Kristin K. Brown

Recent evidence has highlighted the importance of employing culture media designed to emulate the metabolic environment cells would be exposed to in vivo. Here, we utilize the physiologic medium Plasmax to examine the impact of nutrient availability on the human hepatocyte cell line, HepG2. Incubation of HepG2 cells in Plasmax suppressed a transcriptional program driven by Hepatocyte Nuclear Factor 4 (HNF4A), a master regulator of hepatocyte identity, leading to a dedifferentiated phenotype. Given that HepG2 cells were originally isolated from a patient with hepatoblastoma, this suggested reversion to the native state in physiologic medium. Importantly, exclusion of iron from Plasmax reinstated the HNF4A-driven transcriptional program. These studies suggest a relationship between iron availability and the fidelity of hepatocyte cell fate and highlight the importance of more faithfully recapitulating in vivo metabolite availability in vitro.

Chronic exposure of local fibroblasts to the reactive tumour niche results in the emergence of cancer-associated fibroblasts (CAFs), which can be classed into multiple subtypes with distinct functional and molecular characteristics. Of these subtypes, myofibroblastic CAFs (myCAFs), contribute to tumour progression primarily by depositing and remodelling extracellular matrix (ECM) within the tumour microenvironment (TME). ECM production is known to be a metabolically demanding process, but specific metabolic pathways that are reprogrammed during myCAF activation are poorly understood. Here, we show that cholesterol biosynthesis is elevated in myCAFs relative to normal fibroblasts. We find that cholesterol is specifically enriched in the myCAF endoplasmic reticulum (ER) membrane and is associated with augmented ER mass and enhanced ER secretory function. Importantly, we demonstrate that pharmacological or genetic inhibition of cholesterol biosynthesis plays a critical role in regulating the ECM-secreting and ECM remodelling function of myCAFs. Moreover, we show that inhibition of cholesterol biosynthesis in myCAFs markedly constrains mammary tumour metastasis in vivo . These studies suggest that cholesterol biosynthesis represents a metabolic vulnerability that can be exploited to normalise myCAF-mediated ECM dysfunction in the TME.

Nuclear factor erythroid 2-related factor 2 (NRF2) is a transcription factor that plays a role in the regulation of redox homeostasis and cellular metabolism. Activating mutations in the NRF2 pathway have been identified in approximately 15% of liver cancer patients. However, the mechanisms by which NRF2 promotes liver tumorigenesis are poorly understood. Employing a transgenic zebrafish model with hepatocyte-specific, inducible expression of a clinically relevant constitutively active NRF2 mutant (NRF2 ^T80K ), we show that constitutive activation of NRF2 drives hepatocyte to cholangiocyte transdifferentiation. Importantly, we demonstrate that NRF2 affects liver cell plasticity in a cell-autonomous, evolutionarily conserved, and reversible manner. Utilizing an epigenetic-focused chemical screen, the BRG1/BRM inhibitor FHD-286 was identified as a potent suppressor of NRF2-driven transdifferentiation. Overall, our study reveals a novel role for NRF2 in the regulation of liver cell plasticity during tumour initiation and identifies a therapeutic approach to overcome the oncogenic activity of NRF2.

Cancer-associated cachexia is a severe metabolic syndrome marked by dramatic loss of adipose and muscle mass. Although preclinical models have advanced our understanding of cachexia, there are still no approved therapies due to the limited insights into the mechanisms underlying tissue wasting. Here, we utilise a YAP-driven model of liver cancer in zebrafish, which rapidly develops cachexia, to uncover an evolutionarily conserved role for bile acid disruption in the onset of cachexia. Spatial transcriptomic analysis revealed that YAP induces a bi-lineage cholangiocarcinoma phenotype, which was associated with bile acid dysregulation. Mechanistically, we establish that both bile acid synthesis (via CYP7A1) and signalling through the bile acid receptor TGR5 are essential for cachexia induction. Notably, we find that the promotion of bile acid excretion with odevixibat ameliorates cachexia. Together, our findings reveal an evolutionarily conserved mechanism by which YAP promotes cachexia and suggest a potential therapeutic strategy to treat the syndrome.

The anti-apoptotic protein MCL-1 (myeloid cell leukemia-1) is essential for embryogenesis and the survival of many cell types that tolerate loss of its relatives, BCL-XL and BCL-2. Apoptosis-unrelated roles of MCL-1 in metabolism may contribute to this requirement, although their relevance for embryogenesis and postnatal life remains unclear. We hypothesized that BCL-XL and BCL-2 may substitute MCL-1’s anti-apoptotic but not its apoptosis-unrelated functions. Replacing MCL-1 with BCL-XL or BCL-2 supported embryo development by rescuing the Mcl-1 ^−/− preimplantation lethality. Mcl-1 ^{Bcl-xL/Bcl-xL} but not Mcl-1 ^Bcl-2/Bcl-2 mice were born on a mixed background, although they showed metabolic defects. Thus MCL-1’s apoptosis-unrelated functions appear critical in later development, with BCL-XL, but not BCL-2, partially compensating. These findings clarify MCL-1’s distinct physiological roles, critically informing MCL-1 inhibitor development as cancer therapeutics.

Identifying tumor suppressor genes is predicted to inform on the development of novel strategies for cancer therapy. To identify new lymphoma driving processes that cooperate with oncogenic MYC, which is abnormally highly expressed in ~70% of human cancers, we use a genome-wide CRISPR gene knockout screen in Eµ-Myc;Cas9 transgenic hematopoietic stem and progenitor cells in vivo. We discover that loss of any of the GATOR1 complex components - NPRL3, DEPDC5, NPRL2 - significantly accelerates c-MYC-driven lymphoma development in mice. MYC-driven lymphomas lacking GATOR1 display constitutive mTOR pathway activation and are highly sensitive to mTOR inhibitors, both in vitro and in vivo. These findings identify GATOR1 suppression of mTORC1 as a tumor suppressive mechanism in MYC-driven lymphomagenesis and suggest an avenue for therapeutic intervention in GATOR1-deficient lymphomas through mTOR inhibition.

Recent evidence has highlighted the importance of employing culture media designed to emulate the metabolic environment Here, we utilize the physiological medium Plasmax to examine the impact of nutrient availability on the human hepatocyte cell line, HepG2. Incubation of HepG2 cells in Plasmax suppressed a transcriptional program driven by Hepatocyte Nuclear Factor 4 (HNF4A), a master regulator of hepatocyte identity. Given that HepG2 cells were originally isolated from a patient with hepatoblastoma, this suggests reversion to the native state in physiological media. Importantly, exclusion of iron from Plasmax reinstated the HNF4A-driven transcriptional program. These studies suggest a relationship between iron availability and the fidelity of hepatocyte cell fate and highlight the importance of more faithfully recapitulating in vivo metabolite availability in vitro .

Background Cancer-associated fibroblasts present a significant barrier to standard of care immunotherapy through multiple mechanisms including deposition of extracellular matrix, reciprocal signaling with cancer cells, and crosstalk with tumor-infiltrating lymphocytes. The peptidyl-prolyl isomerase Pin1 is an enzyme that catalyzes the cis-trans isomerization of peptidyl-prolyl peptide bonds in phosphorylated proteins, thus playing a crucial role in cellular functions including cell growth and differentiation. Recent evidence points to a key immunosuppressive role for Pin1 in cancer-associated fibroblasts in pancreatic cancer.¹ The present study aimed to further investigate the role of Pin1 in modulating fibroblast phenotypes and regulating the TGF-beta signaling pathway. Methods Our research employed a set of in vitro experiments with Pin1-targeting strategies applied to various fibroblast cell lines. The impact on the fibroblast phenotypes and the TGF-beta signaling was assessed through a detailed cell phenotype and protein analysis using a combination of imaging analysis, ELISA, and Western Blot techniques. Results The data revealed that interventions targeting Pin1 significantly modulated the phenotype of fibroblasts, steering them away from a pro-tumorigenic state. Furthermore, we found that Pin1 acts as a positive regulator of TGF-beta signaling, a key pathway often dysregulated in cancer progression and metastasis. Conclusions The results of our study emphasize the significant role of Pin1 in influencing critical cellular and molecular mechanisms within cancer. By altering cancer-associated fibroblast phenotype and positively regulating TGF-beta signaling, Pin1 presents a promising target for therapeutic interventions. Our findings advance the current understanding of Pin1’s role in cancer biology, supporting the need for further exploration of Pin1-targeted treatment strategies. Reference Koikawa K, Kibe S, Suizu F, et al. Targeting Pin1 renders pancreatic cancer eradicable by synergizing with immunochemotherapy. Cell. 2021;184(18):4753–4771.e27. doi:10.1016/j.cell.2021.07.020

The maintenance of redox and metabolic homeostasis is integral to embryonic development. Nuclear factor erythroid 2-related factor 2 (NRF2) is a stress-induced transcription factor that plays a central role in the regulation of redox balance and cellular metabolism. Under homeostatic conditions, NRF2 is repressed by Kelch-like ECH-associated protein 1 (KEAP1). Here, we demonstrate that Keap1 deficiency induces Nrf2 activation and postdevelopmental lethality. Loss of viability is preceded by severe liver abnormalities characterized by an accumulation of lysosomes. Mechanistically, we demonstrate that loss of Keap1 promotes aberrant activation of transcription factor EB (TFEB)/transcription factor binding to IGHM Enhancer 3 (TFE3)-dependent lysosomal biogenesis. Importantly, we find that NRF2-dependent regulation of lysosomal biogenesis is cell autonomous and evolutionarily conserved. These studies identify a role for the KEAP1–NRF2 pathway in the regulation of lysosomal biogenesis and suggest that maintenance of lysosomal homeostasis is required during embryonic development.

Supplementary movie from Pharmacologic Reduction of Mitochondrial Iron Triggers a Noncanonical BAX/BAK-Dependent Cell Death