Myosin II Reactivation and Cytoskeletal Remodeling as a Hallmark and a Vulnerability in Melanoma Therapy Resistance

Inhibition of the Rho/MRTF pathway improves the response of BRAF-resistant melanoma to PD1/PDL1 blockade

Metastatic cutaneous melanoma is a fatal skin cancer. Resistance to targeted and immune therapies limits the benefits of current treatments. Identifying and adding anti-resistance agents to current treatment protocols can potentially improve clinical responses. Myocardin-related transcription factor (MRTF) is a transcriptional coactivator whose activity is indirectly regulated by actin and the Rho family of GTPases. We previously demonstrated that development of BRAF inhibitor (BRAFi) resistance frequently activates the Rho/MRTF pathway in human and mouse BRAFV600E melanomas. In clinical trials, pretreatment with BRAFi reduces the benefit of immune therapies. We aimed to test the efficacy of concurrent treatment with our MRTF pathway inhibitor CCG-257081 and anti-PD1 in vivo and to examine its effects on the melanoma immune microenvironment. Because MRTF pathway activation upregulates the expression of immune checkpoint inhibitor genes/proteins, we asked whether CCG-257081 can improve the response to immune checkpoint blockade. CCG-257081 reduced the expression of PDL1 in BRAFi-resistant melanoma cells and decreased surface PDL1 levels on both BRAFi-sensitive and -resistant melanoma cells. Using our recently described murine vemurafenib-resistant melanoma model, we found that CCG-257081, in combination with anti-PD1 immune therapy, reduced tumor growth and increased survival. Moreover, anti-PD1/CCG-257081 co-treatment increased infiltration of CD8+ T cells and B cells into the tumor microenvironment and reduced tumor-associated macrophages. Here, we propose CCG-257081 as an anti-resistance and immune therapy-enhancing anti-melanoma agent.

Tumor associated macrophages as key contributors and targets in current and future therapies for melanoma

INTRODUCTION

Despite the success of immunotherapies for melanoma in recent years, there remains a significant proportion of patients who do not yet derive benefit from available treatments. Immunotherapies currently licensed for clinical use target the adaptive immune system, focussing on Tcell interactions and functions. However, the most prevalent immune cells within the tumor microenvironment (TME) of melanoma are macrophages, a diverse immune cell subset displaying high plasticity, to which no current therapies are yet directly targeted. Macrophages have been shown not only to activate the adaptive immune response, and enhance cancer cell killing, but, when influenced by factors within the TME of melanoma, these cells also promote melanoma tumorigenesis and metastasis.

AREAS COVERED

We present a review of the most up-to-date literatureavailable on PubMed, focussing on studies from within the last 10 years. We also include data from ongoing and recent clinical trials targeting macrophages in melanoma listed on clinicaltrials.gov.

EXPERT OPINION

Understanding the multifaceted role of macrophages in melanoma, including their interactions with immune and cancer cells, the influence of current therapies on macrophage phenotype and functions and how macrophages could be targeted with novel treatment approaches, are all critical for improving outcomes for patients with melanoma.

Determinants of resistance and response to melanoma therapy

Metastatic melanoma is among the most enigmatic advanced cancers to clinically manage despite immense progress in the way of available therapeutic options and historic decreases in the melanoma mortality rate. Most patients with metastatic melanoma treated with modern targeted therapies (for example, BRAFV600E/K inhibitors) and/or immune checkpoint blockade (for example, anti-programmed death 1 therapy) will progress, owing to profound tumor cell plasticity fueled by genetic and nongenetic mechanisms and dichotomous host microenvironmental influences. Here we discuss the determinants of tumor heterogeneity, mechanisms of therapy resistance and effective therapy regimens that hold curative promise.

Farnesyltransferase inhibition overcomes oncogene-addicted non-small cell lung cancer adaptive resistance to targeted therapies

Drug-tolerance has emerged as one of the major non-genetic adaptive processes driving resistance to targeted therapy (TT) in non-small cell lung cancer (NSCLC). However, the kinetics and sequence of molecular events governing this adaptive response remain poorly understood. Here, we combine real-time monitoring of the cell-cycle dynamics and single-cell RNA sequencing in a broad panel of oncogenic addiction such as EGFR-, ALK-, BRAF- and KRAS-mutant NSCLC, treated with their corresponding TT. We identify a common path of drug adaptation, which invariably involves alveolar type 1 (AT1) differentiation and Rho-associated protein kinase (ROCK)-mediated cytoskeletal remodeling. We also isolate and characterize a rare population of early escapers, which represent the earliest resistance-initiating cells that emerge in the first hours of treatment from the AT1-like population. A phenotypic drug screen identify farnesyltransferase inhibitors (FTI) such as tipifarnib as the most effective drugs in preventing relapse to TT in vitro and in vivo in several models of oncogenic addiction, which is confirmed by genetic depletion of the farnesyltransferase. These findings pave the way for the development of treatments combining TT and FTI to effectively prevent tumor relapse in oncogene-addicted NSCLC patients.

Proteolysis-free amoeboid migration of melanoma cells through crowded environments via bleb-driven worrying

In crowded microenvironments, migrating cells must find or make a path. Amoeboid cells are thought to find a path by deforming their bodies to squeeze through tight spaces. Yet, some amoeboid cells seem to maintain a near-spherical morphology as they move. To examine how they do so, we visualized amoeboid human melanoma cells in dense environments and found that they carve tunnels via bleb-driven degradation of extracellular matrix components without the need for proteolytic degradation. Interactions between adhesions and collagen at the cell front induce a signaling cascade that promotes bleb enlargement via branched actin polymerization. Large blebs abrade collagen, creating feedback between extracellular matrix structure, cell morphology, and polarization that enables both path generation and persistent movement.

Immune Regulation and Immune Therapy in Melanoma: Review with Emphasis on CD155 Signalling

Melanoma is commonly diagnosed in a younger population than most other solid malignancies and, in Australia and most of the world, is the leading cause of skin-cancer-related death. Melanoma is a cancer type with high immunogenicity; thus, immunotherapies are used as first-line treatment for advanced melanoma patients. Although immunotherapies are working well, not all the patients are benefitting from them. A lack of a comprehensive understanding of immune regulation in the melanoma tumour microenvironment is a major challenge of patient stratification. Overexpression of CD155 has been reported as a key factor in melanoma immune regulation for the development of therapy resistance. A more thorough understanding of the actions of current immunotherapy strategies, their effects on immune cell subsets, and the roles that CD155 plays are essential for a rational design of novel targets of anti-cancer immunotherapies. In this review, we comprehensively discuss current anti-melanoma immunotherapy strategies and the immune response contribution of different cell lineages, including tumour endothelial cells, myeloid-derived suppressor cells, cytotoxic T cells, cancer-associated fibroblast, and nature killer cells. Finally, we explore the impact of CD155 and its receptors DNAM-1, TIGIT, and CD96 on immune cells, especially in the context of the melanoma tumour microenvironment and anti-cancer immunotherapies.

Engines of change: Nonmuscle myosin II in mechanobiology

The emergence of mechanobiology has unveiled complex mechanisms by which cells adjust intracellular force production to their needs. Most communicable intracellular forces are generated by myosin II, an actin-associated molecular motor that transforms adenosine triphosphate (ATP) hydrolysis into contraction in nonmuscle and muscle cells. Myosin II-dependent force generation is tightly regulated, and deregulation is associated with specific pathologies. Here, we focus on the role of myosin II (nonmuscle myosin II, NMII) in force generation and mechanobiology. We outline the regulation and molecular mechanism of force generation by NMII, focusing on the actual outcome of contraction, that is, force application to trigger mechanosensitive events or the building of dissipative structures. We describe how myosin II-generated forces drive two major types of events: modification of the cellular morphology and/or triggering of genetic programs, which enhance the ability of cells to adapt to, or modify, their microenvironment. Finally, we address whether targeting myosin II to impair or potentiate its activity at the motor level is a viable therapeutic strategy, as illustrated by recent examples aimed at modulating cardiac myosin II function in heart disease.

Nonepithelial cancer dissemination: specificities and challenges

Epithelial cancers have served as a paradigm to study tumor dissemination but recent data have highlighted significant differences with nonepithelial cancers. Here, we review the current knowledge on nonepithelial tumor dissemination, drawing examples from the latest developments in melanoma, glioma, and sarcoma research. We underscore the importance of the reactivation of developmental processes during cancer progression and describe the nongenetic mechanisms driving nonepithelial tumor spread. We also outline therapeutic opportunities and ongoing clinical approaches to fight disseminating cancers. Finally, we discuss remaining challenges and emerging questions in the field. Defining the core principles underlying nonepithelial cancer dissemination may uncover actionable vulnerabilities of metastatic tumors and help improve the prognosis of patients with cancer.

Cooperative involvement of zipper-interacting protein kinase (ZIPK) and the dual-specificity cell-division cycle 14A phosphatase (CDC14A) in vascular smooth muscle cell migration

Zipper-interacting protein kinase (ZIPK) is a Ser/Thr protein kinase with regulatory involvement in vascular smooth muscle cell (VSMC) actin polymerization and focal adhesion assembly dynamics. ZIPK silencing can induce cytoskeletal remodeling with disassembly of actin stress fiber networks and coincident loss of focal adhesion kinase (FAK)-pY397 phosphorylation. The link between ZIPK inhibition and FAK phosphorylation is unknown, and critical interactor(s) and regulator(s) are not yet defined. In this study, we further analyzed the ZIPK-FAK relationship in VSMCs. The application of HS38, a selective ZIPK inhibitor, to coronary artery vascular smooth muscle cells (CASMCs) suppressed cell migration, myosin light chain phosphorylation (pT18&pS19) and FAK-pY397 phosphorylation as well. This was associated with the translocation of cytoplasmic FAK to the nucleus. ZIPK inhibition with HS38 was consistently found to suppress the activation of FAK and attenuate the phosphorylation of other focal adhesion protein components (i.e., pCas130, paxillin, ERK). In addition, our study showed a decrease in human cell-division cycle 14A phosphatase (CDC14A) levels with ZIPK-siRNA treatment and increased CDC14A with transient transfection of ZIPK. Proximity ligation assays (PLA) revealed CDC14A localized with ZIPK and FAK. Silencing CDC14A showed an increase of FAK-pY397 phosphorylation. Ultimately, the data presented herein strongly support a regulatory mechanism of FAK in CASMCs by a ZIPK-CDC14A partnership; ZIPK may act as a key signal integrator to control CDC14A and FAK during VSMC migration.

"Baihui" (DU20)-penetrating "Qubin" (GB7) acupuncture on blood-brain barrier integrity in rat intracerebral hemorrhage models via the RhoA/ROCK II/MLC 2 signaling pathway

BACKGROUND

Blocking the RhoA/ROCK II/MLC 2 (Ras homolog gene family member A/Rho kinase II/myosin light chain 2) signaling pathway can initiate neuroprotective mechanisms against neurological diseases such as stroke, cerebral ischemia, and subarachnoid hemorrhage. Nevertheless, it is not clear whether and how disrupting the RhoA/ROCK II/MLC 2 signaling pathway changes the pathogenic processes of the blood-brain barrier (BBB) after intracerebral hemorrhage (ICH). The present investigation included the injection of rat caudal vein blood into the basal ganglia area to replicate the pathophysiological conditions caused by ICH.

METHODS

Scalp acupuncture (SA) therapy was performed on rats with ICH at the acupuncture point "Baihui"-penetrating "Qubin," and the ROCK selective inhibitor fasudil was used as a positive control to evaluate the inhibitory effect of acupuncture on the RhoA/ROCK II/MLC 2 signaling pathway. Post-assessments included neurological deficits, brain edema, Evans blue extravasation, Western blot, quantitative polymerase chain reaction, and transmission electron microscope imaging.

RESULTS

We found that ROCK II acts as a promoter of the RhoA/ROCK II/MLC 2 signaling pathway, and its expression increased at 6 h after ICH, peaked at 3 days, and then decreased at 7 days after ICH, but was still higher than the pre-intervention level. According to some experimental results, although 3 days is the peak, 7 days is the best time point for acupuncture treatment. Starting from 6 h after ICH, the neurovascular structure and endothelial cell morphology around the hematoma began to change. Based on the changes in the promoter ROCK II, a 7-day time point was selected as the breakthrough point for treating ICH model rats in the main experiment. The results of this experiment showed that both SA at "Baihui"-penetrating "Qubin" and treatment with fasudil could improve the expression of endothelial-related proteins by inhibiting the RhoA/ROCK II/MLC 2 signaling pathway and reduce neurological dysfunction, brain edema, and BBB permeability in rats.

CONCLUSION

This study found that these experimental data indicated that SA at "Baihui"-penetrating "Qubin" could preserve BBB integrity and neurological function recovery after ICH by inhibiting RhoA/ROCK II/MLC 2 signaling pathway activation and by regulating endothelial cell-related proteins.

Tanshinone IIA modulates cancer cell morphology and movement via Rho GTPases-mediated actin cytoskeleton remodeling

Actin filaments form unique structures with robust actin bundles and cytoskeletal networks affixed to the extracellular matrix and interact with neighboring cells, which are crucial structures for cancer cells to acquire a motile phenotype. This study aims to investigate a novel antitumor mechanism by which Tanshinone IIA (Tan IIA) modulates the morphology and migration of liver cancer cells via actin cytoskeleton regulation. 97H and Huh7 exhibited numerous tentacle-like protrusions that interacted with neighboring cells. Following treatment with Tan IIA, 97H and Huh7 showed a complete absence of cytoplasmic protrusion and adherens junctions, thereby effectively impeding their migration capability. The fluorescence staining of F-actin and microtubules indicated that these tentacle-like protrusions and cell-cell networks were actin-based structures that led to morphological changes after Tan IIA treatment by retracting and reorganizing beneath the membrane. Tan IIA can reverse the actin depolymerization and cell morphology alterations induced by latrunculin A. Tan IIA down-regulated actin and Rho GTPases expression significantly, as opposed to inducing Rho signaling activation. Preventing the activity of proteasomes and lysosomes had no discernible impact on the modifications in cellular structure and protein expression induced by Tan IIA. However, as demonstrated by the puromycin labeling technique, the newly synthesized proteins were significantly inhibited by Tan IIA. In conclusion, Tan IIA can induce dramatic actin cytoskeleton remodeling by inhibiting the protein synthesis of actin and Rho GTPases, resulting in the suppression of tumor growth and migration. Targeting the actin cytoskeleton of Tan IIA is a promising strategy for HCC treatment.

How important is EMT for cancer metastasis?

Epithelial-to-mesenchymal transition (EMT), a biological phenomenon of cellular plasticity initially reported in embryonic development, has been increasingly recognized for its importance in cancer progression and metastasis. Despite tremendous progress being made in the past 2 decades in our understanding of the molecular mechanism and functional importance of EMT in cancer, there are several mysteries around EMT that remain unresolved. In this Unsolved Mystery, we focus on the variety of EMT types in metastasis, cooperative and collective EMT behaviors, spatiotemporal characterization of EMT, and strategies of therapeutically targeting EMT. We also highlight new technical advances that will facilitate the efforts to elucidate the unsolved mysteries of EMT in metastasis.

hRpn13 shapes the proteome and transcriptome through epigenetic factors HDAC8, PADI4, and transcription factor NF-κB p50

The anti-cancer target hRpn13 is a proteasome substrate receptor. However, hRpn13-targeting molecules do not impair its interaction with proteasomes or ubiquitin, suggesting other critical cellular activities. We find that hRpn13 depletion causes correlated proteomic and transcriptomic changes, with pronounced effects in myeloma cells for cytoskeletal and immune response proteins and bone-marrow-specific arginine deiminase PADI4. Moreover, a PROTAC against hRpn13 co-depletes PADI4, histone deacetylase HDAC8, and DNA methyltransferase MGMT. PADI4 binds and citrullinates hRpn13 and proteasomes, and proteasomes from PADI4-inhibited myeloma cells exhibit reduced peptidase activity. When off proteasomes, hRpn13 can bind HDAC8, and this interaction inhibits HDAC8 activity. Further linking hRpn13 to transcription, its loss reduces nuclear factor κB (NF-κB) transcription factor p50, which proteasomes generate by cleaving its precursor protein. NF-κB inhibition depletes hRpn13 interactors PADI4 and HDAC8. Altogether, we find that hRpn13 acts dually in protein degradation and expression and that proteasome constituency and, in turn, regulation varies by cell type.

Cell state dependent effects of Bmal1 on melanoma immunity and tumorigenicity

The circadian clock regulator Bmal1 modulates tumorigenesis, but its reported effects are inconsistent. Here, we show that Bmal1 has a context-dependent role in mouse melanoma tumor growth. Loss of Bmal1 in YUMM2.1 or B16-F10 melanoma cells eliminates clock function and diminishes hypoxic gene expression and tumorigenesis, which could be rescued by ectopic expression of HIF1α in YUMM2.1 cells. By contrast, over-expressed wild-type or a transcriptionally inactive mutant Bmal1 non-canonically sequester myosin heavy chain 9 (Myh9) to increase MRTF-SRF activity and AP-1 transcriptional signature, and shift YUMM2.1 cells from a Sox10high to a Sox9high immune resistant, mesenchymal cell state that is found in human melanomas. Our work describes a link between Bmal1, Myh9, mouse melanoma cell plasticity, and tumor immunity. This connection may underlie cancer therapeutic resistance and underpin the link between the circadian clock, MRTF-SRF and the cytoskeleton.

RhoA activation promotes glucose uptake to elevate proliferation in MAPK inhibitor resistant melanoma cells

Cutaneous melanomas harboring a B-RafV600E mutation are treated with immune check point inhibitors or kinase inhibitor combination therapies relying on MAPK inhibitors (MAPKi) Dabrafenib and Trametinib (Curti and Faries, 2021). However, cells become resistant to treatments over the timespan of a few months. Resistance to MAPKi has been associated with adoption of an aggressive amoeboid phenotype characterized by elevated RhoA signaling, enhanced contractility and thick cortical filamentous actin (F-actin) structures (Kim et al., 2016; Misek et al., 2020). Targeting active RhoA through Rho-kinase (ROCK) inhibitors, either alone or in combination with immunotherapies, reverts MAPKi-resistance (Misek et al., 2020; Orgaz et al., 2020). Yet, the mechanisms for this behavior remain largely unknown. Given our recent findings of cytoskeleton's role in cancer cell proliferation (Mohan et al., 2019), survival (Weems et al., 2023), and metabolism (Park et al., 2020), we explored possibilities by which RhoA-driven changes in cytoskeleton structure may confer resistance. We confirmed elevated activation of RhoA in a panel of MAPKi-resistant melanoma cell lines, leading to a marked increase in the presence of contractile F-actin bundles. Moreover, these cells had increased glucose uptake and glycolysis, a phenotype disrupted by pharmacological perturbation of ROCK. However, glycolysis was unaffected by disruption of F-actin bundles, indicating that glycolytic stimulation in MAPKi-resistant melanoma is independent of F-actin organization. Instead, our findings highlight a mechanism in which elevated RhoA signaling activates ROCK, leading to the activation of insulin receptor substrate 1 (IRS1) and P85 of the PI3K pathway, which promotes cell surface expression of GLUT1 and elevated glucose uptake. Application of ROCK inhibitor GSK269962A results in reduced glucose uptake and glycolysis, thus impeding cell proliferation. Our study adds a mechanism to the proposed use of ROCK inhibitors for long-term treatments on MAPKi-resistant melanomas.

Integrative approaches based on genomic techniques in the functional studies on enhancers

With the development of sequencing technology and the dramatic drop in sequencing cost, the functions of noncoding genes are being characterized in a wide variety of fields (e.g. biomedicine). Enhancers are noncoding DNA elements with vital transcription regulation functions. Tens of thousands of enhancers have been identified in the human genome; however, the location, function, target genes and regulatory mechanisms of most enhancers have not been elucidated thus far. As high-throughput sequencing techniques have leapt forwards, omics approaches have been extensively employed in enhancer research. Multidimensional genomic data integration enables the full exploration of the data and provides novel perspectives for screening, identification and characterization of the function and regulatory mechanisms of unknown enhancers. However, multidimensional genomic data are still difficult to integrate genome wide due to complex varieties, massive amounts, high rarity, etc. To facilitate the appropriate methods for studying enhancers with high efficacy, we delineate the principles, data processing modes and progress of various omics approaches to study enhancers and summarize the applications of traditional machine learning and deep learning in multi-omics integration in the enhancer field. In addition, the challenges encountered during the integration of multiple omics data are addressed. Overall, this review provides a comprehensive foundation for enhancer analysis.

Mechanotransduction in response to ECM stiffening impairs cGAS immune signaling in tumor cells

The tumor microenvironment (TME) plays decisive roles in disabling T cell-mediated antitumor immunity, but the immunoregulatory functions of its biophysical properties remain elusive. Extracellular matrix (ECM) stiffening is a hallmark of solid tumors. Here, we report that the stiffened ECM contributes to the immunosuppression in TME via activating the Rho-associated coiled-coil-containing protein kinase (ROCK)-myosin IIA-filamentous actin (F-actin) mechanosignaling pathway in tumor cells to promote the generation of TRIM14-scavenging nonmuscle myosin heavy chain IIA (NMHC-IIA)-F-actin stress fibers, thus accelerating the autophagic degradation of cyclic guanosine monophosphate (GMP)-AMP synthase (cGAS) to deprive tumor cyclic GMP-AMP (cGAMP) and further attenuating tumor immunogenicity. Pharmacological inhibition of myosin IIA effector molecules with blebbistatin (BLEB) or the RhoA upstream regulator of this pathway with simvastatin (SIM) restored tumor-intrinsic cGAS-mediated cGAMP production and enhanced antitumor immunity. Our work identifies that ECM stiffness is an important biophysical cue to regulate tumor immunogenicity via the ROCK-myosin IIA-F-actin axis and that inhibiting this mechanosignaling pathway could boost immunotherapeutic efficacy for effective solid tumor treatment.

CD73 controls Myosin II-driven invasion, metastasis, and immunosuppression in amoeboid pancreatic cancer cells

Pancreatic ductal adenocarcinoma (PDAC) has a very poor prognosis because of its high propensity to metastasize and its immunosuppressive microenvironment. Using a panel of pancreatic cancer cell lines, three-dimensional (3D) invasion systems, microarray gene signatures, microfluidic devices, mouse models, and intravital imaging, we demonstrate that ROCK-Myosin II activity in PDAC cells supports a transcriptional program conferring amoeboid invasive and immunosuppressive traits and in vivo metastatic abilities. Moreover, we find that immune checkpoint CD73 is highly expressed in amoeboid PDAC cells and drives their invasive, metastatic, and immunomodulatory traits. Mechanistically, CD73 activates RhoA-ROCK-Myosin II downstream of PI3K. Tissue microarrays of human PDAC biopsies combined with bioinformatic analysis reveal that rounded-amoeboid invasive cells with high CD73-ROCK-Myosin II activity and their immunosuppressive microenvironment confer poor prognosis to patients. We propose targeting amoeboid PDAC cells as a therapeutic strategy.

Understanding the driving force for cell migration plasticity

Cell migration is a complex phenomenon. Not only do different cells migrate in different default modes, but the same cell can also change its migration mode to adapt to different terrains. This complexity has riddled cell biologists and biophysicists for decades in that, despite the development of many powerful tools over the past 30 years, how cells move is still being actively investigated. This is because we have yet to fully understand the mystery of cell migration plasticity, particularly the reciprocal relation between force generation and migration mode transition. Herein we explore the future directions, in terms of measurement platforms and imaging-based techniques, to facilitate the undertaking of elucidating the relation between force generation machinery and migration mode transition. By briefly reviewing the evolution of the platforms and techniques developed in the past, we propose the desirable features to be added to achieve high measurement accuracy and improved temporal and spatial resolution, permitting us to unveil the mystery of cell migration plasticity.

Role of Rho/MRTF in Aggressive Vemurafenib-Resistant Murine Melanomas and Immune Checkpoint Upregulation

Cutaneous melanoma is the deadliest skin cancer. Most have Ras-MAPK pathway (BRAFV600E or NRAS) mutations and highly effective targeted therapies exist; however, they and immune therapies are limited by resistance, in part driven by small GTPase (Rho and Rac) activation. To facilitate preclinical studies of combination therapies to provide durable responses, we describe the first mouse melanoma lines resistant to BRAF inhibitors. Treatment of mouse lines, YUMM1.7 and YUMMER, with vemurafenib (Vem), the BRAFV600E-selective inhibitor, resulted in high-level resistance (IC50 shifts 20-30-fold). Resistant cells showed enhanced activation of Rho and the downstream transcriptional coactivator, myocardin-related transcription factor (MRTF). Resistant cells exhibited increased stress fibers, nuclear translocation of MRTF-A, and an increased MRTF-A gene signature. Pharmacological inhibition of the Rho/MRTF pathway using CCG-257081 reduced viability of resistant lines and enhanced sensitivity to Vem. Remarkably, co-treatment of parental lines with Vem and CCG-257081 eliminated resistant colony development. Resistant cells grew more slowly in vitro, but they developed highly aggressive tumors with a shortened survival of tumor-bearing mice. Increased expression of immune checkpoint inhibitor proteins (ICIs) in resistant lines may contribute to aggressive in vivo behavior. Here, we introduce the first drug-resistant mouse melanoma models for assessing combinations of targeted and immune therapies.

Combination of immune-checkpoint inhibitors and targeted therapies for melanoma therapy: The more, the better?

The approval of immune-checkpoint inhibitors (CPI) and mitogen activated protein kinase inhibitors (MAPKi) in recent years significantly improved the treatment management and survival of patients with advanced malignant melanoma. CPI aim to counter-act receptor-mediated inhibitory effects of tumor cells and immunomodulatory cell types on effector T cells, whereas MAPKi are intended to inhibit tumor cell survival. In agreement with these complementary modes of action preclinical data indicated that the combined application of CPI and MAPKi or their optimal sequencing might provide additional clinical benefit. In this review the rationale and preclinical evidence that support the combined application of MAPKi and CPI either in concurrent or consecutive regimens are presented. Further, we will discuss the results from clinical trials investigating the sequential or combined application of MAPKi and CPI for advanced melanoma patients and their implications for clinical practice. Finally, we outline mechanisms of MAPKi and CPI cross-resistance which limit the efficacy of currently available treatments, as well as combination regimens.

AMPK is a mechano-metabolic sensor linking cell adhesion and mitochondrial dynamics to Myosin-dependent cell migration

Cell migration is crucial for cancer dissemination. We find that AMP-activated protein kinase (AMPK) controls cell migration by acting as an adhesion sensing molecular hub. In 3-dimensional matrices, fast-migrating amoeboid cancer cells exert low adhesion/low traction linked to low ATP/AMP, leading to AMPK activation. In turn, AMPK plays a dual role controlling mitochondrial dynamics and cytoskeletal remodelling. High AMPK activity in low adhering migratory cells, induces mitochondrial fission, resulting in lower oxidative phosphorylation and lower mitochondrial ATP. Concurrently, AMPK inactivates Myosin Phosphatase, increasing Myosin II-dependent amoeboid migration. Reducing adhesion or mitochondrial fusion or activating AMPK induces efficient rounded-amoeboid migration. AMPK inhibition suppresses metastatic potential of amoeboid cancer cells in vivo, while a mitochondrial/AMPK-driven switch is observed in regions of human tumours where amoeboid cells are disseminating. We unveil how mitochondrial dynamics control cell migration and suggest that AMPK is a mechano-metabolic sensor linking energetics and the cytoskeleton.

JMJD2A participates in cytoskeletal remodeling to regulate castration-resistant prostate cancer docetaxel resistance

BACKGROUND

To investigate underlying mechanism of JMJD2A in regulating cytoskeleton remodeling in castration-resistant prostate cancer (CRPC) resistant to docetaxel.

METHODS

Tissue samples from CRPC patients were collected, and the expression of JMJD2A, miR-34a and cytoskeleton remodeling-related proteins were evaluated by qPCR, western blot and immunohistochemistry, and pathological changes were observed by H&E staining. Further, JMJD2A, STMN1 and TUBB3 were knocked down using shRNA in CRPC cell lines, and cell viability, apoptosis and western blot assays were performed. The interaction between miR-34a/STMN1/β3-Tubulin was analyzed with dual-luciferase reporter and co-immunoprecipitation assays.

RESULTS

In clinical experiment, the CRPC-resistant group showed higher expression of JMJD2A, STMN1, α-Tubulin, β-Tubulin and F-actin, and lower expression of miR-34a and β3-Tubulin compared to the sensitive group. In vitro experiments showed that JMJD2A could regulate cytoskeletal remodeling through the miR-34a/STMN1/β3-Tubulin axis. The expression of miR-34a was elevated after knocking down JMJD2A, and miR-34a targeted STMN1. The overexpression of miR-34a was associated with a decreased expression of STMN1 and elevated expression of β3-Tubulin, which led to the disruption of the microtubule network, decreased cancer cell proliferation, cell cycle arrest in the G0/G1 phase, and increased apoptosis.

CONCLUSION

JMJD2A promoted docetaxel resistance in prostate cancer cells by regulating cytoskeleton remodeling through the miR-34a/STMN1/β3-Tubulin axis.

High expression of Talin-1 is associated with tumor progression and recurrence in melanoma skin cancer patients

BACKGROUND

Talin-1 as a component of multi-protein adhesion complexes plays a role in tumor formation and migration in various malignancies. This study investigated Talin-1 in protein levels as a potential prognosis biomarker in skin tumors.

METHODS

Talin-1 was evaluated in 106 skin cancer (33 melanomas and 73 non-melanomas skin cancer (NMSC)) and 11 normal skin formalin-fixed paraffin-embedded (FFPE) tissue samples using immunohistochemical technique on tissue microarrays (TMAs). The association between the expression of Talin-1 and clinicopathological parameters, as well as survival outcomes, were assessed.

RESULTS

Our findings from data minings through bioinformatics tools indicated dysregulation of Talin-1 in mRNA levels for skin cancer samples. In addition, there was a statistically significant difference in Talin-1 expression in terms of intensity of staining, percentage of positive tumor cells, and H-score in melanoma tissues compared to NMSC (P = 0.001, P < 0.001, and P < 0.001, respectively). Moreover, high cytoplasmic expression of Talin-1 was found to be associated with significantly advanced stages (P = 0.024), lymphovascular invasion (P = 0.023), and recurrence (P = 0.006) in melanoma cancer tissues. Our results on NMSC showed a statistically significant association between high intensity of staining and the poor differentiation (P = 0.044). No significant associations were observed between Talin-1 expression levels and survival outcomes of melanoma and NMSC patients.

CONCLUSION

Our observations showed that higher expression of Talin1 in protein level may be significantly associated with more aggressive tumor behavior and advanced disease in patients with skin cancer. However, further studies are required to find the mechanism of action of Talin-1 in skin cancers.

Myo1e overexpression in lung adenocarcinoma is associated with increased risk of mortality

This study aims to perform a comprehensive genomic analysis to assess the influence of overexpression of MYO1E in non-small cell lung carcinoma (NSCLC) and whether there are differences in survival and mortality risk in NSCLC patients depending on both DNA methylation and RNA expression of MYO1E. The DNA methylation probe cg13887966 was inversely correlated with MYO1E RNA expression in both LUAD and LUSC subpopulations showing that lower MYO1E RNA expression was associated with higher MYO1E DNA methylation. Late stages of lung cancer showed significantly lower MYO1E DNA methylation and significantly higher MYO1E RNA expression for LUAD but not for LUSC. Low DNA methylation as well as high RNA expression of MYO1E are associated with a shorter median survival time and an increased risk of mortality for LUAD, but not for LUSC. This study suggests that changes in MYO1E methylation and expression in LUAD patients may have an essential role in lung cancer's pathogenesis. It shows the utility of MYO1E DNA methylation and RNA expression in predicting survival for LUAD patients. Also, given the low normal expression of MYO1E in blood cells MYO1E DNA methylation has the potential to be used as circulating tumor marker in liquid biopsies.

Blebs promote cell survival by assembling oncogenic signalling hubs

Most human cells require anchorage for survival. Cell-substrate adhesion activates diverse signalling pathways, without which cells undergo anoikis-a form of programmed cell death1. Acquisition of anoikis resistance is a pivotal step in cancer disease progression, as metastasizing cells often lose firm attachment to surrounding tissue2,3. In these poorly attached states, cells adopt rounded morphologies and form small hemispherical plasma membrane protrusions called blebs4-11. Bleb function has been thoroughly investigated in the context of amoeboid migration, but it has been examined far less in other scenarios12. Here we show by three-dimensional imaging and manipulation of cell morphological states that blebbing triggers the formation of plasma membrane-proximal signalling hubs that confer anoikis resistance. Specifically, in melanoma cells, blebbing generates plasma membrane contours that recruit curvature-sensing septin proteins as scaffolds for constitutively active mutant NRAS and effectors. These signalling hubs activate ERK and PI3K-well-established promoters of pro-survival pathways. Inhibition of blebs or septins has little effect on the survival of well-adhered cells, but in detached cells it causes NRAS mislocalization, reduced MAPK and PI3K activity, and ultimately, death. This unveils a morphological requirement for mutant NRAS to operate as an effective oncoprotein. Furthermore, whereas some BRAF-mutated melanoma cells do not rely on this survival pathway in a basal state, inhibition of BRAF and MEK strongly sensitizes them to both bleb and septin inhibition. Moreover, fibroblasts engineered to sustain blebbing acquire the same anoikis resistance as cancer cells even without harbouring oncogenic mutations. Thus, blebs are potent signalling organelles capable of integrating myriad cellular information flows into concerted cellular responses, in this case granting robust anoikis resistance.

Preclinical to clinical utility of ROCK inhibitors in cancer

ROCK belongs to the AGC family of Ser/Thr protein kinases that are involved in many cellular processes. ROCK-driven actomyosin contractility regulates cytoskeletal dynamics underpinning cell migration, proliferation, and survival in many cancer types. ROCK1/2 play key protumorigenic roles in several subtypes and stages of cancer development. Therefore, successfully targeting ROCK and its downstream effectors presents an interesting avenue for cancer treatment. Because local use of ROCK inhibitors will reduce the side effects of systemic administration, we propose different therapeutic strategies and latest-generation ROCK inhibitors for use in the clinic.

Endoplasmic reticulum-targeted NIR-II phototherapy combined with inflammatory vascular suppression elicits a synergistic effect against TNBC

Recurrence and metastasis are the main reasons for failure in the treatment of triple-negative breast cancer (TNBC). Phototherapy, one of the most well-known potent cancer treatment models is highlighted by ablating primitive tumors with immunogenic cell death (ICD) and is associated with endoplasmic reticulum (ER) stress to elicit long-lasting anti-tumor immunity. However, the provoked inflammatory response after phototherapy will stimulate angiogenesis, which provides nutrition for tumor recurrence. Here, an ER-targeted nanoplatform was constructed based on hollow mesoporous Cu_2-XS (HMCu_2-XS) nanoparticles to suppress recurrence and metastasis of TNBC by combining photo-ablation and microenvironment remodeling. Profiting from the metal ion coordination and large hollow space, HMCu_2-XS can be easily modified with p-toluenesulfonamide for ER-targeting and quantitatively loaded celecoxib (CXB) as a vascular inhibitor, thus obtaining ER-HMCu_2-XS/CXB. ER-HMCu_2-XS showed great photothermal and photodynamic efficiency for ablating 4T1 tumors and inducing ICD under NIR-II laser irradiation. Compared with non-ER-targeted nanosystems, the ER-targeted nanosystem elicited stronger ICDs and recruited more immune cells. Moreover, the thermal-responsively released CXB successfully inhibited angiogenesis after photothermal therapy. The data showed that the ER-HMCu_2-XS/CXB mediated the triplicate therapeutic effect of photo-ablation, immune response activation, and vascular suppression effectively, preventing the recurrence and metastasis of TNBC. In conclusion, this work provides a synergistic strategy to enhance therapeutic outcomes in TNBC.

ASAP1 activates the IQGAP1/CDC42 pathway to promote tumor progression and chemotherapy resistance in gastric cancer

Abnormal expression and remodeling of cytoskeletal regulatory proteins are important mechanisms for tumor development and chemotherapy resistance. This study systematically analyzed the relationship between differential expression of cytoskeleton genes and prognosis in gastric cancer (GC). We found the Arf GTP-activating protein ASAP1 plays a key role in cytoskeletal remodeling and prognosis in GC patients. Here we analyzed the expression level of ASAP1 in tissue microarrays carrying 564 GC tissues by immunohistochemistry. The results showed that ASAP1 expression was upregulated in GC cells and can be served as a predictor of poor prognosis. Moreover, ASAP1 promoted the proliferation, migration, and invasion of GC cells both in vitro and in vivo. We also demonstrated that ASAP1 inhibited the ubiquitin-mediated degradation of IQGAP1 and thus enhanced the activity of CDC42. The activated CDC42 upregulated the EGFR-MAPK pathway, thereby promoting the resistance to chemotherapy in GC. Taken together, our results revealed a novel mechanism by which ASAP1 acts in the progression and chemotherapy resistance in GC. This may provide an additional treatment option for patients with GC.

The mechanical phenotypic plasticity of melanoma cell: an emerging driver of therapy cross-resistance

Advanced cutaneous melanoma is the deadliest form of skin cancer and one of the most aggressive human cancers. Targeted therapies (TT) against BRAF mutated melanoma and immune checkpoints blockade therapies (ICB) have been a breakthrough in the treatment of metastatic melanoma. However, therapy-driven resistance remains a major hurdle in the clinical management of the metastatic disease. Besides shaping the tumor microenvironment, current treatments impact transition states to promote melanoma cell phenotypic plasticity and intratumor heterogeneity, which compromise treatment efficacy and clinical outcomes. In this context, mesenchymal-like dedifferentiated melanoma cells exhibit a remarkable ability to autonomously assemble their own extracellular matrix (ECM) and to biomechanically adapt in response to therapeutic insults, thereby fueling tumor relapse. Here, we review recent studies that highlight mechanical phenotypic plasticity of melanoma cells as a hallmark of adaptive and non-genetic resistance to treatment and emerging driver in cross-resistance to TT and ICB. We also discuss how targeting BRAF-mutant dedifferentiated cells and ECM-based mechanotransduction pathways may overcome melanoma cross-resistance.

Emerging targets for cancer treatment: S100A9/RAGE

Developing better treatments that work for the majority of patients with brain metastasis (BM) is highly necessary. Complementarily, avoiding those therapeutic procedures that will not benefit a specific patient is also very relevant. In general, existing therapies for patients with BM could be improved in terms of molecular stratification and therapeutic efficacy. By questioning the benefit of whole brain radiotherapy as provided nowadays and the lack of biomarkers detecting radioresistance, we identified S100A9 and receptor for advanced glycation end-products (RAGE) as a liquid biopsy biomarker and a potential target for a radiosensitizer, respectively. Both of them are being clinically tested as part of the first comprehensive molecular strategy to personalized radiotherapy in BM.

FOXD3 confers chemo-sensitivity in ovarian cancer through a miR-335/DAAM1/myosin II axis-dependent mechanism

BACKGROUND

Chemotherapy is among the most common treatment methods for ovarian cancer (OC). However, chemoresistance limits the effectiveness of chemotherapy and leads to treatment failure. We herein investigate the biological effect of forkhead box D3 (FOXD3) in the chemoresistance of OC cells.

METHODS

Expression of FOXD3, miR-335 and disheveled-associated activator of morphogenesis 1 (DAAM1) was detected in OC cells and tissues. The regulatory network of FOXD3/miR-335/DAAM1 was validated by dual-luciferase reporter and ChIP assays in vitro. After ectopic expression and depletion experiments in carboplatin/paclitaxel (CP)-resistant (A2780CP) or sensitive (A2780S) OC cells, cell viability, colony formation and apoptosis were tested by CCK-8 assay, colony formation assay and flow cytometry respectively. Effects of FOXD3 on the chemoresistance of OC cells in vivo were evaluated in OC xenografts in nude mice.

RESULTS

Overexpression of FOXD3 impaired the proliferation and chemoresistance of OC cells, which was related to the promotion of the miR-335 expression. Functionally, DAAM1 was a putative target of miR-335. Silencing of DAAM1 was responsible for the inhibition of myosin II activation, consequently leading to suppressed OC cell proliferation and chemoresistance. In vivo results further showed that FOXD3 weakened the chemoresistance of OC cells to CP.

CONCLUSION

Taken together, we unveil a novel FOXD3/miR-335/DAAM1/myosin II axis that regulates the chemoresistance of OC both in vitro and in vivo.

Amoeboid migration in health and disease: Immune responses versus cancer dissemination

Cell migration is crucial for efficient immune responses and is aberrantly used by cancer cells during metastatic dissemination. Amoeboid migrating cells use myosin II-powered blebs to propel themselves, and change morphology and direction. Immune cells use amoeboid strategies to respond rapidly to infection or tissue damage, which require quick passage through several barriers, including blood, lymph and interstitial tissues, with complex and varied environments. Amoeboid migration is also used by metastatic cancer cells to aid their migration, dissemination and survival, whereby key mechanisms are hijacked from professionally motile immune cells. We explore important parallels observed between amoeboid immune and cancer cells. We also consider key distinctions that separate the lifespan, state and fate of these cell types as they migrate and/or fulfil their function. Finally, we reflect on unexplored areas of research that would enhance our understanding of how tumour cells use immune cell strategies during metastasis, and how to target these processes.

LAP1 supports nuclear adaptability during constrained melanoma cell migration and invasion

Metastasis involves dissemination of cancer cells away from a primary tumour and colonization at distal sites. During this process, the mechanical properties of the nucleus must be tuned since they pose a challenge to the negotiation of physical constraints imposed by the microenvironment and tissue structure. We discovered increased expression of the inner nuclear membrane protein LAP1 in metastatic melanoma cells, at the invasive front of human primary melanoma tumours and in metastases. Human cells express two LAP1 isoforms (LAP1B and LAP1C), which differ in their amino terminus. Here, using in vitro and in vivo models that recapitulate human melanoma progression, we found that expression of the shorter isoform, LAP1C, supports nuclear envelope blebbing, constrained migration and invasion by allowing a weaker coupling between the nuclear envelope and the nuclear lamina. We propose that LAP1 renders the nucleus highly adaptable and contributes to melanoma aggressiveness.

The role of RAS oncogenes in controlling epithelial mechanics

Mutations in RAS are key oncogenic drivers and therapeutic targets. Oncogenic Ras proteins activate a network of downstream signalling pathways, including extracellular signal-regulated kinase (ERK) and phosphatidylinositol 3-kinase (PI3K), promoting cell proliferation and survival. However, there is increasing evidence that RAS oncogenes also alter the mechanical properties of both individual malignant cells and transformed tissues. Here we discuss the role of oncogenic RAS in controlling mechanical cell phenotypes and how these mechanical changes promote oncogenic transformation in single cells and tissues. RAS activation alters actin organisation and actomyosin contractility. These changes alter cell rheology and impact mechanosensing through changes in substrate adhesion and YAP/TAZ-dependent mechanotransduction. We then discuss how these changes play out in cell collectives and epithelial tissues by driving large-scale tissue deformations and the expansion of malignant cells. Uncovering how RAS oncogenes alter cell mechanics will lead to a better understanding of the morphogenetic processes that underlie tumour formation in RAS-mutant cancers.

HER2 inhibition increases non-muscle myosin IIA to promote tumorigenesis in HER2+ breast cancers

HER2 is over-expressed in around 15% to 20% of breast cancers. HER3 plays a critical role in HER2 mediated tumorigenesis. Increased HER3 transcription and protein levels occur upon inhibition of HER2. We aimed to identify proteins that bound to HER3 upon inhibition of the HER family with the pan-HER inhibitor neratinib in HER2+ breast cancer cells. Immunoprecipitation of HER3 followed by mass spectrometry experiments found non-muscle myosin IIA (NMIIA) increased upon neratinib treatment relative to vehicle DMSO treatment. MYH9 is the gene that encodes for the heavy chain of NMIIA. Breast cancer patients with high MYH9 were significantly associated with a shorter disease specific survival compared to patients with low MYH9 expression from the METABRIC cohort of patients. In addition, high MYH9 expression was associated with HER2+ tumors from this cohort. Immunoblots of whole cell lysates of BT474 and MDA-MB-453 HER2+ breast cancer cells demonstrated elevated HER3 and NMIIA protein levels upon neratinib treatment for 24 hours. To examine the role of NMIIA in HER2+ breast cancer, we modulated NMIIA levels in BT474 and MDA-MB-453 cells using doxycycline inducible shRNA targeting MYH9. MYH9 knockdown reduces HER3 protein levels and concomitant reduction in downstream P-Akt. In addition, loss of MYH9 suppresses cell growth, proliferation, migration, and invasion. Our data reveals that NMIIA regulates HER3 and loss of NMIIA reduces HER2+ breast cancer growth.

Multiplex chromogenic immunohistochemistry to stain and analyze paraffin tissue sections from the mouse or human

Here we describe a multiplex chromogenic immunohistochemistry platform to stain and analyze two markers in paraffin tissue sections from mouse or human. The basis of the protocol is a series of stripping and re-probing steps with subsequent image analysis, which allows the user to perform multiplex imaging in a reliable and affordable manner. Here, we describe specific usage to assess the levels of PD-L1 in tumor-associated macrophages. We have used different antibodies and assessed this protocol for up to five consecutive antibodies per slide. For complete details on the use and execution of this protocol, please refer to Orgaz et al. (2020).¹.

HBXIP blocks myosin-IIA assembly by phosphorylating and interacting with NMHC-IIA in breast cancer metastasis

Tumor metastasis depends on the dynamic balance of the actomyosin cytoskeleton. As a key component of actomyosin filaments, non-muscle myosin-IIA disassembly contributes to tumor cell spreading and migration. However, its regulatory mechanism in tumor migration and invasion is poorly understood. Here, we found that oncoprotein hepatitis B X-interacting protein (HBXIP) blocked the myosin-IIA assemble state promoting breast cancer cell migration. Mechanistically, mass spectrometry analysis, co-immunoprecipitation assay and GST-pull down assay proved that HBXIP directly interacted with the assembly-competent domain (ACD) of non-muscle heavy chain myosin-IIA (NMHC-IIA). The interaction was enhanced by NMHC-IIA S1916 phosphorylation via HBXIP-recruited protein kinase PKCβII. Moreover, HBXIP induced the transcription of PRKCB, encoding PKCβII, by coactivating Sp1, and triggered PKCβII kinase activity. Interestingly, RNA sequencing and mouse metastasis model indicated that the anti-hyperlipidemic drug bezafibrate (BZF) suppressed breast cancer metastasis via inhibiting PKCβII-mediated NMHC-IIA phosphorylation in vitro and in vivo. We reveal a novel mechanism by which HBXIP promotes myosin-IIA disassembly via interacting and phosphorylating NMHC-IIA, and BZF can serve as an effective anti-metastatic drug in breast cancer.

Influencing tumor-associated macrophages in malignant melanoma with monoclonal antibodies

The application of monoclonal antibodies (mAbs) for the treatment of melanoma has significantly improved the clinical management of this malignancy over the last decade. Currently approved mAbs for melanoma enhance T cell effector immune responses by blocking immune checkpoint molecules PD-L1/PD-1 and CTLA-4. However, more than half of patients do not benefit from treatment. Targeting the prominent myeloid compartment within the tumor microenvironment, and in particular the ever-abundant tumor-associated macrophages (TAMs), may be a promising strategy to complement existing therapies and enhance treatment success. TAMs are a highly diverse and plastic subset of cells whose pro-tumor properties can support melanoma growth, angiogenesis and invasion. Understanding of their diversity, plasticity and multifaceted roles in cancer forms the basis for new promising TAM-centered treatment strategies. There are multiple mechanisms by which macrophages can be targeted with antibodies in a therapeutic setting, including by depletion, inhibition of specific pro-tumor properties, differential polarization to pro-inflammatory states and enhancement of antitumor immune functions. Here, we discuss TAMs in melanoma, their interactions with checkpoint inhibitor antibodies and emerging mAbs targeting different aspects of TAM biology and their potential to be translated to the clinic.

Role of extracellular matrix architecture and signaling in melanoma therapeutic resistance

The extracellular matrix (ECM) is critical for maintaining tissue homeostasis therefore its production, assembly and mechanical stiffness are highly regulated in normal tissues. However, in solid tumors, increased stiffness resulting from abnormal ECM structural changes is associated with disease progression, an increased risk of metastasis and poor survival. As a dynamic and key component of the tumor microenvironment, the ECM is becoming increasingly recognized as an important feature of tumors, as it has been shown to promote several hallmarks of cancer via biochemical and biomechanical signaling. In this regard, melanoma cells are highly sensitive to ECM composition, stiffness and fiber alignment because they interact directly with the ECM in the tumor microenvironment via cell surface receptors, secreted factors or enzymes. Importantly, seeing as the ECM is predominantly deposited and remodeled by myofibroblastic stromal fibroblasts, it is a key avenue facilitating their paracrine interactions with melanoma cells. This review gives an overview of melanoma and further describes the critical roles that ECM properties such as ECM remodeling, ECM-related proteins and stiffness play in cutaneous melanoma progression, tumor cell plasticity and therapeutic resistance. Finally, given the emerging importance of ECM dynamics in melanoma, future perspectives on therapeutic strategies to normalize the ECM in tumors are discussed.

Tripartite split-GFP assay to identify selective intracellular nanobody that suppresses GTPase RHOA subfamily downstream signaling

Strategies based on intracellular expression of artificial binding domains present several advantages over manipulating nucleic acid expression or the use of small molecule inhibitors. Intracellularly-functional nanobodies can be considered as promising macrodrugs to study key signaling pathways by interfering with protein-protein interactions. With the aim of studying the RAS-related small GTPase RHOA family, we previously isolated, from a synthetic phage display library, nanobodies selective towards the GTP-bound conformation of RHOA subfamily proteins that lack selectivity between the highly conserved RHOA-like and RAC subfamilies of GTPases. To identify RHOA/ROCK pathway inhibitory intracellular nanobodies, we implemented a stringent, subtractive phage display selection towards RHOA-GTP followed by a phenotypic screen based on F-actin fiber loss. Intracellular interaction and intracellular selectivity between RHOA and RAC1 proteins was demonstrated by adapting the sensitive intracellular protein-protein interaction reporter based on the tripartite split-GFP method. This strategy led us to identify a functional intracellular nanobody, hereafter named RH28, that does not cross-react with the close RAC subfamily and blocks/disrupts the RHOA/ROCK signaling pathway in several cell lines without further engineering or functionalization. We confirmed these results by showing, using SPR assays, the high specificity of the RH28 nanobody towards the GTP-bound conformation of RHOA subfamily GTPases. In the metastatic melanoma cell line WM266-4, RH28 expression triggered an elongated cellular phenotype associated with a loss of cellular contraction properties, demonstrating the efficient intracellular blocking of RHOA/B/C proteins downstream interactions without the need of manipulating endogenous gene expression. This work paves the way for future therapeutic strategies based on protein-protein interaction disruption with intracellular antibodies.

Biomechanics of cancer stem cells

Cancer stem cells (CSCs) have been believed to be one driving force for tumor progression and drug resistance. Despite the significance of biochemical signaling in malignancy, highly malignant tumor cells or CSCs exhibit lower cellular stiffness than weakly malignant cells or non-CSCs, which are softer than their healthy counterparts, suggesting the inverse correlation between cell stiffness and malignancy. Recent years have witnessed the rapid accumulation of evidence illustrating the reciprocity between cell cytoskeleton/mechanics and CSC functions and the potential of cellular stiffness for specific targeting of CSCs. However, a systematic understanding of tumor cell mechanics and their role in CSCs and tumor progression is still lacking. The present review summarizes the recent progress in the alterations of tumor cell cytoskeleton and stiffness at different stages of tumor progression and recapitulates the relationship between cellular stiffness and CSC functions. The altered cell mechanics may mediate the mechanoadaptive responses that possibly empower CSCs to survive and thrive during metastasis. Furthermore, we highlight the possible impact of tumor cell mechanics on CSC malignancy, which may potentiate low cell stiffness as a mechanical marker for CSC targeting.

Analysis of Alternative mRNA Splicing in Vemurafenib-Resistant Melanoma Cells

Alternative mRNA splicing is common in cancers. In BRAF V600E-mutated malignant melanoma, a frequent mechanism of acquired resistance to BRAF inhibitors involves alternative splicing (AS) of BRAF. The resulting shortened BRAF protein constitutively dimerizes and conveys drug resistance. Here, we have analysed AS in SK-MEL-239 melanoma cells and a BRAF inhibitor (vemurafenib)-resistant derivative that expresses an AS, shortened BRAF V600E transcript. Transcriptome analysis showed differential expression of spliceosome components between the two cell lines. As there is no consensus approach to analysing AS events, we used and compared four common AS softwares based on different principles, DEXSeq, rMATS, ASpli, and LeafCutter. Two of them correctly identified the BRAF V600E AS in the vemurafenib-resistant cells. Only 12 AS events were identified by all four softwares. Testing the AS predictions experimentally showed that these overlapping predictions are highly accurate. Interestingly, they identified AS caused alterations in the expression of melanin synthesis and cell migration genes in the vemurafenib-resistant cells. This analysis shows that combining different AS analysis approaches produces reliable results and meaningful, biologically testable hypotheses.

Suppression of Endothelial Cell FAK Expression Reduces Pancreatic Ductal Adenocarcinoma Metastasis after Gemcitabine Treatment

Despite substantial advances in the treatment of solid cancers, resistance to therapy remains a major obstacle to prolonged progression-free survival. Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive cancers, with a high level of liver metastasis. Primary PDAC is highly hypoxic, and metastases are resistant to first-line treatment, including gemcitabine. Recent studies have indicated that endothelial cell (EC) focal adhesion kinase (FAK) regulates DNA-damaging therapy-induced angiocrine factors and chemosensitivity in primary tumor models. Here, we show that inducible loss of EC-FAK in both orthotopic and spontaneous mouse models of PDAC is not sufficient to affect primary tumor growth but reduces liver and lung metastasis load and improves survival rates in gemcitabine-treated, but not untreated, mice. EC-FAK loss did not affect primary tumor angiogenesis, tumor blood vessel leakage, or early events in metastasis, including the numbers of circulating tumor cells, tumor cell homing, or metastatic seeding. Phosphoproteomics analysis showed a downregulation of the MAPK, RAF, and PAK signaling pathways in gemcitabine-treated FAK-depleted ECs compared with gemcitabine-treated wild-type ECs. Moreover, low levels of EC-FAK correlated with increased survival and reduced relapse in gemcitabine-treated patients with PDAC, supporting the clinical relevance of these findings. Altogether, we have identified a new role of EC-FAK in regulating PDAC metastasis upon gemcitabine treatment that impacts outcome.

SIGNIFICANCE

These findings establish the potential utility of combinatorial endothelial cell FAK targeting together with gemcitabine in future clinical applications to control metastasis in patients with pancreatic ductal adenocarcinoma.

MrgprF acts as a tumor suppressor in cutaneous melanoma by restraining PI3K/Akt signaling

The incidence of cutaneous melanoma (CM) has been increasing annually worldwide. In this study, we identify that MrgprF, a MAS related GPR family member, is decreased in cutaneous melanoma tissues and cell lines due to hypermethylation of its promoter region, and show that patients with CM expressing high levels of MrgprF exhibit an improved clinical outcome. We demonstrate that MrgprF forced expression inhibits tumor cell proliferation, migration, xenograft tumor growth, and metastasis. On the contrary, MrgprF knockdown promotes tumor cell proliferation and transformation of immortalized human keratinocyte-HaCaT cells, supporting the inhibitory role of MrgprF during tumor progression. Mechanistic studies reveal that MrgprF reduces the phosphoinositol‑3‑kinase (PI3K) complex formation between p101 and p110γ subunits, the critical step for phosphatidylinositol-(3, 4)-P2 (PIP2) conversion to phosphatidylinositol-(3, 4, 5)-P3 (PIP3), and then reduces the activation of PI3K/Akt signaling. This effect can be reversed by Akt specific agonist SC79. In addition, AMG 706, a previously documented inhibitor for endothelial cell proliferation, is identified as a potential agonist for MrgprF, and can impede tumor growth both in vitro and in vivo. Taken together, our findings suggest that MrgprF, a novel tumor suppressor in cutaneous melanoma, may be useful as a therapeutic target in the future.

Discovery of a signaling feedback circuit that defines interferon responses in myeloproliferative neoplasms

Interferons (IFNs) are key initiators and effectors of the immune response against malignant cells and also directly inhibit tumor growth. IFNα is highly effective in the treatment of myeloproliferative neoplasms (MPNs), but the mechanisms of action are unclear and it remains unknown why some patients respond to IFNα and others do not. Here, we identify and characterize a pathway involving PKCδ-dependent phosphorylation of ULK1 on serine residues 341 and 495, required for subsequent activation of p38 MAPK. We show that this pathway is essential for IFN-suppressive effects on primary malignant erythroid precursors from MPN patients, and that increased levels of ULK1 and p38 MAPK correlate with clinical response to IFNα therapy in these patients. We also demonstrate that IFNα treatment induces cleavage/activation of the ULK1-interacting ROCK1/2 proteins in vitro and in vivo, triggering a negative feedback loop that suppresses IFN responses. Overexpression of ROCK1/2 is seen in MPN patients and their genetic or pharmacological inhibition enhances IFN-anti-neoplastic responses in malignant erythroid precursors from MPN patients. These findings suggest the clinical potential of pharmacological inhibition of ROCK1/2 in combination with IFN-therapy for the treatment of MPNs.

Interferon alpha (IFNalpha) therapy is showing promising results to treat myeloproliferative neoplasms (MPNs). Here, the authors show that IFNalpha response requires ULK1 phosphorylation to induce p38-MAPK signalling but it is counteracted by ROCK1-2 activation suggesting combination therapy of IFNalpha-ROCK1-2 inhibition may improve MPNs treatment.

Nectin-1 and Non-muscle Myosin Heavy Chain-IIB: Major Mediators of Herpes Simplex Virus-1 Entry Into Corneal Nerves

Herpes Simplex Virus 1 (HSV-1) invades corneal nerves upon its infection of the cornea and then establishes latency in the trigeminal ganglion (TG). The latent virus in TG is often reactivated and travels back to the cornea, causing recurrent herpes simplex keratitis (HSK). The entry of HSV-1 into the corneal nerve is considered the initial step of infection resulting in HSV-1 latency and HSK recurrence. Several gD and gB receptors have been identified, including nectin-1, herpes virus entry medium (HVEM) and 3-O-sulfated heparan sulfate (3-OS-HS) as gD receptors, and non-muscle myosin heavy chain IIA (NMHC-IIA), NMHC-IIB and myelin-associated glycoprotein (MAG) as gB receptors. However, which receptors contribute to the entry of HSV-1 into corneal nerves are yet to be determined. This study observed that receptors nectin-1, HVEM, 3-OS-HS, NMHC-IIA, and NMHC-IIB, not MAG, were expressed in healthy corneal nerves. Further, we cultured TG neurons extracted from mice in vitro to screen for functional gD/gB receptors. Both in vitro siRNA knockdown and in vivo antibody blocking of either nectin-1 or NMHC-IIB reduced the entry and the replication of HSV-1 as shown by qPCR analysis and immunofluorescence measure, respectively. Also, we observed that the re-localization and the upregulation expression of NMHC-IIB after HSV-1 exposure were inhibited when gD receptor nectin-1 was knocked down. These data suggest that nectin-1 was the main gD receptor and NMHC-IIB was the main gB receptor in mediating HSV-1 entry and hold promise as therapeutic targets for resolving HSV-1 latency and HSK recurrence.