Colorectal Cancer
Copyright ©2008 The WJG Press and Baishideng. All rights reserved.
World J Gastroenterol. Jun 28, 2008; 14(24): 3829-3840
Published online Jun 28, 2008. doi: 10.3748/wjg.14.3829
Bcl-xL and Myeloid cell leukaemia-1 contribute to apoptosis resistance of colorectal cancer cells
Henning Schulze-Bergkamen, Roland Ehrenberg, Lothar Hickmann, Binje Vick, Toni Urbanik, Christoph C Schimanski, Martin R Berger, Arno Schad, Achim Weber, Steffen Heeger, Peter R Galle, Markus Moehler
Henning Schulze-Bergkamen, Roland Ehrenberg, Lothar Hickmann, Binje Vick, Toni Urbanik, Christoph C Schimanski, Peter R Galle, Markus Moehler, First Department of Medicine, Johannes-Gutenberg-University Mainz, Mainz 55101, Germany
Martin R Berger, German Cancer Research Center, Heidelberg 69120, Germany
Arno Schad, Institute of Pathology, University of Mainz, Mainz 55101, Germany
Achim Weber, Department of Pathology, Institute of Surgical Pathology, University Hospital, Zürich 8091, Switzerland
Steffen Heeger, Merck Pharma GmbH, Darmstadt 64293, Germany
Author contributions: Schulze-Bergkamen H, Ehrenberg R contributed equally to this work; Schulze-Bergkamen H, Ehrenberg R, Hickmann L, Urbanik T and Vick B performed the experiments of the study and made substantial contributions to conception and design of the study, interpretation of the data and statistical analysis; Schulze-Bergkamen H drafted the manuscript; Moehler M, Heeger S and Galle PR made substantial contributions to conception, design and interpretation of data; Schimanski CC and Berger MR participated in the design of the study and in the analysis of colorectal carcinoma tissue samples; Schad A and Weber A performed the immunhistochemical analysis of colorectal carcinoma tissues; all authors read and approved the final manuscript; this study contains essential parts of the medical thesis work of Ehrenberg R and Hickmann L.
Correspondence to: Henning Schulze-Bergkamen, MD, PhD, First Department of Medicine, Johannes-Gutenberg-University Mainz, Langenbeckstrasse 1, Mainz 55101, Germany. bergkam@uni-mainz.de
Telephone: +49-6131-172462
Fax: +49-6131-175529
Received: March 4, 2008
Revised: May 8, 2008
Accepted: May 15, 2008
Published online: June 28, 2008
Abstract

AIM: To explore the role of Bcl-xL and Myeloid cell leukaemia (Mcl)-1 for the apoptosis resistance of colorectal carcinoma (CRC) cells towards current treatment modalities.

METHODS: Bcl-xL and Mcl-1 mRNA and protein expression were analyzed in CRC cell lines as well as human CRC tissue by Western blot, quantitative PCR and immunohistochemistry. Bcl-xL and Mcl-1 protein expression was knocked down or increased in CRC cell lines by applying specific siRNAs or expression plasmids, respectively. After modulation of protein expression, CRC cells were treated with chemotherapeutic agents, an antagonistic epidermal growth factor receptor (EGFR1) antibody, an EGFR1 tyrosine kinase inhibitor, or with the death receptor ligand TRAIL. Apoptosis induction and cell viability were analyzed.

RESULTS: Here we show that in human CRC tissue and various CRC cell lines both Bcl-xL and Mcl-1 are expressed. Bcl-xL expression was higher in CRC tissue than in surrounding non-malignant tissue, both on protein and mRNA level. Mcl-1 mRNA expression was significantly lower in malignant tissues. However, protein expression was slightly higher. Viability rates of CRC cells were significantly decreased after knock down of Bcl-xL expression, and, to a lower extent, after knock down of Mcl-1 expression. Furthermore, cells with reduced Bcl-xL or Mcl-1 expression was more sensitive towards oxaliplatin- and irinotecan-induced apoptosis, and in the case of Bcl-xL also towards 5-FU-induced apoptosis. On the other hand, upregulation of Bcl-xL by transfection of an expression plasmid decreased chemotherapeutic drug-induced apoptosis. EGF treatment clearly induced Bcl-xL and Mcl-1 expression in CRC cells. Apoptosis induction upon EGFR1 blockage by cetuximab or PD168393 was increased by inhibiting Mcl-1 and Bcl-xL expression. More strikingly, CD95- and TRAIL-induced apoptosis was increased by Bcl-xL knock down.

CONCLUSION: Our data suggest that Bcl-xL and, to a lower extent, Mcl-1, are important anti-apoptotic factors in CRC. Specific downregulation of Bcl-xL is a promising approach to sensitize CRC cells towards chemotherapy and targeted therapy.

Keywords: Colorectal carcinoma; Bcl-xL; Myeloid cell leukaemia-1; Epidermal growth factor receptor 1; Apoptosis; 5-fluorouracil; Irinotecan; Oxaliplatin