FIGURE 7.

c-MYC can also regulate transcription of a large set of ABC transporter genes. A, modulation of c-MYC expression by tetracycline (TET) in P493-6 cells was monitored by Western blot (upper panel). RNA expression of the 48 ABC transporter genes was determined by quantitative reverse transcription-PCR as a function of c-MYC silencing. Cluster 3 was used to generate an image map showing expression levels of ABC genes as a function of tetracycline treatment time, relative to expression at time 0 and processed in log space. Hierarchical clustering was determined as described in Fig. 2. Green indicates genes positively regulated by c-MYC, whereas red indicates those negatively regulated (lower panel). B, Venn diagram representing the overlap of ABC transporter genes regulated by both MYCN and c-MYC transcription factors in TET21/N cells or neuroblastoma tumors and in P493-6 cells. C, protein (upper panel) and mRNA (lower panel) levels of ABCC1, ABCC3, and ABCC4 in MCF-7 and SJ-G2 cell lines after treatment with a specific c-MYC siRNA.