A quantitative analysis of modulations occurring in cellular c-myc protein content, %S phase and growth balance under growth-inhibitory conditions.

The c-myc protein was one of the first proto-oncogene products to be linked to the increased proliferative activity of neoplastic cells. However, few studies have attempted to quantify changes occurring in cellular c-myc protein content in response to growth-inhibitory conditions, or to relate such changes to total cellular protein (TCP) levels, %S phase cells and/or cellular growth balance. Knowledge of such relationships is important for determining the biological relevance of the c-myc protein as a marker for proliferating cells. In this study, a dual-laser flow cytometric technique employing three fluorescent dyes was used to quantify cellular changes in c-myc protein, TCP, DNA and growth balance in exponentially-growing and serum deprived U118MG, A-172 and HL-60 cells. Results obtained by flow cytometry were verified using other techniques. Changes in c-myc protein content were found to occur independently of changes in TCP, %S phase or cellular growth balance, and varied between cell lines. These results indicate that cellular c-myc protein determinations convey information that is unique from other indicators of cellular growth and proliferation. Such information may be linked, however, to the nutritional status and origin of the cells being assayed.