The role of the Bcl-2 BH3 domain in thymocyte apoptosis (P4416)

Abstract

Abstract Over-expression of Bcl-2 has been shown to protect thymocytes from apoptosis by many stimuli except strong T cell receptor signals during negative selection. This might be due to Bcl-2 taking on a pro-apoptotic function during negative selection mediated through its BH3 domain, which is exposed upon interaction with the nuclear orphan receptor Nur77. To test this, we generated a T cell-specific transgenic mouse over-expressing Bcl-2 with a mutated BH3 domain. Consistent with our hypothesis, we observed that thymocytes expressing the Bcl-2 BH3 transgene were better protected from apoptosis by TCR stimuli in vitro than those expressing a wild-type transgene. To evaluate TCR-induced apoptosis in vivo, the Bcl-2 BH3 mutant transgenic mice were crossed to F5 and HY TCR transgenic mice. Vibratome cut thymic slices were treated acutely with F5 and HY TCR-specific peptides, circumventing the peripheral cytotoxic effects of in vivo peptide injection. Bcl-2 BH3 mutant transgenic thymocytes were almost completely rescued from peptide-induced apoptosis, but surprisingly, thymocytes expressing the wild-type Bcl-2 transgene were equivalently protected. Thus our results indicate that Bcl-2 has some pro-apoptotic function, but in contrast to previously published data in TCR-transgenic models, we conclude that Bcl-2 over-expression affords substantial protection from apoptosis accompanying negative selection.