MYC and MET cooperatively drive hepatocellular carcinoma with distinct molecular traits and vulnerabilities

Enhanced activation of the transcription factor MYC and of the receptor tyrosine kinase MET are among the events frequently occurring in hepatocellular carcinoma (HCC). Both genes individually act as drivers of liver cancer initiation and progression. However, their concomitant alteration in HCC has not been explored, nor functionally documented. Here, we analysed databases of five independent human HCC cohorts and found a subset of patients with high levels of MYC and MET (MYC^high/MET^high) characterised by poor prognosis. This clinical observation drove us to explore the functionality of MYC and MET co-occurrence in vivo, combining hydrodynamic tail vein injection for MYC expression in the R26^stopMet genetic setting, in which wild-type MET levels are enhanced following the genetic deletion of a stop cassette. Results showed that increased MYC and MET expression in hepatocytes is sufficient to induce liver tumorigenesis even in the absence of pre-existing injuries associated with a chronic disease state. Intriguingly, ectopic MYC in MET tumours increases expression of the Mki67 proliferation marker, and switches them into loss of Afp, Spp1, Gpc3, Epcam accompanied by an increase in Hgma1, Vim, and Hep-Par1 levels. We additionally found a switch in the expression of specific immune checkpoints, with an increase in the Ctla-4 and Lag3 lymphocyte co-inhibitory responses, and in the Icosl co-stimulatory responses of tumour cells. We provide in vitro evidence on the vulnerability of some human HCC cell lines to combined MYC and MET targeting, which are otherwise resistant to single inhibition. Mechanistically, combined blockage of MYC and MET converts a partial cytostatic effect, triggered by individual blockage of MYC or MET, into a cytotoxic effect. Together, these findings highlight a subgroup of HCC characterised by MYC^high/MET^high, and document functional cooperativity between MYC and MET in liver tumorigenesis. Thus, the MYC-R26^Met model is a relevant setting for HCC biology, patient classification and treatment.

C3G down-regulation enhances pro-migratory and stemness properties of oval cells by promoting an epithelial-mesenchymal-like process

Previous data indicate that C3G (RapGEF1) main isoform is highly expressed in liver progenitor cells (or oval cells) compared to adult mature hepatocytes, suggesting it may play an important role in oval cell biology. Hence, we have explored C3G function in the regulation of oval cell properties by permanent gene silencing using shRNAs. We found that C3G knock-down enhanced migratory and invasive ability of oval cells by promoting a partial epithelial to mesenchymal transition (EMT). This is likely mediated by upregulation of mRNA expression of the EMT-inducing transcription factors, Snail1, Zeb1 and Zeb2, induced in C3G-silenced oval cells. This EMT is associated to a higher expression of the stemness markers, CD133 and CD44. Moreover, C3G down-regulation increased oval cells clonogenic capacity by enhancing cell scattering. However, C3G knock-down did not impair oval cell differentiation into hepatocyte lineage. Mechanistic studies revealed that HGF/MET signaling and its pro-invasive activity was impaired in oval cells with low levels of C3G, while TGF-β signaling was increased. Altogether, these data suggest that C3G might be tightly regulated to ensure liver repair in chronic liver diseases such as non-alcoholic steatohepatitis. Hence, reduced C3G levels could facilitate oval cell expansion, after the proliferation peak, by enhancing migration.

Enhanced Wild-Type MET Receptor Levels in Mouse Hepatocytes Attenuates Insulin-Mediated Signaling

Compelling evidence points to the MET receptor tyrosine kinase as a key player during liver development and regeneration. Recently, a role of MET in the pathophysiology of insulin resistance and obesity is emerging. Herein, we aimed to determine whether MET regulates hepatic insulin sensitivity. To achieve this, mice in which the expression of wild-type MET in hepatocytes is slightly enhanced above endogenous levels (Alb-R26^Met mice) were analyzed to document glucose homeostasis, energy balance, and insulin signaling in hepatocytes. We found that Alb-R26^Met mice exhibited higher body weight and food intake when compared to R26^stopMet control mice. Metabolic analyses revealed that Alb-R26^Met mice presented age-related glucose and pyruvate intolerance in comparison to R26^stopMet controls. Additionally, in Alb-R26^Met mice, high MET levels decreased insulin-induced insulin receptor (IR) and AKT phosphorylation compared to control mice. These results were corroborated in vitro by analyzing IR and AKT phosphorylation in primary mouse hepatocytes from Alb-R26^Met and R26^stopMet mice upon insulin stimulation. Moreover, co-immunoprecipitation assays revealed MET-IR interaction under both basal and insulin stimulation conditions; this effect was enhanced in Alb-R26^Met hepatocytes. Altogether, our results indicate that enhanced MET levels alter hepatic glucose homeostasis, which can be an early event for subsequent liver pathologies.

Abstract 1974: C3G down-regulation in glioblastoma induces a pro-invasive and glycolytic phenotype, accompanied by RTKs dysregulation

C3G is a guanine-nucleotide exchange factor (GEF) for Rap1, although it can act through GEF-independent mechanisms. C3G plays a dual role in cancer, acting as either a tumor suppressor or inducer depending on the tumor type/stage. It regulates different key aspects of the tumorigenic process such as invasion, apoptosis or proliferation. In colon carcinoma, C3G represses invasion through down-regulation of p38αMAPK activity and promotes tumor growth. We have now analyzed the role of C3G in glioblastoma (GBM), a tumor characterized by its aggressiveness and disseminative capacity. To do it, we have used different experimental approaches: permanent gene silencing, knock-out using CRISPR/Cas9 technology and transient overexpression in U87 cell line and patient-derived GBM cells. We found that C3G down-regulation enhances invasion through the induction of an epithelial/glial to mesenchymal transition-like process. C3G deficiency also facilitates foci generation in anchorage-dependent and independent growth assays, but with lower cell density as a consequence of a reduced proliferation. In in vivo analyses, cells with C3G knock-down generated larger tumors in xenografts and chick chorioallantoic membrane xenografts assays with increased angiogenesis and α-SMA+ fibroblasts, but a lower proliferation. Mechanistically, C3G down-regulation impairs EGF/EGFR signaling by decreasing EGFR cell membrane localization, leading to a reduction in EGF/EGFR-induced invasiveness. In contrast, C3G down-regulation promotes the activation of several receptor tyrosine kinases (RTKs) that might promote invasion. In particular, the enhanced FGF2/FGFR1 signaling increases invasion in C3G-silenced cells, through a mechanism likely dependent on ERKs. Moreover, a proteomic analysis revealed that C3G down-regulation increases the levels of different key glycolytic enzymes, such as aldolase, phosphoglycerate kinase, enolase and pyruvate kinase (PK). The activity of PK and lactate dehydrogenase as well as lactate release to the extracellular environment were also increased upon C3G silencing. In conclusion, our data demonstrate that C3G inhibits invasion of GBM cells, while increasing their proliferative capacity. Moreover, we show a distinct dependency on C3G for EGF/EGFR signaling versus other RTKs, suggesting that assessing C3G levels may discriminate GBM patient responders to different RTK inhibitors. In addition, our results indicate that C3G regulates not only GBM growth and invasiveness, but it also contributes to reprogram its glycolytic metabolism. Hence, low levels of C3G correlate with a more mesenchymal and glycolytic phenotype with enhanced aggressiveness and worse patient prognosis. This promising role of C3G as a key player in GBM should be further characterized to define its prognostic value and its potential relevance as a predictor of the response to therapy.

Citation Format: Sara Manzano, Óscar Herranz, Paloma Bragado, Patricia Jáuregui, María Rodrigo, Celia Sequera, Cristina Baquero, Nerea Palao, Ignacio Rubio, Álvaro Gutierrez-Uzquiza, Carmen Guerrero, Almudena Porras. C3G down-regulation in glioblastoma induces a pro-invasive and glycolytic phenotype, accompanied by RTKs dysregulation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1974.

ADAMTSL5 is an epigenetically activated gene underlying tumorigenesis and drug resistance in hepatocellular carcinoma

BACKGROUND & AIMS

The tumour microenvironment shapes tumour growth through cellular communications that include both direct interactions and secreted factors. The aim of this study was to characterize the impact of the secreted glycoprotein ADAMTSL5, whose role in cancer has not been previously investigated, on hepatocellular carcinoma (HCC).

METHODS

ADAMTSL5 methylation status was evaluated through bisulfite sequencing, and publicly available data analysis. ADAMTSL5 RNA and protein expression were assessed in mouse models and HCC patient samples and compared to data from published datasets. Functional studies, including association of ADAMTSL5 depletion with responsiveness to clinically relevant drugs, were performed in cellular and in vivo models. Molecular alterations associated with ADAMTSL5 targeting were determined using proteomics, biochemistry, and reverse-transcription quantitative PCR.

RESULTS

Methylome analysis revealed hypermethylated gene body CpG islands at the ADAMTSL5 locus in both mouse and human HCC, correlating with higher ADAMTSL5 expression. ADAMTSL5 targeting interfered with tumorigenic properties of HCC cells in vitro and in vivo, whereas ADAMTSL5 overexpression conferred tumorigenicity to pre-tumoural hepatocytes sensitized to transformation by a modest level of MET receptor expression. Mechanistically, ADAMTSL5 abrogation led to a reduction of several oncogenic inputs relevant to HCC, including reduced expression and/or phosphorylation levels of receptor tyrosine kinases MET, EGFR, PDGFRβ, IGF1Rβ, or FGFR4. This phenotype was associated with significantly increased sensitivity of HCC cells to clinically relevant drugs, namely sorafenib, lenvatinib, and regorafenib. Moreover, ADAMTSL5 depletion drastically increased expression of AXL, accompanied by a sensitization to bemcentinib.

CONCLUSIONS

Our results point to a role for ADAMTSL5 in maintaining the function of key oncogenic signalling pathways, suggesting that it may act as a master regulator of tumorigenicity and drug resistance in HCC.

LAY SUMMARY

The environment of cancer cells has profound effects on establishment, progression, and response of a tumour to treatment. Herein, we show that ADAMTSL5, a protein secreted by liver cancer cells and overlooked in cancer so far, is increased in this tumour type, is necessary for tumour formation and supports drug resistance. Adamtsl5 removal conferred sensitivity of liver cancer cells to drugs used in current treatment. This suggests ADAMTSL5 as a potential marker in liver cancer as well as a possible drug target.

How Rap and its GEFs control liver physiology and cancer development. C3G alterations in human hepatocarcinoma

Rap proteins regulate liver physiopathology. For example, Rap2B promotes hepatocarcinoma (HCC) growth, while Rap1 might play a dual role. The RapGEF, Epac1, activates Rap upon cAMP binding, regulating metabolism, survival, and liver regeneration. A liver specific Epac2 isoform lacking cAMP-binding domain also activates Rap1, promoting fibrosis in alcoholic liver disease. C3G (RapGEF1) is also present in the liver, but mainly as shorter isoforms. Its function in the liver remains unknown. Information from different public genetic databases revealed that C3G mRNA levels increase in HCC, although they decrease in metastatic stages. In addition, several mutations in RapGEF1 gene are present, associated with a reduced patient survival. Based on this, C3G might represent a new HCC diagnostic and prognostic marker, and a therapeutic target.

C3G knock-down enhances migration and invasion by increasing Rap1-mediated p38α activation, while it impairs tumor growth through p38α-independent mechanisms

C3G, a Guanine nucleotide Exchange Factor (GEF) for Rap1 and R-Ras, has been shown to play important roles in development and cancer. Previous studies determined that C3G regulates cell death through down-regulation of p38α MAPK activity. Here, we found that C3G knock-down in MEFs and HCT116 cells promotes migration and invasion through Rap1-mediated p38α hyper-activation. These effects of C3G were inhibited by Rap1 knock-down or inactivation. The enhanced migration observed in C3G depleted HCT116 cells was associated with reduction in E-cadherin expression, internalization of ZO-1, actin cytoskeleton reorganization and decreased adhesion. We also found that matrix metalloproteases MMP2 and MMP9 are involved in the pro-invasive effect of C3G down-regulation. Additionally, our studies revealed that both C3G and p38α collaborate to promote growth of HCT116 cells in vitro and in vivo, possibly by enhancing cell survival. In fact, knocking-down C3G or p38α individually or together promoted cell death in vitro, although only the double C3G-p38α silencing was able to increase cell death within tumors. Notably, we found that the pro-tumorigenic function of C3G does not depend on p38α or Rap1 activation. Altogether, our studies uncover novel mechanisms by which C3G controls key aspects of tumorigenesis.

C3G promotes a selective release of angiogenic factors from activated mouse platelets to regulate angiogenesis and tumor metastasis

Previous observations indicated that C3G (RAPGEF1) promotes α-granule release, evidenced by the increase in P-selectin exposure on the platelet surface following its activation. The goal of the present study is to further characterize the potential function of C3G as a modulator of the platelet releasate and its implication in the regulation of angiogenesis. Proteomic analysis revealed a decreased secretion of anti-angiogenic factors from activated transgenic C3G and C3G∆Cat platelets. Accordingly, the secretome from both transgenic platelets had an overall pro-angiogenic effect as evidenced by an in vitro capillary-tube formation assay with HUVECs (human umbilical vein endothelial cells) and by two in vivo models of heterotopic tumor growth. In addition, transgenic C3G expression in platelets greatly increased mouse melanoma cells metastasis. Moreover, immunofluorescence microscopy showed that the pro-angiogenic factors VEGF and bFGF were partially retained into α-granules in thrombin- and ADP-activated mouse platelets from both, C3G and C3GΔCat transgenic mice. The observed interaction between C3G and Vesicle-associated membrane protein (Vamp)-7 could explain these results. Concomitantly, increased platelet spreading in both transgenic platelets upon thrombin activation supports this novel function of C3G in α-granule exocytosis. Collectively, our data point out to the co-existence of Rap1GEF-dependent and independent mechanisms mediating C3G effects on platelet secretion, which regulates pathological angiogenesis in tumors and other contexts. The results herein support an important role for platelet C3G in angiogenesis and metastasis.

TWEAK promotes migration and invasion in MEFs through a mechanism dependent on ERKs activation and Fibulin 3 down-regulation

TWEAK regulates multiple physio-pathological processes in fibroblasts such as fibrosis. It also induces migration and invasion in tumors and it can activate p38 MAPK in various cell types. Moreover, p38α MAPK promotes migration and invasion in several cancer cells types and in mouse embryonic fibroblasts (MEFs). However, it remains unknown if TWEAK could promote migration in fibroblasts and whether p38α MAPK might play a role. Our results reveal that TWEAK activates ERKs, Akt, and p38α/β MAPKs and reduces secreted Fibulin 3 in MEFs. TWEAK also increases migration and invasion in wt and p38α deficient MEFs, which indicates that p38α MAPK is not required to mediate these effects. In contrast, ERKs inhibition significantly decreases TWEAK-induced migration and Fibulin 3 knock-down mimics TWEAK effect. These results indicate that both ERKs activation and Fibulin 3 down-regulation would contribute to mediate TWEAK pro-migratory effect. In fact, the additional regulation of ERKs and/or p38β as a consequence of Fibulin 3 decrease might be also involved in the pro-migratory effect of TWEAK in MEFs. In conclusion, our studies uncover novel mechanisms by which TWEAK would favor tissue repair by promoting fibroblasts migration.

p38 MAPK down-regulates fibulin 3 expression through methylation of gene regulatory sequences: role in migration and invasion

p38 MAPKs regulate migration and invasion. However, the mechanisms involved are only partially known. We had previously identified fibulin 3, which plays a role in migration, invasion, and tumorigenesis, as a gene regulated by p38α. We have characterized in detail how p38 MAPK regulates fibulin 3 expression and its role. We describe here for the first time that p38α, p38γ, and p38δ down-regulate fibulin 3 expression. p38α has a stronger effect, and it does so through hypermethylation of CpG sites in the regulatory sequences of the gene. This would be mediated by the DNA methylase, DNMT3A, which is down-regulated in cells lacking p38α, but once re-introduced represses Fibulin 3 expression. p38α through HuR stabilizes dnmt3a mRNA leading to an increase in DNMT3A protein levels. Moreover, by knocking-down fibulin 3, we have found that Fibulin 3 inhibits migration and invasion in MEFs by mechanisms involving p38α/β inhibition. Hence, p38α pro-migratory/invasive effect might be, at least in part, mediated by fibulin 3 down-regulation in MEFs. In contrast, in HCT116 cells, Fibulin 3 promotes migration and invasion through a mechanism dependent on p38α and/or p38β activation. Furthermore, Fibulin 3 promotes in vitro and in vivo tumor growth of HCT116 cells through a mechanism dependent on p38α, which surprisingly acts as a potent inducer of tumor growth. At the same time, p38α limits fibulin 3 expression, which might represent a negative feed-back loop.