Function of p73, not of p53, is inhibited by the physical interaction with RACK1 and its inhibitory effect is counteracted by pRB.
The newly identified p53-related gene, p73, encodes a nuclear transcription factor. Unlike p53, p73 has various isoforms with different NH(2)- and COOH-terminal tails. p73alpha with the longest COOH-terminal extension is most abundantly expressed in many tissues and cells among those splicing isoforms of p73 and the COOH-terminal region appears to have an autoregulatory function. To isolate and characterize the cellular protein(s) that interacts with the unique COOH-terminal region of p73alpha, we employed a yeast two-hybrid screen with a human fetal brain and 293 cell cDNA libraries. We identified the receptor for activated C kinase (RACK1) as a new member of p73alpha-binding proteins. The interaction was confirmed by coimmunoprecipitation experiments, whereas RACK1 did not interact with p53 or p73beta. Ectopic overexpression of RACK1 in SAOS-2 cells reduced the p73alpha-mediated transcription from the p53/p73-responsive promoters, and inhibited the p73alpha-dependent apoptosis. On the other hand, the p53-dependent transcriptional activation as well as apoptosis was unaffected in the presence of RACK1. Furthermore, we found that pRB physically bound to RACK1, and repressed the RACK1-dependent inhibition of p73alpha. Taken together, our observations suggest that pRB diminishes the RACK1-mediated inhibition of p73alpha activity through the interaction with RACK1.
Ozaki
Toshinori
T
Division of Biochemistry, Chiba Cancer Center Research Institute, 666-2 Nitona, Chuoh-ku, Chiba 260-8717, Japan.
Watanabe
Ken-ichi
K
Nakagawa
Takahito
T
Miyazaki
Kou
K
Takahashi
Masato
M
Nakagawara
Akira
A
D000818:Animals; D017209:Apoptosis; D019556:COS Cells; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D019204:GTP-Binding Proteins; D016147:Genes, Tumor Suppressor; D006801:Humans; D009154:Mutation; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000502:physiology; D009369:Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D009687:Nuclear Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011233:Precipitin Tests; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface; D016160:Retinoblastoma Protein / Q000502:physiology*; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured; D000072160:Tumor Protein p73; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000502:physiology*; D025521:Tumor Suppressor Proteins; D020798:Two-Hybrid System Techniques
D004268:DNA-Binding Proteins; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; C419368:RACK1 protein, human; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface; D016160:Retinoblastoma Protein; C000606460:TP73 protein, human; D000072160:Tumor Protein p73; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D019204:GTP-Binding Proteins