5A). Following resting, TCR stimulation can induce phosphorylation of Akt at S473 and Foxo1a at S256 in WT T cells. Such phosphorylation was decreased in TSC1KO thymocytes and peripheral T cells (Fig. 5B).

However, TCR-induced Akt phophorylation at T308 was similar between WT and TSC1KO T cells (data not shown). Thus, while mTORC1 signaling is enhanced, mTORC2 signaling and Akt activities are impaired in TSC1-deficient T cells. Akt is activated by phosphorylation at T308 and S473 by PI3K/PDK1 and mTORC2 respectively 29, 31, 32. To determine if the decreased Akt activity observed in TSC1KO T cells may contribute to the increased death subsequent to TCR stimulation, check details we transduced these cells with retrovirus expressing either the constitutively active (ca) form of Akt (Akt-DD) or Akt-S374D mutant. Death of the GFP+ Akt-DD-expressing TSC1KO T cells was significantly reduced in comparison to the MigR1-GFP+ vector control cells in both CD4+ and CD8+ T-cell subsets after TCR stimulation (Fig. 5C). However, Akt-S473D manifested minimal effects in preventing death of TSC1KO T cells. Thus, although enhanced Akt activity can promote TSC1KO T-cell survival,

relief of the requirement of mTORC2-mediated Akt activation is not sufficient to rescue TSC1KO T cells from death, suggesting complex regulation of T-cell survival by Kinase Inhibitor Library purchase TSC1. CD28 co-stimulatory receptor promotes PI3K/Akt activation during T-cell activation. Stimulation of TSC1KO CD4+ T cells through the TCR and CD28 reduced TSC1KO CD4+ T-cell death, correlated with decreased ROS production, and improved mitochondrial integrity as compared with stimulation by TCR

Sodium butyrate alone. However, the protective effect of CD28 was not observed in TSC1KO CD8+ T cells (Fig. 5D). In addition, CD28 co-stimulation was not able to restore Akt phosphorylation at S473 in TSC1KO T cells (Fig. 5E), suggesting that CD28 promotes TSC1KO T-cell survival through an mTORC2-independent mechanism. We further asked whether the increase in ROS production may contribute to the death of TSC1KO T cells. Treatment with N-acetylcysteine (NAC), a ROS scavenger, resulted in decreased death of TSC1KO CD4+ T cells, but not CD8+ T cells, suggesting that increased ROS production contributes to increased death of TSC1KO CD4+ T cells. Inhibition of mTOR activity has been reported to enhance survival and reduce contraction of viral specific CD8+ T cells 10. However, rapamycin treatment could not prevent increased ROS production, restore mitochondrial membrane integrity, or rescue the cells from death. In fact, it made TSC1KO T cells more prone to death (Fig. 5D). Similarly, rapamycin treatment could not restore early activation of TSC1KO T cells, although CD28 co-stimulation can slightly increase CD25 and CD69 expression (Fig. 5F).