Assessment of the Myc Dose Response In An Abl-Transformed Pre-B Cell Line

The Myc transcription factor is a complex proto-oncogene known to both stimulate proliferation of cells while blocking terminal differentiation and trigger apoptosis in certain contexts. In addition, Myc has been found to be deregulated in human cancers, most frequently in colon, breast, and prostate cancers. Such phenomena indicate the possibility of a dose-dependent effect of Myc expression on the crucial cellular decisions between survival and death, or proliferation and differentiation. Here we have created a tamoxifen-inducible MYC fusion with GFP and cloned it into a library of viral constructs, each with a distinct level of expression. This estrogen responsive (ER) domain prevents Myc localization to the nucleus until tamoxifen is added. We have transduced this construct into PD31 cells, a v-Abl immortalized pre-B cell line and have demonstrated a range of Myc expression using flow cytometry and qPCR.  Upon tamoxifen induction, we have measured the effect of Myc dosage on the cell line’s proliferation rate under decreasing amounts of serum, a condition known to decrease endogenous Myc expression using a fluorescence-based dye and flow cytometry.  Transduced, tamoxifen-treated cells were shown to express downstream Myc targets such as Npm1 in response to ectopic Myc expression. The ability to express an active, inducible, fluorescent Myc fusion over a range of expression levels may prove useful in tandem with another gene of interest, e.g., the Ras oncongene; such an experiment could yield insight on how Myc interacts with other oncoproteins at the signaling and phenotypic levels over a broad 2-D expression space.