Ferroptosis in liver cancer: a key role of post-translational modifications.

Ferroptosis is an emerging form of regulated cell death in an oxidative stress- and iron-dependent manner, primarily induced by the over-production of reactive oxygen species (ROS). Manipulation of ferroptosis has been considered a promising therapeutic approach to inhibit liver tumor growth. Nevertheless, the development of resistance to ferroptosis in liver cancer poses a significant challenge in cancer treatment. Post-translational modifications (PTMs) are crucial enzymatic catalytic reactions that covalently regulate protein conformation, stability and cellular activities. Additionally, PTMs play pivotal roles in various biological processes and divergent programmed cell death, including ferroptosis. Importantly, key PTMs regulators involved in ferroptosis have been identified as potential targets for cancer therapy. PTMs function of two proteins, SLC7A11, GPX4 involved in ferroptosis resistance have been extensively investigated in recent years. This review will summarize the roles of PTMs in ferroptosis-related proteins in hepatocellular carcinoma (HCC) treatment.

Protocol to screen for Sorafenib resistance regulators using pooled lentiviral shRNA library and a Sorafenib-resistant hepatocellular carcinoma cell model.

Approaches to study therapy resistance in HCC (hepatocellular carcinoma) are limited, especially when using HCC models in vitro. Here, we present a protocol to establish an in vitro Sorafenib-resistant human HCC cell model and conduct an shRNA-mediated synthetic lethal screen in established Sorafenib-resistant HCC cell lines to identify critical regulators of Sorafenib resistance. We describe steps for RNA sequencing and functional analysis to reveal the mode of action of potential candidates in conferring therapy resistance to HCC cells. For complete details on the use and execution of this protocol, please refer to Gao et al. (2021a)1 and Gao et al. (2021b).2.

Distinct contributions of partial and full EMT to breast cancer malignancy.

Epithelial-mesenchymal transition (EMT) is a transient, reversible process of cell de-differentiation where cancer cells transit between various stages of an EMT continuum, including epithelial, partial EMT, and mesenchymal cell states. We have employed Tamoxifen-inducible dual recombinase lineage tracing systems combined with live imaging and 5-cell RNA sequencing to track cancer cells undergoing partial or full EMT in the MMTV-PyMT mouse model of metastatic breast cancer. In primary tumors, cancer cells infrequently undergo EMT and mostly transition between epithelial and partial EMT states but rarely reach full EMT. Cells undergoing partial EMT contribute to lung metastasis and chemoresistance, whereas full EMT cells mostly retain a mesenchymal phenotype and fail to colonize the lungs. However, full EMT cancer cells are enriched in recurrent tumors upon chemotherapy. Hence, cancer cells in various stages of the EMT continuum differentially contribute to hallmarks of breast cancer malignancy, such as tumor invasion, metastasis, and chemoresistance.

YAP/TAZ and ATF4 drive resistance to Sorafenib in hepatocellular carcinoma by preventing ferroptosis.

Understanding the mechanisms underlying evasive resistance in cancer is an unmet medical need to improve the efficacy of current therapies. In this study, a combination of shRNA-mediated synthetic lethality screening and transcriptomic analysis revealed the transcription factors YAP/TAZ as key drivers of Sorafenib resistance in hepatocellular carcinoma (HCC) by repressing Sorafenib-induced ferroptosis. Mechanistically, in a TEAD-dependent manner, YAP/TAZ induce the expression of SLC7A11, a key transporter maintaining intracellular glutathione homeostasis, thus enabling HCC cells to overcome Sorafenib-induced ferroptosis. At the same time, YAP/TAZ sustain the protein stability, nuclear localization, and transcriptional activity of ATF4 which in turn cooperates to induce SLC7A11 expression. Our study uncovers a critical role of YAP/TAZ in the repression of ferroptosis and thus in the establishment of Sorafenib resistance in HCC, highlighting YAP/TAZ-based rewiring strategies as potential approaches to overcome HCC therapy resistance.

USP29-mediated HIF1α stabilization is associated with Sorafenib resistance of hepatocellular carcinoma cells by upregulating glycolysis.

Understanding the mechanisms underlying evasive resistance in cancer is an unmet medical need to improve the efficacy of current therapies. In hepatocellular carcinoma (HCC), aberrant expression of hypoxia-inducible factor 1 α (HIF1α) and increased aerobic glycolysis metabolism are drivers of resistance to therapy with the multi-kinase inhibitor Sorafenib. However, it has remained unknown how HIF1α is activated and how its activity and the subsequent induction of aerobic glycolysis promote Sorafenib resistance in HCC. Here, we report the ubiquitin-specific peptidase USP29 as a new regulator of HIF1α and of aerobic glycolysis during the development of Sorafenib resistance in HCC. In particular, we identified USP29 as a critical deubiquitylase (DUB) of HIF1α, which directly deubiquitylates and stabilizes HIF1α and, thus, promotes its transcriptional activity. Among the transcriptional targets of HIF1α is the gene encoding hexokinase 2 (HK2), a key enzyme of the glycolytic pathway. The absence of USP29, and thus of HIF1α transcriptional activity, reduces the levels of aerobic glycolysis and restores sensitivity to Sorafenib in Sorafenib-resistant HCC cells in vitro and in xenograft transplantation mouse models in vivo. Notably, the absence of USP29 and high HK2 expression levels correlate with the response of HCC patients to Sorafenib therapy. Together, the data demonstrate that, as a DUB of HIF1α, USP29 promotes Sorafenib resistance in HCC cells, in parts by upregulating glycolysis, thereby opening new avenues for therapeutically targeting Sorafenib-resistant HCC in patients.

Transcriptional Enhancer Factor Domain Family member 4 Exerts an Oncogenic Role in Hepatocellular Carcinoma by Hippo-Independent Regulation of Heat Shock Protein 70 Family Members.

Transcriptional enhancer factor domain family member 4 (TEAD4) is a downstream effector of the conserved Hippo signaling pathway, regulating the expression of genes involved in cell proliferation and differentiation. It is up-regulated in several cancer types and is associated with metastasis and poor prognosis. However, its role in hepatocellular carcinoma (HCC) remains largely unexplored. Using data from The Cancer Genome Atlas, we found that TEAD4 was overexpressed in HCC and was associated with aggressive HCC features and worse outcome. Overexpression of TEAD4 significantly increased proliferation and migration rates in HCC cells in vitro as well as tumor growth in vivo. Additionally, RNA sequencing analysis of TEAD4-overexpressing HCC cells demonstrated that TEAD4 overexpression was associated with the up-regulation of genes involved in epithelial-to-mesenchymal transition, proliferation, and protein-folding pathways. Among the most up-regulated genes following TEAD4 overexpression were the 70-kDa heat shock protein (HSP70) family members HSPA6 and HSPA1A. Chromatin immunoprecipitation-quantitative real-time polymerase chain reaction experiments demonstrated that TEAD4 regulates HSPA6 and HSPA1A expression by directly binding to their promoter and enhancer regions. The pharmacologic inhibition of HSP70 expression in TEAD4-overexpressing cells reduced the effect of TEAD4 on cell proliferation. Finally, by overexpressing TEAD4 in yes-associated protein (YAP)/transcriptional coactivator with PDZ binding motif (TAZ)-knockdown HCC cells, we showed that the effect of TEAD4 on cell proliferation and its regulation of HSP70 expression does not require YAP and TAZ, the main effectors of the Hippo signaling pathway. Conclusion: A novel Hippo-independent mechanism for TEAD4 promotes cell proliferation and tumor growth in HCC by directly regulating HSP70 family members.

OBF1 and Oct factors control the germinal center transcriptional program.

OBF1 is a specific coactivator of the POU family transcription factors OCT1 and OCT2. OBF1 and OCT2 are B cell-specific and indispensable for germinal center (GC) formation, but their mechanism of action is unclear. Here, we show by chromatin immunoprecipitation-sequencing that OBF1 extensively colocalizes with OCT1 and OCT2. We found that these factors also often colocalize with transcription factors of the ETS family. Furthermore, we showed that OBF1, OCT2, and OCT1 bind widely to the promoters or enhancers of genes involved in GC formation in mouse and human GC B cells. Short hairpin RNA knockdown experiments demonstrated that OCT1, OCT2, and OBF1 regulate each other and are essential for proliferation of GC-derived lymphoma cell lines. OBF1 downregulation disrupts the GC transcriptional program: genes involved in GC maintenance, such as BCL6, are downregulated, whereas genes related to exit from the GC program, such as IRF4, are upregulated. Ectopic expression of BCL6 does not restore the proliferation of GC-derived lymphoma cells depleted of OBF1 unless IRF4 is also depleted, indicating that OBF1 controls an essential regulatory node in GC differentiation.

LATS1-Beclin1 mediates a non-canonical connection between the Hippo pathway and autophagy.

Understanding the mechanisms of evasive resistance in cancer is of great importance to develop efficient therapies. Analyzing the molecular mechanisms underlying therapy resistance of hepatocellular carcinoma (HCC), we have discovered a kinase-activity independent role of LATS1 (large tumor suppressor) but not LATS2 in regulating sorafenib-induced lethal autophagy in HCC. We have found that the autophagy regulatory role of LATS1 is a general phenomenon in response to various stimuli of autophagy induction which relies on a LATS1-specific protein domain. Mechanistically, the autophagy regulatory role of LATS1 is coupled with Beclin-1 (BECN1) K27-linked ubiquitination and BECN1 self-dimerization. Our study highlights a LATS1-mediated non-classical interaction between the Hippo signaling pathway and autophagy in therapy response and carcinogenesis.

The cross-talk between the Hippo signaling pathway and autophagy:implications on physiology and cancer.

Organ development is precisely guided by spatiotemporal cross-talks between a variety of signaling pathways regulating cell differentiation, proliferation, growth arrest and physiological cell death. Aberrant signaling inputs invariably lead to tissue dysfunction and to certain conditions, even malignant transformation. In this review, we focus on the functional interplay between the Hippo signaling pathway and autophagy in normal tissue homeostasis and in malignant tumor progression. Mounting experimental evidence for the regulation of cancer cell malignancy and therapy resistance by the functional cross-talk between Hippo signaling and autophagy highlights this signaling axis as a suitable therapeutic target to combat cancer.

LATS1 but not LATS2 represses autophagy by a kinase-independent scaffold function.

Autophagy perturbation represents an emerging therapeutic strategy in cancer. Although LATS1 and LATS2 kinases, core components of the mammalian Hippo pathway, have been shown to exert tumor suppressive activities, here we report a pro-survival role of LATS1 but not LATS2 in hepatocellular carcinoma (HCC) cells. Specifically, LATS1 restricts lethal autophagy in HCC cells induced by sorafenib, the standard of care for advanced HCC patients. Notably, autophagy regulation by LATS1 is independent of its kinase activity. Instead, LATS1 stabilizes the autophagy core-machinery component Beclin-1 by promoting K27-linked ubiquitination at lysine residues K32 and K263 on Beclin-1. Consequently, ubiquitination of Beclin-1 negatively regulates autophagy by promoting inactive dimer formation of Beclin-1. Our study highlights a functional diversity between LATS1 and LATS2, and uncovers a scaffolding role of LATS1 in mediating a cross-talk between the Hippo signaling pathway and autophagy.

PKB/Akt-dependent regulation of inflammation in cancer.

Chronic inflammation is a major cause of human cancer. Clinical cancer therapies against inflammatory risk factors are strategically determined. To rationally guide a novel drug development, an improved mechanistic understanding on the pathological connection between inflammation and carcinogenesis is essential. PI3K-PKB signaling axis has been extensively studied and shown to be one of the key oncogenic drivers in most types of cancer. Pharmacological inhibition of the components along this signaling axis is of great interest for developing novel therapies. Interestingly, emerging studies have shown a close association between PKB activation and inflammatory activity in the vicinity of the tumor, and either blockade of PKB or attenuation of para-tumoral inflammation reveals a mutual-interactive pattern through pathway crosstalk. In this review, we intend to discuss recent advances of PKB-regulated chronic inflammation and its potential impacts on tumor development.

mTORC1/autophagy-regulated MerTK in mutant BRAFV600 melanoma with acquired resistance to BRAF inhibition.

BRAF inhibitors (BRAFi) and the combination therapy of BRAF and MEK inhibitors (MEKi) were recently approved for therapy of metastatic melanomas harbouring the oncogenic BRAFV600 mutation. Although these therapies have shown pronounced therapeutic efficacy, the limited durability of the response indicates an acquired drug resistance that still remains mechanistically poorly understood at the molecular level. We conducted transcriptome gene profiling in BRAFi-treated melanoma cells and identified that Mer tyrosine kinase (MerTK) is specifically upregulated. MerTK overexpression was demonstrated not only in melanomas resistant to BRAFi monotherapy (5 out of 10 samples from melanoma patients) but also in melanoma resistant to BRAFi+MEKi (1 out of 3), although MEKi alone does not affect MerTK. Mechanistically, BRAFi-induced activation of Zeb2 stimulates MerTK in BRAFV600 melanoma through mTORC1-triggered activation of autophagy. Co-targeting MerTK and BRAFV600 significantly reduced tumour burden in xenografted mice, which was pheno-copied by co-inhibition of autophagy and mutant BRAFV600.

The kinases NDR1/2 act downstream of the Hippo homolog MST1 to mediate both egress of thymocytes from the thymus and lymphocyte motility.

The serine and threonine kinase MST1 is the mammalian homolog of Hippo. MST1 is a critical mediator of the migration, adhesion, and survival of T cells; however, these functions of MST1 are independent of signaling by its typical effectors, the kinase LATS and the transcriptional coactivator YAP. The kinase NDR1, a member of the same family of kinases as LATS, functions as a tumor suppressor by preventing T cell lymphomagenesis, which suggests that it may play a role in T cell homeostasis. We generated and characterized mice with a T cell-specific double knockout of Ndr1 and Ndr2 (Ndr DKO). Compared with control mice, Ndr DKO mice exhibited a substantial reduction in the number of naïve T cells in their secondary lymphoid organs. Mature single-positive thymocytes accumulated in the thymus in Ndr DKO mice. We also found that NDRs acted downstream of MST1 to mediate the egress of mature thymocytes from the thymus, as well as the interstitial migration of naïve T cells within popliteal lymph nodes. Together, our findings indicate that the kinases NDR1 and NDR2 function as downstream effectors of MST1 to mediate thymocyte egress and T cell migration.

Integrated Akt/PKB signaling in immunomodulation and its potential role in cancer immunotherapy.

T cell development and maturation involve a variety of defined and coordinated developmental stages under the control of a variety of signaling networks. They function as the major mediator in cell-based immunity that defends against pathogen infections and executes immune surveillance against tumor cells. Protein kinase B (PKB, also called Akt) is central to multiple signaling pathways and transduces extracellular signals to dictate cellular responses towards proliferation, migration, anti-apoptosis, and maintenance of metabolic homeostasis. Although the prosurvival function of PKB was thought to be responsible for most of the functions regulated by PKB, emerging evidence has started to dissect its role in immunomodulation. More importantly, hyperactivation of PKB in cancer stroma frequently occurs in patients treated clinically with targeted cancer therapies, where it acts as a key mediator involved in the trapping of host immune cells in the vicinity of tumors, which supports cancer cell invasion and the escape of cancer cells from host immune surveillance. Encouragingly, recent studies have shown that inhibition of PKB improves the recognition of cancer cells by the host immune system, indicating a potential clinical strategy to rekindle the suppressed host immune response through the specific targeting of PKB. In this review, we explore how PKB signaling contributes to T cell development and cellular immune responses and discuss the mechanistic roles that PKB plays in the creation of immunosuppressive conditions and the escaping of immune recognition in the microenvironment of cancer.

NDR functions as a physiological YAP1 kinase in the intestinal epithelium.

BACKGROUND: Phosphorylation of the transcriptional coactivator YAP1 is a key event in defining Hippo signaling outputs. Previous studies demonstrated that phosphorylation of YAP1 at serine 127 (S127) sequesters YAP1 in the cytoplasm and consequently inhibits YAP1 transcriptional activity. Mammalian tissue-culture experiments suggest that downstream of MST1/2 signaling, LATS1/2 function as YAP1-S127 kinases. However, studies of Mst1/2 knockout mouse models revealed that the identity of the physiological YAP1-S127 kinase(s) in certain tissues, such as the intestine, remains unknown. RESULTS: We show that mammalian NDR1/2 kinases phosphorylate YAP1 on S127 and thereby negatively regulate YAP1 activity in tissue-cultured cells. By studying NDR1/2-deficient mice, we demonstrate the in vivo relevance of NDR1/2-mediated regulation of YAP1. Specifically, upon loss of NDR1/2 in the intestinal epithelium, endogenous S127 phosphorylation is decreased whereas total YAP1 levels are increased. Significantly, ablation of NDR1/2 from the intestinal epithelium renders mice exquisitely sensitive to chemically induced colon carcinogenesis. Analysis of human colon cancer samples further revealed that NDR2 and YAP1 protein expression are inversely correlated in the majority of samples with high YAP1 expression. Collectively, we report NDR1/2 as physiological YAP1-S127 kinases that might function as tumor suppressors upstream of YAP1 in human colorectal cancer. CONCLUSIONS: We establish mammalian NDR1/2 as bona fide kinases that target YAP1 on S127 in vitro and in vivo. Our findings therefore have important implications for a broad range of research efforts aimed at decoding and eventually manipulating YAP1 biology in cancer settings, regenerative medicine, and possibly also noncancer human diseases.

hMOB3 modulates MST1 apoptotic signaling and supports tumor growth in glioblastoma multiforme.

New therapeutic targets are needed that circumvent inherent therapeutic resistance of glioblastoma multiforme (GBM). Here, we report such a candidate target in the uncharacterized adaptor protein hMOB3, which we show is upregulated in GBM. In a search for its biochemical function, we found that hMOB3 specifically interacts with MST1 kinase in response to apoptotic stimuli and cell-cell contact. Moreover, hMOB3 negatively regulated apoptotic signaling by MST1 in GBM cells by inhibiting the MST1 cleavage-based activation process. Physical interaction between hMOB3 and MST1 was essential for this process. In vivo investigations established that hMOB3 sustains GBM cell growth at high cell density and promotes tumorigenesis. Our results suggest hMOB3 as a candidate therapeutic target for the treatment of malignant gliomas.

Split intein facilitated tag affinity purification for recombinant proteins with controllable tag removal by inducible auto-cleavage.

Purification tags are robust tools that can be used to purify a variety of target proteins. However, tag removal remains an expensive and significant issue that must be resolved. Based on the affinity and the trans-splicing activity between the two domains of Ssp DnaB split-intein, a novel approach for tag affinity purification of recombinant proteins with controllable tag removal by inducible auto-cleavage has been developed. This system provides a new affinity method and avoids premature splicing of the intein fused proteins expressed in host cells. The affinity matrix can be reused. In addition, this method is compatible with his-tag affinity purification technique. Our methods provide the insights for establishing a novel recombinant protein preparation system.

A novel strategy for proteome-wide ligand screening using cross-linked phage matrices.

To find a suitable ligand from a complex antigen system is still a mission to be accomplished. Here we have explored a novel "library against proteome" panning strategy for ligand screening and antigen purification from a complex system using phage-displayed antibody technology. Human plasma proteome was targeted for phage library panning. During the process, the panning was carried out in solution, using a biotin/streptavidin beads separation system, for three rounds. Nine monoclonal phages, bound tightly to a number of unknown plasma proteins, were selected from the last round, six of which were directly employed as cross-linked matrices to purify their corresponding antigens from the plasma. The proteins isolated by G5 and E1 matrices were identified as amyloid protein and apolipoprotein A-I precursor, respectively. The results demonstrated that it was feasible to simultaneously obtain a number of ligand phages for various antigens, including low abundant proteins in a non-comparative proteome-wide system.

Expression, purification and characterization of aprotinin and a human analogue of aprotinin.

Aprotinin is a Kunitz-type inhibitor with a relatively broad specificity. It has been shown to be clinically useful for the management of hemorrhagic complications. In this report, small ubiquitin-related modifier (SUMO) linked with a hexa-histidine tag was used as a fusion partner for the production of recombinant aprotinin and a human aprotinin analogue (cloned form human cDNA library). Both fusion proteins were overexpressed mainly as inclusion bodies in Escherichia coli and accounted for approximately 28% of the total cell proteins. After purification by Ni-Sepharose affinity chromatography and renaturation, the fusion proteins were cleaved with SUMO protease 1. Aprotinin and its analogue were separated from the fusion partner by the subtractive chromatography using Ni-Sepharose and then further purified with CM-cellulose. Kinetic studies demonstrated that the amidolytic activity of plasmin was competitively inhibited by recombinant aprotinin with a K(i) of 8.6+/-2.4 nM, which was similar to the K(i) (7.5+/-2.7 nM) of natural aprotinin. The K(i) of human aprotinin analogue was 22.7+/-6.5 nM. The expression strategy described in this study allows convenient high yield and easy purification of small recombinant protease inhibitors with complete native sequences.