Abstract
The molecular basis for the pharmacologic effects of N‐(4‐hydroxyphenyl)retinamide (4HPR) was investigated by studying the gene(s) that this compound may upregulate in cultured human epithelial tumor cells. Treatment of the cultured human nasopharyngeal carcinoma‐derived cells (CNE3) with 4HPR caused modest cell‐cycle arrest at G~1~ and apoptosis. The mRNA levels of a total of 20 genes were downregulated with the majority of them involved in cell cycle‐related functions. Only the mRNA level of the growth arrest and DNA‐damage inducible gene (gadd153) was upregulated by approximately 7‐fold, with a concomitant increase in intracellular protein level. Similar upregulation of gadd153 by 4HPR was observed in HeLa and 2 other tumor cell lines. The 4HPR‐induced apoptosis was markedly enhanced in the CNE3 cells that transiently overexpressed the gadd153 protein. Unlike 4HPR, all‐trans‐retinoic acid (ATRA) had no effect on the mRNA or protein level of gadd153. The ability of 4HPR and ATRA to stimulate the promoter activity of gadd153 was then examined. In the HeLa cells, both 4HPR and ATRA caused a 2‐ to 4‐fold stimulation of the promoter activity of gadd153, but similar to the CNE3 cells, ATRA was incapable of upregulating the protein level of gadd153. This is the first demonstration that gadd153 is a 4HPR‐responsive gene in tumor cells and may have a functional role to play in 4HPR‐induced apoptosis. Furthermore, our data suggest that the expression of gadd153 can be regulated by 4HPR at the transcriptional level. © 2002 Wiley‐Liss, Inc.