Molecular and Cellular Endocrinology 214 (2004) 149–153 Pdcd4 inhibits growth of tumor cells by suppression of carbonic anhydrase type II B. Lankat-Buttgereit a , C. Gregel a , A. Knolle b , A. Hasilik c , R. Arnold a , R. Göke a,∗ a Clinical Research Unit for Gastrointestinal Endocrinology, University of Marburg, Baldingerstrasse, 35033 Marburg, Germany b Department of Pathology and Laboratory Medicine, School of Medicine, University of Pennsylvania, Philadelphia, PA, USA c Institute of Physiological Chemistry, University of Marburg, Baldingerstrasse, 35033 Marburg, Germany Received 19 August 2003; accepted 22 October 2003 Abstract To identify new genes that are upregulated during apoptosis we previously cloned rat pdcd4. While the role of pdcd4 is still unclear it seems to possess a tumor suppressor activity. Pdcd4 directly interacts with the RNA helicase eIF4A and inhibits protein synthesis by interfering with the assembly of the cap-dependent translation initiation complex. In the present study, we show that pdcd4 suppresses carbonic anhydrase type II protein expression in HEK293 and Bon-1 carcinoid cells. Since tumor cells require a high bicarbonate flux for their growth, carbonic anhydrase suppression results in growth inhibition. Similar to pdcd4, carbonic anhydrase inhibitor ethoxyzolamide reduces growth of several endocrine tumor cell lines. Thus, the translation inhibitor pdcd4 represses endocrine tumor cell growth by suppression of carbonic anhydase II. Furthermore, carbonic anhydrase inhibitors might represent promising tools for anti-endocrine tumor treatment. © 2003 Elsevier Ireland Ltd. All rights reserved. Keywords: Pdcd4; Carbonic anhydrase; Endocrine tumor; Ethoxyzolamide; Translation 1. Introduction Programmed cell death, also termed apoptosis, plays a fundamental role in many biological processes as embryo- genesis, normal tissue turnover and immune homeostasis (Saikumar et al., 1999; Evan and Littlewood, 1998; Thorn- berry and Lazebnik, 1998; Ashkenazi and Dixit, 1998). Although to date a number of caspase-dependent and in- dependent apoptotic pathways have been identified, the mechanisms of cell death are very complex and are still largely unknown. In an attempt to identify genes which are involved in the regulation of apoptosis we cloned rat pdcd4 (death upregulated gene; DUG) (Göke et al., 2002). Pdcd4 is constitutively expressed at low levels in normal cells but is upregulated after induction of apoptosis by different stimuli like death ligands and serum/glucose starvation. Pdcd4 is highly conserved during evolution indicating an important biological function of this protein. Analysis of the amino acid sequence revealed the presence of two conserved ∗ Corresponding author. Tel.: +49-6421-2862714; fax: +49-6421-2868924. E-mail address: rgoeke@gmx.net (R. Göke). -helical MA3 domains, which are known to be involved in protein–protein interactions. The eukaryotic translation ini- tiation factor 4G interacts with the RNA helicase eIF4A via the MA3 domain (Ponting, 2000). eIF4A which is part of the cap-dependent translation initiation complex unwinds the mRNA allowing the ribosome to scan along the mRNA to locate the initiating AUG codon. Recently, we showed that pdcd4 like eIF4G interacts with eIF4A (Göke et al., 2002). Our assumption that pdcd4 inhibits translation by direct interaction with eIF4A was confirmed by Yang et al., 2003. Carbonic anhydrase catalyzes the hydration of CO 2 to bicarbonate. Bicarbonate is an important substrate for many fundamental biological pathways as gluconeogenesis, li- pogenesis, ureagenesis, pyrimidine synthesis and synthesis of several amino acids (Chegwidden et al., 2000). Can- cer cells have a higher replication rate than normal cells requiring a high flux of bicarbonate into these metabolic pathways. Therefore, providing bicarbonate as substrate, carbonic anhydrase isoforms seem to play an important role for tumor cell growth. In accordance with this assumption, it was reported that expression of carbonic anhydrase I and II correlated with aggessiveness of colorectal cancer and synchronous distant metastasis (Bekku et al., 2000). 0303-7207/$ – see front matter © 2003 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.mce.2003.10.058