Differential Expression and Localization of the mRNA Binding Proteins, AU‐Rich Element mRNA Binding Protein (AUF1) and Hu Antigen R (HuR), in Neoplastic Lung Tissue

Modulation of gene expression at the level of mRNA stability has emerged as an important regulatory paradigm. In this context, differential expression of numerous mRNAs in normal versus neoplastic tissues has been described. Altered expression of these genes, at least in part, has been demonstrated to be at the level of mRNA stability. Two ubiquitously expressed mRNA binding proteins have recently been implicated in the stabilization (Hu antigen R/HuR) or destabilization (AU‐rich element mRNA binding protein [AUF1]/heterogeneous nuclear ribonucleoprotein D) of target mRNAs. Further, their functional activity appears to require cytoplasmic localization. In the present study, we demonstrate a strong correlation between increased cytoplasmic expression of both AUF1 and HuR with urethane‐induced neoplasia and with butylated hydroxytoluene–induced compensatory hyperplasia in mouse lung tissue. In addition, when compared with slower growing cells, rapidly growing neoplastic lung epithelial cell lines expressed a consistently higher abundance of both AUF1 and HuR proteins. Moreover, in nontumorigenic cell lines, both AUF1 and HuR protein abundance decreased with confluence and growth arrest. In contrast, in spontaneous transformants, AUF1 and HuR abundance was unaffected by changes in cell density. We suggest that growth‐regulated alterations in AUF1 and HuR abundance may have pleiotropic effects on the expression of a number of highly regulated mRNAs and that this significantly impacts the onset, maintenance, and progression of the neoplastic phenotype. Mol. Carcinog. 28:76–83, 2000. © 2000 Wiley‐Liss, Inc.