In order to identify transcription factorsmost likely to bind and regulate
the activity of the ABCB10 promoter, we performed a detailed in
silico analysis of ABCB10 promoter with MatInspector software which
revealed presence of numerous putative binding sites. Among them,
two types of potential binding sites/response element stood out by
their number and conserved character: those for the Sp and E2F families
of transcription factors (data not shown and Fig. 1). Already in our recent
publication [20],wherewe analysed promoters of ABC transporters
that were identified as potential factors for melanoma multidrug resistance,
we found that GC-boxes binding Sp factors are overrepresented
within ABCB10 promoter. Moreover, using mithramycin A, an inhibitor
of Sp factor binding, we were able to decrease the expression of
ABCB10 (and other ABC genes) in a melanoma cell line [20]. However,
since Sp1 is mostly associated with constitutive maintenance of basal
expression level of CpG-rich promoter-containing genes, in the present
work we focused on the other prominent group of potential regulatory
factors we identified – the E2F family – since they are more likely to be
relevant to physiological modulation of ABCB10 expression.We identified
six high-probability E2F binding motifs within the location of the
putative proximal ABCB10 promoter, labelling them sites 1 through 6
(Fig. 1), corresponding to three different types of consensus E2F response
element sequences (Fig. 1) reported in literature [21,22].