The LIM domain protein LMO4 interacts with the cofactor CtIP and the tumor suppressor BRCA1 and inhibits BRCA1 activity.
LMO4 belongs to the LIM-only (LMO) group of transcriptional regulators that appear to function as molecular adaptors for protein-protein interactions. Expression of the LMO4 gene is developmentally regulated in the mammary gland and is up-regulated in primary breast cancers. Using LMO4 in a yeast two-hybrid screen, we have identified the cofactor CtIP as an LMO4-binding protein. Interaction with CtIP appeared to be specific for the LMO subclass of LIM domain proteins and could be mediated by a single LIM motif of LMO4. We further identified the breast tumor suppressor BRCA1 as an LMO4-associated protein. The C-terminal BRCT domains of BRCA1, previously shown to bind CtIP, also mediated interaction with LMO4. Tumor-associated mutations within the BRCT repeats that abolish interaction between BRCA1 and CtIP had no effect on the association of BRCA1 with LMO4. A stable complex comprising LMO4, BRCA1, and CtIP was demonstrated in vivo. The LIM domain binding-protein Ldb1 also participated in this multiprotein complex. In functional assays, LMO4 was shown to repress BRCA1-mediated transcriptional activation in both yeast and mammalian cells. These findings reveal a novel complex between BRCA1, LMO4, and CtIP and indicate a role for LMO4 as a repressor of BRCA1 activity in breast tissue.
Sum
Eleanor Y M
EY
Walter and Eliza Hall Institute of Medical Research and Bone Marrow Research Laboratories, Melbourne, Victoria 3050, Australia.
Peng
Benjamin
B
Yu
Xin
X
Chen
Junjie
J
Byrne
Jennifer
J
Lindeman
Geoffrey J
GJ
Visvader
Jane E
JE
D048868:Adaptor Proteins, Signal Transducing; D019313:BRCA1 Protein / Q000737:chemistry / Q000378:metabolism*; D015152:Blotting, Northern; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000378:metabolism; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D002455:Cell Division; D002460:Cell Line; D018076:DNA, Complementary / Q000378:metabolism; D004706:Endodeoxyribonucleases; D004847:Epithelial Cells / Q000378:metabolism; D018398:Homeodomain Proteins / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D060588:LIM Domain Proteins; D009687:Nuclear Proteins / Q000737:chemistry / Q000378:metabolism*; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014157:Transcription Factors / Q000737:chemistry / Q000378:metabolism*; D015533:Transcriptional Activation; D020798:Two-Hybrid System Techniques
D048868:Adaptor Proteins, Signal Transducing; D019313:BRCA1 Protein; D002352:Carrier Proteins; D018076:DNA, Complementary; D018398:Homeodomain Proteins; D060588:LIM Domain Proteins; C114905:LMO4 protein, human; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D004706:Endodeoxyribonucleases; C410741:RBBP8 protein, human