Establishment and characterization of a CHO cell line producing a secreted form of human ciliary neurotrophic factor: neuroprotective effects of the recombinant protein

Screening of CHO cell clones expressing histidine-tagged major S hepatitis B surface protein using a semi-quantitative PCR protocol

Different mammalian cells have been used successfully for the expression of the hepatitis B surface antigen (HBsAg). The patterns of expression of the HBsAg seem to depend on the cell type and the number of gene copies integrated into cellular genome. The expression of an HBsAg fused to histidine tag (His-HBsAg), had not been reported in mammalian cells. This paper describes a semi-quantitative polymerase chain reaction (PCR) employed to investigate the patterns of expression of His-HBsAg in stably transfected Chinese hamster ovary (CHO) cell clones. pcDNA4CR20, a mammalian expressing vector, encoding His-HBsAg, was constructed. The correlation between His-HBsAg expression and the number of integrated copies of the HBsAg gene into cell clones genome was evaluated by the semi-quantitative PCR, with limit dilutions of the genomic DNA as template. The results show a positive correlation between the expression levels of His-HBsAg with the number of the HBsAg gene copies integrated into CHO cell clones. The approach of a semi-quantitative PCR proved to be a good and non-expensive alternative strategy to analyze the patterns of expression of integrated genes into CHO cells genome.

Constitutive activation of STAT3 is associated with the acquisition of an interleukin 6–independent phenotype by murine plasmacytomas and hybridomas

Interleukin 6 (IL-6), the major growth factor for myeloma cells, signals through the activation of signal transducers and activators of transcription (STAT) proteins. An important step in the malignant progression of murine plasmacytomas is the transition from dependence on IL-6 to a state of IL-6 independence. To elucidate the mechanism whereby IL-6 independence occurs, intracellular signaling events elicited by IL-6 in both IL-6–dependent and –independent plasmacytomas and hybridomas were compared. It was found that STAT3, a key molecule involved in IL-6 signaling, was constitutively activated and phosphorylated in IL-6–independent cell lines compared to the IL-6–dependent cells. Further comparison of upstream signaling pathways revealed that JAK-1 was constitutively present in anti-phosphotyrosine immunoprecipitates of IL-6–independent cells; gp130 was constitutively phosphorylated in a subset of IL-6–independent plasmacytomas, whereas other IL-6–independent lines showed no detectable gp130 phosphorylation in the absence of exogenous IL-6. Secretion of a factor capable of supporting the growth of IL-6–dependent cells was observed in one of the IL-6–independent plasmacytomas, but not in others, making an autocrine mechanism an unlikely explanation for IL-6 independence. These findings provide evidence that the constitutive activation of STAT3, either in the absence of detectable receptor-proximal events or associated with the concomitant activation of gp130, can contribute to the process of IL-6 independence.

Constitutive activation of STAT3 is associated with the acquisition of an interleukin 6–independent phenotype by murine plasmacytomas and hybridomas

Interleukin 6 (IL-6), the major growth factor for myeloma cells, signals through the activation of signal transducers and activators of transcription (STAT) proteins. An important step in the malignant progression of murine plasmacytomas is the transition from dependence on IL-6 to a state of IL-6 independence. To elucidate the mechanism whereby IL-6 independence occurs, intracellular signaling events elicited by IL-6 in both IL-6–dependent and –independent plasmacytomas and hybridomas were compared. It was found that STAT3, a key molecule involved in IL-6 signaling, was constitutively activated and phosphorylated in IL-6–independent cell lines compared to the IL-6–dependent cells. Further comparison of upstream signaling pathways revealed that JAK-1 was constitutively present in anti-phosphotyrosine immunoprecipitates of IL-6–independent cells; gp130 was constitutively phosphorylated in a subset of IL-6–independent plasmacytomas, whereas other IL-6–independent lines showed no detectable gp130 phosphorylation in the absence of exogenous IL-6. Secretion of a factor capable of supporting the growth of IL-6–dependent cells was observed in one of the IL-6–independent plasmacytomas, but not in others, making an autocrine mechanism an unlikely explanation for IL-6 independence. These findings provide evidence that the constitutive activation of STAT3, either in the absence of detectable receptor-proximal events or associated with the concomitant activation of gp130, can contribute to the process of IL-6 independence.