Imaging, Diagnosis, Prognosis Prognostic Impact of DTAp73 Isoform Levels and Their Target Genes in Colon Cancer Patients Beatriz Soldevilla 1 , Raquel Díaz 1 , Javier Silva 1 , Yolanda Campos-Martín 3 , Concepci  on Muñoz 2 , Vanesa García 1 , Jos e M García 1 , Cristina Peña 1 , Mercedes Herrera 1 , Marta Rodriguez 1 , Irene G omez 1 , Nagat Mohamed 1 , Margarita M. Marques 4 ,F elix Bonilla 1 , and Gemma Domínguez 1 Abstract Purpose: Cumulative data support the role of DTAp73 variants in tumorigenic processes such as drug resistance. We evaluate the impact of TP73 isoforms and their putative target genes ABCB1, HMGB1, and CASP1 on the survival of colon cancer patients and the correlation between their expressions. Experimental Design: We determined in 77 colon cancer patients the expression of DEx2p73, DEx2/ 3p73, DNp73, TAp73, ABCB1, HMGB1, and CASP1 by quantitative real-time reverse transcriptase-PCR. Tumor characteristics, disease-free survival, and overall survival (OS) were examined in each patient. Functional experiments were carried out to check whether ectopic expression of DNp73 modifies the proliferation, drug resistance, migration, and invasion properties of colon tumor cells and the expression of ABCB1, HMGB1, and CASP1. Results: Positive correlations were observed between the expression levels of DTAp73 variants and HMGB1. Furthermore, a trend was observed for ABCB1. Overexpression of DEx2/3p73 and DNp73 isoforms was significantly associated with advanced stages (P ¼ 0.04 and P ¼ 0.03, respectively) and predicted shortened OS (P ¼ 0.04 and P ¼ 0.05, respectively). High levels of ABCB1 and HMGB1 were associated with shorter OS (P ¼ 0.04 and P ¼ 0.05, respectively). Multivariate analysis showed that, in addition to the tumor stage, ABCB1 and HMGB1 had independent relationships with OS (P ¼ 0.008). Ectopic expression of DNp73 was associated with an increase in proliferation and drug resistance. Conclusions: The positive correlation between DTAp73 variants and HMGB1 and ABCB1 expression supports them as TP73 targets. The fact that upregulation of DTAp73 isoforms was associated with shortened OS, increase in proliferation, and drug resistance confirms their oncogenic role and plausible value as prognostic markers. ABCB1 and HMGB1, putative DTAp73 target genes, strongly predict OS in an independent manner, making clear the importance of studying downstream TP73 targets that could predict the outcome of colon cancer patients better than DTAp73 variants themselves do. Clin Cancer Res; 17(18); 6029–39. Ó2011 AACR. Introduction TP73, a member of the p53 family, is expressed in multiple variants. TAp73 isoforms (full-length) have tu- mor-suppressor potential (1), whereas DTAp73 variants (DEx2p73, DEx2/3p73, DNp73, and DNC ¸ p73), lacking the transactivation domain, show oncogenic properties (2–7). TP53 and TP73 share significant structural and functional homology (8), although some evidence shows that their roles differ in human tumorigenesis. The 2 genes are activated through different pathways after DNA dam- age, and are capable of inducing cell-cycle arrest and cell death. Unlike TP53, inactivating mutations of TP73 are extremely rare in human tumors (9). Moreover, although TP73 can activate some TP53-responsive genes to varying degrees, such as those induced after DNA damage (10, 11), recent analyses showed that p73 has its own set of target genes (11, 12), indicating unique and overlapping func- tions for this family. Further complexity is revealed by the fact that the members of the TP53 family can transactivate common target genes but through the recognition of dis- tinct binding elements (11). In addition, several reports have indicated that DNp73 acts downstream from TP53 and TAp73 as a transcriptional negative regulator that Authors' Affiliations: 1 Servicio de Oncología M edica, Hospital Universi- tario Puerta de Hierro Majadahonda, Departamento de Medicina, Univer- sidad Aut onoma de Madrid, Madrid; 2 Servicio de Gastroenterología and 3 Servicio de Patología, Hospital Virgen de la Salud, Toledo; and 4 Instituto de Desarrollo Ganadero, Universidad de Le on, Le on, Spain Corresponding Authors: Gemma Domínguez, Department of Medical Oncology, Hospital Universitario Puerta de Hierro, C/Manuel de Falla, 1, 28220-Majadahonda, Madrid, Spain. Phone: 34-91-1917769. Fax: 34-91- 1916806; E-mail: gdominguez.hpth@salud.madrid.org; or F elix Bonilla, Department of Medical Oncology, Hospital Universitario Puerta de Hierro, C/Manuel de Falla, 1, 28220-Majadahonda, Madrid, Spain. E-mail: fbonilla.hpth@salud.madrid.org doi: 10.1158/1078-0432.CCR-10-2388 Ó2011 American Association for Cancer Research. Clinical Cancer Research www.aacrjournals.org 6029 on June 12, 2020. © 2011 American Association for Cancer Research. clincancerres.aacrjournals.org Downloaded from Published OnlineFirst August 1, 2011; DOI: 10.1158/1078-0432.CCR-10-2388