Negative regulation of CD8 expression via Cd8 enhancer–mediated recruitment of the zinc finger protein MAZR

Abstract

Coreceptor expression is tightly regulated during thymocyte development. Deletion of specific Cd8 enhancers leads to variegated expression of CD8alphabeta heterodimers in double-positive thymocytes. Here we show CD8 variegation is correlated with an epigenetic 'off' state, linking Cd8 enhancer function with chromatin remodeling of the adjacent genes Cd8a and Cd8b1 (Cd8). The zinc finger protein MAZR bound the Cd8 enhancer and interacted with the nuclear receptor corepressor N-CoR complex in double-negative thymocytes. MAZR was downregulated in double-positive and CD8 single-positive thymocytes. 'Enforced' expression of MAZR led to impaired Cd8 activation and variegated CD8 expression. Our results demonstrate epigenetic control of the Cd8 loci and identify MAZR as an important regulator of Cd8 expression.

The Epigenetic Landscape of Lineage Choice: Lessons From the Heritability of Cd4 and Cd8 Expression

“…Further, variegated CD8 expression on E8 I/II deficient DP cells (Ellmeier et al, 2002) was partially relieved by MAZR deletion (Sakaguchi et al, 2010), suggesting that E8 I/II antagonizes MAZR-mediated Cd8 silencing during the DN to DP transition. This effect may be mediated through the direct binding of MAZR as has been observed at multiple elements in the Cd8 locus (Bilic et al, 2006). Analysis of CD8 expression in mice with combined deletion of MAZR and various Cd8 locus elements could reveal elements through which MAZR functions to repress Cd8.…”

“…Analysis of CD8 expression in mice with combined deletion of MAZR and various Cd8 locus elements could reveal elements through which MAZR functions to repress Cd8. Interestingly, deletion of the maintenance DNA methyltransferase Dnmt1 on an E8 I/II deficient background also partially rescued variegated CD8 expression (Bilic et al, 2006). While it is tempting to speculate that MAZR contributes to Cd8 repression through recruitment or maintenance of DNA methylation, no clear link has been established between MAZR and initiating or maintenance DNA methyltransferases.…”

“…MAZR is highly expressed in DN cells, and is downregulated at the DP stage as CD8 expression is activated (Bilic et al, 2006). Forced expression of MAZR results in variegated CD8 expression at the DP stage (Bilic et al, 2006).…”

“…MAZR is highly expressed in DN cells, and is downregulated at the DP stage as CD8 expression is activated (Bilic et al, 2006). Forced expression of MAZR results in variegated CD8 expression at the DP stage (Bilic et al, 2006). Further, variegated CD8 expression on E8 I/II deficient DP cells (Ellmeier et al, 2002) was partially relieved by MAZR deletion (Sakaguchi et al, 2010), suggesting that E8 I/II antagonizes MAZR-mediated Cd8 silencing during the DN to DP transition.…”

“…Indeed the importance of Runx and MAZR proteins to lineage choice was first identified through examination of the Cd4 and Cd8 loci, respectively (Bilic et al, 2006;Taniuchi et al, 2002a). The fact that the loci are transiently co-expressed in DP cells and stably expressed or repressed in helper and cytotoxic cells, also makes them an excellent model to study transcriptional regulation and the mechanisms that control temporary versus permanent gene expression states.…”