Myeloid ZFP36L1 does not regulate inflammation or host defense in mouse models of acute bacterial infection.

Zinc finger protein 36, C3H type-like 1 (ZFP36L1) is one of several Zinc Finger Protein 36 (Zfp36) family members, which bind AU rich elements within 3' untranslated regions (UTRs) to negatively regulate the post-transcriptional expression of targeted mRNAs. The prototypical member of the family, Tristetraprolin (TTP or ZFP36), has been well-studied in the context of inflammation and plays an important role in repressing pro-inflammatory transcripts such as TNF-α. Much less is known about the other family members, and none have been studied in the context of infection. Using macrophage cell lines and primary alveolar macrophages we demonstrated that, like ZFP36, ZFP36L1 is prominently induced by infection. To test our hypothesis that macrophage production of ZFP36L1 is necessary for regulation of the inflammatory response of the lung during pneumonia, we generated mice with a myeloid-specific deficiency of ZFP36L1. Surprisingly, we found that myeloid deficiency of ZFP36L1 did not result in alteration of lung cytokine production after infection, altered clearance of bacteria, or increased inflammatory lung injury. Although alveolar macrophages are critical components of the innate defense against respiratory pathogens, we concluded that myeloid ZFP36L1 is not essential for appropriate responses to bacteria in the lungs. Based on studies conducted with myeloid-deficient ZFP36 mice, our data indicate that, of the Zfp36 family, ZFP36 is the predominant negative regulator of cytokine expression in macrophages. In conclusion, these results imply that myeloid ZFP36 may fully compensate for loss of ZFP36L1 or that Zfp36l1-dependent mRNA expression does not play an integral role in the host defense against bacterial pneumonia.

Zcchc11 uridylates mature miRNAs to enhance neonatal IGF-1 expression, growth, and survival.

The Zcchc11 enzyme is implicated in microRNA (miRNA) regulation. It can uridylate let-7 precursors to decrease quantities of the mature miRNA in embryonic stem cell lines, suggested to mediate stem cell maintenance. It can uridylate mature miR-26 to relieve silencing activity without impacting miRNA content in cancer cell lines, suggested to mediate cytokine and growth factor expression. Broader roles of Zcchc11 in shaping or remodeling the miRNome or in directing biological or physiological processes remain entirely speculative. We generated Zcchc11-deficient mice to address these knowledge gaps. Zcchc11 deficiency had no impact on embryogenesis or fetal development, but it significantly decreased survival and growth immediately following birth, indicating a role for this enzyme in early postnatal fitness. Deep sequencing of small RNAs from neonatal livers revealed roles of this enzyme in miRNA sequence diversity. Zcchc11 deficiency diminished the lengths and terminal uridine frequencies for diverse mature miRNAs, but it had no influence on the quantities of any miRNAs. The expression of IGF-1, a liver-derived protein essential to early growth and survival, was enhanced by Zcchc11 expression in vitro, and miRNA silencing of IGF-1 was alleviated by uridylation events observed to be Zcchc11-dependent in the neonatal liver. In neonatal mice, Zcchc11 deficiency significantly decreased IGF-1 mRNA in the liver and IGF-1 protein in the blood. We conclude that the Zcchc11-mediated terminal uridylation of mature miRNAs is pervasive and physiologically significant, especially important in the neonatal period for fostering IGF-1 expression and enhancing postnatal growth and survival. We propose that the miRNA 3' terminus is a regulatory node upon which multiple enzymes converge to direct silencing activity and tune gene expression.

Terminal uridyltransferase enzyme Zcchc11 promotes cell proliferation independent of its uridyltransferase activity.

Zcchc11 is a uridyltransferase protein with enzymatic activity directed against diverse RNA species. On the basis of its known uridylation targets, we hypothesized that Zcchc11 might regulate cell proliferation. Confirming this, loss-of-function and complementary gain-of-function experiments consistently revealed that Zcchc11 promotes the transition from G(1) to S phase of the cell cycle. This activity takes place through both Rb-dependent and Rb-independent mechanisms by promoting the expression of multiple G(1)-associated proteins, including cyclins D(1) and A and CDK4. Surprisingly, a Zcchc11 construct with point mutations inactivating the uridyltransferase domain enhanced cell proliferation as effectively as wild-type Zcchc11. Furthermore, truncated mutant constructs revealed that the cell cycle effects of Zcchc11 were driven by the N-terminal region of the protein that lacks the RNA-binding domains and uridyltransferase activity of the full protein. Therefore, the N-terminal portion of Zcchc11, which lacks nucleotidyltransferase capabilities, is biologically active and mediates a previously unrecognized role for Zcchc11 in facilitating cell proliferation.