RESUMO
Isotype switch variants of the IgG3 secreting hybridoma BR55-2 were developed with gamma 1, gamma 2b and gamma 2a heavy chains. The variants have the same affinity for antigen and expected affinities for the Fc receptor. The Y antigen defined by MAb BR55-2 has a restricted distribution to breast, colorectal, pancreatic, gastric and small cell lung carcinomas. The MAb BR55-2 also bound to prostatic and laryngeal carcinomas. The BR55-2 defined epitope is expressed by gastrointestinal cancer cell lines as a glycolipid, while the breast carcinoma cells express the same epitope on glycoproteins. These differences may influence tumor cell susceptibility to lysis by MAb BR55-2 and its isotype switch variants.
Assuntos
Anticorpos Monoclonais/imunologia , Glicoesfingolipídeos/análise , Isotipos de Imunoglobulinas/biossíntese , Animais , Afinidade de Anticorpos , Especificidade de Anticorpos , Antígenos/análise , Neoplasias da Mama , Sequência de Carboidratos , Linhagem Celular , Células Cultivadas , Variação Genética , Glicolipídeos/imunologia , Glicoproteínas/imunologia , Humanos , Imunoglobulina G/biossíntese , Camundongos , Camundongos Endogâmicos BALB C , Dados de Sequência Molecular , Células Tumorais Cultivadas/análiseRESUMO
The mechanism of resistance to the toxic effects of copper was investigated using a series of copper-resistant hepatoma cell lines maintained in copper-enriched medium. Gel electrophoresis of carboxyamidated cell extracts demonstrated the presence of a pair of low molecular mass cysteine-rich proteins in wild-type and resistant cell lines. These proteins were purified to homogeneity and contained approx. 60% of the total cellular copper. Comparisons of molecular masses, pI values and amino-acid compositions for the purified hepatoma proteins with authentic rat liver metallothionein, as well as cross-reactivity with anti-rat metallothionein antibody, confirmed that the cysteine-rich hepatoma proteins were metallothioneins. The cellular concentration of these hepatoma copper-metallothioneins was proportional to both the level of metal resistance and the amount of copper accumulated by individual cell lines. Further, resistant cells removed from copper-enriched medium for 6-12 months, yet maintaining their level of resistance, showed only a slight decrease in metallothionein concentration. Thus it is proposed that the level of resistance to metal toxicity is mediated by the concentration of copper-metallothionein. It is also suggested that the steady-state level of copper metallothionein is controlled by the degree of metal exposure.
Assuntos
Carcinoma Hepatocelular/análise , Cobre/toxicidade , Metalotioneína/isolamento & purificação , Proteínas de Neoplasias/isolamento & purificação , Células Tumorais Cultivadas/efeitos dos fármacos , Aminoácidos/isolamento & purificação , Animais , Linhagem Celular , Cisteína/metabolismo , Resistência a Medicamentos , Neoplasias Hepáticas , Peso Molecular , Ratos , Células Tumorais Cultivadas/análiseRESUMO
Exponentially growing MCF7 human breast cancer cells were separated in Percoll gradients into six different fractions of increasing density (A to F). These fractions could be subcultured and were found to contain different cellular subpopulations as defined by the following criteria: ability to generate other cellular subpopulations; growth rate; DNA synthesis; and expression of estrogen receptors, ras oncogene-encoded protein p21, and carcinoembryonic antigen. One of the minor fractions (E), which contained about 5% of the total cell number, appeared to contain the stem cells, on the basis of the following criteria: (i) its ability to reproduce the other cellular subpopulations, (ii) its high rate of growth and DNA synthesis, and (iii) the inability of the other subpopulations to generate it. The most differentiated subpopulation appeared to be the densest one (F), since it was the slowest growing and appeared to be the end point of the other subpopulations.