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 biosynthesis of metallothioneins (MT), a group of low molecular weight, cysteine-rich metal-binding proteins, believed to play a role in zinc homeostasis. In humans, they are encoded by a family of genes, located at 16q13 containing 10 functional and 7 non-functional MT isoforms. In this work we analyzed the spectrum of different isoforms in human peripheral blood lymphocytes. It was demonstrated by RT-PCR that the MT-2a, MT-1a, MT-1e, MT-1f, MT-1g, MT-1h and MT-1x genes are expressed in these cells and that these isoforms are further upregulated by zinc, as examined by quantitative RT-PCR. Surprisingly, RT-PCR also showed the presence, even in unstimulated cells, of MT-3 transcripts, which are considered as brain-specific isoforms. In an effort to determine whether MTmRNA abundance is translated into MT protein, MT isolated from zinc-treated lymphocytes by gel chromatography was resolved into 7 metal-binding fractions by using RP-HPLC. Automatic Edman-degradation of the different fractions revealed the presence of MT-2a, MT-1a, MT-1e, MT-1f, MT-1g, MT-1h, MT-1x and MT-1k, an isoform which until now was only identified at the level of protein in human liver and kidney tissue.