Deletion of the COOH-terminal region of p73alpha enhances both its transactivation function and DNA-binding activity but inhibits induction of apoptosis in mammalian cells.
The candidate tumor suppressor p73 has a high sequence homology with p53 within the NH2-terminal transactivation domain, the sequence-specific DNA-binding region, and the oligomerization domain. However, p73alpha, which is most abundantly expressed in many tissues and cells among the alternatively spliced forms of p73, has an additional long COOH-terminal tail that might distinguish the function of p53 and p73alpha or other p73 splicing variants. To examine the functional role of the p73alpha COOH-terminal region, we generated a series of p73alpha truncation mutants including p73alpha(1-247) (retaining only a transactivation domain), p73alpha(1-427) (lacking the most COOH-terminal region including a SAM domain), and p73alpha(1-548) (deleting an extreme COOH-terminal region except a SAM domain). When transfected into COS cells, all of p73alpha, p73alpha(1-548), and p73alpha(1-427) localized in the cellular nucleus, whereas p73alpha(1-247) localized in both nucleus and cytoplasm. Intriguingly, when compared with p73alpha, both p73alpha(1-427) and p73alpha(1-548) showed a significant stimulation of the transcription of luciferase reporters harboring three p53-responsive promoters (p21(Waf1), Mdm2, and Bax) in p53-deficient SAOS-2 cells. Gel retardation assays showed that DNA-binding activity of p73alpha(1-427) and p73alpha(1-548) was increased as compared with that of the full-length p73alpha. However, the colony formation assays using SAOS-2 cells demonstrated that, contrary to p73alpha, transfection of p73alpha(1-427) or p73alpha(1-548) resulted in no significant reduction of the number of colonies. These suggest that the distal COOH-terminal region of p73alpha is a cis- or trans-acting regulatory domain and regulates its functions diversely.
Ozaki
T
T
Division of Biochemistry, Chiba Cancer Center Research Institute, Japan.
Naka
M
M
Takada
N
N
Tada
M
M
Sakiyama
S
S
Nakagawara
A
A
D017398:Alternative Splicing; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D019556:COS Cells; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D016147:Genes, Tumor Suppressor; D006801:Humans; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011994:Recombinant Proteins / Q000378:metabolism; D017384:Sequence Deletion; D015534:Trans-Activators / Q000378:metabolism; D015533:Transcriptional Activation; D014162:Transfection; D014407:Tumor Cells, Cultured; D000072160:Tumor Protein p73; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins
D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D011994:Recombinant Proteins; C000606460:TP73 protein, human; D015534:Trans-Activators; D000072160:Tumor Protein p73; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins