Abstract
Tumor necrosis factor [alpha] (TNF[alpha]) acts as a beneficial mediator in the process of host defence. In recent years major interest has focused on the AU-rich elements (AREs) present in the 3'-untranslated region (3'-UTR) of TNF[alpha] mRNA as this region plays a pivotal role in post-transcriptional control of TNF[alpha] production. Certain stimuli, such as lipopolysaccharides, a component of the Gram-negative bacterial cell wall, have the ability to relinquish the translational suppression of TNF[alpha] mRNA imposed by these AREs in macrophages, thereby enabling the efficient production of the TNF[alpha]. In this study we show that the polymorphism (GAU trinucleotide insertional mutation) present in the regulatory 3'-UTR of TNF[alpha] mRNA of NZW mice results in the hindered binding of RNA-binding proteins, thereby leading to a significantly reduced production of TNF[alpha] protein. We also show that the binding of macrophage proteins to the main ARE is also decreased by another trinucleotide (CAU) insertion in the TNF[alpha] 3'-UTR. One of the proteins affected by the GAU trinucleotide insertional mutation was identified as HuR, a nucleo-cytoplasmic shuttling protein previously shown to play a prominent role in the stability and translatability of mRNA containing AREs. Since binding of this protein most likely modulates the stability, translational efficiency and transport of TNF[alpha] mRNA, these results suggest that mutations in the ARE of TNF[alpha] mRNA decrease the production of TNF[alpha] protein in macrophages by hindering the binding of HuR to the ARE.