ZXDC, a novel zinc finger protein that binds CIITA and activates MHC gene transcription

Abstract

The class II trans-activator (CIITA) is recognized as the master regulator of major histocompatibility complex (MHC) class II gene transcription and contributes to the transcription of MHC class I genes. To better understand the function of CIITA, we performed yeast two-hybrid with the C-terminal 807 amino acids of CIITA, and cloned a novel human cDNA named zinc finger, X-linked, duplicated family member C (ZXDC). The 858 amino acid ZXDC protein contains 10 zinc fingers and a transcriptional activation domain, and was found to interact with the region of CIITA containing leucine-rich repeats. Over-expression of ZXDC in human cell lines resulted in super-activation of MHC class I and class II promoters by CIITA. Conversely, silencing of ZXDC expression reduced the ability of CIITA to activate transcription of MHC class II genes. Given the specific interaction between the ZXDC and CIITA proteins, as well as the effect of ZXDC on MHC gene transcription, it appears that ZXDC is an important regulator of both MHC class I and class II transcription.

The Zinc Finger Proteins ZXDA and ZXDC Form a Complex that Binds CIITA and Regulates MHC II Gene Transcription

“…There was also modest identity (∼50%) just C-terminal of the zinc fingers, a region that we functionally defined in ZXDC as a transcriptional activation domain. 24 Significantly, the ZXDA/B proteins lack approximately 60 amino acid residues on their C termini that are present in ZXDC; this is the region of ZXDC that we defined previously as important for ZXDC-CIITA association, though the zinc finger region of ZXDC also contributed significantly. 24 Interestingly, although ZXDC has ten exons, both ZXDA and ZXDB are single exon genes, suggesting that they may have originated from retrotransposition of ZXDC mRNA.…”

“…24 Significantly, the ZXDA/B proteins lack approximately 60 amino acid residues on their C termini that are present in ZXDC; this is the region of ZXDC that we defined previously as important for ZXDC-CIITA association, though the zinc finger region of ZXDC also contributed significantly. 24 Interestingly, although ZXDC has ten exons, both ZXDA and ZXDB are single exon genes, suggesting that they may have originated from retrotransposition of ZXDC mRNA. Nucleotide sequence comparisons across species (employing BLAT 30 ) revealed that while mouse and chimpanzee have ZXDA, ZXDB and ZXDC genes, chicken, Xenopus and zebrafish have orthologues to only the ZXDC gene.…”

“…24 A BLAT search of the human genome with the nucleotide sequence of the ZXDC gene 30 identified two highly related genes known as ZXDA and ZXDB, that to date have no known function. ZXDA and ZXDB share 98.7% nucleotide identity over their coding regions, with 97% amino acid identity.…”

“…Through different approaches, we were able to demonstrate a convincing role for the ZXDC protein in the activation of MHC II gene transcription by CIITA: over-expression of ZXDC resulted in super-activation, whereas silencing of ZXDC expression reduced the ability of CIITA to activate transcription. 24 We report here that not only is ZXDC involved in the function of CIITA, but that a ZXDC-family member known as ZXDA also plays a role in regulating MHC II transcription. We found that silencing expression of either ZXDA or ZXDC produced a significant decrease in the induction of MHC II gene transcription by IFN-γ, without altering the expression of CIITA.…”

“…23 We recently identified an additional CIITA-binding protein known as zinc finger X-linked duplicated family member C (ZXDC), which we isolated by yeast two-hybrid screen with the C-terminal region of the CIITA protein. 24 ZXDC contains ten zinc fingers and a relatively potent transcriptional activation domain. ZXDC interacts with the region of CIITA that contains leucine-rich repeats.…”