RESUMO
The zinc finger X-linked duplicated A (ZXDA) and ZXDC proteins are both required for robust transcription of major histocompatibility complex class II (MHC II) genes. Aside from the full length ZXDC mRNA transcript, at least one additional mRNA is produced by the ZXDC gene, in which transcription initiates within the first exon and terminates within the seventh intron. The protein product produced from this transcript, which we have named ZXDC2, is truncated on both the N- and C-terminus. We demonstrate here that ZXDC2 functions to repress MHC II transcription induced in HeLa cells treated with IFN-gamma. We further demonstrate that ZXDC2 interacts with both ZXDA and ZXDC, suggesting a mechanism by which ZXDC2 may inhibit MHC II transcription. These studies not only provide additional support for the role of ZXD proteins in regulating MHC II transcription, but also demonstrate a unique mechanism for the synthesis of a mRNA isoform.
Assuntos
Genes MHC da Classe II/genética , Proteínas Mutantes/fisiologia , Transativadores/fisiologia , Transcrição Gênica , Células Cultivadas , Regulação para Baixo , Células HeLa , Humanos , Proteínas Mutantes/química , Proteínas Mutantes/genética , Proteínas Mutantes/metabolismo , Regiões Promotoras Genéticas , Ligação Proteica , Isoformas de Proteínas/química , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismo , Isoformas de Proteínas/fisiologia , Estrutura Terciária de Proteína/genética , Estrutura Terciária de Proteína/fisiologia , Proteínas Repressoras/fisiologia , Transativadores/química , Transativadores/genética , Transativadores/metabolismo , Fatores de Transcrição , Sítio de Iniciação de Transcrição , TransfecçãoRESUMO
The transcription of major histocompatibility complex class II (MHC II) genes depends critically upon the activity of the class II trans-activator (CIITA) protein. We previously described a novel CIITA-binding protein named zinc finger X-linked duplicated family member C (ZXDC) that contributes to the activity of CIITA and the transcription of MHC II genes. Here, we examined the contribution of a closely related family member of ZXDC, the ZXDA protein, to MHC II gene transcription. ZXDA has a domain organization similar to ZXDC, containing ten zinc fingers and a transcriptional activation domain. Knockdown and overexpression of ZXDA demonstrated its importance in the transcriptional activation of MHC II genes. We found that ZXDA and ZXDC can self-associate, and also form a complex with each other. The regions of the two proteins that contain zinc fingers mediate these interactions. Importantly, we found that the ZXDA-ZXDC complex interacts with CIITA, rather than either protein alone. Given our additional finding that ZXDC is present at MHC II promoters in HeLa cells, prior to and after treatment with IFN-gamma, it appears that ZXDA and ZXDC form an important regulatory complex for MHC II gene transcription.
Assuntos
Antígenos de Histocompatibilidade Classe II/genética , Proteínas Nucleares/metabolismo , Transativadores/metabolismo , Dedos de Zinco , Células Cultivadas , Regulação da Expressão Gênica/efeitos dos fármacos , Inativação Gênica , Antígenos HLA-DR/genética , Cadeias alfa de HLA-DR , Antígenos de Histocompatibilidade Classe II/metabolismo , Humanos , Interferon gama/farmacologia , Família Multigênica , Complexos Multiproteicos , Proteínas Nucleares/genética , Regiões Promotoras Genéticas , Estrutura Terciária de Proteína , Transativadores/genética , Fatores de Transcrição , Transcrição GênicaRESUMO
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.
