RSK2 phosphorylates T-bet to attenuate colon cancer metastasis and growth

RSK1 and RSK2 as therapeutic targets: an up-to-date snapshot of emerging data

INTRODUCTION

The four members of the p90 ribosomal S6 kinase (RSK) family are serine/threonine protein kinases, which are phosphorylated and activated by ERK1/2. RSK1/2/3 are further phosphorylated by PDK1. Receiving inputs from two major signaling pathways places RSK as a key signaling node in numerous pathologies. A plethora of RSK1/2 substrates have been identified, and in the majority of cases the causative roles these RSK substrates play in the pathology are unknown.

AREAS COVERED

The majority of studies have focused on RSK1/2 and their functions in a diverse group of cancers. However, RSK1/2 are known to have important functions in cardiovascular disease and neurobiological disorders. Based on the literature, we identified substrates that are common in these pathologies with the goal of identifying fundamental physiological responses to RSK1/2.

EXPERT OPINION

The core group of targets in pathologies driven by RSK1/2 are associated with the immune response. However, there is a paucity of the literature addressing RSK function in inflammation, which is critical to know as the pan RSK inhibitor, PMD-026, is entering phase II clinical trials for metastatic breast cancer. A RSK inhibitor has the potential to be used in numerous diverse diseases and disorders.

Role of Post-Translational Modifications in Colorectal Cancer Metastasis

Colorectal cancer (CRC) is one of the most common malignant tumors of the digestive tract. CRC metastasis is a multi-step process with various factors involved, including genetic and epigenetic regulations, which turn out to be a serious threat to CRC patients. Post-translational modifications (PTMs) of proteins involve the addition of chemical groups, sugars, or proteins to specific residues, which fine-tunes a protein's stability, localization, or interactions to orchestrate complicated biological processes. An increasing number of recent studies suggest that dysregulation of PTMs, such as phosphorylation, ubiquitination, and glycosylation, play pivotal roles in the CRC metastasis cascade. Here, we summarized recent advances in the role of post-translational modifications in diverse aspects of CRC metastasis and its detailed molecular mechanisms. Moreover, advances in drugs targeting PTMs and their cooperation with other anti-cancer drugs, which might provide novel targets for CRC treatment and improve therapeutic efficacy, were also discussed.

Hepatitis B Virus X Protein Modulates p90 Ribosomal S6 Kinase 2 by ERK to Promote Growth of Hepatoma Cells

Hepatitis B virus (HBV) infection is a leading cause of hepatocellular carcinoma (HCC), one of the most prevalent malignant tumors worldwide that poses a significant threat to human health. The multifunctional regulator known as Hepatitis B virus X-protein (HBx) interacts with host factors, modulating gene transcription and signaling pathways and contributing to hepatocellular carcinogenesis. The p90 ribosomal S6 kinase 2 (RSK2) is a member of the 90 kDa ribosomal S6 kinase family involved in various intracellular processes and cancer pathogenesis. At present, the role and mechanism of RSK2 in the development of HBx-induced HCC are not yet clear. In this study, we found that HBx upregulates the expression of RSK2 in HBV-HCC tissues, HepG2, and SMMC-7721 cells. We further observed that reducing the expression of RSK2 inhibited HCC cell proliferation. In HCC cell lines with stable HBx expression, RSK2 knockdown impaired the ability of HBx to promote cell proliferation. The extracellularly regulated protein kinases (ERK) 1/2 signaling pathway, rather than the p38 signaling pathway, mediated HBx-induced upregulation of RSK2 expression. Additionally, RSK2 and cyclic adenosine monophosphate (cAMP) response element binding protein (CREB) were highly expressed and positively correlated in HBV-HCC tissues and associated with tumor size. This study showed that HBx upregulates the expression of RSK2 and CREB by activating the ERK1/2 signaling pathway, promoting the proliferation of HCC cells. Furthermore, we identified RSK2 and CREB as potential prognostic markers for HCC patients.

P90 ribosomal S6 kinases: A bona fide target for novel targeted anticancer therapies?

The 90 kDa ribosomal S6 kinase (RSK) family of proteins is a group of highly conserved Ser/Thr kinases. They are downstream effectors of the Ras/ERK/MAPK signaling cascade. ERK1/2 activation directly results in the phosphorylation of RSKs, which further, through interaction with a variety of different downstream substrates, activate various signaling events. In this context, they have been shown to mediate diverse cellular processes like cell survival, growth, proliferation, EMT, invasion, and metastasis. Interestingly, increased expression of RSKs has also been demonstrated in various cancers, such as breast, prostate, and lung cancer. This review aims to present the most recent advances in the field of RSK signaling that have occurred, such as biological insights, function, and mechanisms associated with carcinogenesis. We additionally present and discuss the recent advances but also the limitations in the development of pharmacological inhibitors of RSKs, in the context of the use of these kinases as putative, more efficient targets for novel anticancer therapeutic approaches.

RSK inhibitors as potential anticancer agents: Discovery, optimization, and challenges

Ribosomal S6 kinase (RSK) family is a group of serine/threonine kinases, including four isoforms (RSK1/2/3/4). As a downstream effector of the Ras-mitogen-activated protein kinase (Ras-MAPK) pathway, RSK participates in many physiological activities such as cell growth, proliferation, and migration, and is intimately involved in tumor occurrence and development. As a result, it is recognized as a potential target for anti-cancer and anti-resistance therapies. There have been several RSK inhibitors discovered or designed in recent decades, but only two have entered clinical trials. Low specificity, low selectivity, and poor pharmacokinetic properties in vivo limit their clinical translation. Published studies performed structure optimization by increasing interaction with RSK, avoiding hydrolysis of pharmacophores, eliminating chirality, adapting to binding site shape, and becoming prodrugs. Besides enhancing efficacy, the focus of further design will move towards selectivity since there are functional differences among RSK isoforms. This review summarized the types of cancers associated with RSK, along with the structural characteristics and optimization process of the reported RSK inhibitors. Furthermore, we addressed the importance of RSK inhibitors' selectivity and discussed future drug development directions. This review is expected to shed light on the emergence of RSK inhibitors with high potency, specificity, and selectivity.

Immunotherapies catering to the unmet medical need of cold colorectal cancer

As a common malignant tumor of gastrointestinal tract, the incidence of colorectal cancer (CRC) has gradually increased in recent years. In western developed countries, it has even become the second largest malignant tumor next to lung cancer. Immunotherapy is a hot topic in the field of cancer therapy, including immune checkpoint blockade (ICB), adoptive cell therapy (ACT), cancer vaccines and cytokines, aiming to improve the ability of the immune system to recognize, target and eliminate cancer cells. However, cold CRC, which accounts for a high proportion of CRC, is not so reactive to it. The development of immunotherapy to prevent cancer cells from forming "immune escape" pathways to the immune system in cold CRC, has been under increasing study attention. There is proof that an organic combination of radiotherapy, chemotherapy, and several immunotherapies can considerably boost the immune system's capacity to eradicate tumor cells. In this review, we summarized the role of immunotherapy in colorectal cancer. In addition, we propose a breakthrough and strategy to improve the role of immunotherapy in cold CRC based on its characteristics.

Tumor-Derived Exosomes Modulate Primary Site Tumor Metastasis

Tumor-derived exosomes (TDEs) are actively produced and released by tumor cells and carry messages from tumor cells to healthy cells or abnormal cells, and they participate in tumor metastasis. In this review, we explore the underlying mechanism of action of TDEs in tumor metastasis. TDEs transport tumor-derived proteins and non-coding RNA to tumor cells and promote migration. Transport to normal cells, such as vascular endothelial cells and immune cells, promotes angiogenesis, inhibits immune cell activation, and improves chances of tumor implantation. Thus, TDEs contribute to tumor metastasis. We summarize the function of TDEs and their components in tumor metastasis and illuminate shortcomings for advancing research on TDEs in tumor metastasis.

Oxethazaine inhibits esophageal squamous cell carcinoma proliferation and metastasis by targeting aurora kinase A

Esophageal squamous cell carcinoma (ESCC), a malignant neoplasm with high incidence, is a severe global public health threat. The current modalities used for treating ESCC include surgery, chemotherapy, and radiotherapy. Although ESCC management and treatment strategies have improved over the last decade, the overall 5-year survival rate remains <20%. Therefore, the identification of novel therapeutic strategies that can increase ESCC patient survival rates is urgently needed. Oxethazaine, an amino-amide anesthetic agent, is mainly prescribed in combination with antacids to relieve esophagitis, dyspepsia, and other gastric disorders. In the present study, we found that oxethazaine inhibited the proliferation and migration of esophageal cancer cells. According to the results of in vitro screening and binding assays, oxethazaine binds directly to AURKA, suppresses AURKA activity, and inhibits the downstream effectors of AURKA. Notably, we found that oxethazaine suppressed tumor growth in three patient-derived esophageal xenograft mouse models and tumor metastasis in vivo. Our findings suggest that oxethazaine can inhibit ESCC proliferation and metastasis in vitro and in vivo by targeting AURKA.

T-bet transduction enhances anti-tumor efficacy of IFN-producing dendritic cell (IKDC) against hepatocellular carcinoma via apoptosis induction

Hepatocellular carcinoma (HCC) remains a public health challenge that requires dedication to develop new treatment options due to its high recurrence rate and poor prognosis. Interferon-producing killer dendritic cell (IKDC) is a subset of INF-γ secreting immune cells that modulates acquired immunity and possesses cytolytic ability. We modified IKDC isolated from the murine spleen with T-bet lentiviral transduction to enhance its cytotoxicity against HCC, and acquired IKDC overexpressing T-bet (T-bet-IKDC) for the first time. T-bet-IKDC has increased INF-γ secretion and surface expression of NKG2D and TRAIL. In vitro study by MTS assay and flow cytometry showed enhanced anti-tumor effect against H22 cells via apoptosis induction in a dose- and time-dependent manner. In vivo study on H22-bearing mice confirmed increased INF-γ secretion, reduced tumor size, increased caspase 3 cleavage, and up-regulation of cytotoxic molecules after T-bet-IKDC administration. The study suggested prospective application of T-bet-IKDC in future immunotherapy for HCC treatment.

Akt regulates RSK2 to alter phosphorylation level of H2A.X in breast cancer

Histone H2AX (H2A.X) is a variant of the histone H2A family. Phosphorylation of H2A.X is a marker of DNA strand breaks and the presence or absence of H2A.X is closely related to tumor susceptibility and drug resistance. The present study found that the activity of the serine/threonine kinase Akt was negatively associated with H2A.X phosphorylated at the Ser16 site (H2A.X S16ph), but the mechanism of the inverse relationship remains elusive. The aim of the present study was to elucidate the mechanism of action between Akt and H2A.X S16ph and the exact role of this mechanism. Western blot analysis was performed to detect the regulatory association between p-Akt and H2A.X S16ph/p-RSK2, and immunoprecipitation and chromatin immunoprecipitation were performed to prove that Akt, RSK2 and H2A.X combine and interact in human breast cancer cells. The changes of cellular proliferation and migration induced by the interaction of Akt, RSK2 and H2A.X was determined by MTT, soft agar colony formation and cell migration experiments. The effect of interaction of Akt, RSK2 and H2A.X on cancer-promoting genes, such as PSAT-1 was determined via reverse transcription-quantitative PCR analysis. The current study indicated that the serine/threonine kinase ribosomal S6 kinase 2 (RSK2) as a kinase of H2A.X could be phosphorylated by Akt at Ser19 site. Moreover, Akt positively regulated the phosphorylation of RSK2 to inhibit phosphorylation of H2A.X, thereby affecting the affinity between RSK2 and substrate histone, promoting the survival and migration of breast cancer cells. In conclusion, Akt-mediated phosphorylation of RSK2 regulated the phosphorylation of H2A.X, thereby promoting oncogenic activity. This finding provides new insights to understand the pathogenesis and treatment mechanisms of breast cancer.

The expression of seven key genes can predict distant metastasis of colorectal cancer to the liver or lung

OBJECTIVE

It is unclear how primary colorectal cancer (CRC) cells select to metastasize to the liver or lungs, the most frequent distant metastasis of CRC. We aimed to identify the key genes and pathways that may predict the distant metastasis of CRC to these sites.

METHODS

Three gene expression array datasets from the Gene Expression Omnibus were analyzed. Protein-protein network analyses, best subsets regressions and backward stepwise regression analyses were used to screen the key genes and their expressions were used to construct a predictive logistic regression model. Expression data from local clinical samples were used as a validation dataset. The receiver operating characteristic (ROC) curve was used to test the performance of the predictive model.

RESULTS

In total, 59 differentially expressed genes (DEG) related to liver-metastasis, 90 related to lung metastasis and 45 related to both liver and lung metastasis were identified. The KEGG pathways and gene oncology (GO) terms that were enriched in liver and lung metastasis were identified. A predictive logistic regression model consisted of SPARC, COL1A2, MMP9, COL11A1, COL3A1, CXCL12 and THBS2 was established. The area under the ROC curve reached 0.839 in predicting liver and lung metastasis, using our clinical samples as the validation dataset.

CONCLUSIONS

Seven key genes capable of predicting liver and lung metastasis of colorectal cancer were identified, which provides clues for exploring the mechanism of selecting target organs during the metastatic process in CRC and inspires the researches for new potential targets for therapy to inhibit metastasis.

The Global Phosphorylation Landscape of SARS-CoV-2 Infection

The causative agent of the coronavirus disease 2019 (COVID-19) pandemic, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has infected millions and killed hundreds of thousands of people worldwide, highlighting an urgent need to develop antiviral therapies. Here we present a quantitative mass spectrometry-based phosphoproteomics survey of SARS-CoV-2 infection in Vero E6 cells, revealing dramatic rewiring of phosphorylation on host and viral proteins. SARS-CoV-2 infection promoted casein kinase II (CK2) and p38 MAPK activation, production of diverse cytokines, and shutdown of mitotic kinases, resulting in cell cycle arrest. Infection also stimulated a marked induction of CK2-containing filopodial protrusions possessing budding viral particles. Eighty-seven drugs and compounds were identified by mapping global phosphorylation profiles to dysregulated kinases and pathways. We found pharmacologic inhibition of the p38, CK2, CDK, AXL, and PIKFYVE kinases to possess antiviral efficacy, representing potential COVID-19 therapies.

Post-Translational Modifications of Transcription Factors Harnessing the Etiology and Pathophysiology in Colonic Diseases

Defects in mucosal immune balance can lead to colonic diseases such as inflammatory bowel diseases and colorectal cancer. With the advancement of understanding for the immunological and molecular basis of colonic disease, therapies targeting transcription factors have become a potential approach for the treatment of colonic disease. To date, the biomedical significance of unique post-translational modifications on transcription factors has been identified, including phosphorylation, methylation, acetylation, ubiquitination, SUMOylation, and O-GlcNAcylation. This review focuses on our current understanding and the emerging evidence of how post-translational regulations modify transcription factors involved in the etiology and pathophysiology of colonic disease as well as the implications of these findings for new therapeutic approaches in these disorders.

TOPK promotes metastasis of esophageal squamous cell carcinoma by activating the Src/GSK3β/STAT3 signaling pathway via γ-catenin

Background

Esophageal squamous cell carcinoma (ESCC) is a fatal disease with poor prognosis. The predominant reason for ESCC-related death is distal metastasis. A comprehensive understanding of the molecular mechanism underlying metastasis is needed for improving patient prognosis. T-LAK cell-originated protein kinase (TOPK) is a MAPKK-like kinase, which plays a vital role in various physiological and pathophysiological processes. However, the role of TOPK in ESCC metastasis is unclear.

Methods

Tissue array was used to evaluate the correlation between TOPK expression and ESCC lymph node metastasis. Wound healing assay, transwell assay, and lung metastasis mice model were used to examine the role of TOPK in the migration of ESCC cells in vitro and in vivo. Protein kinase array, mass spectrometry (MS), and molecular modeling were used to examine the pathways and direct target proteins of TOPK that are involved in ESCC metastasis. Additionally, immunofluorescence and western blotting analyses were performed to verify these findings.

Results

The enhanced expression of TOPK was correlated with lymph node metastasis in the ESCC tissues. TOPK knockdown or treatment with the TOPK inhibitor (HI-TOPK-032) decreased the invasion and migration of ESCC cells in vitro. HI-TOPK-032 also inhibited the lung metastasis in ESCC cell xenograft in vivo model. Moreover, TOPK promoted the invasion of ESCC cells by activating the Src/GSK3β/STAT3 and ERK signaling pathways via γ-catenin.

Conclusion

The findings of this study reveal that TOPK is involved in ESCC metastasis and promoted the ESCC cell mobility by activating the Src/GSK3β/STAT3 and ERK signaling pathways. This indicated that TOPK may be a potential molecular therapeutic target for ESCC metastasis.