Novel mutation in the PML/RAR alpha chimeric gene exhibits dramatically decreased ligand-binding activity and confers acquired resistance to retinoicacid in acute promyelocytic leukemia
N. Takayama et al., Novel mutation in the PML/RAR alpha chimeric gene exhibits dramatically decreased ligand-binding activity and confers acquired resistance to retinoicacid in acute promyelocytic leukemia, EXP HEMATOL, 29(7), 2001, pp. 864-872
Objective. All-trans retinoic acid (RA) resistance in acute promyelocytic l
eukemia (API.) has been a serious clinical problem in differentiation-induc
ing therapy. However, the mechanisms underlying acquired PA resistance in A
PL patients are not well understood.
Materials and Methods. We recently established a spontaneous RA-resistant A
PI, cell line (UF-I) from a patient and used this cell line as an excellent
in vitro model for KA-resistant clinical situations, We investigated the s
tructural and functional abnormalities of chimeric PML/RAR alpha gene in UF
-1 cells and preserved materials from the original patient.
Results. A novel point mutation was detected in the ligand-binding (E) doma
in of the RAR alpha portion of the PML/RAR alpha gene in UF-1 cells. This m
utation resulted in amino acid substitution of Arg611 ((C) under bar GG) fo
r Trp611 ((T) under bar GG) in the short-form PML/RAR alpha protein, which
corresponded to Arg276 in wild-type RAR alpha. Importantly, the same mutati
on was also detected in the preserved materials from the original patient.
COS-1 cells were transiently transfected with cNA encoding wild- type and m
utant PML/RAR alpha constructed by site-directed mutagenesis and performed
RA-binding assay. Interestingly, RA-binding activity was dramatically decre
ased in the mutant PML/RAR alpha compared with that of the wild-type chimer
ic protein, suggesting that this single amino acid substitution is critical
for RA binding,
Conclusions. These results strongly suggest that a novel point mutation in
the ligand-binding domain of the RAR alpha portion (Arg611) of the chimeric
PML/RAR alpha gene decreased sensitivity to all-trans RA, We conclude that
acquisition of the PML/RAR alpha mutation is one possible mechanism for de
velopment of RA resistance in patients with APL in vivo. (C) 2001 Internati
onal Society for Experimental Hematology, Published by Elsevier Science Inc
.