Identification of Putative Trafficking Motifs in System x(c)(-)

Sara Lang, Hope College
Anne Georges, Hope College
Leah A. Chase, Hope College

(Meeting Abstract Supplement) 1017.9

Abstract

System x_c^–is a heterodimeric plasma membrane transporter, comprised of xCT and CD98, that facilitates the stoichiometric exchange of extracellular cystine for intracellular glutamate. System x_c^– serves to protect the cell from oxidative stress, and brief exposure of cells to oxidative agents leads to an increase in trafficking of xCT to the plasma membrane. However, little is known about the mechanisms which govern the constitutive and regulated trafficking of xCT. In the present study, we sought to identify the role of the C-terminus of the light chain, xCT, in the observed constitutive trafficking behavior of system x_c^–. To do this, we created two constructs, myc-xCT and HA-CD98, and used site-direct mutagenesis to disrupt putative trafficking motifs within the C-terminus of xCT. When these mutants were expressed in COS-7 cells, we found that the C-terminus of xCT is critical for the proper trafficking of xCT, and further identified a specific motif within the C-terminus that, when disrupted, alters basal surface expression of xCT. We hypothesize that the motif is a tyrosine-based, clathrin-dependent endocytic motif that contributes to the constitutive internalization of xCT. The key amino acid of the motif, a tyrosine, is conserved in 6 of 7 members of the SLC7 family and is hypothetically located in a position accessible to intracellular proteins. This research was supported by NSF-RUI #0848564.