A Shortcut from Metabolic-Associated Fatty Liver Disease (MAFLD) to Hepatocellular Carcinoma (HCC): c-MYC a Promising Target for Preventative Strategies and Individualized Therapy

Background: Metabolic-associated fatty liver disease (MAFLD) has risen as one of the leading etiologies for hepatocellular carcinoma (HCC). Oncogenes have been suggested to be responsible for the high risk of MAFLD-related HCC. We analyzed the impact of the proto-oncogene c-MYC in the development of human and murine MAFLD and MAFLD-associated HCC. Methods: alb-myctg mice were studied at baseline conditions and after administration of Western diet (WD) in comparison to WT littermates. c-MYC expression was analyzed in biopsies of patients with MAFLD and MAFLD-associated HCC by immunohistochemistry. Results: Mild obesity, spontaneous hyperlipidaemia, glucose intolerance and insulin resistance were characteristic of 36-week-old alb-myctg mice. Middle-aged alb-myctg exhibited liver steatosis and increased triglyceride content. Liver injury and inflammation were associated with elevated ALT, an upregulation of ER-stress response and increased ROS production, collagen deposition and compensatory proliferation. At 52 weeks, 20% of transgenic mice developed HCC. WD feeding exacerbated metabolic abnormalities, steatohepatitis, fibrogenesis and tumor prevalence. Therapeutic use of metformin partly attenuated the spontaneous MAFLD phenotype of alb-myctg mice. Importantly, upregulation and nuclear localization of c-MYC were characteristic of patients with MAFLD and MAFLD-related HCC. Conclusions: A novel function of c-MYC in MAFLD progression was identified opening new avenues for preventative strategies.

CX3CR1 But Not CCR2 Expression Is Required for the Development of Autoimmune Peripheral Neuropathy in Mice

One hallmark of Guillain-Barre syndrome (GBS), a prototypic autoimmune peripheral neuropathy (APN) is infiltration of leukocytes (macrophages and T cells) into peripheral nerves, where chemokines and their receptors play major roles. In this study, we aimed to understand the potential contribution of chemokine receptors CCR2 and CX3CR1 in APN by using a well-established mouse model, B7.2 transgenic (L31) mice, which possesses a predisposed inflammatory background. We crossbred respectively CCR2KO and CX3CR1KO mice with L31 mice. The disease was initiated by partial ligation on one of the sciatic nerves. APN pathology and neurological function were evaluated on the other non-ligated sciatic nerve/limb. Our results revealed that L31/CX3CR1KO but not L31/CCR2KO mice were resistant to APN. CX3CR1 is needed for maintaining circulating monocyte and CD8+ T cell survival. While migration of a significant number of activated CD8+ T cells to peripheral nerves is essential in autoimmune response in nerve, recruitment of monocytes into PNS seems optional. Disease onset is independent of CCR2 mediated blood-derived macrophage recruitment, which can be replaced by compensatory proliferation of resident macrophages in peripheral nerve. CX3CR1 could also contribute to APN via its critical involvement in maintaining nerve macrophage phagocytic ability. We conclude that blockade of CX3CR1 signaling may represent an interesting anti-inflammatory strategy to improve therapeutic management for GBS patients.

Mis-regulation of the Nucleoporins 98 and 96 lead to defects in protein synthesis that promote hallmarks of tumorigenesis.

The Nucleoporin 98KD (Nup98) is one of the most promiscuous translocation partners in hematological malignancies, contributing to at least 31 different truncation—fusion proteins. To date, nearly all disease models of Nup98 translocations involve ectopic expression of transgenes recapitulating the fusion protein under study, leaving the endogenous Nup98 loci unperturbed. Overlooked in these approaches is that translocation leads to the loss of one copy of normal Nup98 in addition to the loss of Nup96, a second Nucleoporin encoded within the same mRNA and reading frame as Nup98. Nup98 and 96 are also mutated in a number of other cancer types and are located near a tumor suppressor region known to be epigenetically silenced, suggesting that their disruption is not limited to blood cancers. We found that reducing Nup98—96 function via an RNAi approach in Drosophila melanogaster (where the Nup98—96 shared mRNA and reading frame gene structure is conserved) deregulates the cell cycle. We find evidence of overproliferation in Nup98—96 deficient tissues, counteracted by elevated apoptosis and aberrant Wingless and JNK signaling associated with chronic wound healing. When the knockdown of Nup98—96 is combined with inhibition of apoptosis, we see synergism leading to dramatic tissue overgrowth, consistent with a tumor suppressor function for endogenous Nup98 and 96. To understand how growth and proliferation become misregulated when Nup98—96 levels are reduced, we performed RNAseq and uncovered a gene expression signature consistent with defects in ribosome biogenesis. We found that reducing Nup 98 and 96 function limits nuclear export of the ribosome component RpL10A, leading to defects in protein synthesis. Defects in protein synthesis are sufficient to trigger JNK signaling that contributes to compensatory proliferation and hallmarks of tumorigenesis when apoptosis is inhibited. Based upon our data, we suggest that the partial loss of Nup98 and Nup96 function in translocations could de-regulate protein synthesis leading to stress signaling that cooperates with other mutations in cancer to promote tumorigenesis.

Mechanics defines the spatial pattern of compensatory proliferation

The number of cells in tissues is tightly controlled by cell division and cell death, and misregulation of cell numbers could lead to pathological conditions such as cancer. To maintain cell numbers in a tissue, a cell elimination process named programmed cell death or apoptosis, stimulates the proliferation of neighboring cells. This mechanism is called apoptosis-induced compensatory proliferation, which was originally reported more than 40 years ago. While only a limited number of the neigboring cells need to divide to compensate for apoptotic cell loss, the mechanisms that select cells for undergoing division remain an open question. Here we found that the spatial inhomogeneity in mechanotransduction through a growth-promoting transcription co-activator Yes-associated protein (YAP) in the neighboring tissue, accounts for the inhomogeneity of compensatory proliferation. Such inhomogeneous mechanotransduction arises from the combination of the non-uniform distribution of nuclear size, which is inherent in tissues, and the non-uniform pattern of mechanical force applied to the neighboring cells upon apoptosis. Our findings from a mechanical perspective complement the current biochemical understanding of compensatory growth and provide additional insights into cellular functions of how tissue precisely maintains its homeostasis.

Loss of PGRMC1 Delays the Progression of Hepatocellular Carcinoma via Suppression of Pro-Inflammatory Immune Responses

Pgrmc1 is a non-canonical progesterone receptor related to the lethality of various types of cancer. PGRMC1 has been reported to exist in co-precipitated protein complexes with epidermal growth factor receptor (EGFR), which is considered a useful therapeutic target in hepatocellular carcinoma (HCC). Here, we investigated whether Pgrmc1 is involved in HCC progression. In clinical datasets, PGRMC1 transcription level was positively correlated with EGFR levels; importantly, PGRMC1 level was inversely correlated with the survival duration of HCC patients. In a diethylnitrosamine (DEN)-induced murine model of HCC, the global ablation of Pgrmc1 suppressed the development of HCC and prolonged the survival of HCC-bearing mice. We further found that increases in hepatocyte death and suppression of compensatory proliferation in the livers of DEN-injured Pgrmc1-null mice were concomitant with decreases in nuclear factor κB (NF-κB)-dependent production of interleukin-6 (IL-6). Indeed, silencing of Pgrmc1 in murine macrophages led to reductions in NF-κB activity and IL-6 production. We found that the anti-proinflammatory effect of Pgrmc1 loss was mediated by reductions in EGFR level and its effect was not observed after exposure of the EGFR inhibitor erlotinib. This study reveals a novel cooperative role of Pgrmc1 in supporting the EGFR-mediated development of hepatocellular carcinoma, implying that pharmacological suppression of Pgrmc1 may be a useful strategy in HCC treatment.

Bab2 activates JNK signaling to reprogram Drosophila wing disc development

In response to cellular stress and damage, certain tissues are able to regenerate and to restore tissue homeostasis. In Drosophila imaginal wing discs, dying cells express mitogens that induce compensatory proliferation in the surrounding tissue. Here we report that high levels of the BTB/POZ transcription factor Bab2 in the posterior compartment of wing discs activates c-Jun N-terminal kinase (JNK) signaling and local, cell-autonomous apoptotic cell death. This in turn triggered the upregulation of the Dpp mitogen and cellular proliferation in the anterior compartment in a JNK-dependent manner. In the posterior compartment, however, dpp expression was suppressed, most likely by direct transcriptional repression by Bab2. This dual-mode of JNK-signaling, autocrine pro-apoptotic signaling and paracrine pro-proliferative signaling, led to opposite effects in the two compartments and reprogramming of the adult wing structure. We establish Bab2 as a regulator of wing disc development, with the capacity to reprogram development via JNK activation in a cell-autonomous and non-cell-autonomous manner.Summary statementZhao et al. shows that the BTB/POZ transcription factor Bab2 is a potent activator of JNK signaling, apoptosis and compensatory proliferation, thereby driving both pro-tumorigenic and anti-tumorigenic processes.

The early endosomal protein Rab21 is critical for enterocyte functions and intestinal homeostasis

ABSTRACTMembrane trafficking is defined as the vesicular transport of molecules into, out of, and throughout the cell. In intestinal enterocytes, defects in endocytic/recycling pathways result in impaired function and are linked to genetic diseases. However, how these trafficking pathways regulate intestinal tissue homeostasis is poorly understood. Using the Drosophila intestine as an in vivo model system, we investigated enterocyte-specific functions for the early endosomal trafficking machinery in gut homeostasis. We focused on the small GTPase Rab21, which regulates specific steps in early endosomal trafficking. Rab21-depleted guts showed severe abnormalities in intestinal morphology, with deregulated homeostasis associated with a gain in mitotic cells and increased cell death. Increases in both apoptosis and yorkie signaling were responsible for compensatory proliferation and tissue inflammation. Using a RNA interference screen, we identified specific regulators of autophagy and membrane trafficking that phenocopied Rab21 loss. We further showed that Rab21-induced hyperplasia was rescued by inhibition of epidermal growth factor receptor signaling, and identified improperly trafficked cargoes in Rab21-depleted enterocytes. Our data shed light on an important role for early endosomal trafficking, and particularly Rab21, in enterocyte-mediated intestinal homeostasis.

Toll-9 interacts with Toll-1 to mediate a feedback loop during apoptosis-induced proliferation in Drosophila

Drosophila Toll-1 and all mammalian Toll-like receptors regulate innate immunity. However, the functions of the remaining eight Toll-related proteins in Drosophila are not fully understood. Here, we show that Drosophila Toll-9 is necessary and sufficient for a special form of compensatory proliferation after apoptotic cell loss (undead apoptosis-induced proliferation (AiP)). Mechanistically, for AiP, Toll-9 interacts with Toll-1 to activate the intracellular Toll-1 pathway for nuclear translocation of the NF-κB-like transcription factor Dorsal which induces expression of the pro-apoptotic genes reaper and hid. This activity contributes to the feedback amplification loop that operates in undead cells. Given that Toll-9 also functions in loser cells during cell competition, we define a general role of Toll-9 in cellular stress situations leading to the expression of pro-apoptotic genes which trigger apoptosis and apoptosis-induced processes such as AiP. This work identifies conceptual similarities between cell competition and AiP.

Cell Death in the Tumor Microenvironment: Implications for Cancer Immunotherapy

The physiological fate of cells that die by apoptosis is their prompt and efficient removal by efferocytosis. During these processes, apoptotic cells release intracellular constituents that include purine nucleotides, lysophosphatidylcholine (LPC), and Sphingosine-1-phosphate (S1P) that induce migration and chemo-attraction of phagocytes as well as mitogens and extracellular membrane-bound vesicles that contribute to apoptosis-induced compensatory proliferation and alteration of the extracellular matrix and the vascular network. Additionally, during efferocytosis, phagocytic cells produce a number of anti-inflammatory and resolving factors, and, together with apoptotic cells, efferocytic events have a homeostatic function that regulates tissue repair. These homeostatic functions are dysregulated in cancers, where, aforementioned events, if not properly controlled, can lead to cancer progression and immune escape. Here, we summarize evidence that apoptosis and efferocytosis are exploited in cancer, as well as discuss current translation and clinical efforts to harness signals from dying cells into therapeutic strategies.