RT-PCR confirmation of differential gene expression. Two tumor samples from each genotype were used to extract total RNA. First, 2 to 5 μg total RNA from tumor tissues was reverse transcribed, and one-twentieth of each reaction was subjected to PCR amplification with the use of gene-specific primers as described in “Materials and methods.” RT-PCR assays were performed under linear amplification conditions. Then, 20 μL each reaction was visualized on a 1% agarose gel. S15 rRNA expression served as a control. Representative results from 1 of 3 independent experiments are shown. Fold difference of RNA expression was calculated by densitometry scanning of the agarose gels, and values from one representative experiment are shown here.