Our data show that T-cell development is not dependent on Akt HM phosphorylation. These findings are consistent with our previously proposed model in which mTORC2-dependent Akt HM phosphorylation is required to confer Akt specificity toward a limited subset of Akt substrates []. Our data also suggest that
Akt, when activated via phosphorylation of activation loop, plays a central role for DN–DP transition, most likely by controlling the survival of thymic T cells. Furthermore, our data suggest that phosphorylation of Akt at the activation loop may be sufficient to support TCR/CD3-mediated peripheral T-cell proliferation and survival. Since mTOR is an evolutionarily conserved regulator of cellular growth and metabolism, we investigated if Sin1 deletion may affect the size of resting peripheral T cells or activated T cells and proliferation. GSK-3 assay Sin1 deficiency had little effect on resting T-cell growth and activation induced blast cell growth. Furthermore, Sin1 deficiency did not impair antigen receptor/co-receptor-dependent T-cell proliferation in vitro. These results contrast with those reported Apoptosis inhibitor in mice bearing a T-cell-specific rictor deletion that show a modest defect in activation induced T-cell proliferation [[12, 21]]. It is possible that the differences in the in vitro T-cell stimulation conditions
between our assays may account for the difference in experimental results since we stimulated our T cells in the presence of plate-bound anti-CD3 antibody plus soluble anti-CD28 in the presence of exogenous IL-2. FoxO1 is an mTORC2-dependent Akt substrate that has been shown to play a key role in regulating T-cell development, homeostasis, and
effector cell differentiation [[16, 22]]. FoxO1 is required for proper expression of the genes that encode L-selectin (CD62L), interleukin 7 receptor alpha chain (CD127), and Foxp3 [[15, 16, 22]]. We have previously shown that Sin1 Oxymatrine deficiency results in decreased FoxO1 phosphorylation at the Akt target sites, leading to increased FoxO1 transcriptional activity [[6, 13]]. Consistently, we observed an increased proportion of Foxp3 expressing nTreg cells in the thymus and an increased expression of CD62L expression on naive peripheral CD4+ T cells in Sin1−/− chimeric mice. Surprisingly, Sin1 deficiency did not affect IL-7R expression on resting peripheral T cells. We have previously shown that in developing progenitor B cells, the mTORC2-Akt-FoxO1 signaling negatively regulates IL-7R expression []. IL-7R expression is suppressed in antigen activated T cells. It is possible that the loss of mTORC2 function has no effect on IL-7R expression in resting T cells because these cells normally have a very low level of Akt signaling.