Ribosomal s6 protein kinase 4: a prognostic factor for renal cell carcinoma

Ribosome biogenesis and ribosomal proteins in cancer stem cells: a new therapeutic prospect

Ribosome has been considered as the fundamental macromolecular machine involved in protein synthesis in both prokaryotic and eukaryotic cells. This protein synthesis machinery consists of several rRNAs and numerous proteins. All of these factors are synthesized, translocated and assembled in a tightly regulated process known as ribosome biogenesis. Any impairment in this process causes development of several diseases like cancer. According to growing evidences, cancer cells display alteration of several ribosomal proteins. Besides, most of them are considered as key molecules involved in ribosome biogenesis, suggesting a correlation between those proteins and formation of ribosomes. Albeit, defective ribosome biogenesis in several cancers has gained prime importance, regulation of this process in cancer stem cells (CSCs) are still unrecognized. In this article, we aim to summarize the alteration of ribosome biogenesis and ribosomal proteins in CSCs. Moreover, we want to highlight the relation of ribosome biogenesis with hypoxia and drug resistance in CSCs based on the existing evidences. Lastly, this review wants to pay attention about the promising anti-cancer drugs which have potential to inhibit ribosome biogenesis in cancer cells as well as CSCs.

Updating mRNA variants of the human RSK4 gene and their expression in different stressed situations

We determined RNA spectrum of the human RSK4 (hRSK4) gene (also called RPS6KA6) and identified 29 novel mRNA variants derived from alternative splicing, which, plus the NCBI-documented ones and the five we reported previously, totaled 50 hRSK4 RNAs that, by our bioinformatics analyses, encode 35 hRSK4 protein isoforms of 35-762 amino acids. Many of the mRNAs are bicistronic or tricistronic for hRSK4. The NCBI-normalized NM_014496.5 and the protein it encodes are designated herein as the Wt-1 mRNA and protein, respectively, whereas the NM_001330512.1 and the long protein it encodes are designated as the Wt-2 mRNA and protein, respectively. Many of the mRNA variants responded differently to different situations of stress, including serum starvation, a febrile temperature, treatment with ethanol or ethanol-extracted clove buds (an herbal medicine), whereas the same stressed situation often caused quite different alterations among different mRNA variants in different cell lines. Mosifloxacin, an antibiotics and also a functional inhibitor of hRSK4, could inhibit the expression of certain hRSK4 mRNA variants. The hRSK4 gene likely uses alternative splicing as a handy tool to adapt to different stressed situations, and the mRNA and protein multiplicities may partly explain the incongruous literature on its expression and comports.

Ribosomal S6 protein kinase 4 promotes resistance to EZH2 inhibitors in glioblastoma

Glioblastoma (GBM) is a highly malignant type of brain tumor with limited treatment options. Recent research has focused on epigenetic regulatory factors, such as Enhancer of Zeste Homolog 2 (EZH2), which plays a role in gene expression through epigenetic modifications. EZH2 inhibitors have been developed as potential therapeutic agents for GBM, but resistance to these inhibitors remains a considerable challenge. This study aimed to investigate the role of ribosomal S6 protein kinase 4 (RSK4) in GBM and its association with resistance to EZH2 inhibitors. We first induced drug resistance in primary GBM cell lines by treatment with an EZH2 inhibitor and observed increases in the expression of stemness markers associated with glioblastoma stem cells (GSCs) in the drug-resistant cells. We also found high expression of RSK4 in GBM patient samples and identified the correlation of high RSK4 expression with poor prognosis and GSC marker expression. Further experiments showed that knocking down RSK4 in drug-resistant GBM cells restored their sensitivity to EZH2 inhibitors and decreased the expression of GSC markers, thus reducing their self-renewal capacity. From a mechanistic perspective, we discovered that RSK4 directly phosphorylates EZH2, activating the EZH2/STAT3 pathway and promoting resistance to EZH2 inhibitors in GBM. We also found that combining EZH2 inhibitors with an RSK4 inhibitor called BI-D1870 had better inhibitory effects on GBM occurrence and progression in both in vitro and in vivo experiments. In conclusion, this study demonstrates that RSK4 enhances cancer stemness and mediates resistance to EZH2 inhibitors in GBM. Combination treatment with EZH2 inhibitors and RSK4 inhibitors is a promising potential therapeutic strategy for GBM. Collectively, our results strongly demonstrate that RSK4 regulates the EZH2/STAT3 pathway to promote GSC maintenance and EZH2i resistance in a PRC2-independent manner, indicating that RSK4 is a promising therapeutic target for GBM.

Ribosomal S6 kinase 4 (RSK4) tumor suppressor gene promoter methylation status in ovarian cancer

BACKGROUND

Previously, we reported lower RSK4 mRNA and protein levels in malignant ovarian tumors compared to normal and benign ovarian tissues. Also, we observed a significant inverse correlation between the advanced ovarian cancer stages and RSK4 mRNA levels. We did not investigate the mechanisms involved in RSK4-reduced expression in ovarian cancer. Thus, this study investigates whether RSK4 promoter methylation in ovarian cancer tissues is responsible for its low expression. Additionally, the reactivation of RSK4 expression and its effect was studied in ovarian cancer cell lines.

METHODS AND RESULTS

RSK4 promoter methylation percentage in malignant and benign ovarian tumors and normal ovary tissues was determined by combined bisulfite restriction analysis. The reactivation of RSK4 expression by decitabine treatment was studied in OVCAR3, SKOV3, TOV-112D, and TOV-21G cells by Western blotting. Cell proliferation was determined by XTT. A significantly high methylation percentage of the RSK4 promoter was observed among malignant and benign ovarian tumors but not in normal ovarian tissue. RSK4 promoter methylation was not associated with age, histological subtype, or stages of ovarian cancer. RSK4 promoter methylation correlates weakly but not significantly with RSK4 protein expression. No correlation was shown between RSK4 methylation and RSK4 mRNA expression. Decitabine induces RSK4 reactivation in all cell lines. However, cell proliferation was reduced only in TOV-112D cells.

CONCLUSION

These data indicate that although RSK4 promoter methylation is increased in malignant ovarian tumors, this mechanism is unlikely to regulate its expression in ovarian cancer. RSK4 reactivation reduced cell proliferation only in the endometroid histological subtype.

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.

BI-D1870 Induces Mitotic Dysfunction and Apoptosis in Neuroblastoma by Regulating the PI3K-Akt-mTORC1 Signal Axis

Introduction: Neuroblastoma (NB) is one of the most common extracranial solid malignant tumors in children. The 5-year survival rate of high-risk or refractory NB is less than 50%. Therefore, developing new effective therapeutics for NB remains an urgent challenge. Materials and Methods: Based on the NB dataset TARGET-NBL in the TCGA database, the prognosis-related genes were analyzed using univariate cox regression (p < 0.01). The protein network interaction of prognostic genes was analyzed using STRING to obtain 150 hub genes with HR > 1 and 150 hub genes with HR < 1. The Connectivity Map database was used to predict a therapeutic drug: BI-D1870, a ribosomal S6 kinase inhibitor. The inhibitory effect of BI-D1870 on NB was investigated through in vivo and in vitro experiments, and its inhibitory mechanism was explored. Results: Both the in vivo and in vitro experiments showed that BI-D1870 could inhibit tumor proliferation and induce tumor apoptosis. Furthermore, we proved that BI-D1870 caused G2/M phase arrest and mitosis damage in cells. RNA-seq of cells showed that BI-D1870 may inhibit the growth of NB by inhibiting the PI3K-Akt-mTOR axis. Western blot and immunofluorescence testing showed that BI-D1870 inhibited the PI3K-Akt-mTORC1 signal pathway to regulate the phosphorylation of RPS6 and 4E BP1 proteins, inhibit protein translation, and inhibit microtubule formation, thus preventing mitotic proliferation and inducing apoptosis. Conclusions: This study provides strong support that BI-D1870 may be a potential adjuvant therapy for NB.

Differential Expression of RSK4 Transcript Isoforms in Cancer and Its Clinical Relevance

While we previously revealed RSK4 as a therapeutic target in lung and bladder cancers, the wider role of this kinase in other cancers remains controversial. Indeed, other reports instead proposed RSK4 as a tumour suppressor in colorectal and gastric cancers and are contradictory in breast malignancies. One explanation for these discrepancies may be the expression of different RSK4 isoforms across cancers. Four RNAs are produced from the RSK4 gene, with two being protein-coding. Here, we analysed the expression of the latter across 30 normal and 33 cancer tissue types from the combined GTEx/TCGA dataset and correlated it with clinical features. This revealed the expression of RSK4 isoforms 1 and 2 to be independent prognostic factors for patient survival, pathological stage, cancer metastasis, recurrence, and immune infiltration in brain, stomach, cervical, and kidney cancers. However, we found that upregulation of either isoform can equally be associated with good or bad prognosis depending on the cancer type, and changes in the expression ratio of isoforms fail to predict clinical outcome. Hence, differential isoform expression alone cannot explain the contradictory roles of RSK4 in cancers, and further research is needed to highlight the underlying mechanisms for the context-dependent function of this kinase.

DLK2 Acts as a Potential Prognostic Biomarker for Clear Cell Renal Cell Carcinoma Based on Bioinformatics Analysis

Clear cell renal cell carcinoma (ccRCC) is the most common RCC subtype with a high mortality. It has been reported that delta-like 1 homologue (DLK1) participates in the tumor microenvironmental remodeling of ccRCC, but the relationship between delta-like 2 homologue (DLK2, a DLK1 homologue) and ccRCC is still unclear. Thus, this study aims to investigate the role of DLK2 in the biological function and disease prognosis of ccRCC using bioinformatics analysis. The TNMplot database showed that DLK2 was upregulated in ccRCC tissues. From the UALCAN analysis, the overexpression of DLK2 was associated with advanced stage and high grade in ccRCC. Moreover, the Kaplan-Meier plotter (KM Plotter) database showed that DLK2 upregulation was associated with poor survival outcome in ccRCC. By the LinkedOmics analysis, DLK2 signaling may participated in the modulation of ccRCC extracellular matrix (ECM), cell metabolism, ribosome biogenesis, TGF-β signaling and Notch pathway. Besides, Tumor Immune Estimation Resource (TIMER) analysis showed that the macrophage and CD8⁺ T cell infiltrations were associated with good prognosis in ccRCC patients. Finally, DLK2 overexpression was associated with the reduced macrophage recruitments and the M1–M2 polarization of macrophage in ccRCC tissues. Together, DLK2 may acts as a novel biomarker, even therapeutic target in ccRCC. However, this study lacks experimental validation, and further studies are required to support this viewpoint.

Comprehensive characterization of pathological stage-related genes of papillary thyroid cancer along with survival prediction

It is crucial to understand the differences across papillary thyroid cancer (PTC) stages, so as to provide a basis for individualized treatments. Here, comprehensive function characterization of PTC stage‐related genes was performed and a new prognostic signature was developed for advanced patients. Two gene modules were confirmed to be closely associated with PTC stages and further six hub genes were identified that yield excellent diagnostic efficiency between tumour and normal tissues. Genetic alteration analysis indicates that they are much conservative since mutations in the DNA of them rarely occur, but changes of DNA methylation on these six genes show that 12 DNA methylation sites are significantly associated with their corresponding genes' expression. Validation data set testing also suggests that these six stage‐related hub genes would be probably potential biomarkers for marking four stages. Subsequently, a 21‐mRNA‐based prognostic risk model was constructed for PTC stage III/IV patients and it could effectively predict the survival of patients with strong prognostic ability. Functional analysis shows that differential expression genes between high‐ and low‐risk patients would promote the progress of PTC to some extent. Moreover, tumour microenvironment (TME) of high‐risk patients may be more conducive to tumour growth by ESTIMATE analysis.

Repurposed floxacins targeting RSK4 prevent chemoresistance and metastasis in lung and bladder cancer

Lung and bladder cancers are mostly incurable because of the early development of drug resistance and metastatic dissemination. Hence, improved therapies that tackle these two processes are urgently needed to improve clinical outcome. We have identified RSK4 as a promoter of drug resistance and metastasis in lung and bladder cancer cells. Silencing this kinase, through either RNA interference or CRISPR, sensitized tumor cells to chemotherapy and hindered metastasis in vitro and in vivo in a tail vein injection model. Drug screening revealed several floxacin antibiotics as potent RSK4 activation inhibitors, and trovafloxacin reproduced all effects of RSK4 silencing in vitro and in/ex vivo using lung cancer xenograft and genetically engineered mouse models and bladder tumor explants. Through x-ray structure determination and Markov transient and Deuterium exchange analyses, we identified the allosteric binding site and revealed how this compound blocks RSK4 kinase activation through binding to an allosteric site and mimicking a kinase autoinhibitory mechanism involving the RSK4's hydrophobic motif. Last, we show that patients undergoing chemotherapy and adhering to prophylactic levofloxacin in the large placebo-controlled randomized phase 3 SIGNIFICANT trial had significantly increased (P = 0.048) long-term overall survival times. Hence, we suggest that RSK4 inhibition may represent an effective therapeutic strategy for treating lung and bladder cancer.

An epigenomic landscape of cervical intraepithelial neoplasia and cervical cancer using single-base resolution methylome and hydroxymethylome

BACKGROUND

Cervical cancer (CC) is the second leading cause of cancer death among women worldwide. Epigenetic regulation of gene expression through DNA methylation and hydroxymethylation plays a pivotal role during tumorigenesis. In this study, to analyze the epigenomic landscape and identify potential biomarkers for CCs, we selected a series of samples from normal to cervical intra-epithelial neoplasia (CINs) to CCs and performed an integrative analysis of whole-genome bisulfite sequencing (WGBS-seq), oxidative WGBS, RNA-seq, and external histone modifications profiling data.

RESULTS

In the development and progression of CC, there were genome-wide hypo-methylation and hypo-hydroxymethylation, accompanied by local hyper-methylation and hyper-hydroxymethylation. Hydroxymethylation prefers to distribute in the CpG islands and CpG shores, as displayed a trend of gradual decline from health to CIN2, while a trend of increase from CIN3 to CC. The differentially methylated and hydroxymethylated region-associated genes both enriched in Hippo and other cancer-related signaling pathways that drive cervical carcinogenesis. Furthermore, we identified eight novel differentially methylated/hydroxymethylated-associated genes (DES, MAL, MTIF2, PIP5K1A, RPS6KA6, ANGEL2, MPP, and PAPSS2) significantly correlated with the overall survival of CC. In addition, no any correlation was observed between methylation or hydroxymethylation levels and somatic copy number variations in CINs and CCs.

CONCLUSION

Our current study systematically delineates the map of methylome and hydroxymethylome from CINs to CC, and some differentially methylated/hydroxymethylated-associated genes can be used as the potential epigenetic biomarkers in CC prognosis.

Integrated analysis of methylation-driven genes and pretreatment prognostic factors in patients with hepatocellular carcinoma

BACKGROUND

The potential reversibility of aberrant DNA methylation indicates an opportunity for oncotherapy. This study aimed to integrate methylation-driven genes and pretreatment prognostic factors and then construct a new individual prognostic model in hepatocellular carcinoma (HCC) patients.

METHODS

The gene methylation, gene expression dataset and clinical information of HCC patients were downloaded from The Cancer Genome Atlas (TCGA) database. Methylation-driven genes were screened with a Pearson's correlation coefficient less than - 0.3 and a P value less than 0.05. Univariable and multivariable Cox regression analyses were performed to construct a risk score model and identify independent prognostic factors from the clinical parameters of HCC patients. The least absolute shrinkage and selection operator (LASSO) technique was used to construct a nomogram that might act to predict an individual's OS, and then C-index, ROC curve and calibration plot were used to test the practicability. The correlation between clinical parameters and core methylation-driven genes of HCC patients was explored with Student's t-test.

RESULTS

In this study, 44 methylation-driven genes were discovered, and three prognostic signatures (LCAT, RPS6KA6, and C5orf58) were screened to construct a prognostic risk model of HCC patients. Five clinical factors, including T stage, risk score, cancer status, surgical method and new tumor events, were identified from 13 clinical parameters as pretreatment-independent prognostic factors. To avoid overfitting, LASSO analysis was used to construct a nomogram that could be used to calculate the OS in HCC patients. The C-index was superior to that from previous studies (0.75 vs 0.717, 0.676). Furthermore, LCAT was found to be correlated with T stage and new tumor events, and RPS6KA6 was found to be correlated with T stage.

CONCLUSION

We identified novel therapeutic targets and constructed an individual prognostic model that can be used to guide personalized treatment in HCC patients.

Potential prognostic biomarkers related to immunity in clear cell renal cell carcinoma using bioinformatic strategy

The clear cell renal cell carcinoma (ccRCC) is the main pathological subtype of renal cell carcinoma. Immune system evasion, one hallmark of cancer, contributes to cancer cells in escaping from the attack of immune cells. In order to identify potential prognostic biomarkers in ccRCC patients and immune cells fraction, we collected and downloaded profiles from The Cancer Genome Atlas (TCGA) database and Gene Expression Omnibus (GEO) database. We obtained 2 modules significantly associated with tumor stage and immune cells; functional enrichment analysis showed that genes in the module ‘yellow’ were significantly enriched in proteins targeting to membrane and ribosome, as well as the oxidative phosphorylation pathway, while genes in the module ‘green’ mainly participate in molecular functions associated with immunity like activation of T cells. Four LncRNAs (LINC00472, AL590094.1, AL365203.3, and AC147651.3) and RPL27A and RPL22L1 in the module ‘yellow’ and two lncRNAs (LINC00426 and AC129507.2) and five protein-coding genes (CSF1, NOD2, ITGAE, CD7, and PDCD1) in the module ‘green’ represented independent prognostic values in patients with ccRCC. Expression of LINC0042, NOD2, CD7, and PDCD1 were significantly correlated with ratio of immune cells (like T cells CD8 and resting mast cells). LINC00426, with significant correlation with immune cell fraction, shows potential prognostic value in ccRCC patients. Our findings provide a strategy in exploring biomarkers with prognostic significance and significant association with the fraction of immune cells.

Prominent roles of ribosomal S6 kinase 4 (RSK4) in cancer

RSK4 refers to one Ser/Thr protein kinase functioning downstream pertaining to the signaling channel of protein kinase (MAPK) stimulated by Ras/mitogen. RSK4 can regulate numerous substrates impacting cells' surviving state, growing processes and proliferating process. Thus, dysregulated RSK4 active state display a relationship to several carcinoma categories, covering breast carcinoma, esophageal squamous cell carcinoma, glioma, colorectal carcinoma, lung carcinoma, ovarian carcinoma, leukemia, endometrial carcinoma, and kidney carcinoma. Whether RSK4 is a tumor suppressor gene or one oncogene remains controversial. No specific inhibiting elements for RSK4 have been found. This review briefs the existing information regarding RSK4 activating process, the function and mechanism of RSK4 in different tumors, and the research progress and limitations of existing RSK inhibitors. RSK4 may be a potential target of molecular therapy medicine in the future.

Ribosomal S6 protein kinase 4 promotes radioresistance in esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC) is one of the most aggressive cancers and is highly resistant to current treatments. ESCC harbors a subpopulation of cells exhibiting cancer stem-like cell (CSC) properties that contribute to therapeutic resistance including radioresistance, but the molecular mechanisms in ESCC CSCs are currently unknown. Here, we report that ribosomal S6 protein kinase 4 (RSK4) plays a pivotal role in promoting CSC properties and radioresistance in ESCC. RSK4 was highly expressed in ESCC CSCs and associated with radioresistance and poor survival in patients with ESCC. RSK4 was found to be a direct downstream transcriptional target of ΔNp63α, the main p63 isoform, which is frequently amplified in ESCC. RSK4 activated the β-catenin signaling pathway through direct phosphorylation of GSK-3β at Ser9. Pharmacologic inhibition of RSK4 effectively reduced CSC properties and improved radiosensitivity in both nude mouse and patient-derived xenograft models. Collectively, our results strongly suggest that the ΔNp63α/RSK4/GSK-3β axis plays a key role in driving CSC properties and radioresistance in ESCC, indicating that RSK4 is a promising therapeutic target for ESCC treatment.

Overexpression of RSK4 reverses doxorubicin resistance in human breast cancer cells via PI3K/AKT signalling pathway

Doxorubicin (DOX) is one of the most effective chemotherapy drugs for the treatment of metastatic breast cancer (BC), but drug resistance becomes an obstacle to treatment. This study aims to investigate the role of Ribosomal S6 protein kinase 4 (RSK4) in regulating BC resistance to DOX. We first used Kaplan-Meier Plotter to identify the prognostic roles of RSK4 in BC. DOX-resistant BC cells (MCF-7/DOX) were constructed and the expression of RSK4 was determined by reverse transcript polymerase chain reaction and western blot. Subsequently, we overexpressed the RSK4 in MCF-7/DOX cells, and measured drug resistance, colony formation, cell migration, invasion ability and cell apoptosis after transfection. In addition, western blot was used to explore the expression of apoptosis-related proteins and BC-resistance protein. Effects of RSK4 on activation of the PI3K/AKT signalling pathway were also tested. Furthermore, tumour xenograft in nude mice was constructed to observe the effect of RSK4 overexpression on tumour growth in vivo. In conclusion, RSK4 was positively correlated with survival rate in BC patients, which is lowly expressed in MCF-7/DOX. Meanwhile, the overexpression of RSK4 may inhibit drug resistance, cell migration, invasion, apoptosis and tumour growth. RSK4 may effectively attenuate DOX resistance in BC by inhibiting the PI3K/AKT signalling pathway.

RSK4: a new prognostic factor in glioma

Glioma is the most common and fatal brain tumour and has a poor prognosis. Ribosomal S6 protein kinase 4 (RSK4) has been found to be involved in multiple tumour types; however, the role of RSK4 in gliomas and its clinical relevance remain unclear. In the present study, RSK4 expression was found to be significantly increased in glioma tissues compared with matched adjunct non-noncancerous tissues. Moreover, the expression of RSK4 was significantly higher in high-grade (III and IV) glioma tissues than in low-grade (I and II) glioma tissues. The data showed that the expression of RSK4 was significantly correlated with WHO grade, three-year survival rate and five-year survival rate. Kaplan-Meier analyses showed that patients with high RSK4 expression had poor overall survival. In addition, multivariate Cox regression analysis showed that RSK4 might be an independent prognostic factor in glioma patients. Collectively, these results suggest that RSK4 may be a new prognostic factor in glioma patients, and RSK4 is expected to be a potential biomarker and a potential target for glioma therapy.

Expression of RSK4, CD44 and MMP-9 is upregulated and positively correlated in metastatic ccRCC

BACKGROUND

To investigate the expression and function of RSK4, MMP-9 and CD44 in primary clear cell renal cell carcinoma (primary ccRCC) and metastatic clear cell renal cell carcinoma (metastatic ccRCC), as well as the correlation with clinicopathological features of patients.

METHOD

The expression levels of RSK4, CD44 and MMP-9 in 52 primary ccRCC samples and 48 metastatic ccRCC samples were detected by immunohistochemistry, and the relationship between RSK4, CD44 and MMP-9 expression and clinicopathological features as well as prognosis of metastatic ccRCC patients was statistically analysed. Ectopic RSK4 expression in ccRCC cell lines was performed to determine its effect on cell cycle regulation, tumour invasiveness, and metastatic capability.

RESULTS

The positive rates of RSK4, MMP-9 and CD44 expression in metastatic ccRCC tissues were 75, 68.75 and 91.7%, respectively, while the rates in primary ccRCC tissues were 44.2, 34.6 and 69.2%, respectively. Thus, the positive rates in metastatic ccRCC were higher than those in primary ccRCC (PRSK4 = 0. 002; PMMP-9 = 0. 002; PCD44 = 0. 001). However, the expression of RSK4, CD44 and MMP-9 was unrelated to age, gender, or metastatic sites (P > 0.05) but was related to WHO/ISUP nucleolar grade (PRSK4 = 0.019; PCD44 = 0.026; PMMP-9 = 0.049). In metastatic ccRCC, expression among the three proteins showed a positive correlation (P = 0.008). Moreover, expression between RSK4 and CD44 (P = 0.019) and MMP-9 and CD44 (P = 0.05) also showed positive correlations, whereas RSK4 and MMP-9 showed no significant correlation (P = 1.00). Molecular studies showed that overexpression of RSK4 could enhance the invasive and migratory abilities of ccRCC cell lines through the regulation of CD44 and MMP-9 expression and vice versa.

CONCLUSIONS

The overexpression of RSK4, MMP-9 and CD44 is associated with the invasion and metastasis of ccRCC, indicating that they could be potential prognostic factors and serve as new potential therapeutic targets for ccRCC.

Effect of RSK4 on biological characteristics of colorectal cancer

Background

This study aimed to investigate the expression of P90 Ribosomal Protein S6 kinase 4 (RSK4) in colorectal cancer cells and its biological function.

Methods

We selected early SW480 and HCT116 colorectal cancer cell lines, using Lipofectamine™ 2000 transfection reagent carrying RSK4 gene transfected into cells to establish the colorectal cancer cell lines with high expression of RSK4. RT-PCR and western blot (WB) analysis confirmed RSK4 expression in SW480 and HCT116 cancer cell lines. We used methylthiazoltetrazolium (MTT) assay and flow cytometry to detect the proliferation of colorectal cancer cells. After transfection of RSK4, the effect of RSK4 on the RNA levels associated with epithelial–mesenchymal transition (EMT) of colorectal cancer cells was analyzed by real-time fluorescence quantitative PCR and the expression of EMT-related protein was detected by WB analysis.

Results

After transfection of RSK4 overexpression, the MTT assay detected that RSK4 could significantly inhibit the growth of colorectal cancer cells in vitro; flow cytometry detected that S-phase cells decreased significantly, and G0/1 cells increased significantly (P < 0.05). The invasion ability of SW480 and HCT116 cells transfected with RSK4 was markedly lower than that in the control group, and the difference was statistically significant (P < 0.05). Fluorescent quantitative PCR and WB analysis showed that the expression of EMT-associated molecular E-cadherin was remarkably increased and the expression of Snail was significantly decreased (P < 0.01).

Conclusion

RSK4 gene in colorectal cancer cell lines with low expression of RSK4 after transfection can inhibit the growth and invasion of tumor cells. RSK4 gene may inhibit EMT and inhibit metastasis of colorectal cancer cells, may be a potential tumor suppressor gene and inhibit tumor distant metastasis, and may provide the biological basis for new therapeutic targets.

Clinicopathological significance of ribosomal protein S6 kinase A6 in lung squamous cell carcinoma: an immunohistochemical and RNA-seq study

Ribosomal protein S6 kinase A6 (RPS6KA6) is a downstream factor of the ERK-MAPK pathway and has been extensively studied in various types of cancer. However, the role of RPS6KA6 in lung squamous cell carcinoma (LUSC) remains unclear. This study investigated expression of the RPS6KA6 and its clinicopathological correlation with LUSC and explored genetic alterations in the ribosomal protein S6 kinase (RSK) family in LUSC and their impact on the survival of patients. Expression of the RPS6KA6 protein in 175 LUSC samples and 30 normal lung tissues samples was determined by immunohistochemistry (IHC). RPS6KA6 protein expression in the LUSC tissues was significantly higher compared with that in the normal lung tissues (P=0.017). Overexpression of RPS6KA6 protein correlated with tumor size (r=0.260, P=0.001), lymph node metastasis (r=0.683, P<0.001), and TNM stage (r=0.378, P<0.001). RPS6KA6 RNA-seq data were obtained from the Cancer Genome Atlas (TCGA) and ONCOMINE database. RPS6KA6 mRNA expression in the LUSC tissues was significantly higher than that in paired noncancerous samples (TCGA: P=0.005; ONCOMINE: P=0.018). According to the cBioPortal online software, three detecting methods, including Seqv2, Array and U133, identified that the frequency of the genetic alterations in the RSKs in LUSC were 77%, 44%, and 42%, respectively. However, survival analysis of LUSC patients with or without RSKs genetic alterations reached no statistical significance. This study suggests that RPS6KA6 may be an oncogene in LUSC, and that expression of the RPS6KA6 protein is associated with the progression of LUSC. The RSK genes are frequently altered in LUSC, but the alterations have no significant effect on the survival of patients.

Expression of RSK4 in lung adenocarcinoma tissue and its clinicopathological value: a study based on RNA-seq data and immunohistochemistry

The clinical significance of p90-kDa ribosomal S6 kinase (RSK) family members in lung adenocarcinoma (LUAD) is unknown. The aim of this study was to analyze genomic alterations in RSK family membersand investigate the expression and clinicopathological significance of RSK4 in LUAD tissues. Genomic calterations of RSK family, overall survival, andinteraction networks were analyzed in patients with LUAD (n=522), using data from The Cancer Genome Atlas (TCGA) database. The expression of RSK4 protein was investigated in an independent cohort of patients with LUAD (n=127) by immunohistochemistry, and relationships between RSK4 protein levels and clinicopathological parameters of LUAD were analyzed. Patients with LUAD with RSK genomic alterations had significantly better overall survival than patients without alterations (P=0.026). RSK4 mRNA was overexpressed in LUAD compared with noncancerous lung tissue (P=0.013), and the diagnostic value of RSK4 expression was moderate, as evaluated by a value of 0.603 for the area under the receiver operator characteristic curve (95% CI, 0.551-0.655; P=0.01). RSK4 protein levels were significantly higher in LUAD than in para-carcinoma tissue (P=0.002); moreover, RSK4 protein expression was closely associated with TNM stage (P<0.001), tumor diameter (P<0.001), lymphatic metastasis (P<0.001), and distant metastasis (P=0.003). In conclusion, alterations to RSK family members may affect tumor progression in LUAD. RSK4 is a potentially useful molecular biomarker for LAUD diagnosis and may predict disease progression in patients with this condition.

Ribosomal S6 kinase (RSK) modulators: a patent review

INTRODUCTION

The p90 ribosomal S6 kinases (RSK) are a family of Ser/Thr protein kinases that are downstream effectors of MEK1/2-ERK1/2. Increased RSK activation is implicated in the etiology of multiple pathologies, including numerous types of cancers, cardiovascular disease, liver and lung fibrosis, and infections.

AREAS COVERED

The review summarizes the patent and scientific literature on small molecule modulators of RSK and their potential use as therapeutics. The patents were identified using World Intellectual Property Organization and United States Patent and Trademark Office databases. The compounds described are predominantly RSK inhibitors, but a RSK activator is also described. The majority of the inhibitors are not RSK-specific.

EXPERT OPINION

Based on the overwhelming evidence that RSK is involved in a number of diseases that have high mortalities it seems surprising that there are no RSK modulators that have pharmacokinetic properties suitable for in vivo use. MEK1/2 inhibitors are in the clinic, but the efficacy of these compounds appears to be limited by their side effects. We hypothesize that targeting the downstream effectors of MEK1/2, like RSK, are an untapped source of drug targets and that they will generate less side effects than MEK1/2 inhibitors because they regulate fewer effectors.

Role of NSC319726 in ovarian cancer based on the bioinformatics analyses

Aim

This study aimed to explore the molecular mechanisms of NSC319726 in ovarian cancer by bioinformatics analyses.

Methods

Gene expression profile GSE35972 was downloaded from the Gene Expression Omnibus database. The data set contains six samples, including three samples of TOV112D cells untreated and three samples of TOV112D cells treated with NSC319726. The differentially expressed genes (DEGs) between untreated and treated samples were analyzed using the limma package. Kyoto Encyclopedia of Genes and Genomes pathway analysis was performed using the signaling pathway impact analysis package, followed by the functional annotation of DEGs and protein–protein interaction network construction. Finally, the subnetwork was identified, and Gene Ontology functional enrichment analysis was performed on the DEGs enriched in the subnetwork.

Results

A total of 120 upregulated and 126 downregulated DEGs were identified. Six Kyoto Encyclopedia of Genes and Genomes pathways were significantly perturbed by DEGs, and the pathway of oocyte meiosis was identified as the most perturbed one. Oocyte meiosis was enriched by eight downregulated DEGs, such as ribosomal protein S6 kinase, 90 kDa, and polypeptide 6 (RPS6KA6). After functional annotation, eight transcription factors were upregulated (such as B-cell CLL/lymphoma 6 [BCL6]), and three transcription factors were downregulated. Seven tumor suppressor genes, such as forkhead box O3 (FOXO3), were upregulated. Additionally, in the protein–protein interaction network and subnetwork, cyclin B1 (CCNB1) and cell division cycle 20 (CDC20) were hub genes, which were also involved in the functions related to mitotic cell cycle.

Conclusion

NSC319726 may play an efficient role against ovarian cancer via targeting genes, such as RPS6KA6, BCL6, FOXO3, CCNB1, and CDC20, which are involved in oocyte meiosis pathway.

NLRC5 expression in tumors and its role as a negative prognostic indicator in stage III non-small-cell lung cancer patients

Major histocompatibility complex (MHC) class I molecules have a crucial role in tumor immune evasion; however, the association of MHC class I molecules with outcomes in cancer patients remains controversial. Nucleotide-binding oligomerization-like receptor family caspase recruitment domain-containing 5 (NLRC5) has been reported to be a MHC class I transactivator. However, the expression and function of NLRC5 in cancer remains to be elucidated. The present study aimed to retrospectively examine NLRC5 expression in human tumor tissues and its association with clinical outcomes of non-small-cell lung cancer (NSCLC) stage III patients. The expression of MHC class I and NLRC5 in NSCLC were detected using immunohistochemistry (IHC). The association between their expression levels was assessed using the Pearson's χ² test and their association with survival was assessed using Kaplan-Meier analysis and the log-rank test. In addition, the expression of NLRC5 and MHC class I were examined in 323 cases of seven other types of tumors and their correlations were studied. The results revealed that the expression of NLRC5 was correlated with that of MHC class I in NSCLC patients (P=0.008). MHC class I-positive and nuclear NLRC5-positive NSCLC patients were found to have shorter overall survival (OS) rates (log-rank, P=0.032 and P=0.039, respectively). In addition, in the seven different tumor types, there was a significant correlation between MHC class I and NLRC5 nuclear expression (P<0.001) as well as MHC class I and NLRC5 cytoplasmic expression (P=0.003). In conclusion, NLRC5 was demonstrated to be widely expressed in eight tumor tissues and its expression was correlated with that of MHC class I. Of note, nuclear NLRC5-negative and MHC class I-negative stage III NSCLC patients had improved OS rates compared to those with positive expression. Therefore, NLRC5 and MHC class I may be negative prognostic indicators in NSCLC stage III patients.