Notch1 confers a resistance to glucocorticoid-induced apoptosis on developing thymocytes by down-regulating SRG3 expression

Abstract

We previously have reported that SRG3 is required for glucocorticoid (GC)-induced apoptosis in the S49.1 thymoma cell line. Activation of Notch1 was shown to induce GC resistance in thymocytes. However, the specific downstream target of Notch1 that confers GC resistance on thymocytes is currently unknown. We found that the expression level of SRG3 was critical in determining GC sensitivity in developing thymocytes. The expression of SRG3 also was down-regulated by the activated form of Notch1 (NotchIC). The promoter activity of the SRG3 gene also was downregulated by NotchIC. Expression of transgenic SRG3 resulted in the restoration of GC sensitivity in thymocytes expressing transgenic Notch1. These results suggest that SRG3 is the downstream target of Notch1 in regulating GC sensitivity of thymocytes.

Notch1 confers thymocytes a resistance to GC-induced apoptosis through Deltex1 by blocking the recruitment of p300 to the SRG3 promoter

“…10 DP thymocytes from double-transgenic mice overexpressing both SRG3 and NotchIC in T cells became more sensitive to GCs than those from NotchIC transgenic mice. 13 Our results suggest that Deltex1 signaling may play an active role in the rescue of DP thymocytes from the GC-induced apoptosis during differentiation of DP thymocytes to SP. To confirm this, flag-tagged Deltex1 was cloned into S003 retroviral vector and transferred into thymocytes from 4-to 7-week-old C57BL/6 mice.…”

“…13 We then investigated what molecules are involved in the SRG3 repression in the downstream pathway of the Notch signaling. To examine the downstream pathways of Notch signaling repressing the SRG3 expression, several NotchIC derivatives ( Figure 1a) were cotransfected into 16610D9 cells.…”

“…E2A-binding sites in the SRG3 promoter are important for the Notch1-mediated repression Next, to identify a critical element(s) in the SRG3 promoter responsible for the Notch responsiveness, base substitutions were introduced into the two E-box elements of E558 and E84 (E558 element corresponds to E480 element reported previously 13 ) (Figure 3a). Various constructs containing mutations in the E-boxes (D2/m558, D2/m84, and D2/dm) were transfected into 16610D9 cells together with a plasmid expressing NotchIC or the vector alone.…”

“…5 The molecular basis for the acquisition of GC resistance during maturation of DP thymocytes into SP cells has been implicated in recent studies. 10,11,13 We have shown that the GC sensitivity is critically dependent on the expression level of SRG3. 14 SRG3 is a mouse homolog of yeast SWI3 and human BAF155, a core component of SWI/SNF chromatin remodeling complex.…”

“…10 Transgenic expression of SRG3 resulted in the restoration of GC sensitivity in thymocytes expressing transgenic Notch1, suggesting that Notch1 confers developing thymocytes resistance to GCs also by regulating the SRG3 expression. 13 However, downstream modulators of Notch1 signaling regulating the GC sensitivity in developing thymocytes remain unknown.…”