title: Cell density-dependent regulation of p73 in breast cancer cells.
abstract: Molecular regulation of p73, a p53 family member, remains unclear. Here we report that p73 expression is significantly regulated by cell densities. In particular, we found that p73alpha and p73beta are differentially regulated. While p73beta protein levels were inversely correlated with cell densities, p73alpha protein levels behaved oppositely. We further showed that density-dependent changes of p73alpha follow the same patterns as E2F-1 and TAp73 mRNA levels, suggesting transcriptional regulation. Our data also suggest that high levels of p73beta at lower densities may be due to increased protein stability. However, AIP-4/Itch appeared not to be involved in downregulation of p73beta at high densities. Moreover, we also found that subcellular location of p73 isoforms changes with the culture density increases. While high level of p73beta at low density was mainly presented in the nucleus, low levels of this protein at high densities were mainly in the cytosol. Taken together, these findings reveal a novel mechanism that differentially regulates p73 isoforms and underscores the role of cell-cell interaction in p73 regulation, which may advance our understanding of p73 expression and function in human cancers.
authors.affiliation: Department of Pathology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA.
authors.forename: Chaitali
authors.initials: C
authors.lastname: Tophkhane
authors.forename: Shihe
authors.initials: S
authors.lastname: Yang
authors.forename: Zhizhuang Joe
authors.initials: ZJ
authors.lastname: Zhao
authors.forename: Xiaohe
authors.initials: X
authors.lastname: Yang
mesh_terms: D015153:Blotting, Western; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism*; D002450:Cell Communication / Q000502:physiology*; D002452:Cell Count; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000072160:Tumor Protein p73; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D020033:Protein Isoforms; C000606460:TP73 protein, human; D000072160:Tumor Protein p73; D025521:Tumor Suppressor Proteins