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Molecular and Cellular Biology, May 2004, p. 4465-4475, Vol. 24, No. 10
0270-7306/04/$08.00+0 DOI: 10.1128/MCB.24.10.4465-4475.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.
Section of Infectious Disease, Department of Medicine,1 Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas 77030,3 Shanghai Institute of Hematology, Shanghai Rui-Jin Hospital, Shanghai 200025, People's Republic of China2
Received 30 October 2003/ Returned for modification 13 January 2004/ Accepted 12 February 2004
Acute promyelocytic leukemia (APL) cells contain one of five chimeric retinoic acid
-receptor (RAR
) genes (X-RAR
) created by chromosomal translocations or deletion; each generates a fusion protein thought to transcriptionally repress RAR
target genes and block myeloid differentiation by an incompletely understood mechanism. To gain spatiotemporal insight into these oncogenic processes, we employed fluorescence microscopy and fluorescence recovery after photobleaching (FRAP). Fluorescence microscopy demonstrated that the intracellular localization of each of the X-RAR
proteins was distinct from that of RAR
and established which portion(s) of each X-RAR
proteinX, RAR, or bothcontributed to its altered localization. Using FRAP, we demonstrated that the intranuclear mobility of each X-RAR
was reduced compared to that of RAR
. In addition, the mobility of each X-RAR
was reduced further by ligand addition, in contrast to RAR
, which showed no change in mobility when ligand was added. Both the reduced baseline mobility of X-RAR
and the ligand-induced slowing of X-RAR
could be attributed to the protein interaction domain contained within X. RXR
aberrantly colocalized within each X-RAR
; colocalization of RXR
with promyelocytic leukemia (PML)-RAR
resulted in reduced mobility of RXR
. Thus, X-RAR
may interfere with RAR
through its aberrant nuclear dynamics, resulting in spatial and temporal sequestration of RXR
and perhaps other nuclear receptor coregulators critical for myeloid differentiation.
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