Tristetraprolin expression by keratinocytes protects against skin carcinogenesis.

Cancer is caused primarily by genomic alterations resulting in deregulation of gene regulatory circuits in key growth, apoptosis, or DNA repair pathways. Multiple genes associated with the initiation and development of tumors are also regulated at the level of mRNA decay, through the recruitment of RNA-binding proteins to AU-rich elements (AREs) located in their 3'-untranslated regions. One of these ARE-binding proteins, tristetraprolin (TTP; encoded by Zfp36), is consistently dysregulated in many human malignancies. Herein, using regulated overexpression or conditional ablation in the context of cutaneous chemical carcinogenesis, we show that TTP represents a critical regulator of skin tumorigenesis. We provide evidence that TTP controlled both tumor-associated inflammation and key oncogenic pathways in neoplastic epidermal cells. We identify Areg as a direct target of TTP in keratinocytes and show that EGFR signaling potentially contributed to exacerbated tumor formation. Finally, single-cell RNA-Seq analysis indicated that ZFP36 was downregulated in human malignant keratinocytes. We conclude that TTP expression by epidermal cells played a major role in the control of skin tumorigenesis.

The RNA-binding protein tristetraprolin regulates RALDH2 expression by intestinal dendritic cells and controls local Treg homeostasis.

AU-rich element (ARE)-mediated mRNA decay represents a key mechanism to avoid excessive production of inflammatory cytokines. Tristetraprolin (TTP, encoded by Zfp36) is a major ARE-binding protein, since Zfp36-/- mice develop a complex multiorgan inflammatory syndrome that shares many features with spondyloarthritis. The role of TTP in intestinal homeostasis is not known. Herein, we show that Zfp36-/- mice do not develop any histological signs of gut pathology. However, they display a clear increase in intestinal inflammatory markers and discrete alterations in microbiota composition. Importantly, oral antibiotic treatment reduced both local and systemic joint and skin inflammation. We further show that absence of overt intestinal pathology is associated with local expansion of regulatory T cells. We demonstrate that this is related to increased vitamin A metabolism by gut dendritic cells, and identify RALDH2 as a direct target of TTP. In conclusion, these data bring insights into the interplay between microbiota-dependent gut and systemic inflammation during immune-mediated disorders, such as spondyloarthritis.

ARE-mediated decay controls gene expression and cellular metabolism upon oxygen variations.

Hypoxia triggers profound modifications of cellular transcriptional programs. Upon reoxygenation, cells return to a normoxic gene expression pattern and mRNA produced during the hypoxic phase are degraded. TIS11 proteins control deadenylation and decay of transcripts containing AU-rich elements (AREs). We observed that the level of dTIS11 is decreased in hypoxic S2 Drosophila cells and returns to normal level upon reoxygenation. Bioinformatic analyses using the ARE-assessing algorithm AREScore show that the hypoxic S2 transcriptome is enriched in ARE-containing transcripts and that this trend is conserved in human myeloid cells. Moreover, an efficient down-regulation of Drosophila ARE-containing transcripts during hypoxia/normoxia transition requires dtis11 expression. Several of these genes encode proteins with metabolic functions. Here, we show that ImpL3 coding for Lactate Dehydrogenase in Drosophila, is regulated by ARE-mediated decay (AMD) with dTIS11 contributing to ImpL3 rapid down-regulation upon return to normal oxygen levels after hypoxia. More generally, we observed that dtis11 expression contributes to cell metabolic and proliferative recovery upon reoxygenation. Altogether, our data demonstrate that AMD plays an important role in the control of gene expression upon variation in oxygen concentration and contributes to optimal metabolic adaptation to oxygen variations.