Role of the unique N-terminal domain of CtBP2 in determining the subcellular localisation of CtBP family proteins.
BACKGROUND
CtBP1 and CtBP2 are transcriptional co-repressors that modulate the activity of a large number of transcriptional repressors via the recruitment of chromatin modifiers. Many CtBP-regulated proteins are involved in pathways associated with tumorigenesis, including TGF-beta and Wnt signalling pathways and cell cycle regulators such as RB/p130 and HDM2, as well as adenovirus E1A. CtBP1 and CtBP2 are highly similar proteins, although evidence is emerging that their activity can be differentially regulated, particularly through the control of their subcellular localisation. CtBP2s from diverse species contain a unique N-terminus, absent in CtBP1 that plays a key role in controlling the nuclear-cytoplasmic distribution of the protein.


RESULTS
Here we show that amino acids (a.a.) 4-14 of CtBP2 direct CtBP2 into an almost exclusively nuclear distribution in cell lines of diverse origins. Whilst this sequence contains similarity to known nuclear localisation motifs, it cannot drive nuclear localisation of a heterologous protein, but rather has been shown to function as a p300 acetyltransferase-dependent nuclear retention sequence. Here we define the region of CtBP2 required to co-operate with a.a. 4-14 to promote CtBP2 nuclear accumulation as being within a.a. 1-119. In addition, we show that a.a. 120-445 of CtBP2 can also promote CtBP2 nuclear accumulation, independently of a.a. 4-14. Finally, CtBP1 and CtBP2 can form heterodimers, and we show that the interaction with CtBP2 is one mechanism whereby CtBP1 can be recruited to the nucleus.


CONCLUSIONS
Together, these findings represent key distinctions in the regulation of the functions of CtBP family members that may have important implications as to their roles in development, and cell differentiation and survival.
Bergman
Lee M
LM
Cancer Sciences Division, School of Medicine, University of Southampton, Southampton SO16 6YD, UK. l.m.bergman@soton.ac.uk
Morris
Laila
L
Darley
Matthew
M
Mirnezami
Alexander H
AH
Gunatilake
Samal C
SC
Blaydes
Jeremy P
JP
D000429:Alcohol Oxidoreductases / Q000032:analysis; D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D002467:Cell Nucleus / Q000737:chemistry*; D056970:Co-Repressor Proteins; D004268:DNA-Binding Proteins / Q000032:analysis; D005136:Eye Proteins / Q000032:analysis / Q000737:chemistry* / Q000235:genetics; D006801:Humans; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins; D019913:Nuclear Localization Signals; D010802:Phylogeny; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012097:Repressor Proteins / Q000032:analysis / Q000737:chemistry* / Q000235:genetics; D016415:Sequence Alignment
D056970:Co-Repressor Proteins; D004268:DNA-Binding Proteins; D005136:Eye Proteins; D009419:Nerve Tissue Proteins; D019913:Nuclear Localization Signals; D012097:Repressor Proteins; D000429:Alcohol Oxidoreductases; C421248:CTBP2 protein, human; C096794:C-terminal binding protein