MERTK mediated novel site Akt phosphorylation alleviates SAV1 suppression

Molecular mechanisms of Hippo pathway in tumorigenesis: therapeutic implications

The Hippo signaling pathway is a pivotal regulator of tissue homeostasis, organ size, and cell proliferation. Its dysregulation is profoundly implicated in various forms of cancer, making it a highly promising target for therapeutic intervention. This review extensively evaluates the mechanisms underlying the dysregulation of the Hippo pathway in cancer cells and the molecular processes linking these alterations to tumorigenesis. Under normal physiological conditions, the Hippo pathway is a guardian, ensuring controlled cellular proliferation and programmed cell death. However, numerous mutations and epigenetic modifications can disrupt this equilibrium in cancer cells, leading to unchecked cell proliferation, enhanced survival, and metastatic capabilities. The pathway's interaction with other critical signaling networks, including Wnt/β-catenin, PI3K/Akt, TGF-β/SMAD, and EGFR pathways, further amplifies its oncogenic potential. Central to these disruptions is the activation of YAP and TAZ transcriptional coactivators, which drive the expression of genes that promote oncogenesis. This review delves into the molecular mechanisms responsible for the dysregulation of the Hippo pathway in cancer, elucidating how these disruptions contribute to tumorigenesis. We also explore potential therapeutic strategies, including inhibitors targeting YAP/TAZ activity and modulators of upstream signaling components. Despite significant advancements in understanding the Hippo pathway's role in cancer, numerous questions remain unresolved. Continued research is imperative to unravel the complex interactions within this pathway and to develop innovative and effective therapies for clinical application. In conclusion, the comprehensive understanding of the Hippo pathway's regulatory mechanisms offers significant potential for advancing cancer therapies, regenerative medicine, and treatments for chronic diseases. The translation of these insights into clinical practice will necessitate collaborative efforts from researchers, clinicians, and pharmaceutical developers to bring novel and effective therapies to patients, ultimately improving clinical outcomes and advancing the field of oncology.

AKT kinases as therapeutic targets

AKT, or protein kinase B, is a central node of the PI3K signaling pathway that is pivotal for a range of normal cellular physiologies that also underlie several pathological conditions, including inflammatory and autoimmune diseases, overgrowth syndromes, and neoplastic transformation. These pathologies, notably cancer, arise if either the activity of AKT or its positive or negative upstream or downstream regulators or effectors goes unchecked, superimposed on by its intersection with a slew of other pathways. Targeting the PI3K/AKT pathway is, therefore, a prudent countermeasure. AKT inhibitors have been tested in many clinical trials, primarily in combination with other drugs. While some have recently garnered attention for their favorable profile, concern over resistance and off-target effects have continued to hinder their widespread adoption in the clinic, mandating a discussion on alternative modes of targeting. In this review, we discuss isoform-centric targeting that may be more effective and less toxic than traditional pan-AKT inhibitors and its significance for disease prevention and treatment, including immunotherapy. We also touch on the emerging mutant- or allele-selective covalent allosteric AKT inhibitors (CAAIs), as well as indirect, novel AKT-targeting approaches, and end with a briefing on the ongoing quest for more reliable biomarkers predicting sensitivity and response to AKT inhibitors, and their current state of affairs.

Loss of MER Tyrosine Kinase Attenuates Adipocyte Hypertrophy and Leads to Enhanced Thermogenesis in Mice Exposed to High-Fat Diet

Obesity is characterized by low-grade inflammation that originates predominantly from the expanding visceral adipose tissue, in which adipocytes respond to lipid overload with hypertrophy, and consequently die by apoptosis. Recruited adipose tissue macrophages (ATMs) take up the excess lipids and remove the dead cells; however, long-term exposure to high concentrations of lipids alters their phenotype to M1-like ATMs that produce pro-inflammatory cytokines and resistin leading to insulin resistance and other obesity-related pathologies. Mer tyrosine kinase is expressed by macrophages and by being an efferocytosis receptor, and by suppressing inflammation, we hypothesized that it might play a protective role against obesity. To our surprise, however, the loss of Mer protected mice against high-fat diet (HFD)-induced obesity. We report in this paper that Mer is also expressed by adipocytes of both white and brown adipose tissues, and while its activity facilitates adipocyte lipid storage both in vitro and in vivo in mice exposed to HFD, it simultaneously attenuates thermogenesis in the brown adipose tissue contributing to its 'whitening'. Our data indicate that Mer is one of the adipocyte tyrosine kinase receptors, the activity of which contributes to the metabolic decision about the fate of excess lipids favoring their storage within the body.

Preliminary Study of Radionuclide-Labeled MerTK-Targeting PET Imaging Agents for the Diagnosis of Melanoma

MerTK PET imaging holds potential as a promising approach for assessing tumor aggressiveness and monitoring treatment response. In this study, we synthesized a series of 18F- and 68Ga-labeled tracers derived from MerTK inhibitors for detection of MerTK expression. Among the synthesized agents, the dimeric compounds [68Ga]10 and [68Ga]12 demonstrated good in vivo and in vitro stability, high affinities to the MerTK receptor, and good MerTK-targeting specificity. Notably, [68Ga]10 exhibited a tumor uptake of 2.6 ± 0.2%ID/g at 1 h p. i. in B16F10 tumor-bearing mice, nearly tripling the uptake of its monomeric counterpart [68Ga]3. A similar enhancement was observed with [68Ga]12 compared to its monomeric analog [68Ga]6. Additionally, [18F]14 achieved a tumor uptake of 7.6 ± 0.5%ID/g at 2 h p. i., outperforming the previously reported [18F]15. Biodistribution analysis further validated the results, highlighting their potential for clinical investigation.

2'3'-cGAMP interactome identifies 2'3'-cGAMP/Rab18/FosB signaling in cell migration control independent of innate immunity

c-di-GAMP was first identified in bacteria to promote colonization, while mammalian 2'3'-cGAMP is synthesized by cGAS to activate STING for innate immune stimulation. However, 2'3'-cGAMP function beyond innate immunity remains elusive. Here, we report that 2'3'-cGAMP promotes cell migration independent of innate immunity. 2'3'-cGAMP interactome analysis identifies the small GTPase Rab18 as a 2'3'-cGAMP binding partner and effector in cell migration control. Mechanistically, 2'3'-cGAMP binds Rab18 to facilitate GTP loading and subsequent Rab18 activation, which further promotes FosB transcription in facilitating cell migration. Induced synthesis of endogenous 2'3'-cGAMP by intrabreast tumor bacterium S. aureus infection or low-dose doxorubicin treatment facilitates cell migration depending on the cGAS/cGAMP/Rab18/FosB signaling. We find that lovastatin induces Rab18 deprenylation that abolishes 2'3'-cGAMP recognition therefore suppressing cell migration. Together, our study reveals a previously unidentified 2'3'-cGAMP function in cell migration control via the 2'3'-cGAMP/Rab18/FosB signaling that provides additional insights into clinical applications of 2'3'-cGAMP.

Research progress of the Hippo signaling pathway in renal cell carcinoma

Objective

This review aimed to summarize the role of the Hippo signaling pathway in renal cell carcinoma (RCC), a urologic malignancy with subtle initial symptoms and high mortality rates due to metastatic RCC. The Hippo signaling pathway, which regulates tissue and organ sizes, plays a crucial role in RCC progression and metastasis. Understanding the involvement of the Hippo signaling pathway in RCC provides valuable insights for the development of targeted therapies and improved patient outcomes.

Methods

In this review, we explored the impact of the Hippo signaling pathway on RCC. Through an analysis of existing literature, we examined its role in RCC progression and metastasis. Additionally, we discussed potential therapeutic strategies targeting the Hippo pathway for inhibiting RCC cell growth and invasion. We also highlighted the importance of investigating interactions between the Hippo pathway and other signaling pathways such as Wnt, transforming growth factor-beta, and PI3K/AKT, which may uncover additional therapeutic targets.

Results

The Hippo signaling pathway has shown promise as a target for inhibiting RCC cell growth and invasion. Studies have demonstrated its dysregulation in RCC, with altered expression of key components such as yes-associated protein/transcriptional coactivator with PDZ-binding motif (YAP/TAZ). Targeting the Hippo pathway has been associated with suppressed tumor growth and metastasis in preclinical models of RCC. Furthermore, investigating crosstalk between the Hippo pathway and other signaling pathways has revealed potential synergistic effects that could be exploited for therapeutic interventions.

Conclusion

Understanding the role of the Hippo signaling pathway in RCC is of paramount importance. Elucidating its functions and molecular interactions contributes to RCC diagnosis, treatment, and the discovery of novel mechanisms. This knowledge informs the development of innovative therapeutic strategies and opens new avenues for research in RCC. Further investigations are warranted to fully comprehend the complex interplay between the Hippo pathway and other signaling pathways, ultimately leading to improved outcomes for RCC patients.

Therapeutic advances of targeting receptor tyrosine kinases in cancer

Receptor tyrosine kinases (RTKs), a category of transmembrane receptors, have gained significant clinical attention in oncology due to their central role in cancer pathogenesis. Genetic alterations, including mutations, amplifications, and overexpression of certain RTKs, are critical in creating environments conducive to tumor development. Following their discovery, extensive research has revealed how RTK dysregulation contributes to oncogenesis, with many cancer subtypes showing dependency on aberrant RTK signaling for their proliferation, survival and progression. These findings paved the way for targeted therapies that aim to inhibit crucial biological pathways in cancer. As a result, RTKs have emerged as primary targets in anticancer therapeutic development. Over the past two decades, this has led to the synthesis and clinical validation of numerous small molecule tyrosine kinase inhibitors (TKIs), now effectively utilized in treating various cancer types. In this manuscript we aim to provide a comprehensive understanding of the RTKs in the context of cancer. We explored the various alterations and overexpression of specific receptors across different malignancies, with special attention dedicated to the examination of current RTK inhibitors, highlighting their role as potential targeted therapies. By integrating the latest research findings and clinical evidence, we seek to elucidate the pivotal role of RTKs in cancer biology and the therapeutic efficacy of RTK inhibition with promising treatment outcomes.

Emerging Role of Hippo-YAP (Yes-Associated Protein)/TAZ (Transcriptional Coactivator with PDZ-Binding Motif) Pathway Dysregulation in Renal Cell Carcinoma Progression

Although Hippo-YAP/TAZ pathway involvement has been extensively studied in the development of certain cancers, the involvement of this cascade in kidney cancer progression is not well-established and, therefore, will be the focus of this review. Renal cell carcinoma (RCC), the most prevalent kidney tumor subtype, has a poor prognosis and a high mortality rate. Core Hippo signaling inactivation (e.g., LATS kinases) leads to the nuclear translocation of YAP/TAZ where they bind to co-transcriptional factors such as TEAD promoting transcription of genes which initiates various fibrotic and neoplastic diseases. Loss of expression of LATS1/2 kinase and activation of YAP/TAZ correlates with poor survival in RCC patients. Renal-specific ablation of LATS1 in mice leads to the spontaneous development of several subtypes of RCC in a YAP/TAZ-dependent manner. Genetic and pharmacological inactivation of YAP/TAZ reverses the oncogenic potential in LATS1-deficient mice, highlighting the therapeutic benefit of network targeting in RCC. Here, we explore the unique upstream controls and downstream consequences of the Hippo-YAP/TAZ pathway deregulation in renal cancer. This review critically evaluates the current literature on the role of the Hippo pathway in RCC progression and highlights the recent scientific evidence designating YAP/TAZ as novel therapeutic targets against kidney cancer.

Hippo signaling modulation and its biological implications in urological malignancies

Although cancer diagnosis and treatment have rapidly advanced in recent decades, urological malignancies, which have high morbidity and mortality rates, are among the most difficult diseases to treat. The Hippo signaling is an evolutionarily conserved pathway in organ size control and tissue homeostasis maintenance. Its downstream effectors, Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ), are key modulators of numerous physiological and pathological processes. Recent work clearly indicates that Hippo signaling is frequently altered in human urological malignancies. In this review, we discuss the disparate viewpoints on the upstream regulators of YAP/TAZ and their downstream targets and systematically summarize the biological implications. More importantly, we highlight the molecular mechanisms involved in Hippo-YAP signaling to improve our understanding of its role in every stage of prostate cancer, bladder cancer and kidney cancer progression. A better understanding of the biological outcomes of YAP/TAZ modulation will contribute to the establishment of future therapeutic approaches.

Co-targeting JAK1/STAT6/GAS6/TAM signaling improves chemotherapy efficacy in Ewing sarcoma

Ewing sarcoma is a pediatric bone and soft tissue tumor treated with chemotherapy, radiation, and surgery. Despite intensive multimodality therapy, ~50% patients eventually relapse and die of the disease due to chemoresistance. Here, using phospho-profiling, we find Ewing sarcoma cells treated with chemotherapeutic agents activate TAM (TYRO3, AXL, MERTK) kinases to augment Akt and ERK signaling facilitating chemoresistance. Mechanistically, chemotherapy-induced JAK1-SQ phosphorylation releases JAK1 pseudokinase domain inhibition allowing for JAK1 activation. This alternative JAK1 activation mechanism leads to STAT6 nuclear translocation triggering transcription and secretion of the TAM kinase ligand GAS6 with autocrine/paracrine consequences. Importantly, pharmacological inhibition of either JAK1 by filgotinib or TAM kinases by UNC2025 sensitizes Ewing sarcoma to chemotherapy in vitro and in vivo. Excitingly, the TAM kinase inhibitor MRX-2843 currently in human clinical trials to treat AML and advanced solid tumors, enhances chemotherapy efficacy to further suppress Ewing sarcoma tumor growth in vivo. Our findings reveal an Ewing sarcoma chemoresistance mechanism with an immediate translational value.

Disruption of MerTK increases the efficacy of checkpoint inhibitor by enhancing ferroptosis and immune response in hepatocellular carcinoma

Immune checkpoint inhibitors, particularly PD-1/PD-L1 blockades, have been approved for unresectable hepatocellular carcinoma (HCC). However, high resistance rates still limit their efficacy, highlighting the urgent need to understand the underlying mechanisms and develop strategies for overcoming the resistance. In this study, we demonstrate that HCC with high MER proto-oncogene tyrosine kinase (MerTK) expression exhibits anti-PD-1/PD-L1 resistance in two syngeneic mouse models and in patients who received anti-PD-1/PD-L1 therapy. Mechanistically, MerTK renders HCC resistant to anti-PD-1/PD-L1 by limiting ferroptosis with the upregulation of SLC7A11 via the ERK/SP1 pathway and facilitating the development of an immunosuppressive tumor microenvironment (TME) with the recruitment of myeloid-derived suppressor cells (MDSCs). Sitravatinib, an inhibitor of MerTK, sensitizes resistant HCC to anti-PD-L1 therapy by promoting tumor ferroptosis and decreasing MDSC infiltration into the TME. In conclusion, we find that MerTK could serve as a predictive biomarker for patient stratification and as a promising target to overcome anti-PD-1/PD-L1 resistance in HCC.

TAM family kinases as therapeutic targets at the interface of cancer and immunity

Novel treatment approaches are needed to overcome innate and acquired mechanisms of resistance to current anticancer therapies in cancer cells and the tumour immune microenvironment. The TAM (TYRO3, AXL and MERTK) family receptor tyrosine kinases (RTKs) are potential therapeutic targets in a wide range of cancers. In cancer cells, TAM RTKs activate signalling pathways that promote cell survival, metastasis and resistance to a variety of chemotherapeutic agents and targeted therapies. TAM RTKs also function in innate immune cells, contributing to various mechanisms that suppress antitumour immunity and promote resistance to immune-checkpoint inhibitors. Therefore, TAM antagonists provide an unprecedented opportunity for both direct and immune-mediated therapeutic activity provided by inhibition of a single target, and are likely to be particularly effective when used in combination with other cancer therapies. To exploit this potential, a variety of agents have been designed to selectively target TAM RTKs, many of which have now entered clinical testing. This Review provides an essential guide to the TAM RTKs for clinicians, including an overview of the rationale for therapeutic targeting of TAM RTKs in cancer cells and the tumour immune microenvironment, a description of the current preclinical and clinical experience with TAM inhibitors, and a perspective on strategies for continued development of TAM-targeted agents for oncology applications.

Somatic gain-of-function mutations in BUD13 promote oncogenesis by disrupting Fbw7 function

Somatic mutations occurring on key enzymes are extensively studied and targeted therapies are developed with clinical promises. However, context-dependent enzyme function through distinct substrates complicated targeting a given enzyme. Here, we develop an algorithm to elucidate a new class of somatic mutations occurring on enzyme-recognizing motifs that cancer may hijack to facilitate tumorigenesis. We validate BUD13-R156C and -R230Q mutations evading RSK3-mediated phosphorylation with enhanced oncogenicity in promoting colon cancer growth. Further mechanistic studies reveal BUD13 as an endogenous Fbw7 inhibitor that stabilizes Fbw7 oncogenic substrates, while cancerous BUD13-R156C or -R230Q interferes with Fbw7Cul1 complex formation. We also find this BUD13 regulation plays a critical role in responding to mTOR inhibition, which can be used to guide therapy selections. We hope our studies reveal the landscape of enzyme-recognizing motif mutations with a publicly available resource and provide novel insights for somatic mutations cancer hijacks to promote tumorigenesis with the potential for patient stratification and cancer treatment.

Development of VHL-recruiting STING PROTACs that suppress innate immunity

STING acts as a cytosolic nucleotide sensor to trigger host defense upon viral or bacterial infection. While STING hyperactivation can exert anti-tumor effects by increasing T cell filtrates, in other contexts hyperactivation of STING can contribute to autoimmune and neuroinflammatory diseases. Several STING targeting agonists and a smaller subset of antagonists have been developed, yet STING targeted degraders, or PROTACs, remain largely underexplored. Here, we report a series of STING-agonist derived PROTACs that promote STING degradation in renal cell carcinoma (RCC) cells. We show that our STING PROTACs activate STING and target activated/phospho-STING for degradation. Locking STING on the endoplasmic reticulum via site-directed mutagenesis disables STING translocation to the proteasome and resultingly blocks STING degradation. We also demonstrate that PROTAC treatment blocks downstream innate immune signaling events and attenuates the anti-viral response. Interestingly, we find that VHL acts as a bona fide E3 ligase for STING in RCC; thus, VHL-recruiting STING PROTACs further promote VHL-dependent STING degradation. Our study reveals the design and biological assessment of VHL-recruiting agonist-derived STING PROTACs, as well as demonstrates an example of hijacking a physiological E3 ligase to enhance target protein degradation via distinct mechanisms.

STING Suppresses Mitochondrial VDAC2 to Govern RCC Growth Independent of Innate Immunity

STING is an innate immune sensor for immune surveillance of viral/bacterial infection and maintenance of an immune-friendly microenvironment to prevent tumorigenesis. However, if and how STING exerts innate immunity-independent function remains elusive. Here, the authors report that STING expression is increased in renal cell carcinoma (RCC) patients and governs tumor growth through non-canonical innate immune signaling involving mitochondrial ROS maintenance and calcium homeostasis. Mitochondrial voltage-dependent anion channel VDAC2 is identified as a new STING binding partner. STING depletion potentiates VDAC2/GRP75-mediated MERC (mitochondria-ER contact) formation to increase mitochondrial ROS/calcium levels, impairs mitochondria function, and suppresses mTORC1/S6K signaling leading to RCC growth retardation. STING interaction with VDAC2 occurs through STING-C88/C91 palmitoylation and inhibiting STING palmitoyl-transferases ZDHHCs by 2-BP significantly impedes RCC cell growth alone or in combination with sorafenib. Together, these studies reveal an innate immunity-independent function of STING in regulating mitochondrial function and growth in RCC, providing a rationale to target the STING/VDAC2 interaction in treating RCC.

Constructing a novel prognostic signature of tumor driver genes for breast cancer

OBJECTIVES

To systematically explore the function and prognostic ability of tumor-driver genes (TDGs) in breast carcinoma (BRCA).

METHODS

Functional enrichment analysis of BRCA differentially expressed TDGs was assesed. We used univariate Cox, lasso, and multivariate Cox regression to identify the independent prognostic TDGs of BRCA. Then we constructed a prognostic signature and verified its predictive performance. Gene set enrichment analysis of the signal pathway revealed the differences between the prognostic signature high- and low-risk groups. Finally, a nomogram related to the prognostic model was established and verified.

RESULTS

A total of 595 differentially expressed TDGs were identified, which are related to various molecular mechanisms of BRCA progression. We identified 8 independent prognostic TDGs for BRCA and validated their expression and prognosis with public data and clinical samples. The BRCA cohort was divided into training and validation cohorts, and prognostic signatures were constructed separately. The log-rank test showed that the survival rate of the high-risk group was significantly lower than that of the low-risk group in the prognostic signature (P<0.001); the AUC in the three cohorts were 0.805, 0.712, and 0.760, respectively; the nomogram also showed better predictive performance. Analyzing the difference between the two risk subtypes, the high-risk group is mainly enriched in angiogenesis, MTORC1, epithelial-mesenchymal transition and glycolysis, which means it is highly malignant.

CONCLUSIONS

The prognostic signature and nomogram was confirmed to accurately predict the prognosis of patients with BRCA and we validated the hub genes, suggesting their potential as future therapeutic targets.

The Synthesis and Initial Evaluation of MerTK Targeted PET Agents

MerTK (Mer tyrosine kinase), a receptor tyrosine kinase, is ectopically or aberrantly expressed in numerous human hematologic and solid malignancies. Although a variety of MerTK targeting therapies are being developed to enhance outcomes for patients with various cancers, the sensitivity of tumors to MerTK suppression may not be uniform due to the heterogeneity of solid tumors and different tumor stages. In this report, we develop a series of radiolabeled agents as potential MerTK PET (positron emission tomography) agents. In our initial in vivo evaluation, [18F]-MerTK-6 showed prominent uptake rate (4.79 ± 0.24%ID/g) in B16F10 tumor-bearing mice. The tumor to muscle ratio reached 1.86 and 3.09 at 0.5 and 2 h post-injection, respectively. In summary, [18F]-MerTK-6 is a promising PET agent for MerTK imaging and is worth further evaluation in future studies.

YAP1 and PRDM14 converge to promote cell survival and tumorigenesis

The transcriptional co-activator YAP1 oncogene is the downstream effector of the Hippo pathway, which regulates tissue homeostasis, organ size, regeneration, and tumorigenesis. Multiple cancers are dependent on sustained expression of YAP1 for cell proliferation, survival, and tumorigenesis, but the molecular basis of this oncogene dependency is not well understood. To identify genes that can functionally substitute for YAP1, we performed a genome-scale genetic rescue screen in YAP1-dependent colon cancer cells expressing an inducible YAP1-specific shRNA. We found that the transcription factor PRDM14 rescued cell proliferation and tumorigenesis upon YAP1 suppression in YAP1-dependent cells, xenografts, and colon cancer organoids. YAP1 and PRDM14 individually activated the transcription of calmodulin 2 (CALM2) and a glucose transporter SLC2A1 upon YAP1 suppression, and CALM2 or SLC2A1 expression was required for the rescue of YAP1 suppression. Together, these findings implicate PRDM14-mediated transcriptional upregulation of CALM2 and SLC2A1 as key components of oncogenic YAP1 signaling and dependency.

DNA-PK promotes activation of the survival kinase AKT in response to DNA damage through an mTORC2-ECT2 pathway

[Figure: see text].

Targeting Akt in cancer for precision therapy

Biomarkers-guided precision therapeutics has revolutionized the clinical development and administration of molecular-targeted anticancer agents. Tailored precision cancer therapy exhibits better response rate compared to unselective treatment. Protein kinases have critical roles in cell signaling, metabolism, proliferation, survival and migration. Aberrant activation of protein kinases is critical for tumor growth and progression. Hence, protein kinases are key targets for molecular targeted cancer therapy. The serine/threonine kinase Akt is frequently activated in various types of cancer. Activation of Akt promotes tumor progression and drug resistance. Since the first Akt inhibitor was reported in 2000, many Akt inhibitors have been developed and evaluated in either early or late stage of clinical trials, which take advantage of liquid biopsy and genomic or molecular profiling to realize personalized cancer therapy. Two inhibitors, capivasertib and ipatasertib, are being tested in phase III clinical trials for cancer therapy. Here, we highlight recent progress of Akt signaling pathway, review the up-to-date data from clinical studies of Akt inhibitors and discuss the potential biomarkers that may help personalized treatment of cancer with Akt inhibitors. In addition, we also discuss how Akt may confer the vulnerability of cancer cells to some kinds of anticancer agents.

SPOP and OTUD7A Control EWS-FLI1 Protein Stability to Govern Ewing Sarcoma Growth

Chromosomal translocation results in development of an Ewing sarcoma breakpoint region 1-Friend leukemia integration 1 (EWS-FLI1) fusion oncogene in the majority of Ewing sarcoma. The persistent dependence of the tumor for this oncoprotein points to EWS-FLI1 as an ideal drug target. Although EWS-FLI1 transcriptional targets and binding partners are evaluated, the mechanisms regulating EWS-FLI1 protein stability remain elusive. Speckle-type POZ protein (SPOP) and OTU domain-containing protein 7A (OTUD7A) are identified as the bona fide E3 ligase and deubiquitinase, respectively, that control EWS-FLI1 protein turnover in Ewing sarcoma. Casein kinase 1-mediated phosphorylation of the VTSSS degron in the FLI1 domain enhances SPOP activity to degrade EWS-FLI1. Opposing this process, OTUD7A deubiquitinates and stabilizes EWS-FLI1. Depletion of OTUD7A in Ewing sarcoma cell lines reduces EWS-FLI1 protein abundance and impedes Ewing sarcoma growth in vitro and in mice. Performing an artificial-intelligence-based virtual drug screen of a 4-million small molecule library, 7Ai is identified as a potential OTUD7A catalytic inhibitor. 7Ai reduces EWS-FLI1 protein levels and decreases Ewing sarcoma growth in vitro and in a xenograft mouse model. This study supports the therapeutic targeting of OTUD7A as a novel strategy for Ewing sarcoma bearing EWS-FLI1 and related fusions, and may also be applicable to other cancers dependent on aberrant FLI1 expression.

Attacking the PI3K/Akt/mTOR signaling pathway for targeted therapeutic treatment in human cancer

Cancer is the second leading cause of human death globally. PI3K/Akt/mTOR signaling is one of the most frequently dysregulated signaling pathways observed in cancer patients that plays crucial roles in promoting tumor initiation, progression and therapy responses. This is largely due to that PI3K/Akt/mTOR signaling is indispensable for many cellular biological processes, including cell growth, metastasis, survival, metabolism, and others. As such, small molecule inhibitors targeting major kinase components of the PI3K/Akt/mTOR signaling pathway have drawn extensive attention and been developed and evaluated in preclinical models and clinical trials. Targeting a single kinase component within this signaling usually causes growth arrest rather than apoptosis associated with toxicity-induced adverse effects in patients. Combination therapies including PI3K/Akt/mTOR inhibitors show improved patient response and clinical outcome, albeit developed resistance has been reported. In this review, we focus on revealing the mechanisms leading to the hyperactivation of PI3K/Akt/mTOR signaling in cancer and summarizing efforts for developing PI3K/Akt/mTOR inhibitors as either mono-therapy or combination therapy in different cancer settings. We hope that this review will facilitate further understanding of the regulatory mechanisms governing dysregulation of PI3K/Akt/mTOR oncogenic signaling in cancer and provide insights into possible future directions for targeted therapeutic regimen for cancer treatment, by developing new agents, drug delivery systems, or combination regimen to target the PI3K/Akt/mTOR signaling pathway. This information will also provide effective patient stratification strategy to improve the patient response and clinical outcome for cancer patients with deregulated PI3K/Akt/mTOR signaling.

A WW Tandem-Mediated Dimerization Mode of SAV1 Essential for Hippo Signaling

The canonical mammalian Hippo pathway contains a core kinase signaling cascade requiring upstream MST to form a stable complex with SAV1 in order to phosphorylate the downstream LATS/MOB complex. Though SAV1 dimerization is essential for the trans-activation of MST, the molecular mechanism underlying SAV1 dimerization is unclear. Here, we discover that the SAV1 WW tandem containing a short Pro-rich extension immediately following the WW tandem (termed as "WW12ex") forms a highly stable homodimer. The crystal structure of SAV1 WW12ex reveals that the Pro-rich extension of one subunit binds to both WW domains from the other subunit. Thus, SAV1 WW12ex forms a domain-swapped dimer instead of a WW2 homodimerization-mediated dimer. The WW12ex-mediated dimerization of SAV1 is required for the MST/SAV1 complex assembly and MST kinase activation. Finally, we show that several cancer-related SAV1 variants disrupt SAV1 dimer formation, and thus, these mutations may impair the tumor-suppression activity of SAV1.

Tyro3, Axl, Mertk receptor-mediated efferocytosis and immune regulation in the tumor environment

Three structurally related tyrosine receptor cell surface kinases, Tyro3, Axl, and Mertk (TAM) have been recognized to modulate immune function, tissue homeostasis, cardiovasculature, and cancer. The TAM receptor family appears to operate in adult mammals across multiple cell types, suggesting both widespread and specific regulation of cell functions and immune niches. TAM family members regulate tissue homeostasis by monitoring the presence of phosphatidylserine expressed on stressed or apoptotic cells. The detection of phosphatidylserine on apoptotic cells requires intermediary molecules that opsonize the dying cells and tether them to TAM receptors on phagocytes. This complex promotes the engulfment of apoptotic cells, also known as efferocytosis, that leads to the resolution of inflammation and tissue healing. The immune mechanisms dictating these processes appear to fall upon specific family members or may involve a complex of different receptors acting cooperatively to resolve and repair damaged tissues. Here, we focus on the role of TAM receptors in triggering efferocytosis and its consequences in the regulation of immune responses in the context of inflammation and cancer.

TAM kinases as regulators of cell death

Receptor Tyrosine Kinases are critical regulators of signal transduction that support cell survival, proliferation, and differentiation. Dysregulation of normal Receptor Tyrosine Kinase function by mutation or other activity-altering event can be oncogenic or can impact the transformed malignant cell so it becomes particularly resistant to stress challenge, have increased proliferation, become evasive to immune surveillance, and may be more prone to metastasis of the tumor to other organ sites. The TAM family of Receptor Tyrosine Kinases (TYRO3, AXL, MERTK) is emerging as important components of malignant cell survival in many cancers. The TAM kinases are important regulators of cellular homeostasis and proper cell differentiation in normal cells as receptors for their ligands GAS6 and Protein S. They also are critical to immune and inflammatory processes. In malignant cells, the TAM kinases can act as ligand independent co-receptors to mutant Receptor Tyrosine Kinases and in some cases (e.g. FLT3-ITD mutant) are required for their function. They also have a role in immune checkpoint surveillance. At the time of this review, the Covid-19 pandemic poses a global threat to world health. TAM kinases play an important role in host response to many viruses and it is suggested the TAM kinases may be important in aspects of Covid-19 biology. This review will cover the TAM kinases and their role in these processes.

The tumor suppressor role of salvador family WW domain-containing protein 1 (SAV1): one of the key pieces of the tumor puzzle

PURPOSE

In the complex tumor scenario, understanding the function of proteins with protumor or antitumor roles is essential to support advances in the cancer clinical area. Among them, the salvador family WW domain-containing protein 1 (SAV1) is highlighted. This protein plays a fundamental role in the tumor suppressor face of the Hippo pathway, which are responsible for controlling cell proliferation, organ size, development and tissue homeostasis. However, the functional dysregulation of this pathway may contribute to tumorigenesis and tumor progression. As SAV1 is a tumor suppressor scaffold protein, we explored the functions performed by SAV1 with its partners, the regulation of its expression, and its antitumor role in various types of cancer.

METHODS

We selected and analyzed 80 original articles and reviews from Pubmed that focuses on the study of SAV1 in cancer.

RESULTS

SAV1 interacts with several proteins, has different functions and acts as tumor suppressor by other mechanisms besides Hippo pathway. SAV1 expression regulation seems to occur by microRNAs and rarely by mutation or promoter methylation. It is downregulated in different types of cancer, which leads to cancer promotion and progression and is associated with poor prognosis. In vivo models have shown that the loss of SAV1 contributes to tumorigenesis.

CONCLUSION

SAV1 plays a relevant role as tumor suppressor in several types of cancer, highlighting SAV1 and the Hippo pathway's importance to cancer. Thus, encouraging further studies to include the SAV1 as a molecular key piece in cancer biology and in clinical approaches to cancer.

Activation of the tumor suppressive Hippo pathway by triptonide as a new strategy to potently inhibit aggressive melanoma cell metastasis

Metastatic melanoma has a very high mortality rate despite the availability of chemotherapy, radiotherapy, and immunotherapy; therefore, more effective therapeutics are needed. The Hippo pathway plays an inhibitory role in melanoma progression, but the tumor suppressors Salvador homolog-1 (SAV1) and large tumor suppressor 1 (LATS1) in this pathway are down-regulated in melanoma. As a result, the downstream oncogenic Yes-associated protein (YAP) is active, resulting in uncontrolled melanoma growth and metastasis. Therapeutics for remedying SAV1 and LATS1 deficiency in melanoma have not yet been reported in the literature. Here, we show that the small molecule triptonide (MW 358 Da) robustly suppressed melanoma cell tumorigenicity, migration, and invasion. Furthermore, triptonide markedly reduced tumor growth and melanoma lung metastasis in tumor-bearing mice with low toxicity. Molecular mechanistic studies revealed that triptonide promoted SAV1 and LATS1 expression, strongly activated the tumor-suppressive Hippo pathway, degraded oncogenic YAP via the lysosomal pathway, and reduced levels of tumorigenic microphthalmia-associated transcription factor (MITF) in melanoma cells. Triptonide also strongly inhibited activation of AKT, a SAV1-binding signaling protein. Collectively, our results conceptually demonstrate that induction of SAV1 and LATS1 expression and activation of the tumor-suppressive Hippo pathway by triptonide potently inhibits aggressive melanoma cell growth and metastasis. These findings suggest a new strategy for developing therapeutics to treat metastatic melanoma and highlight a novel drug candidate against aggressive melanoma.

Coexpression Module Construction by Weighted Gene Coexpression Network Analysis and Identify Potential Prognostic Markers of Breast Cancer

Background: Breast cancer (BC) is a malignant tumor with the highest morbidity among women, disrupting millions of their lives worldwide each year. However, the molecular mechanisms underlying remain unclear. Methods: The RNA-Sequencing and clinical data of BC patients from The Cancer Genome Atlas (TCGA) database were analyzed by weighted gene coexpression network analysis (WGCNA). Additionally, coexpressed modules were used to detect their correlation with the clinical traits of BC. Next, nodes of the most significant coexpression modules were used for Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway, mRNA-lncRNA coexpression network and survival analyses. Results: In total, 2056 differentially expressed mRNAs (DEmRNAs) and 297 differentially expressed lncRNAs (DElncRNAs) were identified and subjected to WGCNA analysis, and 12 coexpression modules were generated. The top five significant modules (turquoise, green, red, brown, and blue modules) were related to one or more clinical traits of BC. In particular, the turquoise and green modules were chosen for further analysis. Next, by lncRNA-mRNA coexpression analysis of the turquoise and green modules, 12 DEmRNAs and 2 DElncRNAs were identified as hub nodes. The lncRNA-associated mRNAs of the networks were commonly related to several cancer-related pathways. Moreover, these networks also revealed central roles for RP11-389C8.2 and TGFBR2 in the turquoise module and MYLK, KIT, and RP11-394O4.5 in the green module. Furthermore, 16 DEmRNAs and 3 DElncRNAs in these two modules were significantly correlated with the overall survival of BC patients. Conclusions: The authors' study identified some prognostic biomarkers that might play important roles in the development and treatment of BC. In particular, lncRNAs AC016995.3, RP1-193H18.2, and RP11-166D19.1 were novel biomarkers for BC.

MERTK in cancer therapy: Targeting the receptor tyrosine kinase in tumor cells and the immune system

The receptor tyrosine kinase MERTK is aberrantly expressed in numerous human malignancies, and is a novel target in cancer therapeutics. Physiologic roles of MERTK include regulation of tissue homeostasis and repair, innate immune control, and platelet aggregation. However, aberrant expression in a wide range of liquid and solid malignancies promotes neoplasia via growth factor independence, cell cycle progression, proliferation and tumor growth, resistance to apoptosis, and promotion of tumor metastases. Additionally, MERTK signaling contributes to an immunosuppressive tumor microenvironment via induction of an anti-inflammatory cytokine profile and regulation of the PD-1 axis, as well as regulation of macrophage, myeloid-derived suppressor cell, natural killer cell and T cell functions. Various MERTK-directed therapies are in preclinical development, and clinical trials are underway. In this review we discuss MERTK inhibition as an emerging strategy for cancer therapy, focusing on MERTK expression and function in neoplasia and its role in mediating resistance to cytotoxic and targeted therapies as well as in suppressing anti-tumor immunity. Additionally, we review preclinical and clinical pharmacological strategies to target MERTK.

MERTK in cancer therapy: Targeting the receptor tyrosine kinase in tumor cells and the immune system

The receptor tyrosine kinase MERTK is aberrantly expressed in numerous human malignancies, and is a novel target in cancer therapeutics. Physiologic roles of MERTK include regulation of tissue homeostasis and repair, innate immune control, and platelet aggregation. However, aberrant expression in a wide range of liquid and solid malignancies promotes neoplasia via growth factor independence, cell cycle progression, proliferation and tumor growth, resistance to apoptosis, and promotion of tumor metastases. Additionally, MERTK signaling contributes to an immunosuppressive tumor microenvironment via induction of an anti-inflammatory cytokine profile and regulation of the PD-1 axis, as well as regulation of macrophage, myeloid-derived suppressor cell, natural killer cell and T cell functions. Various MERTK-directed therapies are in preclinical development, and clinical trials are underway. In this review we discuss MERTK inhibition as an emerging strategy for cancer therapy, focusing on MERTK expression and function in neoplasia and its role in mediating resistance to cytotoxic and targeted therapies as well as in suppressing anti-tumor immunity. Additionally, we review preclinical and clinical pharmacological strategies to target MERTK.

Correction of the tumor suppressor Salvador homolog-1 deficiency in tumors by lycorine as a new strategy in lung cancer therapy

Salvador homolog-1 (SAV1) is a tumor suppressor required for activation of the tumor-suppressive Hippo pathway and inhibition of tumorigenesis. SAV1 is defective in several cancer types. SAV1 deficiency in cells promotes tumorigenesis and cancer metastasis, and is closely associated with poor prognosis for cancer patients. However, investigation of therapeutic strategies to target SAV1 deficiency in cancer is lacking. Here we found that the small molecule lycorine notably increased SAV1 levels in lung cancer cells by inhibiting SAV1 degradation via a ubiquitin-lysosome system, and inducing phosphorylation and activation of the SAV1-interacting protein mammalian Ste20-like 1 (MST1). MST1 activation then caused phosphorylation, ubiquitination, and degradation of the oncogenic Yes-associated protein (YAP), therefore inhibiting YAP-activated transcription of oncogenic genes and tumorigenic AKT and NF-κB signal pathways. Strikingly, treating tumor-bearing xenograft mice with lycorine increased SAV1 levels, and strongly inhibited tumor growth, vasculogenic mimicry, and metastasis. This work indicates that correcting SAV1 deficiency in lung cancer cells is a new strategy for cancer therapy. Our findings provide a new platform for developing novel cancer therapeutics.

TAM-ing T cells in the tumor microenvironment: implications for TAM receptor targeting

The TAM receptors-TYRO3, AXL, MERTK-are pleiotropically expressed receptors in both healthy and diseased tissue. A complex of the ligands Protein S (PROS1) or Growth Arrest-Specific 6 (GAS6) with apoptotic phosphatidylserine activates the TAM receptors. Hence, this receptor family is essential for the efferocytosis of apoptotic material by antigen-presenting cells. In addition, TAM receptors are expressed by virtually all cells of the tumor microenvironment. They are also potent oncogenes, frequently overexpressed in cancer and involved in survival and therapy resistance. Due to their pro-oncogenic and immune-inhibitory traits, TAM receptors have emerged as promising targets for cancer therapy. Recently, TAM receptors have been described to function as costimulatory molecules on human T cells. TAM receptors' ambivalent functions on many different cell types therefore make therapeutic targeting not straight-forward. In this review we summarize our current knowledge of the function of TAM receptors in the tumor microenvironment. We place particular focus on TAM receptors and the recently unraveled role of MERTK in activated T cells and potential consequences for anti-tumor immunity.

Beyond growth signaling: apoptotic sensor MERTK activates AKT by a novel mechanism

Canonically the oncogenic kinase AKT is activated by growth signals. Our work suggests apoptotic materials, abundant in tumors, also contribute to AKT activation by stimulating MERTK that in turn phosphorylates Y26 in the AKT PH domain. pY26 reverses binding of an AKT endogenous, WW-domain containing inhibitor, SAV1, allowing AKT responsiveness to classic growth signals. This novel mechanism may contribute to drug resistance.