Abstract 4461: Involvement of cleaved p73 isoforms in anoikis

Abstract

Abstract p73, a p53 family member, is a transcription factor that plays an important role in cell cycle control, differentiation and apoptosis. p73 has been shown to be capable of replacing p53, inducing apoptosis in p53-deficient cells. In this study, we tried to determine the role of p73 in anoikis, a type of apoptosis induced by inadequate cell-matrix interaction. Six breast cancer cell lines with different p53 status were treated with doxorubicin (DOX) and anoikis was analyzed 48 hours after treatment. We found that, independently of the p53 status, DOX-induced anoikis was associated with p73 cleavage and the activation of caspases. p73 cleavage was not triggered in caspase-3-null MCF-7 breast cancer cell line. To confirm the implication of p73 cleavage in anoikis, we transfected breast cancer cell lines with plasmids bearing TAp73α, TAp73β or ΔNp73α. The overexpression of p73 isoforms in transfected cells induced detachment of these cells from the culture flask. Anoikis in these cells was associated with cleavage of the transfected isoform of p73. Once again, p73 cleavage was not detected in caspase-3-null MCF-7 cell line confirming the involvement of caspase 3 in p73 cleavage. The use of flag antibody, which recognizes the N-terminus of transfected proteins, and p73 antibodies, which recognize the C-terminus of these proteins, enabled us to demonstrate that there are two possible cleavage sites in TAp73α generating two different cleaved forms. However, when cells were transfected with TAp73β or ΔNp73α, only one cleaved form was generated. TAp73β probably harbors a N-terminal site, while ΔNp73α only harbors a C-terminal site. Cleavage at the N-terminal site, rather than that at the C-terminal site, appears to be important for an efficient apoptotic response, because it is associated with stabilization of cleaved proteins and high toxicity. Further studies are warranted to determine the accurate role of p73 cleavage in anoikis, especially since these cleavages arise independently of the p53 status and therefore could contribute to response to stress in cells with non functional p53. Acknowledgements: this work is supported by “La Ligue contre le cancer - Comité de la Somme” and the Syrian Ministry of Health. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4461.