dendritic cells (DC), we studied DC from various lymphoid tissues and peripheral blood for reactivity with anti-E-cadherin monoclonal antibody. By flow cytometry, DC prepared from skin-associated lymph nodes (LN) expressed E-cadherin, whereas DC prepared from gut-associated LN and spleen did not. However, direct comparison revealed that levels of E-cadherin expressed by DC from skin-associated LN were approximately fivefold lower than those expressed by freshly-prepared LC. Immunohistochemical studies confirmed that E-cadherin was expressed by DC in skin-associated LN in situ, and demonstrated that the number of E-cadherin+ DC in LN draining skin previously treated with the contact allergen 2,4,6-trinitrochlorobenzene was increased relative to the number of E-cadherin+ DC present in LN draining normal skin. DC propagated from the blood of cyclophosphamide-treated mice in granulocyte/macrophage-colony stimulating factor-supplemented media also expressed E-cadherin. E-cadherin immunoprecipitated from DC co-migrated in SDS polyacrylamide gels with that from fibroblasts transfected with murine E-cadherin cDNA, and mRNA encoding extracellular and intracellular regions of E-cadherin was present in DC propagated from blood. These results indicate that E-cadherin expressed by murine dendritic cells is identical to E-cadherin expressed by epithelial cells, and suggest that E-cadherin represents a DC differentiation antigen characteristic of LC and lineage-related cells (skin-associated LN DC).

In an already tumorigenic spontaneously transformed mouse cell, after further transformation by SV40, the virus-specific antigenic function becomes dominant. By transplantation into syngeneic mice SV40 antigen negative revertant tumour cells can be selected out.

A 55-kilodalton (kDal) protein was detected recently in primary cultures of day 12 mouse embryos by immunoprecipitation with serum from simian virus 40 (SV40) tumor-bearing hamsters (T serum), Preliminary evidence suggested that this protein was similar to a cellular 55-kDal protein induced after SV40 transformation of mouse cells. We now show that specific approximately 55-kDal [35S]methionine-labeled proteins precipitate from primary cultures of midgestation mouse, rat, and hamster embryos on addition of T serum or monoclonal antiserum prepared against the SV40-induced mouse 55-kDal proteins. The two-dimensional maps of the [35S]methionine-labeled tryptic peptides of the mouse, hamster, and rat embryo proteins are similar to the maps of the corresponding proteins from SV40-transformed cells. Primary cells from midgestation mouse, hamster, or rat embryos contain one-third to one-half as much 55-kDal protein as a SV40-transformed mouse fibroblast cell and nearly the same amount as F9 mouse embryonal carcinoma cells. The amount of 55-kDal protein is greatly reduced on replating the mouse, rat, or hamster embryo primary cells. The amount of this protein in mouse embryos is dependent on the stage of the embryo. The embryo proteins are phosphoproteins.

In most murine cells transformed by the SV40 virus, virtually all of the cellular phosphoprotein p53 is in a complex with the SV40 T antigen. Here, we report that, in SV40-infected T-antigen-positive Balb 3T12 mouse cells, most (approximately 80%) of the p53 is not in complex. Complex formation was determined by measuring the amounts of [35S]methionine-labeled p53 which coprecipitated with T antigen when using monoclonal antibody to T antigen. The amount of complex formation was expressed as a percentage of total p53 present, measured by the amount of p53 precipitated with the monoclonal antibody to the p53. The values were confirmed by Western blotting procedure, in which the steady-state levels of the proteins were measured. In these measurements after complete precipitation with antibody to T antigen, the residual p53 in the supernatant was precipitated by antibody to p53, and this amount was denoted as free p53. There was no significant difference seen between the [35S]methionine-labeled tryptic peptides of complexed and the free p53 (or between complexed and free T antigens) as determined by two-dimensional gel electrophoresis and chromatography. Virus rescue experiments and retransformation by the rescued virus showed that there was no mutation in the SV40 DNA coding for the T antigen which could account for the lack of complex formation. Both p53 and T antigen were underphosphorylated in cells which exhibited reduced complex formation. Tumorigenicity in syngeneic mice and anchorage-independent cell growth in culture of various cloned mouse cells with or without T antigen expression was compared. The changes in the biologic properties were explainable solely on the basis of known or expected effects of expression of the T antigen and were independent of complex formation or of absence of complex formation between p53 and T antigen.

For the clonal analysis of spontaneous malignant transformation of cells, a clonal cell line of low tumorigenicity, derived from a mouse embryo mass culture, was injected into syngeneic animals in a sufficient dose (10(7) cells) to produce tumors. Cell lines and clones produced from several such tumors had acquired a 10(4)- to 10(5)-fold higher level of tumorigenicity. Anchorage-independent growth did not co-select with tumorigenicity. There was no evidence for overexpression of proto-oncogenes in the highly tumorigenic clones; p53 protein and mRNA levels were also essentially equal and low. There was a specific structural difference in the O-sulfate residues in oligosaccharides of heparan sulfates in all the tumor cell lines when compared with their parent clone, similar to that observed before in SV40 virus-induced cell transformation (Winterbourne and Mora, 1978).

A specific protein of molecular weight (MW) approximately 55,000 (55K) was found recently by immunoprecipitation in all SV40 virus-transformed mammalian cells, in addition to the SV40 large T antigen (appoximately 94K) and small antigen (approximately 17K), which are the only proteins coded by the 'early half' of the SV40 genome. The 55K protein is encoded by cellular DNA; its peptide pattern is different from that of the SV40 antigens and it is species specific in mouse, rat, hamster, monkey and human SV40-transformed (or infected) cells. A 55K protein with a similar peptide pattern was found in mouse embryonal carcinoma cells not exposed to SV40. Similar proteins were reported in mouse sarcomas and leukaemias induced by a great variety of aetiological agents and also in a spontaneously transformed mouse fibroblast cell line, and it has been suggested that the protein may be a general correlated of cellular tumorigenicity. We now report that the approximately 55K protein is present in primary cell cultures from 12-14 day old mouse embryos, but not in 16-day old mouse embryos. The embryo protein has a peptide pattern virtually indistinguishable from that of the SV40-induced protein. We also show by comparing closely related cell families that spontaneously transformed highly tumorigenic mouse cells do not possess the 55K protein.

The phosphoprotein p53 has been investigated mainly because of its relationship with tumorigenic transformation. In this communication, we report that, during the embryonal development of mouse and chicken, there is a decline in the steady-state levels of the p53 protein and an equal decline in p53 mRNA. During the development of the chicken, the relative rates of p53 transcription appear to be constant. p53 mRNA is relatively stable (half-life greater than 12 h) in both chicken and mouse embryos. We conclude that (i) the down-modulation of p53 mRNA (and of protein) during embryonal development has been well conserved during the evolution of the vertebrate, implying that the p53 protein may have a function in embryonal development; and (ii) the mechanism of control is apparently mainly on a post-transcriptional level.

"Spontaneously" or SV40 virus transformed AL/N mouse cell lines were passed repeatedly through syngeneic mice. Cell lines were re-established in culture from minced pieces of tumors in the presence of concentrated fetal calf serum or from tumor cells dispersed by trypsin. The aim of this study was to compare the two cell lines in regard to the selection processes which operate during such procedures by characterization of the resulting cell lines. Measurements of growth in tissue culture on substratum showed no significant difference between any of the transformed cell lines. The SV40 transformed cells and its derivative cells had a low anchorage requirement for growth. The greatest anchorage requirement for growth was in the normal untransformed cells and in the derivative cells from the "spontaneously" transformed cells which were established from minced tumors. The spontaneously transformed cells and all derivative cells had high tumorigenicity (TD50 is less than 10-2). The SV40 transformed cells had no observable tumorigenicity (TD50 is greater than 10-8), except when injected into irradiated mice (TD50 = 1-5 X 10-5 in the immunocompetent mice, 5 X 10-4 in the irradiated mice). The SV40 transformed derivative cells maintained their SV40 specific T antigen and their susceptibility to lysis by specific antiserum.

Quantitative expression of a specific 55,000 (55K)-molecular-weight cellular protein was studied in two groups of mouse embryo fibroblast (clonal) cells originating from two parent clones, one of which possessed high tumorigenicity and the other of which possessed very low tumorigenicity. From the clone with low tumorigenicity, tumor lines and clones were obtained by selecting rare spontaneously transformed highly tumorigenic (mutant) cells. Cells were labeled during exponential growth for 3 h at 37 degrees C, with [35S]methionine, and the cellular 55K protein was immunoprecipitated with a monoclonal antibody and quantitated. There were low and approximately equal amounts of 55K protein in cells (clones) with both low and high tumorigenicity from both groups of cells, and there was no correlation at all between quantitative expression of 55K protein and of cellular tumorigenicity. There was approximately 10- to 20-fold more 55K protein in all simian virus 40-transformed T antigen-positive derivative clones, as shown previously. The T antigen-negative revertant tumor lines and clones obtained by an immunological in vivo selection method had low amounts of 55K protein, similar to the parent cell before simian virus 40 transformation. In all of the T antigen-negative cells, including the highly tumorigenic cells, degradation (turnover?) of the 55K protein was rapid, and a half-life of 15 to 60 min was estimated from pulse-chase experiments. In all of the T antigen-positive cells the 55K protein was stable (half-life greater than 10 h). In primary cells established from the tumors induced by highly tumorigenic cells there was a very low or no detectable amount of the 55K protein. This is in contrast to the primary cells obtained from early murine embryos in which we have reported high amounts of (stable) 55K proteins.

In mouse cell lines transformed by SV40 virus, a decrease was observed in the higher ganglioside homologues disialo-ceramidetetrahexoside and monosialo-ceramidetetrahexoside. Such change was observed only in cells which carry the virus genome, and it correlated with increased saturation density in tissue culture and with rejection in immunologically competent syngeneic host. This indicates that the change is one of the virus-regulated functions, and it is postulated that it relates to the rejection of the virus-transformed cells.

The ganglioside pattern of both SV40- and polyoma virus-transformed mouse cell lines differs from that of the parent cell lines or of cell lines that have transformed spontaneously in tissue culture. This is manifested by a dramatic decrease of gangliosides with an oligosaccharide chain larger than sialyllactose. Present investigations indicate that this change probably cannot be attributed to excessive catabolism of gangliosides, but is caused by impaired synthesis of tri- and tetrahexosyl gangliosides in the virus-transformed cell lines. We present evidence for the block of a required step for the biosynthesis of these ganglioside homologs. The block involves the enzyme catalyzing the transfer of N-acetylgalactosamine from uridine diphosphate N-acetylgalactosamine to hematosides (N-glycolylneuraminyl or N-acetylneuraminylgalactosylglucosyl ceramide). This well-defined enzymatic change opens the way for studies of the biochemical mechanism of the alteration of cell membranes which occurs after transformation by the tumorigenic DNA viruses polyoma and SV40.