RESUMO
Developing B lymphocytes expressing defective or autoreactive pre-B or B cell receptors (BCRs) are eliminated by programmed cell death, but how the balance between death and survival signals is regulated to prevent immunodeficiency and autoimmunity remains incompletely understood. In this study, we show that absence of the essential ATM (ataxia telangiectasia mutated) substrate Chk2-interacting Zn(2+)-finger protein (ASCIZ; also known as ATMIN/ZNF822), a protein with dual functions in the DNA damage response and as a transcription factor, leads to progressive cell loss from the pre-B stage onwards and severely diminished splenic B cell numbers in mice. This lymphopenia cannot be suppressed by deletion of p53 or complementation with a prearranged BCR, indicating that it is not caused by impaired DNA damage responses or defective V(D)J recombination. Instead, ASCIZ-deficient B cell precursors contain highly reduced levels of DYNLL1 (dynein light chain 1; LC8), a recently identified transcriptional target of ASCIZ, and normal B cell development can be restored by ectopic Dynll1 expression. Remarkably, the B cell lymphopenia in the absence of ASCIZ can also be fully suppressed by deletion of the proapoptotic DYNLL1 target Bim. Our findings demonstrate a key role for ASCIZ in regulating the survival of developing B cells by activating DYNLL1 expression, which may then modulate Bim-dependent apoptosis.
Assuntos
Proteínas Reguladoras de Apoptose/metabolismo , Linfócitos B/fisiologia , Proteínas de Transporte/metabolismo , Dineínas/metabolismo , Proteínas de Membrana/metabolismo , Proteínas Nucleares/metabolismo , Proteínas Proto-Oncogênicas/metabolismo , Animais , Apoptose/genética , Proteínas Reguladoras de Apoptose/genética , Linfócitos B/patologia , Proteína 11 Semelhante a Bcl-2 , Proteínas de Transporte/genética , Dineínas do Citoplasma , Dano ao DNA , Dineínas/genética , Regulação da Expressão Gênica , Linfopenia/genética , Linfopenia/patologia , Proteínas de Membrana/genética , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Proteínas Nucleares/genética , Proteínas Proto-Oncogênicas/genética , Fatores de Transcrição , Recombinação V(D)JRESUMO
The highly conserved DYNLL1 (LC8) protein was originally discovered as a light chain of the dynein motor complex, but is increasingly emerging as a sequence-specific regulator of protein dimerization with hundreds of targets and wide-ranging cellular functions. Despite its important roles, DYNLL1's own regulation remains poorly understood. Here we identify ASCIZ (ATMIN/ZNF822), an essential Zn(2+) finger protein with dual roles in the DNA base damage response and as a developmental transcription factor, as a conserved regulator of Dynll1 gene expression. DYNLL1 levels are reduced by â¼10-fold in the absence of ASCIZ in human, mouse and chicken cells. ASCIZ binds directly to the Dynll1 promoter and regulates its activity in a Zn(2+) finger-dependent manner. DYNLL1 protein in turn interacts with ten binding sites in the ASCIZ transcription activation domain, and high DYNLL1 levels inhibit the transcriptional activity of ASCIZ. In addition, DYNLL1 was also required for DNA damage-induced ASCIZ focus formation. The dual ability of ASCIZ to activate Dynll1 gene expression and to sense free DYNLL1 protein levels enables a simple dynamic feedback loop to adjust DYNLL1 levels to cellular needs. The ASCIZ-DYNLL1 feedback loop represents a novel mechanism for auto-regulation of gene expression, where the gene product directly inhibits the transcriptional activator while bound at its own promoter.
