ZFP36L1 Regulates Fgf21 mRNA Turnover and Modulates Alcoholic Hepatic Steatosis and Inflammation in Mice

Silencing of RNA binding protein, ZFP36L1, promotes epithelial-mesenchymal transition in liver cancer cells by regulating transcription factor ZEB2

RNA binding proteins (RBPs) of the zinc finger protein 36 family including zinc finger protein 36 like 1 (ZFP36L1) are implicated in cancer, however, the underlying molecular mechanisms have remained unclear. These proteins function by regulating post-transcriptional gene expression upon binding to the AU-rich elements (ARE's) within the 3'untranslated regions (3'UTRs) of specific mRNAs and increasing their mRNA turnover. Here, we tested the role of ZFP36L1 in hepatocellular carcinoma (HCC) cell lines. ZFP36L1 was under-expressed among the three RBPs in a majority of the HCC cell lines. Silencing of ZFP36L1 in two of the seven HCC cell lines resulted in epithelial-mesenchymal transition (EMT) like morphological changes, which were characterized by the transition of epithelial morphology to elongated mesenchymal morphology and increased migration and invasion potential. Conversely, overexpression of ZFP36L1 abolished these changes. RNA-seq analysis of ZFP36L1-depleted HCC cells revealed a significant upregulation of an EMT-inducing transcription factor, ZEB2 (zinc-finger E-box-binding homeobox 2), and enrichment of pathways associated with mesenchymal cell development and differentiation. ZEB2 mRNA contains AREs within its 3'UTR and its stability was increased following ZFP36L1 knockdown. Conversely, ZEB2 was significantly downregulated following ZFP36L1 overexpression and ZEB2 3'UTR was regulated by ZFP36L1 in luciferase reporter assays. These data identify ZEB2 mRNA as a ZFP36L1 target in HCC cells and demonstrate that ZFP36L1 regulates EMT possibly through direct regulation of ZEB2 mRNA. In summary, our results demonstrate that ZFP36L1 suppresses EMT inliver cancer cells by down-regulating the expression of EMT-inducing transcription factor, ZEB2. These data suggest an important role of ZFP36L1 in the development, progression, and metastasis of hepatocellular cancer.

Beta-hydroxybutyrate dampens adipose progenitors' profibrotic activation through canonical Tgfβ signaling and non-canonical ZFP36-dependent mechanisms

BACKGROUND/PURPOSE

Adipose tissue contains progenitor cells that contribute to beneficial tissue expansion when needed by de novo adipocyte formation (classical white or beige fat cells with thermogenic potential). However, in chronic obesity, they can exhibit an activated pro-fibrotic, extracellular matrix (ECM)-depositing phenotype that highly aggravates obesity-related adipose tissue dysfunction.

METHODS

Given that progenitors' fibrotic activation and fat cell browning appear to be antagonistic cell fates, we have examined the anti-fibrotic potential of pro-browning agents in an obesogenic condition.

RESULTS

In obese mice fed a high fat diet, thermoneutral housing, which induces brown fat cell dormancy, increases the expression of ECM gene programs compared to conventionally raised animals, indicating aggravation of obesity-related tissue fibrosis at thermoneutrality. In a model of primary cultured murine adipose progenitors, we found that exposure to β-hydroxybutyrate selectively reduced Tgfβ-dependent profibrotic responses of ECM genes like Ctgf, Loxl2 and Fn1. This effect is observed in both subcutaneous and visceral-derived adipose progenitors, as well as in 3T3-L1 fibroblasts. In 30 patients with obesity eligible for bariatric surgery, those with higher circulating β-hydroxybutyrate levels have lower subcutaneous adipose tissue fibrotic scores. Mechanistically, β-hydroxybutyrate limits Tgfβ-dependent collagen accumulation and reduces Smad2-3 protein expression and phosphorylation in visceral progenitors. Moreover, β-hydroxybutyrate induces the expression of the ZFP36 gene, encoding a post-transcriptional regulator that promotes the degradation of mRNA by binding to AU-rich sites within 3'UTRs. Importantly, complete ZFP36 deficiency in a mouse embryonic fibroblast line from null mice, or siRNA knock-down in primary progenitors, indicate that ZFP36 is required for β-hydroxybutyrate anti-fibrotic effects.

CONCLUSION

These data unravel the potential of β-hydroxybutyrate to limit adipose tissue matrix deposition, a finding that might exploited in an obesogenic context.