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Abstract
CD9, a member of the tetraspanin superfamily, is expressed in several cell lines and is associated with cellular activities such as migration, proliferation and metastasis in cancer cell lines. Antibody ligation of CD9 has been shown to induce cell death in mouse embryonic stem cells and specific cancer cell lines. Here we have shown CD9 antibody induces cell death in mouse R1 and D3 cells through the release of cytochrome C and cleavage of caspase-3, which are hallmarks of apoptosis. Subsequently, phosphorylation of p38 MAPK, SAPK/JNK and ERK 1/2 occurs as a result of treatment with anti-CD9 antibody (KMC8). Furthermore, we have shown HB-EGF and p38 inhibitor perturbs p38 MAPK phosphorylation, promoting cell survival. Additionally, the ligand for DBA (GalNAc) is present on mouse ES cells but noticeably declines during differentiation. We have shown that DBA ligand can be used to identify cells that are positive for the pluripotent state and early differentiation events. These results indicate that normal function of CD9 suppresses apoptosis and DBA ligand can be used to discriminate pluripotent cells from differentiated cells in a mixed population.