Concanamycin A, a Vacuolar Type H⁺-Atpase Inhibitor, Selectively Induces Cell Death in Activated CD8⁺ CTL

Abstract

Concanamycin A (CMA) and concanamycin B (CMB) are specific inhibitors of vacuolar type H⁺-ATPase (V-ATPase). In our previous studies, it was shown that intraperitoneal injection of CMB suppressed the increase in CD8⁺ CTL population without affecting CD4⁺ and B220⁺ populations in mice immunized with allogeneic tumors. To clarify the molecular basis of the selective decrease in the CD8⁺ CTL population by CMB, we have performed a series of in vitro experiments with use of CMA. Cell viability of the CD8⁺ population prepared from the immunized mice was preferentially decreased by CMA treatment for 4-8 h. Moreover, in the CD8⁺ CTL clone, CMA induced a marked DNA fragmentation characteristic of apoptosis. Anti-CD3 or phorbol ester accelerated the CMA-induced reduction in cell viability of the CD8⁺ CTL clone, but not CD4⁺ T cell clones. However, this rapid cell death was not accompanied by DNA fragmentation. Thus, our data suggest that V-ATPase activity is essential for survival of CD8⁺ CTL especially when activated.