Methylthioadenosine phosphorylase

Phosphorylase which plays an essential role in the polyamine metabolism and thus for the utilization of adenine and methionine. Methylthioadenosine phosphorylase (MTAP) catalyses the phosphorylation of methyl adenosine (MTA), which acts as a potent inhibitor of methyl transferases. MTAP is expressed in most cells and tissues and is considered a "household enzyme" in its function. The encoding gene is located in close proximity to numerous tumour suppressor genes (p15, p16, p14ARF) on chromosome 9p21.

In malignant melanomas a loss of MTAP expression has been demonstrated in vitro as well as in vivo, which in most cases is caused by a strongly decreased expression of promoter methylation (both on mRNA level and protein level). In malignant melanoma this deficiency has an influence on the invasive potential of the tumour cell. In addition, a downregulation of MTAP seems to lead to interferon resistance, so that such patients may not benefit from interferon therapy.