2.2. ABCB10 promoter activity in selected cell lines
Previous studies have shown that ABCB10 is broadly expressed in
many tissues, with the highest expression being observed in the liver,
kidney, muscles and haematopoietic cells [6,3]. This is why we decided
to verify the actual promoter function of the 5′-flanking ABCB10 gene
segment identified as potential core regulatory segment in a reporter
gene assay, using a series of 5′-deletion reporter constructs in K562,
HepG2 and HEK293 cell lines representing cells of different tissue origin
(haematopoietic, liver and kidney, respectively). All cloned fragments
showed significantly higher promoter activity than the promoterless
pGL3-basic vector, confirming their identity as the ABCB10 promoter
(Fig. 2).Moreover, the patterns of relative activity of constructs of varying
length differed for the cell lines we tested. In HEK293 cells, all deletion
fragments demonstrated a similar, rather lowactivity. In contrast to HEK293 cells, the pattern of ABCB10 promoter activity was different in
the other two cell lines. In K562 and HepG2 cell lines, the shortest
phABCB10(−242/+133)Luc vector had relatively low transcriptional
activity (2 and 3 fold higher than control pGL3-basic vector), but longer
vectors (representing sequences−449/+133 bp and−642/+133 bp)
were increasingly more active, suggesting the presence between nucleotides
−642 and −242 of positive regulatory elements active in these
cell lines, dependent on the cellular environment. The longest fragment
of the ABCB10 promoter region (representing sequence −979/
+133 bp) demonstrated a similar or slightly lower activity to that observed
for the−642/+133 bp construct in all cell lines tested, pointing
to the lack of relevant regulatory element in the sequence stretch between
nucleotides −979 and −642 (Fig. 2).