Semi-quantitative fluorescence in situ hybridization analysis indicates that the myc protein is consistently stabilized both before and after transformation of low-grade follicular center to high-grade diffuse large cell lymphoma

We have investigated the expression of the MYC gene at both the mRNA and protein levels to determine how these parameters are related in lymphoma cells and in nonmalignant lymphoid cells. To do this we have adopted a multicolor fluorescence in situ hybridization methodology, which has allowed us to investigate the expression of different genes at the same time in the same cell. We have made use of the digital imaging capabilities of a charge-coupled device camera system to quantify the hybridization signals for the MYC gene and, by comparing these to the expression of a control gene (glyceraldehyde-3-phosphate dehydrogenase; GAPDH), have obtained relative quantitations of MYC mRNA and protein levels. In this study we have compared cells both within and outside the germinal centers in control tissues (reactive lymph nodes and tonsils) and in tow-grade follicular center lymphomas, as well as cells in high-grade diffuse large cell lymphomas. The MYC/GAPDH mRNA hybridization signal ratios were calculated and found to be higher in cell populations containing a majority of malignant cells (p < 0.04). However, when the myc/GAPDH protein hybridization signal ratios were calculated, these were significantly higher in malignant cells from all lymphomas than the ratios observed in the nonmalignant cells (p < 0.0005). These observations indicate that the environment in a malignant cell may contribute to the stabilization of the myc protein, thus enabling it to function for a longer time period than in nonmalignant cells.