Differential gene expression in wild-type and Arnt-defective mouse hepatoma (Hepa1c1c7) cells

The aryl hydrocarbon nuclear translocator (Arnt) is a basic helix-loop-heli x (per/Arnt/Ahr/sim) PAS-containing protein that can heterodimerize with th e aryl hydrocarbon receptor (AhR), the hypoxia-inducible factor-1 alpha, an d other PAS-containing proteins to form transcriptionally active complexes. To identify the genes whose expression is modulated by Arnt, we used the t echnique of differential display to compare the expression of genes in wild -type and Arnt-defective (BPRc1) mouse hepatoma (Hepa1c1c7) cells. Here we report two gene products whose expression was reduced in BPRc1 cells (a WW domain-binding, protein-like factor and one unknown gene product) when comp ared to wild-type cells, and two that were elevated (Steel factor and a ser pin-like protein). Comparison of the relative expression of these gene prod ucts between two independently-derived, Arnt-defective cell lines, as well as in BPRc1 cells in which Arnt expression was restored by a stably integra ted Arnt-expression plasmid, revealed that each gene was expressed in an Ar nt-independent manner. Our results clearly demonstrate that gene expression in the variant cell clones is distinctly different from that of the parent al wild-type Hepa1c1c7 cells from which they were derived and involves gene s in addition to, and unrelated to, that of Arnt. The identification of the se differentially expressed gene products suggests that caution should be e xercised when using these: variant cell lines to confirm the role of the Ah R/Arnt-signaling pathway in a given cellular response.