The BTB/POZ domain targets the LAZ3/BCL6 oncoprotein to nuclear dots and mediates homomerisation in vivo.
The LAZ3/BCL6 gene was identified by its disruption in 3q27 translocations associated with diffuse large cell lymphomas. It is predicted to be a transcription factor as it contains six Krüppel-like Zinc finger motifs and a N-terminal BTB/POZ domain, a protein/protein interaction interface that is widely conserved in Metazoans. Using two antisera raised against non overlapping regions of the predicted ORF, we demonstrate that the LAZ3/BCL6 protein appears as a close ca. 79 kDa doublet in B lymphoid cell lines with either a rearranged or a non rearranged LAZ3/BCL6 locus. By immunofluorescence experiments on transiently transfected COS-1 or NIH3T3 cells, we show that the LAZ3/BCL6 protein displays a punctuated nuclear localisation. This appears to rely on LAZ3/BCL6 proper folding and/or activities as it is impaired in a hormone reversible-fashion through fusion of LAZ3/BCL6 to the ligand-binding domain of the oestrogen receptor. Moreover, deletion of its BTB/POZ domain leads to the disappearance of the nuclear dots although the protein remains nuclear. In addition, by using the yeast two-hybrid system, we show that the LAZ3/BCL6 BTB/POZ domain homomerises in vivo. Thus, the LAZ3/BCL6 BTB/POZ domain has the capability to self-interact and target the protein to discrete nuclear substructures.
U 124 INSERM, IRCL, Lille, France.
P
P
Dhordain
O
O
Albagli
S
S
Ansieau
M H
MH
Koken
C
C
Deweindt
S
S
Quief
D
D
Lantoine
A
A
Leutz
J P
JP
Kerckaert
D
D
Leprince
D016475:3T3 Cells; D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000502:physiology*; D006801:Humans; D051379:Mice; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D051560:Proto-Oncogene Proteins c-bcl-6; D014157:Transcription Factors / Q000502:physiology*; D016335:Zinc Fingers
D004268:DNA-Binding Proteins; D011518:Proto-Oncogene Proteins; D051560:Proto-Oncogene Proteins c-bcl-6; D014157:Transcription Factors