Περίληψη:
The polymorphic sequence (AT)(X)T-Y motif residing 0.5 kb 5’ to the
human beta-globin gene has been shown to be a binding site for a
putative repressor protein, BP1, in K562 cells. The (AT)(X)T-Y sequence
is characterized by variable length and several configurations. The
precise role of the (AT)(X)T-Y repeats on the regulation of the
beta-globin gene remains unclear. In the present study, we identified
the (AT)(X)T-Y motifs which prevail in the Greek population, established
their frequency, and directly investigated their role on P-globin gene
expression by comparing the effects of the four identified (AT)(X)T-Y
motifs using transient expression assays. Four different configurations
were found in the Greek population: the (AT),T, motif was the most
abundant (81.8%) representing the reference sequence, the (AT)(8)T-5
motif (16.1%), and the (AT)(11)T-3 motif (2%), while the (AT)(8)T-4
motif was absent from normal beta(A) chromosomes and was exclusively
found on beta(s) chromosomes. To evaluate their different role on
transcriptional regulation, the four motifs were subcloned upstream of
the luciferase reporter gene. Two expression systems were used; MEL
cells were transfected with a pGL-2 basic plasmid containing one of the
four (AT)(X)T-Y repeats, the beta-globin gene promoter, and the
luciferase gene, while HeLa cells were transfected with a similar
construct (pGL-2 enhancer) including the SV40 enhancer. After 48 h
following transient transfection of the cell lines, the expression level
of the reporter gene was estimated using a photoilluminometer. The
transfected MEL cells exhibited a clearly reduced expression of the
luciferase gene driven by the beta-globin promoter containing the
(AT)(X)T-Y and (AT)(11)T-3 configurations. In contrast, HeLa cells did
not exhibit any differences among the four motifs. On the basis of these
results, we postulate that the (AT),T, and (AT),T, variants residing 0.5
kb 5’ to the beta-globin gene do not represent simple polymorphisms and
can affect its expression in an erythroid environment. (C) 2002 Elsevier
Science (USA).
Συγγραφείς:
Kalotychou, V
Kollia, P
Voskaridou, E
Patargias, T and
Anagnou, NP
Loukopoulos, D
