TRIB2 as a biomarker for diagnosis and progression of melanoma

Biological function and application of melanocytes induced and transformed by mouse bone marrow mesenchymal stem cells

Background

A large number of autologous melanocytes are required for surgical treatment of depigmentation diseases such as vitiligo. The purpose of this experiment is to explore the application of melanocytes induced by mesenchymal stem cells to clinical treatment. Therefore, we have induced mouse bone marrow mesenchymal stem cells (BMMSCs) into melanocytes (miMels) in the previous experiment. This experiment continues the previous experiment to further study the biological functions of miMels and their application in tissue engineering.

Methods

We examined whether miMels can produce active tyrosinase, melanin, and response to α-MSH. The ability of miMels to produce melanin to keratinocytes was tested by co-culture. By applying miMels to tissue-engineered skin, the survival and function of miMels on the surface of nude mice were verified.

Results

MiMels can produce active tyrosinase and melanin, and can pass melanin to the co-cultured keratinocytes. Under the stimulation of α-MSH, the active tyrosinase and melanin content of miMels increased. We tried to apply it to the establishment of tissue-engineered skin and obtained tissue-engineered skin containing miMels. Then we tried to transplant tissue-engineered skin on the back skin of nude mice and succeeded. The transplanted miMels survived in local tissues, synthesized active tyrosinase and melanin, and expressed the marker protein of melanocytes.

Conclusion

In short, miMels can be used as a cell source for tissue engineering skin. MiMels not only have a typical melanocyte morphology but also have the same biological functions as normal melanocytes. What's more important is its successful application in mouse tissue-engineered experiments.

Multiplexed cellular profiling identifies an organoselenium compound as an inhibitor of CRM1-mediated nuclear export

Chromosomal region maintenance 1 (CRM1 also known as Xpo1 and exportin-1) is the receptor for the nuclear export controlling the intracellular localization and function of many cellular and viral proteins that play a crucial role in viral infections and cancer. The inhibition of CRM1 has emerged as a promising therapeutic approach to interfere with the lifecycle of many viruses, for the treatment of cancer, and to overcome therapy resistance. Recently, selinexor has been approved as the first CRM1 inhibitor for the treatment of multiple myeloma, providing proof of concept for this therapeutic option with a new mode of action. However, selinexor is associated with dose-limiting toxicity and hence, the discovery of alternative small molecule leads that could be developed as less toxic anticancer and antiviral therapeutics will have a significant impact in the clinic. Here, we report a CRM1 inhibitor discovery platform. The development of this platform includes reporter cell lines that monitor CRM1 activity by using red fluorescent protein or green fluorescent protein-labeled HIV-1 Rev protein with a strong heterologous nuclear export signal. Simultaneously, the intracellular localization of other proteins, to be interrogated for their capacity to undergo CRM1-mediated export, can be followed by co-culturing stable cell lines expressing fluorescent fusion proteins. We used this platform to interrogate the mode of nuclear export of several proteins, including PDK1, p110α, STAT5A, FOXO1, 3, 4 and TRIB2, and to screen a compound collection. We show that while p110α partially relies on CRM1-dependent nuclear export, TRIB2 is exported from the nucleus in a CRM1-independent manner. Compound screening revealed the striking activity of an organoselenium compound on the CRM1 nuclear export receptor.

Oncogenic TRIB2 interacts with and regulates PKM2 to promote aerobic glycolysis and lung cancer cell procession

PKM2 is an important regulator of the aerobic glycolysis that plays a vital role in cancer cell metabolic reprogramming. In general, Trib2 is considered as a “pseudokinase”, contributing to different kinds of cancer. However, the detailed roles of TRIB2 in regulating cancer metabolism by PKM2 remain unclear. This study demonstrated that TRIB2, not a “pseudokinase”, has the kinase activity to directly phosphorylate PKM2 at serine 37 in cancer cells. The elevated pSer37-PKM2 would subsequently promote the PKM2 dimers to enter into nucleus and increase the expression of LDHA, GLUT1, and PTBP1. The aerobic glycolysis is then elevated to promote cancer cell proliferation and migration in TRIB2- or PKM2-overexpressed cultures. The glucose uptake and lactate production increased, but the ATP content decreased in TRIB2- or PKM2-treated cultures. Experiments of TRIB2^−/− mice further supported that TRIB2 could regulate aerobic glycolysis by PKM2. Thus, these results reveal the new kinase activity of TRIB2 and its mechanism in cancer metabolism may be related to regulating PKM2 to promote lung cancer cell proliferation in vitro and in vivo, suggesting promising therapeutic targets for cancer therapy by controlling cancer metabolism.

A novel 7 RNA-based signature for prediction of prognosis and therapeutic responses of wild-type BRAF cutaneous melanoma

Background

The prognosis of wild-type BRAF cutaneous melanoma (WT Bf-CM) patients remains poor due to the lack of therapeutic options. However, few studies have investigated the factors contributing to the prognosis of WT Bf-CM patients.

Methods

In this paper, we proposed and validated a novel 7-RNA based signature to predict the prognosis of WT Bf-CM by analyzing the information from TCGA database.

Results

Dependence of this signature to other clinical factors were verified and a nomogram was also drawn to promote its application in clinical practice. Functional analysis suggested that the predictive function of this signature might attribute to the prediction of the up-regulation of RNA splicing, transcription, and cellular proliferation in the high-risk group, which have been demonstrated to be linked to malignancy of cancer. Moreover, functional analysis and therapy response analysis supported that the prognosis is highly related to PI3K/Akt/mTOR pathway among WT Bf-CM patients.

Conclusion

Collectively, this study will provide a preliminary bioinformatics evidence for the molecular mechanism and potential drug targets that could improving WT Bf-CM prognosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12575-022-00170-2.

Comprehensive Profiling of Mammalian Tribbles Interactomes Implicates TRIB3 in Gene Repression

The three human Tribbles (TRIB) pseudokinases have been implicated in a plethora of signaling and metabolic processes linked to cancer initiation and progression and can potentially be used as biomarkers of disease and prognosis. While their modes of action reported so far center around protein-protein interactions, the comprehensive profiling of TRIB interactomes has not been reported yet. Here, we have developed a robust mass spectrometry (MS)-based proteomics approach to characterize Tribbles' interactomes and report a comprehensive assessment and comparison of the TRIB1, -2 and -3 interactomes, as well as domain-specific interactions for TRIB3. Interestingly, TRIB3, which is predominantly localized in the nucleus, interacts with multiple transcriptional regulators, including proteins involved in gene repression. Indeed, we found that TRIB3 repressed gene transcription when tethered to DNA in breast cancer cells. Taken together, our comprehensive proteomic assessment reveals previously unknown interacting partners and functions of Tribbles proteins that expand our understanding of this family of proteins. In addition, our findings show that MS-based proteomics provides a powerful tool to unravel novel pseudokinase biology.

Non-coding RNA dysregulation in skin cancers

Skin cancers are the most common cancers worldwide. They can be classified in melanoma and non-melanoma skin cancer (NMSC), the latter includes squamous cell carcinoma (SCC), basal cell carcinoma (BCC) and merkel cell carcinoma (MCC). In recent years, the crucial role of non-coding RNAs (ncRNAs) in skin cancer pathogenesis has become increasingly evident. NcRNAs are functional RNA molecules that lack any protein-coding activity. These ncRNAs are classified based on their length: small, medium-size, and long ncRNAs. Among the most studied ncRNAs there are microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular RNA (circRNAs). ncRNAs have the ability to regulate gene expression at transcriptional and post-transcriptional levels and are involved in skin cancer cell proliferation, angiogenesis, invasion, and metastasis. Many ncRNAs exhibit tissue- or cell-specific expression while others have been correlated to tumor staging, drug resistance, and prognosis. For these reasons, ncRNAs have both a diagnostic and prognostic significance in skin cancers. Our review summarizes the functional role of ncRNAs in skin cancers and their potential clinical application as biomarkers.

Anti-melanoma effects of concomitant inhibition of SIRT1 and SIRT3 in BrafV600E/PtenNULL mice

Novel therapeutic strategies are required for the effective and lasting treatment of metastatic melanoma, one of the deadliest skin malignancies. In this study, we determined the anti-melanoma efficacy of 4'-bromo-resveratrol (4'-BR), which is a small molecule dual inhibitor of SIRT1 and SIRT3 in a Braf^V600E/Pten^NULL mouse model that recapitulates human disease, including metastases. Tumors were induced by topical application of 4-hydroxy-tamoxifen on shaved backs of 10-week-old mice, and the effects of 4'-BR (5-30 mg/kg b.wt.; intraperitoneally; 3d/week for 5 weeks) were assessed on melanoma development and progression. We found that 4'-BR at a dose of 30 mg/kg significantly reduced size and volume of primary melanoma tumors, as well as lung metastasis, with no adverse effects. Further, mechanistic studies on tumors showed significant modulation in markers of proliferation, survival and melanoma progression. As SIRT1 and SIRT3 are linked to immunomodulation, we performed differential gene expression analysis via NanoString PanCancer Immune Profiling panel (770 genes). Our data demonstrated that 4'-BR significantly downregulated genes related to metastasis-promotion, chemokine/cytokine-regulation, and innate/adaptive immune functions. Overall, inhibition of SIRT1 and SIRT3 by 4'-BR is a promising anti-melanoma therapy with anti-metastatic and immunomodulatory activities warranting further detailed studies, including clinical investigations.

A methyltransferase-like 14/miR-99a-5p/tribble 2 positive feedback circuit promotes cancer stem cell persistence and radioresistance via histone deacetylase 2-mediated epigenetic modulation in esophageal squamous cell carcinoma

BACKGROUND

Esophageal squamous cell carcinoma (ESCC) is a highly aggressive and treatment-resistant tumor. The biological implications and molecular mechanism of cancer stem-like cells (CSCs) in ESCC, which contribute to therapeutic resistance such as radioresistance, remain elusive.

METHODS

Quantitative real-time polymerase chain reaction, western blotting, immunohistochemistry, and in situ hybridization assays were used to detect methyltransferase-like 14 miR-99a-5p tribble 2 (METTL14/miR-99a-5p/TRIB2) expression in ESCC. The biological functions of METTL14/miR-99a-5p/TRIB2 were demonstrated in vitro and in vivo. Mass spectrum analysis was used to identify the downstream proteins regulated by TRIB2. Chromatin immunoprecipitation (IP), IP, N6 -methyladenosine (m6 A)-RNA IP, luciferase reporter, and ubiquitination assays were employed to explore the molecular mechanisms underlying this feedback circuit and its downstream pathways.

RESULTS

We found that miR-99a-5p was significantly decreased in ESCC. miR-99a-5p inhibited CSCs persistence and the radioresistance of ESCC cells, and miR-99a-5p downregulation predicted an unfavorable prognosis of ESCC patients. Mechanically, we unveiled a METTL14-miR-99a-5p-TRIB2 positive feedback loop that enhances CSC properties and radioresistance of ESCC cells. METTL14, an m6 A RNA methyltransferase downregulated in ESCC, suppresses TRIB2 expression via miR-99a-5p-mediated degradation of TRIB2 mRNA by targeting its 3' untranslated region, whereas TRIB2 induces ubiquitin-mediated proteasomal degradation of METTL14 in a COP1-dependent manner. METTL14 upregulates miR-99a-5p by modulating m6 A-mediated, DiGeorge critical region 8-dependent pri-mir-99a processing. Hyperactivation of TRIB2 resulting from this positive circuit was closely correlated with radioresistance and CSC characteristics. Furthermore, TRIB2 activates HDAC2 and subsequently induces p21 epigenetic repression through Akt/mTOR/S6K1 signaling pathway activation. Pharmacologic inhibition of HDAC2 effectively attenuates the TRIB2-mediated effect both in vitro and in patient-derived xenograft models.

CONCLUSION

Our data highlight the presence of the METTL14/miR-99a-5p/TRIB2 axis and show that it is positively associated with CSC characteristics and radioresistance of ESCC, suggesting potential therapeutic targets for ESCC treatment.

Tribbles Pseudokinases in Colorectal Cancer

The Tribbles family of pseudokinases controls a wide number of processes during cancer on-set and progression. However, the exact contribution of each of the three family members is still to be defined. Their function appears to be context-dependent as they can act as oncogenes or tumor suppressor genes. They act as scaffolds modulating the activity of several signaling pathways involved in different cellular processes. In this review, we discuss the state-of-knowledge for TRIB1, TRIB2 and TRIB3 in the development and progression of colorectal cancer. We take a perspective look at the role of Tribbles proteins as potential biomarkers and therapeutic targets. Specifically, we chronologically systematized all available articles since 2003 until 2020, for which Tribbles were associated with colorectal cancer human samples or cell lines. Herein, we discuss: (1) Tribbles amplification and overexpression; (2) the clinical significance of Tribbles overexpression; (3) upstream Tribbles gene and protein expression regulation; (4) Tribbles pharmacological modulation; (5) genetic modulation of Tribbles; and (6) downstream mechanisms regulated by Tribbles; establishing a comprehensive timeline, essential to better consolidate the current knowledge of Tribbles' role in colorectal cancer.

The Critical Role of TRIB2 in Cancer and Therapy Resistance

Simple Summary

The Tribbles proteins are members of CAMK Ser/Thr protein kinase family. They are evolutionary conserved pseudokinases found in most tissues of eukaryotic organisms. This ubiquitously expressed protein family is characterized by containing a catalytically deficient kinase domain which lacks amino acid residues required for the productive interaction with ATP and metal ions. Tribbles proteins exert their biological functions mainly through direct interaction with MAPKK and AKT proteins, therefore regulating important pathways involved in cell proliferation, apoptosis and differentiation. Due to the role of MAPKK and AKT signalling in the context of cancer development, Tribbles proteins have been recently considered as biomarkers of cancer progression. Furthermore, as the atypical pseudokinase domain retains a binding platform for substrates, Tribbles targeting provides an attractive opportunity for drug development.

Abstract

The Tribbles pseudokinases family consists of TRIB1, TRIB2, TRIB3 and STK40 and, although evolutionarily conserved, they have distinctive characteristics. Tribbles members are expressed in a context and cell compartment-dependent manner. For example, TRIB1 and TRIB2 have potent oncogenic activities in vertebrate cells. Since the identification of Tribbles proteins as modulators of multiple signalling pathways, recent studies have linked their expression with several pathologies, including cancer. Tribbles proteins act as protein adaptors involved in the ubiquitin-proteasome degradation system, as they bridge the gap between substrates and E3 ligases. Between TRIB family members, TRIB2 is the most ancestral member of the family. TRIB2 is involved in protein homeostasis regulation of C/EBPα, β-catenin and TCF4. On the other hand, TRIB2 interacts with MAPKK, AKT and NFkB proteins, involved in cell survival, proliferation and immune response. Here, we review the characteristic features of TRIB2 structure and signalling and its role in many cancer subtypes with an emphasis on TRIB2 function in therapy resistance in melanoma, leukemia and glioblastoma. The strong evidence between TRIB2 expression and chemoresistance provides an attractive opportunity for targeting TRIB2.

Tribbles homolog 2 promotes hepatic fibrosis and hepatocarcinogenesis through phosphatase 1A-Mediated stabilization of yes-associated protein

BACKGROUND & AIMS

Hepatic stellate cells (HSCs) play critical roles in liver fibrosis and hepatocellular carcinoma (HCC). Tribbles homolog 2 (TRIB2) is an oncogene implicated in a variety of cancers, including liver cancer. However, the biological function and regulatory mechanism of TRIB2 in HSCs are poorly understood. In addition, little is known about its role in liver fibrosis progression to HCC. Here, we revealed the clinical significance of TRIB2 in liver fibrosis and HCC development.

METHODS

We investigated TRIB2 promoting liver fibrosis in vitro and in vivo. In mouse model of liver fibrosis and HCC, we measured hepatic fibrosis and HCC level through knockdown TRIB2 with shRNA. In addition, we performed western blotting, real-time quantitative PCR, immunofluorescence and co-immunoprecipitation assay to study TRIB2 function in LX-2 cells.

RESULTS

TRIB2 expression was strongly upregulated in human fibrotic liver tissues and HCC tissues. TRIB2 colocalized with α-smooth muscle actin (α-SMA) in fibrotic and HCC liver tissues. Knockdown of TRIB2 inhibited HSC activation and liver fibrosis in vitro and in vivo. TRIB2 promoted Yes-associated protein (YAP) stabilization, nuclear localization, and subsequent fibrotic gene expression independent of the MST-LATS phosphorylation cascade in HSCs. TRIB2 interacted with YAP to recruit phosphatase 1A (PP1A), promoting PP1A-mediated YAP dephosphorylation. TRIB2 knockdown potently attenuated the development of fibrosis-associated liver cancer.

CONCLUSIONS

TRIB2 is an attractive target for hepatic fibrosis and fibrosis-associated liver cancer treatment.

Harmine and Piperlongumine Revert TRIB2-Mediated Drug Resistance

Simple Summary

Poor survival and treatment failure of patients with cancer are mainly due to resistance to therapy. Tribbles homologue 2 (TRIB2) has recently been identified as a protein that promotes resistance to several anti-cancer drugs. In this study, RNA sequencing and bioinformatics analysis were used with the aim of characterizing the impact of TRIB2 on the expression of genes and developing pharmacological strategies to revert these TRIB2-mediated changes, thereby overcoming therapy resistance. We show that two naturally occurring alkaloids, harmine and piperlongumine, inverse the gene expression profile produced by TRIB2 and sensitize cancer cells to anti-cancer drugs. Our data suggest that harmine and piperlongumine or similar compounds might have the potential to overcome TRIB2-mediated therapy resistance in cancer patients.

Abstract

Therapy resistance is responsible for most relapses in patients with cancer and is the major challenge to improving the clinical outcome. The pseudokinase Tribbles homologue 2 (TRIB2) has been characterized as an important driver of resistance to several anti-cancer drugs, including the dual ATP-competitive PI3K and mTOR inhibitor dactolisib (BEZ235). TRIB2 promotes AKT activity, leading to the inactivation of FOXO transcription factors, which are known to mediate the cell response to antitumor drugs. To characterize the downstream events of TRIB2 activity, we analyzed the gene expression profiles of isogenic cell lines with different TRIB2 statuses by RNA sequencing. Using a connectivity map-based computational approach, we identified drug-induced gene-expression profiles that invert the TRIB2-associated expression profile. In particular, the natural alkaloids harmine and piperlongumine not only produced inverse gene expression profiles but also synergistically increased BEZ235-induced cell toxicity. Importantly, both agents promote FOXO nuclear translocation without interfering with the nuclear export machinery and induce the transcription of FOXO target genes. Our results highlight the great potential of this approach for drug repurposing and suggest that harmine and piperlongumine or similar compounds might be useful in the clinic to overcome TRIB2-mediated therapy resistance in cancer patients.

Knockdown of circ_0084043 suppresses the development of human melanoma cells through miR-429/tribbles homolog 2 axis and Wnt/β-catenin pathway

AIMS

Circular RNAs (circRNAs) have been emerged as novel regulators in multiple tumorigenesis, including melanoma. CircRNA_0084043 was recently demonstrated to be deregulated in human melanoma cells. Nevertheless, its role and mechanism are largely unrevealed in melanoma.

MATERIALS AND METHODS

Expression of circ_0084043, miRNA (miR)-429 and tribbles homolog 2 (TRIB2) was detected using reverse transcription-quantitative PCR quantitative PCR (RT-qPCR) and western blotting. Cell proliferation, apoptosis, migration and invasion were measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, flow cytometry and transwell assays, respectively. The activation of Wnt/β-catenin pathway was evaluated by western blotting. The target binding among circ_0084043, miR-429 and TRIB2 was confirmed by dual-luciferase reporter assay and RNA immunoprecipitation. In vivo, mice xenograft model was generated to investigate tumor growth.

KEY FINDINGS

Expression of circ_0084043 and TRIB2 was upregulated in human melanoma tissues and cell lines. Both circ_0084043 knockdown and TRIB2 silencing could decrease cell proliferation, migration and invasion, but facilitate apoptosis in A375 and SK-MEL-28 cells. Furthermore, TRIB2 restoration partially abrogated the tumor-suppressive role of circ_0084043 knockdown in melanoma cells in vitro. Then, we verified that circ_0084043 positively and physically controlled TRIB2 expression through sponging miR-429. Besides, expression of β-catenin, c-Myc and cyclinD1 was inhibited in A375 and SK-MEL-28 cells when circ_0084043 was knocked down, accompanied with increased miR-429 and decreased TRIB2. Notably, circ_0084043 downregulation impeded tumor growth of A375 cells in vivo.

SIGNIFICANCE

Knockdown of circ_0084043 suppressed the malignant development of melanoma presumably through modulating miR429/TRIB2 axis and inactivating Wnt/β-catenin signaling pathway.

Pseudokinases: a tribble-edged sword

Advances in the understanding of the Tribbles family of pseudokinases (TRIB1, TRIB2 and TRIB3) reveal these proteins as potentially valuable biomarkers of disease diagnosis, prognosis, prediction and clinical strategy. In their role as signalling mediators and scaffolding proteins, TRIBs lead to changes in protein stability and activity, which impact on diverse cellular processes such as proliferation, differentiation, cell cycle and cell death. We review the role of TRIB proteins as promising therapeutic targets, with an emphasis on their role in cancer, and as biomarkers, with potential application across diverse pathological processes.

Uncovering Potential Therapeutic Targets in Colorectal Cancer by Deciphering Mutational Status and Expression of Druggable Oncogenes

Background: Numerous driver mutations have been identified in colorectal cancer (CRC), but their relevance to the development of targeted therapies remains elusive. The secondary effects of pathogenic driver mutations on downstream signaling pathways offer a potential approach for the identification of therapeutic targets. We aimed to identify differentially expressed genes as potential drug targets linked to driver mutations. Methods: Somatic mutations and the gene expression data of 582 CRC patients were utilized, incorporating the mutational status of 39,916 and the expression levels of 20,500 genes. To uncover candidate targets, the expression levels of various genes in wild-type and mutant cases for the most frequent disruptive mutations were compared with a Mann–Whitney test. A survival analysis was performed in 2100 patients with transcriptomic gene expression data. Up-regulated genes associated with worse survival were filtered for potentially actionable targets. The most significant hits were validated in an independent set of 171 CRC patients. Results: Altogether, 426 disruptive mutation-associated upregulated genes were identified. Among these, 95 were linked to worse recurrence-free survival (RFS). Based on the druggability filter, 37 potentially actionable targets were revealed. We selected seven genes and validated their expression in 171 patient specimens. The best independently validated combinations were DUSP4 (p = 2.6 × 10⁻¹²) in ACVR2A mutated (7.7%) patients; BMP4 (p = 1.6 × 10⁻⁰⁴) in SOX9 mutated (8.1%) patients; TRIB2 (p = 1.35 × 10⁻¹⁴) in ACVR2A mutated patients; VSIG4 (p = 2.6 × 10⁻⁰⁵) in ANK3 mutated (7.6%) patients, and DUSP4 (p = 7.1 × 10⁻⁰⁴) in AMER1 mutated (8.2%) patients. Conclusions: The results uncovered potentially druggable genes in colorectal cancer. The identified mutations could enable future patient stratification for targeted therapy.

The cell biology behind the oncogenic PIP3 lipids

The different mechanisms of phosphoinositide 3-kinase (PI3K) activation in cancer as well as the events that result in PI3K pathway reactivation after patient treatment with PI3K inhibitors was discussed on October 15-17th, 2018, in the medieval town of Baeza (Universidad Internacional de Andalucía, Spain) at the workshop entitled 'The cell biology behind the oncogenic PIP3 lipids'. These topics and the data presented regarding cellular functions altered by PI3K deregulation, the cooperation of PI3K/PTEN mutations with other tumor drivers, and the lessons learned for PI3K-targeted therapy, are discussed below.

TRIB2 functions as novel oncogene in colorectal cancer by blocking cellular senescence through AP4/p21 signaling

Background

Cellular senescence is a state of irreversible cell growth arrest and senescence cells permanently lose proliferation potential. Induction of cellular senescence might be a novel therapy for cancer cells. TRIB2 has been reported to participate in regulating proliferation and drug resistance of various cancer cells. However, the role of TRIB2 in cellular senescence of colorectal cancer (CRC) and its molecular mechanism remains unclear.

Methods

The expression of TRIB2 in colorectal cancer tissues and adjacent tissues was detected by immunohistochemistry and RT-PCR. The growth, cell cycle distribution and cellular senescence of colorectal cancer cells were evaluated by Cell Counting Kit-8 (CCK8) assay, flow cytometry detection and senescence-associated β-galactosidase staining, respectively. Western blot, RT-PCR and luciferase assay were performed to determine how TRIB2 regulates p21. Immunoprecipitation (IP) and chromatin-immunoprecipitation (ChIP) were used to investigate the molecular mechanisms.

Results

We found that TRIB2 expression was elevated in CRC tissues compared to normal adjacent tissues and high TRIB2 expression indicated poor prognosis of CRC patients. Functionally, depletion of TRIB2 inhibited cancer cells proliferation, induced cell cycle arrest and promoted cellular senescence, whereas overexpression of TRIB2 accelerated cell growth, cell cycle progression and blocked cellular senescence. Further studies showed that TRIB2 physically interacted with AP4 and inhibited p21 expression through enhancing transcription activities of AP4. The rescue experiments indicated that silencing of AP4 abrogated the inhibition of cellular senescence induced by TRIB2 overexpression.

Conclusion

These data demonstrate that TRIB2 suppresses cellular senescence through interaction with AP4 to down-regulate p21 expression. Therefore, TRIB2 could be a potential target for CRC treatment.

Electronic supplementary material

The online version of this article (10.1186/s12943-018-0922-x) contains supplementary material, which is available to authorized users.

Covalent inhibitors of EGFR family protein kinases induce degradation of human Tribbles 2 (TRIB2) pseudokinase in cancer cells

A major challenge associated with biochemical and cellular analysis of pseudokinases is a lack of target-validated small-molecule compounds with which to probe function. Tribbles 2 (TRIB2) is a cancer-associated pseudokinase with a diverse interactome, including the canonical AKT signaling module. There is substantial evidence that human TRIB2 promotes survival and drug resistance in solid tumors and blood cancers and therefore is of interest as a therapeutic target. The unusual TRIB2 pseudokinase domain contains a unique cysteine-rich C-helix and interacts with a conserved peptide motif in its own carboxyl-terminal tail, which also supports its interaction with E3 ubiquitin ligases. We found that TRIB2 is a target of previously described small-molecule protein kinase inhibitors, which were originally designed to inhibit the canonical kinase domains of epidermal growth factor receptor tyrosine kinase family members. Using a thermal shift assay, we discovered TRIB2-binding compounds within the Published Kinase Inhibitor Set (PKIS) and used a drug repurposing approach to classify compounds that either stabilized or destabilized TRIB2 in vitro. TRIB2 destabilizing agents, including the covalent drug afatinib, led to rapid TRIB2 degradation in human AML cancer cells, eliciting tractable effects on signaling and survival. Our data reveal new drug leads for the development of TRIB2-degrading compounds, which will also be invaluable for unraveling the cellular mechanisms of TRIB2-based signaling. Our study highlights that small molecule-induced protein down-regulation through drug "off-targets" might be relevant for other inhibitors that serendipitously target pseudokinases.

Trib2 expression in granulocyte-monocyte progenitors drives a highly drug resistant acute myeloid leukaemia linked to elevated Bcl2

Trib2 pseudokinase has oncogenic and tumour suppressive functions depending on the cellular context. We investigated the ability of Trib2 to transform different haemopoietic stem and progenitor cells (HSPCs). Our study identified the granulocyte-macrophage progenitor (GMP) subpopulation as a potent leukaemia initiating cell of Trib2-driven AML in vivo. Trib2 transformed GMPs generated a fully penetrant and short latency AML. AML cells expressing elevated Trib2 led to a chemoresistant phenotype following chemotherapy treatment. We show that Trib2 overexpression results in an increase in BCL2 expression, and high Trib2 expressing cells are highly sensitive to cell killing by BCL2 inhibition (ABT199). Combined treatment with chemotherapeutic agents and BCL2 inhibition resulted in synergistic killing of Trib2+ AML cells. Trib2 transformed GMP AML cells showed more chemoresistance compared with HSPC derived Trib2 AML cells associated with higher Bcl2 expression. There is significant correlation of high TRIB2 and BCL2 expression in patient derived human AML cells. These data demonstrate that the cell of origin influences the leukaemic profile and chemotherapeutic response of Trib2+ AML. Combined TRIB2 and BCL2 expression in AML cells may have clinical utility relevant for monitoring drug resistance and disease relapse.

Identification of a gene signature for discriminating metastatic from primary melanoma using a molecular interaction network approach

Understanding the biological factors that are characteristic of metastasis in melanoma remains a key approach to improving treatment. In this study, we seek to identify a gene signature of metastatic melanoma. We configured a new network-based computational pipeline, combined with a machine learning method, to mine publicly available transcriptomic data from melanoma patient samples. Our method is unbiased and scans a genome-wide protein-protein interaction network using a novel formulation for network scoring. Using this, we identify the most influential, differentially expressed nodes in metastatic as compared to primary melanoma. We evaluated the shortlisted genes by a machine learning method to rank them by their discriminatory capacities. From this, we identified a panel of 6 genes, ALDH1A1, HSP90AB1, KIT, KRT16, SPRR3 and TMEM45B whose expression values discriminated metastatic from primary melanoma (87% classification accuracy). In an independent transcriptomic data set derived from 703 primary melanomas, we showed that all six genes were significant in predicting melanoma specific survival (MSS) in a univariate analysis, which was also consistent with AJCC staging. Further, 3 of these genes, HSP90AB1, SPRR3 and KRT16 remained significant predictors of MSS in a joint analysis (HR = 2.3, P = 0.03) although, HSP90AB1 (HR = 1.9, P = 2 × 10-4) alone remained predictive after adjusting for clinical predictors.

Down-regulated miR-23a Contributes to the Metastasis of Cutaneous Melanoma by Promoting Autophagy

Melanoma is among the most aggressive tumors, and the occurrence of metastasis leads to a precipitous drop in the patients' survival. Therefore, identification of metastasis-associated biomarkers and therapeutic targets will contribute a lot to improving melanoma theranostics. Recently, microRNAs (miRNAs) have been implicated in modulating cancer invasion and metastasis, and are proved as potential non-invasive biomarkers in sera for various tumors. Here, we reported miR-23a as a novel metastasis-associated miRNA that played a remarkable role in modulating melanoma invasive and metastatic capacity and was of great value in predicting melanoma metastasis and prognosis. We found that serum miR-23a level was significantly down-regulated in metastatic melanoma patients and highly correlated with poor clinical outcomes. In addition, miR-23a level was also remarkably decreased in metastatic melanoma tissues and cell lines. Furthermore, overexpressed miR-23a suppressed the invasive and migratory property of melanoma cells by abrogating autophagy through directly targeting ATG12. Specially, miR-23a-ATG12 axis attenuated melanoma invasion and migration through autophagy-mediated AMPK-RhoA pathway. Finally, the overexpression of miR-23a prevented melanoma metastasis in vivo. Taken together, our findings demonstrate that the metastasis-associated miR-23a is not only a potential biomarker, but also a valuable therapeutic target for melanoma.

TRIB2 confers resistance to anti-cancer therapy by activating the serine/threonine protein kinase AKT

Intrinsic and acquired resistance to chemotherapy is the fundamental reason for treatment failure for many cancer patients. The identification of molecular mechanisms involved in drug resistance or sensitization is imperative. Here we report that tribbles homologue 2 (TRIB2) ablates forkhead box O activation and disrupts the p53/MDM2 regulatory axis, conferring resistance to various chemotherapeutics. TRIB2 suppression is exerted via direct interaction with AKT a key signalling protein in cell proliferation, survival and metabolism pathways. Ectopic or intrinsic high expression of TRIB2 induces drug resistance by promoting phospho-AKT (at Ser473) via its COP1 domain. TRIB2 expression is significantly increased in tumour tissues from patients correlating with an increased phosphorylation of AKT, FOXO3a, MDM2 and an impaired therapeutic response. This culminates in an extremely poor clinical outcome. Our study reveals a novel regulatory mechanism underlying drug resistance and suggests that TRIB2 functions as a regulatory component of the PI3K network, activating AKT in cancer cells.

Tribbles in the 21st Century: The Evolving Roles of Tribbles Pseudokinases in Biology and Disease

The Tribbles (TRIB) pseudokinases control multiple aspects of eukaryotic cell biology and evolved unique features distinguishing them from all other protein kinases. The atypical pseudokinase domain retains a regulated binding platform for substrates, which are ubiquitinated by context-specific E3 ligases. This plastic configuration has also been exploited as a scaffold to support the modulation of canonical MAPK and AKT modules. In this review, we discuss the evolution of TRIBs and their roles in vertebrate cell biology. TRIB2 is the most ancestral member of the family, whereas the emergence of TRIB3 homologs in mammals supports additional biological roles, many of which are currently being dissected. Given their pleiotropic role in diseases, the unusual TRIB pseudokinase conformation provides a highly attractive opportunity for drug design.

Pseudoenzymes are inactive counterparts of classical enzymes and have evolved in all kingdoms of life, where they regulate a vast array of biological processes. The pseudokinases are one of the best-studied families of human pseudoenzymes.

Eukaryotic TRIB pseudokinases evolved from a common ancestor (the human TRIB2 homolog), and contain a highly atypical pseudokinase domain fused to a unique docking site in an extended C tail that binds to ubiquitin E3 ligases.

TRIB evolution has led to the appearance of three mammalian TRIB pseudokinases, termed TRIB1, TRIB2, and TRIB3, which contain both unique and shared features.

In cells, TRIB pseudokinases act as modulators of substrate ubiquitination and as molecular scaffolds for the assembly and regulation of signaling modules, including the C/EBPα transcription factor and AKT and ERK networks.

TRIB1 and TRIB2 have potent oncogenic activities in vertebrate cells, and recent evidence also suggests that TRIB2 acts as a tumour suppressor, consistent with the requirement for balanced TRIB signaling in the regulation of transcription, differentiation, proliferation, and apoptosis.

Tribbles breaking bad: TRIB2 suppresses FOXO and acts as an oncogenic protein in melanoma

TRIB2 (tribbles homolog 2) encodes one of three members of the tribbles family in mammals. These members share a Trb (tribbles) domain, which is homologous to protein serine-threonine kinases, but lack the active site lysine. The tribbles proteins interact and modulate the activity of signal transduction pathways in a number of physiological and pathological processes. TRIB2 has been identified as an oncogene that inactivates the transcription factor CCAAT/enhancer-binding protein α (C/EBPα) and causes acute myelogenous leukaemia (AML). Recent research provided compelling evidence that TRIB2 can also act as oncogenic driver in solid tumours, such as lung and liver cancer. In particular, our recent work demonstrated that TRIB2 is dramatically overexpressed in malignant melanomas compared with normal skin and promotes the malignant phenotype of melanoma cells via the down-regulation of FOXO (forkhead box protein O) tumour suppressor activity in vitro and in vivo. TRIB2 was found to be expressed in normal skin, but its expression consistently increased in benign nevi, melanoma and was highest in samples from patients with malignant melanoma. The observation that TRIB2 strongly correlates with the progression of melanocyte-derived malignancies suggests TRIB2 as a meaningful biomarker to both diagnose and stage melanoma. In addition, interfering with TRIB2 activity might be a therapeutic strategy for the treatment of several different tumour types.

Tribbles in normal and malignant haematopoiesis

The tribbles protein family, an evolutionarily conserved group of pseudokinases, have been shown to regulate multiple cellular events including those involved in normal and malignant haematopoiesis. The three mammalian Tribbles homologues, Trib1, Trib2 and Trib3 are characterized by conserved motifs, including a pseudokinase domain and a C-terminal E3 ligase-binding domain. In this review, we focus on the role of Trib (mammalian Tribbles homologues) proteins in mammalian haematopoiesis and leukaemia. The Trib proteins show divergent expression in haematopoietic cells, probably indicating cell-specific functions. The roles of the Trib proteins in oncogenesis are also varied and appear to be tissue-specific. Finally, we discuss the potential mechanisms by which the Trib proteins preferentially regulate these processes in multiple cell types.

TRIB2 and the ubiquitin proteasome system in cancer

Tribbles family of pseudokinase proteins are known to mediate the degradation of target proteins in Drosophila and mammalian systems. The main protein proteolysis pathway in eukaryotic cells is the ubiquitin proteasome system (UPS). The tribbles homolog 2 (TRIB2) mammalian family member has been well characterized for its role in murine and human leukaemia, lung and liver cancer. One of the most characterized substrates for TRIB2-mediated degradation is the myeloid transcription factor CCAAT enhancer binding protein α (C/EBPα). However, across a number of cancers, the molecular interactions that take place between TRIB2 and factors involved in the UPS are varied and have differential downstream effects. This review summarizes our current knowledge of these interactions and how this information is important for our understanding of TRIB2 in cancer.

Serum miR-16: A Potential Biomarker for Predicting Melanoma Prognosis

Melanoma is among the most malignant cancers with notorious aggressiveness, and its prognosis is greatly influenced by progression status. Serum microRNAs are small noncoding RNAs with high stability and easy accessibility in human blood. Their expression profiles are frequently dysregulated in cancers; hence, levels of serum microRNAs may reflect progression status and thus predict melanoma prognosis. In a hospital based case-control study, we found a significant reduction of serum miR-16 level in melanoma patients compared with cancer-free controls (P < 0.001). In addition, serum miR-16 level markedly decreased in melanoma patients with increased tumor thickness, occurrence of ulceration, and advanced American Joint Committee on Cancer stages, and was highly correlated with tissue Ki-67 expression (r = -0.521, P < 0.0001). Kaplan-Meier analysis and Cox proportional hazards regression analysis revealed a prognostic role of serum miR-16 (hazard ratio 2.49, 95% confidence interval 1.10-5.63, P = 0.028), which independently evaluated patients' survival outcome. Finally, the suppressive role of miR-16 in melanoma growth was validated both in vitro and in vivo. In conclusion, we demonstrated that serum miR-16 is a potential biomarker for predicting melanoma prognosis.

Tribbles pseudokinases: novel targets for chemical biology and drug discovery?

Tribbles (TRIB) proteins are pseudokinase mediators of eukaryotic signalling that have evolved important roles in lipoprotein metabolism, immune function and cellular differentiation and proliferation. In addition, an evolutionary-conserved modulation of PI3K/AKT signalling pathways highlights them as novel and rather unusual pharmaceutical targets. The three human TRIB family members are uniquely defined by an acidic pseudokinase domain containing a ‘broken’ α C-helix and a MEK (MAPK/ERK)-binding site at the end of the putative C-lobe and a distinct C-terminal peptide motif that interacts directly with a small subset of cellular E3 ubiquitin ligases. This latter interaction drives proteasomal-dependent degradation of networks of transcription factors, whose rate of turnover determines the biological attributes of individual TRIB family members. Defining the function of individual Tribs has been made possible through evaluation of individual TRIB knockout mice, siRNA/overexpression approaches and genetic screening in flies, where the single TRIB gene was originally described 15 years ago. The rapidly maturing TRIB field is primed to exploit chemical biology approaches to evaluate endogenous TRIB signalling events in intact cells. This will help define how TRIB-driven protein–protein interactions and the atypical TRIB ATP-binding site, fit into cellular signalling modules in experimental scenarios where TRIB-signalling complexes remain unperturbed. In this mini-review, we discuss how small molecules can reveal rate-limiting signalling outputs and functions of Tribs in cells and intact organisms, perhaps serving as guides for the development of new drugs. We predict that appropriate small molecule TRIB ligands will further accelerate the transition of TRIB pseudokinase analysis into the mainstream of cell signalling.