Background
Acute lung injury (ALI) is caused by a variety of illnesses, including aspiration pneumonia and sepsis. The CCR4-NOT complex is a large multimeric protein complex that degrades mRNA through poly(A) tail shortening, whereas it also contributes to regulation of transcription and translation. Cnot3 is a scaffold component of the CCR4-NOT complex and is essential for the integrity of the complex; loss of Cnot3 leads to depletion of whole complex. While the significance of cytokine mRNA degradation in limiting inflammation has been established, the roles of CCR4-NOT complex-mediated in ALI remain elusive.
Methods
The effects of Cnot3 haploinsufficiency in the pathology and cytokine expression were analyzed in the mouse lungs of acid aspiration-induced acute lung injury. The decay rate and transcription activity of cytokine mRNAs under Cnot3 heterozygous deletion were analyzed in lipopolysaccharide (LPS) -stimulated mouse embryonic fibroblasts (MEFs).
Results
Tamoxifen-induced heterozygous deletion of Cnot3 in adult mice (Cnot3 Hetz) did not show body weight loss or any apparent abnormality. Under acid aspiration-induced acute lung injury, Cnot3 Hetz mice exhibited increased pulmonary edema, worse lung pathologies and more severe inflammation compared with wild type mice. mRNA expression of pro-inflammatory genes
Il1b
and
Nos2
were significantly upregulated in the lungs of Cnot3 Hetz mice. Consistently, mRNA expression of
Il1b
and
Nos2
was upregulated in LPS-stimulated Cnot3 Hetz MEFs. Mechanistically, while heterozygous depletion of Cnot3 stabilized both
Il1b
and
Nos2
mRNAs, the nascent pre-mRNA level of
Il1b
was upregulated in Cnot3 Hetz MEFs, implicating Cnot3-mediated transcriptional repression of
Il1b
expression in addition to destabilization of
Il1b
and
Nos2
mRNAs. PU.1 (Spi1) was identified as a causative transcription factor to promote
Il1b
expression under Cnot3 haploinsufficient conditions.
Conclusion
CNOT3 plays a protective role in ALI by suppressing expression of pro-inflammatory genes
Il1b
and
Nos2
through both post-transcriptional and transcriptional mechanisms, including mRNA stability control of Spi1.