The Physiological and Pathophysiological Roles of Melanotransferrin

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Melanotransferrin (MTf) is a membrane bound molecule that was originally identified in the malignant melanoma skin cancer and other tumours. Interestingly, MTf has many similarities to the serum iron-binding protein, transferrin, and initially MTf was thought to play a role in iron uptake by these cells. However, a series of studies by the applicant demonstrated that MTf did not play a major role in iron uptake by melanoma cells (Richardson et al. 1990, 1991a,b). In fact, most iron taken up by these cells was via the binding of transferrin to the transferrin receptor. More recently, under the current NHMRC grant, we have been able to confirm and signficantly extend our previous studies to convincingly show that MTf is not involved in iron uptake by melanoma cells where it is expressed at very high levels (Richardson 2000 Eur. J. Biochem. 267 (in press). In addition, we showed that the expression of MTf in 50 human tissues was very different to transferrin and the transferrin receptor (TfR) that are well known to be involved in iron transport. For example, the TfR is expressed at high levels in tissues that require large amounts of iron eg. the placenta and bone marrow. In contrast, MTf was not expressed at high levels in these tissues, but was found in large amounts in unexpected locations such as the salivary gland. Furthermore, the expression of MTf was widespread through a variety of tissues, and in contrast to expectations, was found at higher levels in normal rather than fetal tissues. It is also intesting that MTf is found in the blood and brain of Alzheimer's disease patients. Our results suggest that MTf may play other unexpected roles apart from iron uptake. The present proposal will assess the roles of MTf in cellular functioning. This information will be very important in understanding the function of MTf in cancer cells, Alzheimer's disease and also in other tissues (eg. the salivary gland) where it is expressed at very high levels.