Quantitative polymerase chain reaction was used to assess the mRNA expression levels of various clock genes and revealed that, following the knockdown of <i>PER2</i> in SCC15 cells, the mRNA expression levels of <i>PER3</i>, brain and muscle ARNT-like 1, deleted in esophageal cancer <i>(DEC)1, DEC2</i>, cryptochrome circadian clock (<i>CRY</i>)2, timeless circadian clock, retinoic acid receptor-related orphan receptor-alpha and neuronal PAS domain protein 2 were significantly downregulated, while the mRNA expression levels of <i>PER1</i> and nuclear receptor subfamily 1 group D member 1 were significantly upregulated.
Given the reduced expression of the DEC1 gene in esophageal cancer, the high frequency of LOH at 9q32 in esophageal carcinomas, and the fact that the DEC1 cDNA can suppress growth of some cancer cells in vitro, we suggest that the DEC1 gene is a candidate tumor suppressor in 9q32.