Inhibition of the CRAF/prohibitin interaction reverses CRAF-dependent resistance to vemurafenib

Targeting CRAF kinase in anti-cancer therapy: progress and opportunities

The RAS/mitogen-activated protein kinase (MAPK) signaling cascade is commonly dysregulated in human malignancies by processes driven by RAS or RAF oncogenes. Among the members of the RAF kinase family, CRAF plays an important role in the RAS-MAPK signaling pathway, as well as in the progression of cancer. Recent research has provided evidence implicating the role of CRAF in the physiological regulation and the resistance to BRAF inhibitors through MAPK-dependent and MAPK-independent mechanisms. Nevertheless, the effectiveness of solely targeting CRAF kinase activity remains controversial. Moreover, the kinase-independent function of CRAF may be essential for lung cancers with KRAS mutations. It is imperative to develop strategies to enhance efficacy and minimize toxicity in tumors driven by RAS or RAF oncogenes. The review investigates CRAF alterations observed in cancers and unravels the distinct roles of CRAF in cancers propelled by diverse oncogenes. This review also seeks to summarize CRAF-interacting proteins and delineate CRAF's regulation across various cancer hallmarks. Additionally, we discuss recent advances in pan-RAF inhibitors and their combination with other therapeutic approaches to improve treatment outcomes and minimize adverse effects in patients with RAF/RAS-mutant tumors. By providing a comprehensive understanding of the multifaceted role of CRAF in cancers and highlighting the latest developments in RAF inhibitor therapies, we endeavor to identify synergistic targets and elucidate resistance pathways, setting the stage for more robust and safer combination strategies for cancer treatment.

Essential Protein PHB2 and Its Regulatory Mechanisms in Cancer

Prohibitins (PHBs) are a highly conserved class of proteins and have an essential role in transcription, epigenetic regulation, nuclear signaling, mitochondrial structural integrity, cell division, and cellular membrane metabolism. Prohibitins form a heterodimeric complex, consisting of two proteins, prohibitin 1 (PHB1) and prohibitin 2 (PHB2). They have been discovered to have crucial roles in regulating cancer and other metabolic diseases, functioning both together and independently. As there have been many previously published reviews on PHB1, this review focuses on the lesser studied prohibitin, PHB2. The role of PHB2 in cancer is controversial. In most human cancers, overexpressed PHB2 enhances tumor progression, while in some cancers, it suppresses tumor progression. In this review, we focus on (1) the history, family, and structure of prohibitins, (2) the essential location-dependent functions of PHB2, (3) dysfunction in cancer, and (4) the promising modulators to target PHB2. At the end, we discuss future directions and the clinical significance of this common essential gene in cancer.

Prohibitin mediates the cellular invasion of spring viremia of the carp virus

Spring viremia of carp virus (SVCV) is strongly contagious and pathogenic to common carp and cyprinoid species. However, knowledge of how SVCV enters host cells is still inadequate. In this study, mass spectrometry (MS) was incorporated with tandem affinity purification (TAP) to identify host proteins that interact with SVCV glycoprotein, the main attachment protein of SVCV. Specifically, prohibitin (PHB) received the utmost attention from all the candidate proteins, and its interaction with the SVCV-G protein was confirmed by immunoprecipitation and immunofluorescence assays. Treatment with PHB-specific inhibitors or knockdown of the expression of PHB by siRNAs resulted in a marked reduction in binding and entry of SVCV on host cells, while overexpression of PHB increased SVCV attachment and invasion. Furthermore, binding of SVCV to ZF4 and FHM cells was inhibited by pre-incubating the virus with recombinant PHB protein (rPHB) or blocking the cell surface PHB with its polyclonal antibodies. In addition, overexpression of PHB on SVCV-nonpermissive Grouper spleen cells (GSs) conferred susceptibility to SVCV infection. In vivo, treatment of rPHB could significantly inhibit SVCV propagation within zebrafish and benefit the survival rate of SVCV-infected zebrafish. These results demonstrate that PHB plays a crucial role in both the attachment and entry stages of SVCV infection.

Analyses of Transcriptomics Cell Signalling for Pre-Screening Applications in the Integrated Approach for Testing and Assessment of Non-Genotoxic Carcinogens

With recent rapid advancement of methodological tools, mechanistic understanding of biological processes leading to carcinogenesis is expanding. New approach methodologies such as transcriptomics can inform on non-genotoxic mechanisms of chemical carcinogens and can be developed for regulatory applications. The Organisation for the Economic Cooperation and Development (OECD) expert group developing an Integrated Approach to the Testing and Assessment (IATA) of Non-Genotoxic Carcinogens (NGTxC) is reviewing the possible assays to be integrated therein. In this context, we review the application of transcriptomics approaches suitable for pre-screening gene expression changes associated with phenotypic alterations that underlie the carcinogenic processes for subsequent prioritisation of downstream test methods appropriate to specific key events of non-genotoxic carcinogenesis. Using case studies, we evaluate the potential of gene expression analyses especially in relation to breast cancer, to identify the most relevant approaches that could be utilised as (pre-) screening tools, for example Gene Set Enrichment Analysis (GSEA). We also consider how to address the challenges to integrate gene panels and transcriptomic assays into the IATA, highlighting the pivotal omics markers identified for assay measurement in the IATA key events of inflammation, immune response, mitogenic signalling and cell injury.

Targeting RAS–RAF–MEK–ERK signaling pathway in human cancer: Current status in clinical trials

Molecular target inhibitors have been regularly approved by Food and Drug Administration (FDA) for tumor treatment, and most of them intervene in tumor cell proliferation and metabolism. The RAS-RAF-MEK-ERK pathway is a conserved signaling pathway that plays vital roles in cell proliferation, survival, and differentiation. The aberrant activation of the RAS-RAF-MEK-ERK signaling pathway induces tumors. About 33% of tumors harbor RAS mutations, while 8% of tumors are driven by RAF mutations. Great efforts have been dedicated to targeting the signaling pathway for cancer treatment in the past decades. In this review, we summarized the development of inhibitors targeting the RAS-RAF-MEK-ERK pathway with an emphasis on those used in clinical treatment. Moreover, we discussed the potential combinations of inhibitors that target the RAS-RAF-MEK-ERK signaling pathway and other signaling pathways. The inhibitors targeting the RAS-RAF-MEK-ERK pathway have essentially modified the therapeutic strategy against various cancers and deserve more attention in the current cancer research and treatment.

Genomic and Transcriptomic Underpinnings of Melanoma Genesis, Progression, and Metastasis

Melanoma is a deadly skin cancer with rapidly increasing incidence worldwide. The discovery of the genetic drivers of melanomagenesis in the last decade has led the World Health Organization to reclassify melanoma subtypes by their molecular pathways rather than traditional clinical and histopathologic features. Despite this significant advance, the genomic and transcriptomic drivers of metastatic progression are less well characterized. This review describes the known molecular pathways of cutaneous and uveal melanoma progression, highlights recently identified pathways and mediators of metastasis, and touches on the influence of the tumor microenvironment on metastatic progression and treatment resistance. While targeted therapies and immune checkpoint blockade have significantly aided in the treatment of advanced disease, acquired drug resistance remains an unfortunately common problem, and there is still a great need to identify potential prognostic markers and novel therapeutic targets to aid in such cases.

Targeted intervention of eIF4A1 inhibits EMT and metastasis of pancreatic cancer cells via c-MYC/miR-9 signaling

Background

Owing to the lack of effective treatment options, early metastasis remains the major cause of pancreatic ductal adenocarcinoma (PDAC) recurrence and mortality. However, the molecular mechanism of early metastasis is largely unknown. We characterized the function of eukaryotic translation initiation factors (eIFs) in epithelial-mesenchymal-transition (EMT) and metastasis in pancreatic cancer cells to investigate whether eIFs and downstream c-MYC affect EMT and metastasis by joint interference.

Methods

We used The Cancer Genome Atlas (TCGA) and Genome Tissue Expression (GTEx) databases to analyze eIF4A1 expression in PDAC tissues and further validated the findings with a microarray containing 53 PDAC samples. Expression regulation and pharmacological inhibition of eIF4A1 and c-MYC were performed to determine their role in migration, invasion, and metastasis in pancreatic cancer cells in vitro and in vivo.

Results

Elevated eIF4A1 expression was positively correlated with lymph node infiltration, tumor size, and indicated a poor prognosis. eIF4A1 decreased E-cadherin expression through the c-MYC/miR-9 axis. Loss of eIF4A1 and c-MYC decreased the EMT and metastasis capabilities of pancreatic cancer cells, whereas upregulation of eIF4A1 attenuated the inhibition of EMT and metastasis induced by c-MYC downregulation. Treatment with the eIF4A1 inhibitor rocaglamide (RocA) or the c-MYC inhibitor Mycro3 either alone or in combination significantly decreased the expression level of EMT markers in pancreatic cancer cells in vitro. However, the efficiency and safety of RocA alone were not inferior to those of the combination treatment in vivo.

Conclusion

Overexpression of eIF4A1 downregulated E-cadherin expression through the c-MYC/miR-9 axis, which promoted EMT and metastasis of pancreatic cancer cells. Despite the potential feedback loop between eIF4A1 and c-MYC, RocA monotherapy is a promising treatment inhibiting eIF4A1-induced PDAC metastasis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-02390-0.

Role of Prohibitins in Aging and Therapeutic Potential Against Age-Related Diseases

A decline in mitochondrial function has long been associated with age-related health decline. Several lines of evidence suggest that interventions that stimulate mitochondrial autophagy (mitophagy) can slow aging and prolong healthy lifespan. Prohibitins (PHB1 and PHB2) assemble at the mitochondrial inner membrane and are critical for mitochondrial homeostasis. In addition, prohibitins (PHBs) have diverse roles in cell and organismal biology. Here, we will discuss the role of PHBs in mitophagy, oxidative phosphorylation, cellular senescence, and apoptosis. We will also discuss the role of PHBs in modulating lifespan. In addition, we will review the links between PHBs and diseases of aging. Finally, we will discuss the emerging concept that PHBs may represent an attractive therapeutic target to counteract aging and age-onset disease.

Simultaneous blocking of the pan-RAF and S100B pathways as a synergistic therapeutic strategy against malignant melanoma

Melanoma is a very aggressive form of skin cancer. Although BRAF inhibitors have been utilized for melanoma therapy, advanced melanoma patients still face a low five-year survival rate. Recent studies have shown that CRAF can compensate for BRAF depletion via regulating DNA synthesis to remain melanoma proliferation. Hence, targeting CRAF either alone or in combination with other protein pathways is a potential avenue for melanoma therapy. Based on our previously reported CRAF-selective inhibitor for renal cancer therapy, we have herein discovered an analogue (complex 1) from the reported CRAF library suppresses melanoma cell proliferation and melanoma tumour growth in murine models of melanoma via blocking the S100B and RAF pathways. Intriguingly, we discovered that inhibiting BRAF together with S100B exerts a novel synergistic effect to significantly restore p53 transcription activity and inhibit melanoma cell proliferation, whereas blocking BRAF together with CRAF only had an additive effect. We envision that blocking the pan-RAF and S100B/p53 pathways might be a novel synergistic strategy for melanoma therapy and that complex 1 is a potential inhibitor against melanoma via blocking the pan-RAF and S100B pathways.

Mechanisms of Resistance to BRAF-Targeted Melanoma Therapies

About half of all cutaneous melanomas harbor activating mutations in the BRAF oncogene. Dependence on this pathway makes the tumors vulnerable to BRAF (and downstream MEK) inhibition, and three drug combinations are approved to target this vulnerability in advanced melanomas with BRAFV600 mutations. Responses to BRAF/MEK inhibitors are usually fast, but durability of response can be limited. Five-year data from BRAF/MEK inhibitors show long-term survival benefit for a third of the patients. There is a wide variety of known mechanisms of resistance to BRAF/MEK inhibition, such as mitogen-activated protein kinase reactivation, activation of parallel pathways, alterations in cell-cycle regulation, and non-genetic resistance mechanisms. Strategies that have been explored to overcome these mechanisms include alternative dosing regimens, addition of another kinase inhibitor, and use of anti-PD-1 immunotherapy either in combination or post-relapse on BRAF/MEK inhibitor therapies.

A20 regulates the therapeutic effect of anti-PD-1 immunotherapy in melanoma

Background

The therapeutic effect of immune checkpoint blockers, especially the neutralizing antibodies of programmed cell death (PD-1) and its ligand programmed death ligand 1 (PD-L1), has been well verified in melanoma. Nevertheless, the dissatisfactory response rate and the occurrence of resistance significantly hinder the treatment effect. Inflammation-related molecules like A20 are greatly implicated in cancer immune response, but the role of tumorous A20 in antitumor immunity and immunotherapy efficacy remains elusive.

Methods

The association between tumorous A20 expression and the effect of anti-PD-1 immunotherapy was determined by immunoblotting, immunofluorescence staining and flow cytometry analysis of primary tumor specimens from melanoma patients. Preclinical mouse model, in vitro coculture system, immunohistochemical staining and flow cytometry analysis were employed to investigate the role of A20 in regulating the effect of anti-PD-1 immunotherapy. Bioinformatics, mass spectrum analysis and a set of biochemical analyzes were used to figure out the underlying mechanism.

Results

We first discovered that upregulated A20 was associated with impaired antitumor capacity of CD8⁺T cells and poor response to anti-PD-1 immunotherapy in melanoma patients. Subsequent functional studies in preclinical mouse model and in vitro coculture system proved that targeting tumorous A20 prominently improved the effect of immunotherapy through the invigoration of infiltrating CD8⁺T cells via the regulation of PD-L1. Mechanistically, A20 facilitated the ubiquitination and degradation of prohibitin to potentiate STAT3 activation and PD-L1 expression. Moreover, tumorous A20 expression was highly associated with the ratio of Ki-67 percentage in circulating PD-1⁺CD8⁺T cells to tumor burden.

Conclusions

Together, our findings uncover a novel crosstalk between inflammatory molecules and antitumor immunity in melanoma, and highlight that A20 can be exploited as a promising target to bring clinical benefit to melanomas refractory to immune checkpoint blockade.

Mechanisms of Acquired BRAF Inhibitor Resistance in Melanoma: A Systematic Review

This systematic review investigated the literature on acquired v-raf murine sarcoma viral oncogene homolog B1 (BRAF) inhibitor resistance in patients with melanoma. We searched MEDLINE for articles on BRAF inhibitor resistance in patients with melanoma published since January 2010 in the following areas: (1) genetic basis of resistance; (2) epigenetic and transcriptomic mechanisms; (3) influence of the immune system on resistance development; and (4) combination therapy to overcome resistance. Common resistance mutations in melanoma are BRAF splice variants, BRAF amplification, neuroblastoma RAS viral oncogene homolog (NRAS) mutations and mitogen-activated protein kinase kinase 1/2 (MEK1/2) mutations. Genetic and epigenetic changes reactivate previously blocked mitogen-activated protein kinase (MAPK) pathways, activate alternative signaling pathways, and cause epithelial-to-mesenchymal transition. Once BRAF inhibitor resistance develops, the tumor microenvironment reverts to a low immunogenic state secondary to the induction of programmed cell death ligand-1. Combining a BRAF inhibitor with a MEK inhibitor delays resistance development and increases duration of response. Multiple other combinations based on known mechanisms of resistance are being investigated. BRAF inhibitor-resistant cells develop a range of 'escape routes', so multiple different treatment targets will probably be required to overcome resistance. In the future, it may be possible to personalize combination therapy towards the specific resistance pathway in individual patients.

Mechanisms of resistance and predictive biomarkers of response to targeted therapies and immunotherapies in metastatic melanoma

PURPOSE OF REVIEW

Thanks to mitogen-activated protein kinase inhibitors (MAPKi) and immune checkpoint inhibitors (ICI), major progress has been made in the field of melanoma treatment. However, long-term success is still scarce because of the development of resistance. Understanding these mechanisms of resistance and identifying predictive genomic biomarkers are now key points in the therapeutic management of melanoma patients.

RECENT FINDINGS

Multiple and complex mechanisms of resistance to MAPKi or ICI have been uncovered in the past few years. The lack of response can be driven by mutations and nonmutational events in tumor cells, as well as by changes in the tumor microenvironment. Melanoma cells are also capable of rapidly switching their molecular and cellular phenotype, leading to an initial drug-tolerant favorizing melanoma resistance. Tumor molecular profiling and circulating tumor cell analyses are of high interest as predictive biomarkers as well as studying immunogenic changes and microbiome in ICI-treated patients.

SUMMARY

Resistance to MAPKi and ICI is a key point in therapeutic management of metastatic melanoma patients. Validated biomarkers predicting response to therapy are urgently needed to move toward personalized medicine. Combinatory treatments guided by the understanding of resistance mechanisms will be of major importance in the future of melanoma therapy.

Prohibitin ligands: a growing armamentarium to tackle cancers, osteoporosis, inflammatory, cardiac and neurological diseases

Over the last three decades, the scaffold proteins prohibitins-1 and -2 (PHB1/2) have emerged as key signaling proteins regulating a myriad of signaling pathways in health and diseases. Small molecules targeting PHBs display promising effects against cancers, osteoporosis, inflammatory, cardiac and neurodegenerative diseases. This review provides an updated overview of the various classes of PHB ligands, with an emphasis on their mechanism of action and therapeutic potential. We also describe how these ligands have been used to explore PHB signaling in different physiological and pathological settings.

Molecular alterations associated with acquired resistance to BRAFV600E targeted therapy in melanoma cells

Selective inhibition of the mutant BRAF protein is a highly promising therapeutic approach for melanoma patients carrying the BRAF mutation. Despite the remarkable clinical response, most patients develop resistance and experience tumour regrowth. To clarify the molecular background of BRAF inhibitor resistance, we generated four drug-resistant melanoma cell lines from paired primary/metastatic cell lines using a vemurafenib analogue PLX4720. Three of the resistant cell lines showed decreased proliferation after drug withdrawal, but the proliferation of one cell line (WM278) increased notably. Furthermore, we observed opposite phenomena in which a 'drug holiday' could not only be beneficial but also contribute to tumour progression. Using genomic and proteomic approaches, we found significantly different alterations between the sensitive and resistant cell lines, some of which have not been reported previously. In addition to several other changes, copy number gains were observed in all resistant cell lines on 8q24.11-q24.12 and 8q21.2. Gene expression analysis showed that most genes upregulated in the resistant cell lines were associated with cell motility and angiogenesis. Increased expression of six proteins (ANGPLT4, EGFR, Endoglin, FGF2, SerpinE1 and VCAM-1) and decreased expression of two proteins (osteopontin and survivin) were observed consistently in all resistant cell lines. In summary, we identified new genomic alterations and characterized the protein expression patterns associated with the resistant phenotype. Although several proteins have been shown to be associated with BRAF resistance, our study is the first to describe the association of VCAM-1 and osteopontin with BRAF resistance.

Strategic Combinations to Prevent and Overcome Resistance to Targeted Therapies in Oncology

Recent advances in the understanding of underlying molecular signaling mechanisms of cancer susceptibility and progression have led to an increase in the use of targeted therapies for cancer treatment. Despite improvements in survival with new treatment options in oncology, resistance to therapy is a major obstacle to the long-term effectiveness of targeted agents in metastatic cancer treatment, culminating in insensitivity to treatment and tumor outgrowth. Adaptive resistance can play an important role in primary and upfront resistance to therapy as well as in secondary or acquired resistance. By focusing on colorectal and breast tumors, we discuss how therapeutic combinations based on specific drivers of tumor biology can be used to overcome resistance. We present how monitoring tumor dynamics over time may allow early adaptation of treatment. Breast cancer is the most common malignancy in women worldwide, and the majority of these cancers are sensitive to endocrine therapy (ET) blocking the production of or response to estrogen. However, primary and acquired resistance limits efficacy. Recent combinations of agents targeted to pathways that drive tumor growth resistance with ET have resulted in remarkable improvements in disease response and control, improving survival in some settings. In this review, we summarize adaptive resistance mechanisms, approaches to combination strategies, and dynamic tumor monitoring to improve efficacy and overcome resistance. We provide examples of combination therapy to enhance the efficacy of targeted therapies in breast and colorectal tumors.

A novel function of Prohibitin on melanosome transport in melanocytes

Prohibitin (PHB, also known as PHB1 or BAP32), is a highly conserved 31kDa protein that expressed in many cellular compartments, such as mitochondria, nucleus, cytosol, and plasma membrane, and plays roles in regulating the transcription of genes, apoptosis, and mitochondrial biogenesis. There is a report that Prohibitin expression is required for the stimulation of pigmentation by melanogenin. However, no studies have been published on the function of PHB in melanocytes, especially in melanosome transport.

Methods: Immunofluorescence was performed to confirm the localization of PHB. siRNA transfections, Co-immunoprecipitation, western blotting and proximity ligation assay were performed to find binding state between proteins and demonstrate functions of PHB on melanosome transport.

Results: PHB is located in the melanosome and perinuclear aggregation of melanosome is induced when expression of PHB is reduced with no influence on melanin contents. PHB binds directly to Rab27a and Mlph but not Myosin-Va. Rab27a and Mlph bind to specific domains of PHB. Reduced expression of PHB led to the impaired binding affinity between Rab27a and Mlph.

Conclusion: PHB regulates melanosome transport by linking to Rab27a and Mlph in melanocytes. Targeting and regulating PHB not only manages pigmentation in melanocytes, but also controls hyperpigmentation in melanoma

Prohibitin promotes de-differentiation and is a potential therapeutic target in neuroblastoma

Gain of the long arm of chromosome 17 (17q) is a cytogenetic hallmark of high-risk neuroblastoma, yet its contribution to neuroblastoma pathogenesis remains incompletely understood. Combining whole-genome and RNA sequencing of neuroblastomas, we identified the prohibitin (PHB) gene as highly expressed in tumors with 17q gain. High PHB expression correlated with poor prognosis and was associated with loss of gene expression programs promoting neuronal development and differentiation. PHB depletion induced differentiation and apoptosis and slowed cell cycle progression of neuroblastoma cells, at least in part through impaired ERK1/2 activation. Conversely, ectopic expression of PHB was sufficient to increase proliferation of neuroblastoma cells and was associated with suppression of markers associated with neuronal differentiation and favorable neuroblastoma outcome. Thus, PHB is a 17q oncogene in neuroblastoma that promotes tumor cell proliferation, and de-differentiation.

Significance of prohibitin domain family in tumorigenesis and its implication in cancer diagnosis and treatment

Prohibitin (PHB) was originally isolated and characterized as an anti-proliferative gene in rat liver. The evolutionarily conserved PHB gene encodes two human protein isoforms with molecular weights of ~33 kDa, PHB1 and PHB2. PHB1 and PHB2 belong to the prohibitin domain family, and both are widely distributed in different cellular compartments such as the mitochondria, nucleus, and cell membrane. Most studies have confirmed differential expression of PHB1 and PHB2 in cancers compared to corresponding normal tissues. Furthermore, studies verified that PHB1 and PHB2 are involved in the biological processes of tumorigenesis, including cancer cell proliferation, apoptosis, and metastasis. Two small molecule inhibitors, Rocaglamide (RocA) and fluorizoline, derived from medicinal plants, were demonstrated to interact directly with PHB1 and thus inhibit the interaction of PHB with Raf-1, impeding Raf-1/ERK signaling cascades and significantly suppressing cancer cell metastasis. In addition, a short peptide ERAP and a natural product xanthohumol were shown to target PHB2 directly and prohibit cancer progression in estrogen-dependent cancers. As more efficient biomarkers and targets are urgently needed for cancer diagnosis and treatment, here we summarize the functional role of prohibitin domain family proteins, focusing on PHB1 and PHB2 in tumorigenesis and cancer development, with the expectation that targeting the prohibitin domain family will offer more clues for cancer therapy.

C-RAF function at the genome-wide transcriptome level: A systematic view

C-RAF was the first member of the RAF kinase family to be discovered. Since its discovery, C-RAF has been found to regulate many fundamental cell processes, such as cell proliferation, cell death, and metabolism. However, the majority of these functions are achieved through interactions with different proteins; the genes regulated by C-RAF in its active or inactive state remain unclear. In the work, we used RNA-seq analysis to study the global transcriptomes of C-RAF bearing or C-RAF knockout cells in quiescent or EGF activated states. We identified 3353 genes that are promoted or suppressed by C-RAF. Gene ontology and Kyoto Encyclopedia of Genes and Genomes analyses revealed that these genes are involved in drug addiction, cardiomyopathy, autoimmunity, and regulation of cell metabolism. Our results provide a panoramic view of C-RAF function, including known and novel functions, and have revealed potential targets for elucidating the role of C-RAF.

Accumulation of prohibitin is a common cellular response to different stressing stimuli and protects melanoma cells from ER stress and chemotherapy-induced cell death

Melanoma is responsible for most deaths among skin cancers and conventional and palliative care chemotherapy are limited due to the development of chemoresistance. We used proteomic analysis to identify cellular responses that lead to chemoresistance of human melanoma cell lines to cisplatin. A systems approach to the proteomic data indicated the participation of specific cellular processes such as oxidative phosphorylation, mitochondrial organization and homeostasis, as well as the unfolded protein response (UPR) to be required for the survival of cells treated with cisplatin. Prohibitin (PHB) was among the proteins consistently accumulated, interacting with the functional clusters associated with resistance to cisplatin. We showed PHB accumulated at different levels in melanoma cell lines under stressing stimuli, such as (i) treatment with temozolomide (TMZ), dacarbazine (DTIC) and cisplatin; (ii) serum deprivation; (iii) tunicamycin, an UPR inducer. Prohibitin accumulated in the mitochondria of melanoma cells after cisplatin and tunicamycin treatment and its de novo accumulation led to chemoresistance melanoma cell lines. In contrast, PHB knock-down sensitized melanoma cells to cisplatin and tunicamycin treatment. We conclude that PHB participates in the survival of cells exposed to different stress stimuli, and can therefore serve as a target for the sensitization of melanoma cells to chemotherapy.

Prohibitin plays a critical role in Enterovirus 71 neuropathogenesis

A close relative of poliovirus, enterovirus 71 (EV71) is regarded as an important neurotropic virus of serious public health concern. EV71 causes Hand, Foot and Mouth Disease and has been associated with neurological complications in young children. Our limited understanding of the mechanisms involved in its neuropathogenesis has hampered the development of effective therapeutic options. Here, using a two-dimensional proteomics approach combined with mass spectrometry, we have identified a unique panel of host proteins that were differentially and dynamically modulated during EV71 infection of motor-neuron NSC-34 cells, which are found at the neuromuscular junctions where EV71 is believed to enter the central nervous system. Meta-analysis with previously published proteomics studies in neuroblastoma or muscle cell lines revealed minimal overlapping which suggests unique host-pathogen interactions in NSC-34 cells. Among the candidate proteins, we focused our attention on prohibitin (PHB), a protein that is involved in multiple cellular functions and the target of anti-cancer drug Rocaglamide (Roc-A). We demonstrated that cell surface-expressed PHB is involved in EV71 entry into neuronal cells specifically, while membrane-bound mitochondrial PHB associates with the virus replication complex and facilitates viral replication. Furthermore, Roc-A treatment of EV71-infected neuronal cells reduced significantly virus yields. However, the inhibitory effect of Roc-A on PHB in NSC-34 cells was not through blocking the CRAF/MEK/ERK pathway as previously reported. Instead, Roc-A treated NSC-34 cells had lower mitochondria-associated PHB and lower ATP levels that correlated with impaired mitochondria integrity. In vivo, EV71-infected mice treated with Roc-A survived longer than the vehicle-treated animals and had significantly lower virus loads in their spinal cord and brain, whereas virus titers in their limb muscles were comparable to controls. Together, this study uncovers PHB as the first host factor that is specifically involved in EV71 neuropathogenesis and a potential drug target to limit neurological complications.

MicroRNA-195 acts as an anti-proliferative miRNA in human melanoma cells by targeting Prohibitin 1

Background

Melanoma is the most lethal type of skin cancer. Since chemoresistance is a significant barrier, identification of regulators affecting chemosensitivity is necessary in order to create new forms of intervention. Prohibitin 1 (PHB1) can act as anti-apoptotic or tumor suppressor molecule, depending on its subcellular localization. Our recent data shown that accumulation of PHB1 protects melanoma cells from chemotherapy-induced cell death. Lacking of post-transcriptional regulation of PHB1 could explain this accumulation. Interestingly, most of melanoma patients have down-regulation of microRNA-195. Here, we investigate the role of miR-195, its impact on PHB1 expression, and on chemosensitivity in melanoma cells.

Methods

TCGA-RNAseq data obtained from 341 melanoma patient samples as well as a panel of melanoma cell lines were used in an expression correlation analysis between PHB1 and predicted miRNAs. miR-195 impact on PHB1 mRNA and protein levels and relevance of this regulation were investigated in UACC-62 and SK-MEL-5 melanoma lines by RT-qPCR and western blot, luciferase reporter and genetic rescue experiments. Cell proliferation, cell-cycle analysis and caspase 3/7 assay were performed to investigate the potential action of miR-195 as chemosensitizer in melanoma cells treated with cisplatin and temozolomide.

Results

Analysis of the TCGA-RNAseq revealed a significant negative correlation (Pearson) between miR-195 and PHB1 expression. Moreover, RT-qPCR data showed that miR-195 is down-regulated while PHB1 is up-regulated in a collection of melanoma cells. We demonstrated that miR-195 regulates PHB1 directly by RT-qPCR and western blot in melanoma cells and luciferase assays. To establish PHB1 as a relevant target of miR-195, we conducted rescue experiments in which we showed that PHB1 transgenic expression could antagonize the suppressive effect miR-195 on the proliferation of melanoma cells. Finally, transfection experiments combined with drug treatments performed in the UACC-62 and SK-MEL-5 melanoma cells corroborated miR-195 as potential anti-proliferative agent, with potential impact in sensitization of melanoma cell death.

Conclusions

This study support the role of miR-195 as anti-proliferative miRNA via targeting of PHB1 in melanoma cells.

Electronic supplementary material

The online version of this article (10.1186/s12885-017-3721-7) contains supplementary material, which is available to authorized users.

Targeting prohibitins with chemical ligands inhibits KRAS-mediated lung tumours

KRAS is one of the most frequently mutated oncogenes in human non-small cell lung cancers (NSCLCs). RAS proteins trigger multiple effector signalling pathways including the highly conserved RAF-MAPK pathway. CRAF, a direct RAS effector protein, is required for KRAS-mediated tumourigenesis. Thus, the molecular mechanisms driving the activation of CRAF are intensively studied. Prohibitin 1 (PHB1) is an evolutionarily conserved adaptor protein and interaction of CRAF with PHB1 at the plasma membrane is essential for CRAF activation. Here, we demonstrate that PHB1 is highly expressed in NSCLC patients and correlates with poor survival. Targeting of PHB1 with two chemical ligands (rocaglamide and fluorizoline) inhibits epidermal growth factor (EGF)/RAS-induced CRAF activation. Consistently, treatment with rocaglamide inhibited proliferation, migration and anchorage-independent growth of KRAS-mutated lung carcinoma cell lines. Surprisingly, rocaglamide treatment inhibited Ras-GTP loading in KRAS-mutated cells as well as in EGF-stimulated cells. Rocaglamide treatment further prevented the oncogenic growth of KRAS-driven lung cancer allografts and xenografts in mouse models. Our results suggest rocaglamide as a RAS inhibitor and that targeting plasma membrane-associated PHB1 with chemical ligands would be a viable therapeutic strategy to combat KRAS-mediated NSCLCs.

The role of lipid raft translocation of prohibitin in regulation of Akt and Raf-protected apoptosis of HaCaT cells upon ultraviolet B irradiation

Prohibitin (PHB) plays a role in regulation of ultraviolet B light (UVB)-induced apoptosis of human keratinocytes, HaCaT cells. The regulatory function of PHB appears to be associated with its lipid raft translocation. However, the detailed mechanism for PHB-mediated apoptosis of these keratinocytes upon UVB irradiation is not clear. In this report, we determined the role of lipid raft translocation of PHB in regulation of UVB-induced apoptosis. Our data show that upon UVB irradiation PHB is translocated from the non-raft membrane to the lipid rafts, which is correlated with a release of both Akt and Raf from membrane. Overexpression of Akt and/or Raf impedes UVB-induced lipid raft translocation of PHB. Immunoprecipitation analysis indicates that UVB alters the interactions among PHB, Akt, and Raf. Reduced expression of PHB leads to a decreased phosphorylation of Akt and ERK, as well as a decreased activity of Akt, and increased apoptosis of the cells upon UVB irradiation. These results suggest that PHB regulates UVB-induced apoptosis of keratinocytes via a mechanism that involves detachment from Akt and Raf on the plasma membrane, and sequential lipid raft translocation.