Jeffrey A. Willy

Selective mRNA translation during eIF2 phosphorylation induces expression of IBTKα

This study measured changes in global mRNA translation in response to ER stress. The analysis suggests that translation of a majority of gene transcripts is either repressed or resistant, whereas select key regulators are subject to preferential translation. From this last group, IBTKα is identified as a novel target of the UPR central to cell fate.

CHOP Links Endoplasmic Reticulum Stress to NF-κB Activation in the Pathogenesis of Nonalcoholic Steatohepatitis

During metabolic stress, the UPR transcription factor CHOP activates NF-κB through a pathway involving IRAK2 expression, resulting in hepatocyte secretion of cytokines IL-8 and TNFα, which trigger inflammation and hepatocellular death.

Ribosome reinitiation directs gene-specific translation and regulates the integrated stress response

Background: eIF2α-P induced GADD34 and constitutively expressed CReP target PP1c to dephosphorylate eIF2α-P to dictate translation control of the ISR. Results: Differential expression of GADD34 and CReP is regulated by upstream ORF (uORF)-mediated ribosome reinitiation. Conclusion: uORFs regulate differential expression of GADD34 and CReP and are important for cell adaptation to stress. Significance: Regulation of eIF2α-P is central for protein homeostasis and cell viability. In the integrated stress response, phosphorylation of eIF2α (eIF2α-P) reduces protein synthesis to conserve resources and facilitate preferential translation of transcripts that promote stress adaptation. Preferentially translated GADD34 (PPP1R15A) and constitutively expressed CReP (PPP1R15B) function to dephosphorylate eIF2α-P and restore protein synthesis. The 5′-leaders of GADD34 and CReP contain two upstream ORFs (uORFs). Using biochemical and genetic approaches we show that features of these uORFs are central for their differential expression. In the absence of stress, translation of an inhibitory uORF in GADD34 acts as a barrier that prevents reinitiation at the GADD34 coding region. Enhanced eIF2α-P during stress directs ribosome bypass of the uORF, facilitating translation of the GADD34 coding region. CReP expression occurs independent of eIF2α-P via an uORF that allows for translation reinitiation at the CReP coding region independent of stress. Importantly, alterations in the GADD34 uORF affect the status of eIF2α-P, translational control, and cell adaptation to stress. These results show that properties of uORFs that permit ribosome reinitiation are critical for directing gene-specific translational control in the integrated stress response.

Novel role of miR-29a in pancreatic cancer autophagy and its therapeutic potential

Pancreatic Ductal Adenocarcinoma (PDAC) is a highly lethal malignancy that responds poorly to current therapeutic modalities. In an effort to develop novel therapeutic strategies, we found downregulation of miR-29 in pancreatic cancer cells, and overexpression of miR-29a sensitized chemotherapeutic resistant pancreatic cancer cells to gemcitabine, reduced cancer cell viability, and increased cytotoxicity. Furthermore, miR-29a blocked autophagy flux, as evidenced by an accumulation of autophagosomes and autophagy markers, LC3B and p62, and a decrease in autophagosome-lysosome fusion. In addition, miR-29a decreased the expression of autophagy proteins, TFEB and ATG9A, which are critical for lysosomal function and autophagosome trafficking respectively. Knockdown of TFEB or ATG9A inhibited autophagy similar to miR-29a overexpression. Finally, miR-29a reduced cancer cell migration, invasion, and anchorage independent growth. Collectively, our findings indicate that miR-29a functions as a potent autophagy inhibitor, sensitizes cancer cells to gemcitabine, and decreases their invasive potential. Our data provides evidence for the use of miR-29a as a novel therapeutic agent to target PDAC.

Function of inhibitor of Bruton's tyrosine kinase isoform α (IBTKα) in nonalcoholic steatohepatitis links autophagy and the unfolded protein response

Nonalcoholic fatty liver disease (steatosis) is the most prevalent liver disease in the Western world. One of the advanced pathologies is nonalcoholic steatohepatitis (NASH), which is associated with induction of the unfolded protein response (UPR) and disruption of autophagic flux. However, the mechanisms by which these processes contribute to the pathogenesis of human diseases are unclear. Herein, we identify the α isoform of the inhibitor of Brutons tyrosine kinase (IBTKα) as a member of the UPR, whose expression is preferentially translated during endoplasmic reticulum (ER) stress. We found that IBTKα is located in the ER and associates with proteins LC3b, SEC16A, and SEC31A and plays a previously unrecognized role in phagophore initiation from ER exit sites. Depletion of IBTKα helps prevent accumulation of autophagosome intermediates stemming from exposure to saturated free fatty acids and rescues hepatocytes from death. Of note, induction of IBTKα and the UPR, along with inhibition of autophagic flux, was associated with progression from steatosis to NASH in liver biopsies. These results indicate a function for IBTKα in NASH that links autophagy with activation of the UPR.