Abstract 1045: Src-mediated Tyr20 phosphorylation of transferrin receptor 1 (TfR1) promotes its anti-apoptotic effect: A novel function of TfR1 in cancer cells

Abstract

Abstract Transferrin receptor 1 (TfR1) is highly expressed in cancer cells and its overexpression is widely thought to be a result of the increased requirement of iron uptake for cell growth. In the present study, we have found that two ligands of TfR1, gambogic acid (GA) but not holo-transferrin (Tf) induced apoptosis in breast cancer MDA-MB-231 cells and activated the JNK and p38 signal pathways. Furthermore, PP2, an inhibitor of steroid receptor coactivator (Src), a tyrosine kinase, greatly promoted GA-mediated apoptosis. These results indicate that Src is involved in GA-mediated TfR1-dependent apoptotic pathway. Following immunoprecipitation of TfR1 and immunoblotting of Src or verse versa, TfR1 was found to be associated with Src. This association was further illustrated by their co-localization with confocal fluorescence microscope and shown resulting in constitutive tyrosine phosphorylations of the TfR1. A type II membrane receptor, TfR1 contains a short intracellular N-terminal domain with 61 amino acids. 20YTRF23, the only Tyr(Y) site within the cytoplasmic domain, has been shown as the motif essential for TfR1-Tf complex internalization. To elucidate which Tyr is phosphorylated, we used a Chinese hamster ovary (CHO)-TRVb cell line that does not express TfR1. Point mutation Y20L showed that Tyr20 of TfR1 was the phosphorylation site by Src. Further treatments of wild type and point mutant revealed that it is the Tyr20 phosphorylation that enhanced the anti-apoptotic effects of TfR1 against GA. Our results indicate that in addition to the known function of iron transport, TfR1 has a novel function of regulating cell survival and antiapoptosis through its Tyr20 phosphorylation by Src. This new function is particularly significant and relevant to cancer cells since high expression of TfR1 not only fulfills the requirement of more iron as a co-factor in DNA synthesis but also enhances their survival. This work is supported by R21 CA132684. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1045. doi:10.1158/1538-7445.AM2011-1045