Restoration of CD44S in non-small cell lung cancer cells enhanced their susceptibility to the macrophage cytotoxicity

CD44 is a cell surface receptor for osteopontin (OPN) and hyaluronate. Transformation of normal tissue to a variety of cancers has been demonstrated to be associated with alterations of CD44 isoform expression. However, few reports have paid attention on differences in CD44S expression between non-small cell lung cancer (NSCLC) and adjacent normal lung tissue. In this study, we demonstrate that CD44S expression is down-regulated in NSCLC tissue when compared with paired normal lung tissue. To investigate the role of CD44S down-regulation in NSCLC cells, we reintroduced the CD44S back into the NSCLC cell line, H322 cells, which originally lack CD44S expression. The cytotoxicity by activated macrophage (RAW264.7 cells stimulated with lipopolysaccharide and interferon-γ) against the H322 cells transfected with the CD44S gene (H322ΔS) is more prominent than that against the H322 control transfectants (H322Δneo). The enhanced susceptibility of H322ΔS cells to the activated macrophage cytotoxicity appears to be mediated by the interaction between CD44S expression on H322ΔS cells and OPN produced by activated macrophages since it is completely blocked by either anti-OPN or anti-CD44 antibody. Moreover, H322ΔS cells are attracted toward OPN produced by activated RAW264.7 cells to a much greater extent than H322Δneo cells. These findings suggest that CD44S down-regulation in NSCLC cells may confer a protective advantage of allowing escape from tumoricidal effector cells including activated macrophages of the host.