It is well accepted that inoculation of B7-1-transfected tumor cells into normal mice leads to tumor rejection and subsequent resistance to challenge. However, the effectiveness of B7-2-transfected ...tumor cells in eliciting protective antitumor immunity is less clear. Here we show that B7-2-transfected P815 tumor cells (B7-2+) are as effective as B7-1-transfected P815 tumor cells (B7-1+) in eliciting protective immunity in normal DBA/2 mice. In addition, B7-2+ cells were found to be at least as effective as B7-1+ cells retarding tumor progression when admixed with parental P815 tumor cells prior to inoculation into normal mice. Moreover, the B7-2+ cells and the B7-1+ cells were equivalent in their ability to retard tumor growth when administered peritumorally into mice bearing established (approx. 3 mm in diameter) parental P815 tumors. Finally, P815 tumor cells infected with a recombinant replication-defective adenovirus encoding the murine B7-2 gene were effective in retarding the growth of established parental P815 tumors. Thus, B7-1 and B7-2 are comparable in terms of their ability to stimulate the generation of tumor-eradicating immunity in normal mice as well as in mice bearing established parental tumors. Moreover, adenovirus vectors can be used to generate B7-2-expressing tumor cells effective in the immunotherapy of established parental tumors.
The slow/cardiac troponin C (cTnC) gene has been used as a model system for defining the molecular mechanisms that regulate cardiac and skeletal muscle-specific gene expression during mammalian ...development. cTnC is expressed continuously in both embryonic and adult cardiac myocytes but is expressed only transiently in embryonic fast skeletal myotubes. We have reported previously that cTnC gene expression in skeletal myotubes is controlled by a developmentally regulated, skeletal muscle-specific transcriptional enhancer located within the first intron of the gene (bp 997 to 1141). In this report, we show that cTnC gene expression in cardiac myocytes both in vitro and in vivo is regulated by a distinct and independent transcriptional promoter and enhancer located within the immediate 5' flanking region of the gene (bp -124 to +32). DNase I footprint and electrophoretic mobility shift assay analyses demonstrated that this cardiac-specific promoter/enhancer contains five nuclear protein binding sites (designated CEF1, CEF-2, and CPF1-3), four of which bind novel cardiac-specific nuclear protein complexes. Functional analysis of the cardiac-specific cTnC enhancer revealed that mutation of either the CEF-1 or CEF-2 nuclear protein binding site abolished the activity of the cTnC enhancer in cardiac myocytes. Taken together, these results define a novel mechanism for developmentally regulating a single gene in multiple muscle cell lineages. In addition, they identify previously undefined cardiac-specific transcriptional regulatory motifs and trans-acting factors. Finally, they demonstrate distinct transcriptional regulatory pathways in cardiac and skeletal muscle.
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