To elucidate the possible function of LY6D in the senescence program, an expression vector containing N-terminal HA-tagged LY6D was constructed and introduced into human osteosarcoma U2OS cells (Fig. 1, A; Δ1-20 LY6D mutant lacking N-terminal 20 amino acids was also used, as discussed later). This evidence concerns the gene LY6D and osteosarcoma.