Metallothionein isoform gene expression in zinc-treated human peripheral blood lymphocytes

Zinc plays an important role in the maintenance of the immune system. While the mechanisms of zinc ions interaction with immune cells are still poorly understood, a striking concurrent effect of zinc is the induction of the b iosynthesis of metallothioneins (MT), a group of low molecular weight, cyst eine-rich metal-binding proteins, believed to play a role in zinc homeostas is. In humans, they are encoded by a family of genes, located at 16q13 cont aining 10 functional and 7 non-functional MT isoforms. In this work we anal yzed the spectrum of different isoforms in human peripheral blood lymphocyt es. It was demonstrated by RT-PCR that the MT-2a, MT-la, MT-1e, MT-if, MT-1 g, MT-1h and MT-1x genes are expressed in these cells and that these isofo rms are further upregulated by zinc, as examined by quantitative RT-PCR. Su rprisingly, RT-PCR also showed the presence, even in unstimulated cells, of MT-3 transcripts, which are considered as brain-specific isoforms. In an e ffort to determine whether MT mRNA abundance is translated into MT protein, MT isolated from zinc-treated lymphocytes by gel chromatography was resolv ed into 7 metal-binding fractions by using RP-HPLC. Automatic Edman-degrada tion of the different fractions revealed the presence of MT-2a, MT-la, MT-l e, MT-if, MT-1g, MT-1h, MT-lx and MT-lk, an isoform which until now was onl y identified at the level of protein in human liver and kidney tissue.