Human NDRG2 (N-Myc downstream regulated gene 2) was identified as a candidate tumor suppressor gene due to its low expression in human glioma and other cancer tissues. However, the mechanisms that lead to inactivation of the NDRG2 gene remain unknown. In the present study, semi-quantitative RT-PCR and Western blot analysis were used to confirm that NDRG2 mRNA and protein levels are decreased in several cancer cell lines. We found heterozygous deletion of NDRG2 in MCF-7 cells, and showed that mutation (at -13 bp (C > T)) and methylation of the NDRG2 promoter occurred in several cancer cell lines. Furthermore, mutation (-13 bp (C > T)) of the NDRG2 core promoter significantly reduced NDRG2 activity. Finally, we showed that NDRG2 expression was decreased in several breast cancer tissues. Unexpectedly, changes in the NDRG2 gene were not observed. Here, we describe for the first time, the mechanisms involved in NDRG2 gene down-regulation. (c) 2007 Elsevier Inc. All rights reserved.