In mammals, β1 integrin adhesion receptors generate signals that mediate cell spreading, migration, proliferation, and survival. CD98, a heterodimeric transmembrane protein, physically associates with certain integrin β subunit cytoplasmic domains (tails) via its heavy chain, CD98hc (SLC3A2), and loss of CD98hc impairs integrin signaling. Here we have used the lack of CD98hc interaction with the Drosophila integrin βPS tail for a homology scanning analysis that implicated the C-terminal 8 residues of β3 (Thr755-Thr802) in CD98hc binding. We then identified point mutations in the β3 C terminus (T755K and T758M) that abolish CD98hc association and a double mutation in the corresponding residues in the βPS tail (K839T,M842T), which resulted in gain of CD98hc interaction. Furthermore, the loss of function β3(T755K) mutation or the gain of function β3/βPS(K839T,M842T) led to a loss or gain of integrin-mediated cell spreading, respectively. Thus, we have identified critical integrin residues required for CD98hc interaction and in doing so have shown that CD98c interaction with the integrin β tail is required for its ability to mediate integrin signaling. These studies also provide new insights into how CD98hc may cooperate with other cytoplasmic domain binding proteins to modulate integrin functions and into the evolution of integrin signaling.
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