Phenotypic expression in cybrids derived from teratocarcinoma cells fused with myoblast cytoplasms

Analysis of polypeptide expression in benign and malignant human breast lesions: down-regulation of cytokeratins

Malignant progression of tumour cells is caused by the accumulation of genetic defects, which when combined will generate a large phenotypic diversity. Simultaneous quantitation of a large number of gene products in tumour cells is desirable, but difficult to achieve. We have here quantitated the levels of a number of abundant polypeptides in human breast carcinoma cells using two-dimensional gel electrophoresis (2-DE; PDQUEST). For this purpose, tumour cells were prepared from the tissue of 17 breast carcinomas. Fibroadenoma tissue was used as reference for benign cells. An increase of the spot density of the PCNA polypeptide was observed in rapidly proliferating tumour cells, confirming the validity of the procedures used. In the set of 24 polypeptide spots with known identity, decreases in cytokeratin and tropomyosin levels were observed. The levels of all cytokeratin forms resolved (CK7, CK8, CK15 and CK18) were significantly lower in carcinomas than in fibroadenomas. The levels of tropomyosin 2 and 3 were lower in carcinomas than in fibroadenomas. In contrast, the levels of some members of the stress protein family (pHSP60, HSP90 and calreticulin) were higher in carcinomas. Furthermore, changes in the expression of lactate dehydrogenase and GT-pi, but not in nm23, were observed. We conclude that simultaneous analysis of multiple polypeptides in human carcinomas can be achieved by 2-DE and may be useful in prognostic studies, and that malignant progression of breast carcinomas results in the decreased expression of cytokeratin polypeptides. This phenomenon must be considered in studies where cytokeratins are used as markers to identify the epithelial cell compartment in breast carcinomas.

Sample preparation of human tumors prior to two-dimensional electrophoresis of proteins

Sample preparation procedures are critical for obtaining high quality two-dimensional electrophoresis (2-DE) separations from clinical tumor materials. In this communication, we describe procedures which we have found satisfactory for preparing various tumor samples for 2-DE. By these procedures, tumor cells are enriched from serum proteins and contaminating stromal cells. Tumors can be prepared with good reproducibility to obtain high resolution using these techniques.

Nonenzymatic extraction of cells from clinical tumor material for analysis of gene expression by two-dimensional polyacrylamide gel electrophoresis

We have compared different methods of preparation of malignant cells for two-dimensional electrophoresis (2-DE). We found all methods using fresh tissue to be superior compared to methods using frozen tissue. Our results indicate that nonenzymatic methods of preparation of tumor cells, including fine needle aspiration, scraping and squeezing, have advantages over methods using enzymatic extraction of cells. Nonenzymatic methods are rapid, appear to reduce loss of high molecular protein species, and alleviate the necessity of separating viable and nonviable cells by Percoll gradient centrifugation. Using these techniques, high-quality 2-DE maps were derived from tumors of the lung and breast. In the resulting polypeptide patterns, heat shock proteins, non-muscle tropomyosins and intermediate filament were identified. We conclude that nonenzymatic extraction of malignant cells from fresh tumor tissue improves the possibilities that these techniques may be useful in clinical diagnosis.

Cytoplasmic requirement for peroxisome biogenesis in Chinese hamster ovary cells

Hybrids constructed by fusion of wild-type Chinese hamster ovary cells (CHO-K1) to peroxisome-deficient CHO mutants (ZR-78.1) contain normal peroxisomes, demonstrating that the mutation(s) are recessive. "Nuclear hybrids" prepared by fusion of CHO-K1 karyoplasts to mutant ZR-78.1 occasionally fail to regain intact peroxisomes (approximately 1/300 cells). These peroxisome-deficient nuclear hybrids closely resemble the original mutant cells by biochemical criteria, but their modal chromosome number is 36-38, the same as that of CHO hybrids generated from intact cells. When the peroxisome-deficient nuclear hybrids are fused to wild-type cytoplasts, a fraction of the fusion products (at least 70%) continue to propagate normal peroxisomes indefinitely. Peroxisome biogenesis cannot be reinitiated in cells of mutant ZR-78.1 by fusion to wild-type cytoplasts. Our results suggest that a wild-type nucleus by itself is necessary but not sufficient for restoration of normal peroxisome biogenesis and that a cytoplasmic component of wild-type cells, possibly a normal peroxisome, is also required.

Pleiotropic phenotypic expression in cybrids derived from mouse teratocarcinoma cells fused with rat myoblast cytoplasts

Cybrid clones were isolated by fusing mouse embryonal carcinoma (PCC4) cells with cytoplasts of rat myoblastic cells (L6TG X CAPr). Although some clones were similar to PCC4 (Type II), a high proportion (88%) were differentiated; the differentiated cells had a mesh-like arrangement (Type I) or were flat with many projections (Type III). Protein patterns of both Type I and Type III cells changed markedly from that of PCC4 cells. Type III cells lacked alkaline phosphatase and expressed endo A and B proteins predominantly. One Type III clone produced alpha-fetoprotein and plasminogen activator (visceral endoderm-like), while another clone consisted of trophectodermal cell-like giant cells. Therefore it was shown that introduction of the somatic cell cytoplasm induces differentiation of teratocarcinoma stem cells, suggesting a cytoplasmic element (or elements) regulating gene expression.

Uptake and stability of human and bovine acid alpha-glucosidase in cultured fibroblasts and skeletal muscle cells from glycogenosis type II patients

Acid alpha-glucosidase (EC 3.2.1.20) was purified from human placenta and bovine testis by affinity chromatography using concanavalin A (conA) and Sephadex G 200. When added to the culture medium of human fibroblasts, the enzyme purified from bovine testis is taken up with a 200-fold higher efficiency than the enzyme from human placenta. Uptake of acid alpha-glucosidase from bovine testis is mediated by the mannose-6-phosphate receptor, whereas only a minor fraction of placental enzyme appears to be equipped with the mannose-6-phosphate recognition marker. Once internalized, both human and bovine acid alpha-glucosidase demonstrate a half-life of about 10 days in fibroblasts from control individuals and patients with different clinical forms of glycogenosis type II (Pompe's disease, acid alpha-glucosidase deficiency). Evidence is presented that the mannose-6-phosphate receptor is also present on the plasma membrane of the clonal myogenic skeletal muscle cell lines G8-1 and L6J1 (respectively from mouse and rat origin) and on cultured human skeletal muscle cells derived from a muscle biopsy. Addition of bovine testis acid alpha-glucosidase to skeletal muscle cell cultures from an adult patient with glycogenosis type II leads to complete correction of the enzyme deficiency.

Isolation and characterization of intraspecific cybrids. Effect of mitochondrial DNA on their cellular properties

Cybrid clones were obtained by fusing whole cells of rat glioma C6BU-1, resistant to 5-bromodeoxyuridine (BrdU), with cytoplasts of embryonic rat 3Y1CAP cells, resistant to chloramphenicol (CAP), in selective medium with BrdU and CAP. The clones resistant to BrdU and CAP were confirmed to be cybrids by chromosome and mtDNA analyses. More than half the mtDNA of all the cybrid clones was from the 3Y1CAP cells. After cultivation of a cybrid clone Y22 for 3 months in the absence of CAP, subclones were isolated. One subclone Y22-22 contained predominantly mitochondrial DNA (mtDNA) from the 3Y1CAP cells. Using this subclone, the effects of the mitochondrial genome on cellular properties were examined. The growth patterns, expression of glioma-specific beta-adrenergic receptor, and composition of the major proteins of C6BU-1 cells were not affected by transmitted mtDNA from the 3Y1CAP cells. This procedure for isolating cells containing predominantly foreign mtDNA will be useful in studies on the interaction between genomes of the mitochondria and nucleus.

Amplification of hypoxanthine-guanine phosphoribosyltransferase genes in chromosome-mediated gene transferents

Hypoxanthine-guanine phosphoribosyltransferase (HPRT) enzyme activities may be elevated in genetically unstable chromosome-mediated gene transferents selected for transfer of the HPRT gene. Increased levels of HPRT polypeptides in unstable mouse L cell gene transferents were demonstrated by two-dimensional gel electrophoresis and immunoprecipitation. No additional polypeptides were found to be overexpressed. HPRT mRNA levels were elevated 10- to 15-fold in the unstable gene transferent GT427C. Southern blot hybridization experiments showed that overexpression of HPRT correlated with a 5- to 15-fold amplification of HPRT gene sequences in two unstable cell lines. Stabilized gene transferents displayed reduced HPRT copy numbers. The amplification of HPRT gene sequences in the unstable transferent GT427C was associated with the presence of multiple minute chromosome fragments. An average of 9.6 fragments was found per metaphase, but the variation was considerable, ranging from 0 to 53. We conclude that genomic DNA sequences may be amplified in unstable chromosome-mediated gene transferents and that such amplification may be associated with the occurrence of multiple chromosomal fragments.

Amplification of hypoxanthine-guanine phosphoribosyltransferase genes in chromosome-mediated gene transferents

Hypoxanthine-guanine phosphoribosyltransferase (HPRT) enzyme activities may be elevated in genetically unstable chromosome-mediated gene transferents selected for transfer of the HPRT gene. Increased levels of HPRT polypeptides in unstable mouse L cell gene transferents were demonstrated by two-dimensional gel electrophoresis and immunoprecipitation. No additional polypeptides were found to be overexpressed. HPRT mRNA levels were elevated 10- to 15-fold in the unstable gene transferent GT427C. Southern blot hybridization experiments showed that overexpression of HPRT correlated with a 5- to 15-fold amplification of HPRT gene sequences in two unstable cell lines. Stabilized gene transferents displayed reduced HPRT copy numbers. The amplification of HPRT gene sequences in the unstable transferent GT427C was associated with the presence of multiple minute chromosome fragments. An average of 9.6 fragments was found per metaphase, but the variation was considerable, ranging from 0 to 53. We conclude that genomic DNA sequences may be amplified in unstable chromosome-mediated gene transferents and that such amplification may be associated with the occurrence of multiple chromosomal fragments.

Computer applications in analysis, mapping and cataloging of proteins separated by two dimensional electrophoresis

Two dimensional electrophoretic separation of complex mixtures of proteins can only be exploited to its fullest potential using sophisticated computerized spot detection, quantification, pattern recognition, pattern normalization, data reduction and data storage. We present a discussion of some of the technical problems and of the options available which will ultimately lead toward full computerization of the data.

Protein synthesis by rat hepatoma x mouse teratocarcinoma somatic cell hybrids

The synthesis of intracellular and secretory proteins by rat hepatoma (MHC) and mouse teratocarcinoma (PCC4AZAl) cells and MHC X PCC4AZAl somatic cell hybrids was examined with two-dimensional (O'Farrell) electrophoresis. The gels of the PCC4AZAl and hybrid cells were nearly identical and were quite different from those of the MHC cells. The teratocarcinoma phenotype was, therefore, dominant in the teratocarcinoma X hepatoma somatic cell hybrids.

Induction of supermelanin synthesis and morphological changes in interspecific reconstituted cells and its reversal by tumor promoter

Chloramphenicol-resistant (CAPr) reconstituted cells and cybrids were isolated by fusion of karyoplasts (or intact cells) of mouse amelanotic melanoma B16 cells with cytoplasts of hypoxanthine-guanine phosphoribosyltransferase (HGPRT) -deficient, CAPr rat myoblastic cells, L6TG.CAPr, and double selection in HAT medium containing CAP. Reconstituted cells or cybrids exhibited unique cellular arrangement, and about one third of the isolated clones expressed high tyrosinase activity and marked melanin synthesis, although the parental mouse cells expressed low tyrosinase activity and the parental rat cells did not express tyrosinase activity. These phenotypic changes have been stable for more than a year. The phenotypic reversions of these clonal cells were induced by treatment with a tumor promoter. There were changes in the morphology of the treated cells to that of the mouse B16 cells and extinction of tyrosinase activity and melanin synthesis in pigmented clonal cells. These phenotypic changes and reversions induced by a promoter were repeatedly reversible.

Detrimental effect of mitochondria on hybrid cell survival

A genetic technique has been developed for isolating nuclear hybrids which are products of fusion between karyoplasts and whole cells. Nuclear hybrids have greatly reduced mitochondrial component obtained from the nuclear donor and exhibit differences when compared to the corresponding whole-cell hybrids, such as better long-term survival and accelerated chromosome segregation. These results suggest that divergent mitochondria in a cell-fusion product may have adverse effects on survival.

On suppression of tumorigenicity in hybrid and cybrid mouse cells

The contribution of cytoplasm in the suppression of tumorigenicity was examined in cybrids constructed by fusing whole tumorigenic mouse mammary cells (Balb/c, cell line C2B2 from line MT29240) with enucleated nontumorigenic cells (BALB/c, cell line THOC from clone A31). Chloramphenicol resistance was used as a cytoplasmic marker in selecting the cybrids. Hybrids from parental nonenucleated cells were also isolated and analyzed for the expression of tumorigenicity. A reduction of the tumorigenic capacity in terms of tumor incidence and latency was clearly expressed in most of the cybrid clones studied. In the cybrids, saturation density and colony formation in agarose was also reduced. In most of the hybrid clones studied, a reduction was also observed in the tumorigenic capacity but not in saturation density or anchorage independence.