T-2 toxin-induced apoptosis in the mouse lymphoid and hematopoietic tissues

Abstract

To clarify the characteristics and mechanisms of T-2 toxin-induced cell death in the lymphoid and hematopoietic tissues, in vivo and in vitro studies were carried out. As a result, T-2 toxin-induced lesions in the thymus, spleen and bone marrow of mice were shown to be brought about by apoptosis of component cells. The sequence of T-2 toxin-induced apoptosis varied among tissues, and apoptosis was occurred earlier in the hematopoietic tissues than in the lymphoid tissues. By RT-PCR method, the expression of c-fos mRNA increased immediately after T-2 toxin-inoculation and remained high levels throughout the observation period. Cycloheximide, a protein synthesis inhibitor, blocked apoptosis in the thymus of T-2 toxin-inoculated mice. As observed in in vivo study, in Con A-stimulated mouse thymocyte cultures, T-2 toxin induced the elevation of c-fos mRNA expression prior to the development of apoptosis. BAPTA/AM and Quin-2/AM, intracellular calcium chelators, and H-7, a PKC inhibitor, blocked the increase in the level of c-fos mRNA expression after T-2 toxin-treatment. These intracellular calcium chelators also inhibited DNA fragmentation after T-2 toxintreatment. These results suggest that T-2 toxin attacks cells with high proliferating activity such as lymphoid and hematopoietic cells, c-fos gene plays an important role in the early phase of T-2 toxin-induced apoptotic cell death probably through sythesis of a certain protein such as heat shock protein, and the elevation of c-fos mRNA expression may require the mobilization of [Ca²⁺]i and partially involve a PKC-dependent pathway. The mobilization of [Ca²⁺]i seemed to activate calcium-dependent enzymes, resulting in internucleosomal DNA fragmentation.