The melanoma tumor antigen, melanotransferrin (p97): A 25-year hallmark - From iron metabolism to tumorigenesis

Melanotransferrin (MTf) or melanoma tumor antigen p97 is a transferrin (Tf) homolog that is found predominantly bound to the cell membrane via a glycosyl phosphatidylinositol anchor. The molecule is a member of the Tf superfamily and binds iron through a single high-affinity iron(III)-binding site. Since its discovery on the plasma membrane of melanoma cells, the function of MTf has remained intriguing, particularly in relation to its role in cancer cell iron transport. In fact, considering the crucial role of iron in many metabolic pathways, e.g., DNA synthesis, it was important to understand the function of MTf in the transport of this vital nutrient. MTf has also been implicated in diverse physiological processes, such as plasminogen activation, angiogenesis and cell migration. However, recent studies using a knockout mouse and post-transcriptional gene silencing have demonstrated that MTf is not involved in iron metabolism, but plays a vital role in melanoma cell proliferation and tumorigenesis. In this review, we discuss the possible biological functions of MTf, particularly in relation to cancer.