Biology subjects

Rutkowski, D. T.

Publications and source records attributed to Rutkowski, D. T..

4 recordsLinked to original sources

bioRxiv2026

CHOP promotes the transition to chronic integrated stress response signaling with suppression of hepatocyte identity

The transcription factor CHOP promotes cell death during ER stress, but it is strongly induced even by moderate stresses that do not result in appreciable cell death. Its role during less severe stresses--especially in intact tissues in vivo--is poorly understood. Here, we both deleted and restored CHOP specifically in hepatocytes and challenged animals with ER stress in vivo. We found that CHOP influenced stress-dependent hepatocyte gene expression through two previously unappreciated mechanisms. It directly suppressed the expression of transcriptional master regulators of hepatocyte identity and metabolism. And more broadly, it exacerbated ER stress through the promotion of protein synthesis, which led to persistent activation of the integrated stress response (ISR) despite dephosphorylation of eIF2. This shift to second-phase ISR signaling was phenocopied by deletion of the protective UPR sensor ATF6, suggesting that it reflects a transition from an acute stress response to a chronic one. Our findings show that CHOP augments the capacity of the ISR and UPR to continue to mount a protective response even after eIF2 phosphorylation has been suppressed. In vivo, where ISR signaling intersects with hepatocyte gene regulatory networks, this transition favors lipid dysregulation, highlighting a pathway through which CHOP impacts tissue function independent of cell death.

cell biology↗

bioRxiv2023

CHOP drives cells to mutually exclusive cell fates--death and proliferation--during ER stress

Cellular stresses elicit signaling cascades that are capable of either mitigating the inciting dysfunction or initiating cell death. During endoplasmic reticulum (ER) stress, the transcription factor CHOP is widely recognized to promote cell death. However, it is not clear whether CHOP also has a beneficial role during adaptation. Here, we have combined a new, versatile, genetically modified Chop allele with single cell analysis and with stresses of physiological intensity, to rigorously examine the contribution of CHOP to cell fate. Paradoxically, we found that CHOP promoted death in some cells, but proliferation--and hence recovery--in others. Strikingly, this function of CHOP conferred to cells a stress-specific competitive growth advantage. The dynamics of CHOP expression and UPR activation at the single cell level suggested that CHOP maximizes UPR activation, which in turn favors stress resolution, subsequent UPR deactivation, and proliferation. Taken together, these findings suggest that CHOPs function can be better described as a "stress test" that drives cells into either of two mutually exclusive fates--adaptation or death--during stresses of physiological intensity.

cell biology↗

bioRxiv2023

Interference with the HNF4-dependent gene regulatory network diminishes ER stress in hepatocytes

In all eukaryotic cell types, the unfolded protein response (UPR) upregulates factors that promote protein folding and misfolded protein clearance to help alleviate endoplasmic reticulum (ER) stress. Yet ER stress in the liver is uniquely accompanied by the suppression of metabolic genes, the coordination and purpose of which is largely unknown. Here, we used unsupervised machine learning to identify a cluster of correlated genes that were profoundly suppressed by persistent ER stress in the liver. These genes, which encode diverse functions including metabolism, coagulation, drug detoxification, and bile synthesis, are likely targets of the master regulator of hepatocyte differentiation HNF4. The response of these genes to ER stress was phenocopied by liver-specific deletion of HNF4. Strikingly, while deletion of HNF4 exacerbated liver injury in response to an ER stress challenge, it also diminished UPR activation and partially preserved ER ultrastructure, suggesting attenuated ER stress. Conversely, pharmacological maintenance of hepatocyte identity in vitro enhanced sensitivity to stress. Several pathways potentially link HNF4 to ER stress sensitivity, including control of expression of the tunicamycin transporter MFSD2A; modulation of IRE1/XBP1 signaling; and regulation of Pyruvate Dehydrogenase. Together, these findings suggest that HNF4 activity is linked to hepatic ER homeostasis through multiple mechanisms.

cell biology↗

bioRxiv2019

NADPH and glutathione redox link TCA cycle activity to endoplasmic reticulum stress

Endoplasmic reticulum (ER) stress is associated with dysregulated metabolism, but little is known about how the ER responds to metabolic activity. Here, working primarily in mouse hepatocytes, we show that decreasing the availability of substrate for the TCA cycle diminished NADPH production and attenuated ER stress in a manner that depended on glutathione oxidation. ER stress was also alleviated by impairing either TCA-dependent NADPH production or Glutathione Reductase. Conversely, stimulating TCA activity favored NADPH production, glutathione reduction, and ER stress. Validating these findings, we show that deletion of the mitochondrial pyruvate carrier, which is known to decrease TCA cycle activity and protect the liver from diet-induced injury, also diminished NADPH, elevated glutathione oxidation, and alleviated ER stress. These results provide independent genetic evidence that mitochondrial oxidative metabolism is linked to ER homeostasis. Our results demonstrate a novel pathway of communication between mitochondria and the ER, through relay of redox metabolites.

cell biology↗