MKK4 acts as a potential tumor suppressor in ovarian cancer

MicroRNAs as the critical regulators of protein kinases in prostate and bladder cancers

Background

Bladder cancer (BCa) and prostate cancer (PCa) are frequent urothelial and genital malignancies with a high ratio of morbidity and mortality which are more common among males. Since BCa and PCa cases are mainly diagnosed in advanced stages with clinical complications, it is required to introduce the efficient early detection markers. Protein kinases are critical factors involved in various cellular processes such as cell growth, motility, differentiation, and metabolism. Deregulation of protein kinases can be frequently observed through the neoplastic transformation and tumor progression. Therefore, kinases are required to be regulated via different genetic and epigenetic processes. MicroRNAs (miRNAs) are among the critical factors involved in epigenetic regulation of protein kinases. Since miRNAs are noninvasive and more stable factors in serum and tissues compared with mRNAs, they can be used as efficient diagnostic markers for the early detection of PCa and BCa.

Main body

In present review, we have summarized all of the reported miRNAs that have been associated with regulation of protein kinases in bladder and prostate cancers.

Conclusions

For the first time, this review highlights the miRNAs as critical factors in regulation of protein kinases during prostate and bladder cancers which paves the way of introducing a noninvasive kinase-specific panel of miRNAs for the early detection of these malignancies. It was observed that the class VIII receptors of tyrosine kinases and non-receptor tyrosine kinases were the most frequent targets for the miRNAs in bladder and prostate cancers, respectively.

MAP2K4 interacts with Vimentin to activate the PI3K/AKT pathway and promotes breast cancer pathogenesis

Mitogen-activated protein kinase kinase 4 (MAP2K4) is a member of the mitogen-activated protein kinase (MAPK) activator family. MAPK signaling plays a significant role in cell proliferation, differentiation, transcriptional regulation, and development. However, specific function and mechanism of MAP2K4 in breast cancer have not been clarified. According to our study, overexpressed MAP2K4 in breast cancer cells increased proliferation, migration, and invasion in vivo and in vitro, while MAP2K4 knockdown restored the effects. Subsequent mechanistic analyses demonstrated that MAP2K4 promoted cell proliferation, migration, and invasion by activating phosphoinositide-3-kinase (PI3K)/AKT signaling, the downstream proteins, c-JUN, the G1/S cell cycle, and the epithelial-to-mesenchymal transition (EMT). Meanwhile, MAP2K4 interacted with Vimentin and further propagated the malignant phenotype. Furthermore, patients with high MAP2K4 and Vimentin expression levels had poorer overall survival rates than those with low expression levels of both proteins. Our studies demonstrated that MAP2K4 has the potential to serve as an oncogene in breast cancer and it activates the phosphorylated PI3K/AKT signaling pathway to activate downstream cycle-associated proteins and EMT signals while interacting with Vimentin to promote breast cancer cells proliferation, migration, and invasion. In our study, MAP2K4 and Vimentin co-expression is confirmed to be an unfavorable factor in breast cancer.

Downregulation of phosphorylated MKK4 is associated with a poor prognosis in colorectal cancer patients

Mitogen-activated protein kinase kinase 4 (MKK4) is a key mediator of Jun N-terminal kinase signaling and influences malignant metastasis. Here, we used immunohistochemistry to assess phosphorylated MMK4 (pMKK4) levels and examine their association with the clinicopathological features of a pilot set of patient samples consisting of normal colonic mucosa (NCM), colorectal adenoma (CA), and colorectal cancer (CRC) tissues. pMKK4 levels were also assessed in a validation set of CRC cases with accompanying follow-up data to confirm their clinicopathological and prognostic significance. pMKK4 levels, which were high in 79.17% of NCM samples, were downregulated in 33.33% of CA and 63.54% of CRC samples. pMKK4 downregulation was associated with metastasis, especially to the liver. In the validation set, pMKK4 downregulation was associated with increases in invasive depth, lymph node metastasis, distant metastasis, and TNM stage. Univariate analysis indicated that pMKK4 score, tumor differentiation, and TNM stage were correlated with disease-free survival and overall survival. Multivariate analysis indicated that decreased pMKK4 expression was an independent risk factor for disease-free survival in CRC patients. These results suggest that CRC patients with low pMKK4 immunochemistry scores should be monitored carefully for early detection of possible recurrences, especially liver metastasis.

MicroRNA‑136 inhibits prostate cancer cell proliferation and invasion by directly targeting mitogen‑activated protein kinase kinase 4

Prostate cancer (PCa) is the second most common type of cancer and the 6th leading cause of cancer‑associated mortality worldwide. Accumulated evidence suggests that PCa initiation and progression are controlled by microRNAs (miRNAs). Therefore, investigating PCa‑associated miRNAs may provide novel biomarkers for the diagnosis and treatment of patients with PCa. In the present study it was demonstrated that miRNA‑136 (miR‑136) expression was significantly downregulated in PCa tissues and cell lines. The resumption of miR‑136 expression suppressed cell proliferation and invasion in PCa cells. Bioinformatics analysis predicted that mitogen‑activated protein kinase kinase 4 (MAP2K4) was a direct target of miR‑136. This prediction was experimentally confirmed by a luciferase reporter assay, RT‑qPCR and western blot analysis. MAP2K4 was highly expressed in PCa tissues and inversely correlated with the miR‑136 expression level. Additionally, the restoration of MAP2K4 expression significantly blocked the inhibitory effects of miR‑136 on cell proliferation and invasion in PCa cells. Therefore, miR‑136 may suppress the proliferation and invasion of PCa cells by targeting MAP2K4 and may be a novel candidate target for cancer therapy against PCa.

MicroRNA-145 protects follicular granulosa cells against oxidative stress-induced apoptosis by targeting Krüppel-like factor 4

Oxidative stress-induced follicular granulosa cell (GC) apoptosis plays an essential role in abnormal follicular atresia, which may trigger ovarian dysfunction. To investigate the role of microRNA (miR)-145 in the regulation of GC apoptosis and modulation of the apoptotic pathway in the setting of oxidative stress, we employed an H2O2-induced in vitro model and a 3-nitropropionic acid (NP)-induced in vivo model of ovarian oxidative stress. We demonstrated in vitro that miR-145 expression was significantly down-regulated in KGN cells and mouse granulosa cells (mGCs) treated with H2O2, whereas miR-145 over-expression attenuated H2O2-induced apoptosis in GCs. Moreover, miR-145 protected GCs against H2O2-induced apoptosis by targeting KLF4, which promoted H2O2-induced GC apoptosis via the BAX/BCL-2 pathway. Importantly, decreased miR-145 expression in the in vivo ovarian oxidative stress model promoted apoptosis by up-regulating KLF4 expression, whereas GC-specific miR-145 over-expression attenuated apoptosis by targeting KLF4. In conclusion, miR-145 protects GCs against oxidative stress-induced apoptosis by targeting KLF4.

Genomic and oncogenic preference of HBV integration in hepatocellular carcinoma

Hepatitis B virus (HBV) can integrate into the human genome, contributing to genomic instability and hepatocarcinogenesis. Here by conducting high-throughput viral integration detection and RNA sequencing, we identify 4,225 HBV integration events in tumour and adjacent non-tumour samples from 426 patients with HCC. We show that HBV is prone to integrate into rare fragile sites and functional genomic regions including CpG islands. We observe a distinct pattern in the preferential sites of HBV integration between tumour and non-tumour tissues. HBV insertional sites are significantly enriched in the proximity of telomeres in tumours. Recurrent HBV target genes are identified with few that overlap. The overall HBV integration frequency is much higher in tumour genomes of males than in females, with a significant enrichment of integration into chromosome 17. Furthermore, a cirrhosis-dependent HBV integration pattern is observed, affecting distinct targeted genes. Our data suggest that HBV integration has a high potential to drive oncogenic transformation.

Hepatitis B infection is a risk factor for hepatocellular carcinoma. Here, the authors characterise viral infection in a cohort of hepatocellular carcinoma patients and find viral integration is more frequent in males than females.

[Expressions of MAP2K4 and estrogen receptor and their clinical significance in invasive breast cancer]

OBJECTIVE

To explore the association of mitogen-activated protein kinase kinase-4 (MAP2K4) with the pathological features, prognosis and expression of estrogen receptor (ER) in patients with breast cancer.

METHODS

The expression of MAP2K4 was detected immunohistochemically in 102 breast cancer tissues. Chi square test was used to analyze the correlation of MAP2K4 expression with the clinicopathological features of the patients. Kaplan-Meier and log rank test were used for survival analysis of the patients. Multivariate survival analysis was performed using Cox proportional hazard regression model. The correlation between the expressionsof MAP2K4 and ER was investigated using Spearman rank correlation test.

RESULTS

Immunohistochemical analysis revealed low MAP2K4 expression in 55.9%(57/102) and high MAP2K4 expression in 44.1%(45/102) of the breast cancer tissues. The expression of MAP2K4 was significantly correlated with the pathological grades of breast cancer (P=0.011). Kaplan-Meier survival analysis showed that patients with a high expression of MAP2K4 had a shorter overall survival rate than those with low MAP2K4 expressions (P=0.009). Multivariate analysis identified high expression of MAP2K4 as the independent predictor of a poor outcome of patients with breast cancer. The expressions of MAP2K4 and ER were not significantly correlated, but ER-negative patients with a high MAP2K4 expressionshowed the shortest overall survival time.

CONCLUSION

Overexpression of MAP2K4 promotes the progression in breast cancer and is associated with a poor outcome of the patients. TheER-negativepatients with a high MAP2K4 expression have the shortest overall survival time, suggestingthe value of combined examination of MAP2K4 and ER in accurate estimation of the prognosis of breast cancer patients.

Registered report: Diverse somatic mutation patterns and pathway alterations in human cancers

The Reproducibility Project: Cancer Biology seeks to address growing concerns about reproducibility in scientific research by conducting replications of selected experiments from a number of high-profile papers in the field of cancer biology. The papers, which were published between 2010 and 2012, were selected on the basis of citations and Altmetric scores (Errington et al., 2014). This Registered Report describes the proposed replication plan of key experiments from "Diverse somatic mutation patterns and pathway alterations in human cancers" by Kan and colleagues published in Nature in 2010 (Kan et al., 2010). The experiments to be replicated are those reported in Figures 3D-F and 4C-F. Kan and colleagues utilized mismatch repair detection (MRD) technology to identify somatic mutations in primary human tumor samples and identified a previously uncharacterized arginine 243 to histidine (R243H) mutation in the G-protein α subunit GNAO1 in breast carcinoma tissue. In Figures 3D-F, Kan and colleagues demonstrated that stable expression of mutant GNAO1(R243D) conferred a significant growth advantage in human mammary epithelial cells, confirming the oncogenic potential of this mutation. Similarly, expression of variants with somatic mutations in MAP2K4, a JNK pathway kinase (shown in Figures 4C-E) resulted in a significant increase in anchorage-independent growth. Interestingly, these mutants exhibited reduced kinase activity compared to wild type MAP2K4, indicating these mutations impose a dominant-negative influence to promote growth (Figure 4F). The Reproducibility Project: Cancer Biology is a collaboration between the Center for Open Science and Science Exchange and the results of the replications will be published in eLife.

Recurrent MLK4 Loss-of-Function Mutations Suppress JNK Signaling to Promote Colon Tumorigenesis

MLK4 is a member of the mixed-lineage family of kinases that regulate the JNK, p38, and ERK kinase signaling pathways. MLK4 mutations have been identified in various human cancers, including frequently in colorectal cancer, where their function and pathobiological importance have been uncertain. In this study, we assessed the functional consequences of MLK4 mutations in colon tumorigenesis. Biochemical data indicated that a majority of MLK4 mutations are loss-of-function (LOF) mutations that can exert dominant-negative effects. In seeking to understand the abrogated activity of these mutants, we elucidated a new MLK4 catalytic domain structure. To determine whether MLK4 is required to maintain tumorigenic phenotypes, we reconstituted its signaling axis in colon cancer cells harboring MLK4-inactivating mutations. We found that restoring MLK4 activity reduced cell viability, proliferation, and colony formation in vitro and delayed tumor growth in vivo. Mechanistic investigations established that restoring the function of MLK4 selectively induced the JNK pathway and its downstream targets, cJUN, ATF3, and the cyclin-dependent kinase inhibitors CDKN1A and CDKN2B. Our work indicates that MLK4 is a novel tumor-suppressing kinase harboring frequent LOF mutations that lead to diminished signaling in the JNK pathway and enhanced proliferation in colon cancer.

Mitogen-activated protein kinase kinase 4 (MAP2K4) promotes human prostate cancer metastasis

Prostate cancer (PCa) is the second leading cause of cancer death in the US. Death from PCa primarily results from metastasis. Mitogen-activated protein kinase kinase 4 (MAP2K4) is overexpressed in invasive PCa lesions in humans, and can be inhibited by small molecule therapeutics that demonstrate favorable activity in phase II studies. However, MAP2K4's role in regulating metastatic behavior is controversial and unknown. To investigate, we engineered human PCa cell lines which overexpress either wild type or constitutive active MAP2K4. Orthotopic implantation into mice demonstrated MAP2K4 increases formation of distant metastasis. Constitutive active MAP2K4, though not wild type, increases tumor size and circulating tumor cells in the blood and bone marrow. Complementary in vitro studies establish stable MAP2K4 overexpression promotes cell invasion, but does not affect cell growth or migration. MAP2K4 overexpression increases the expression of heat shock protein 27 (HSP27) protein and protease production, with the largest effect upon matrix metalloproteinase 2 (MMP-2), both in vitro and in mouse tumor samples. Further, MAP2K4-mediated increases in cell invasion are dependent upon heat shock protein 27 (HSP27) and MMP-2, but not upon MAP2K4's immediate downstream targets, p38 MAPK or JNK. We demonstrate that MAP2K4 increases human PCa metastasis, and prolonged over expression induces long term changes in cell signaling pathways leading to independence from p38 MAPK and JNK. These findings provide a mechanistic explanation for human studies linking increases in HSP27 and MMP-2 to progression to metastatic disease. MAP2K4 is validated as an important therapeutic target for inhibiting human PCa metastasis.

A Direct in vivo RNAi screen identifies MKK4 as a key regulator of liver regeneration

The liver harbors a distinct capacity for endogenous regeneration; however, liver regeneration is often impaired in disease and therefore insufficient to compensate for the loss of hepatocytes and organ function. Here we describe a functional genetic approach for the identification of gene targets that can be exploited to increase the regenerative capacity of hepatocytes. Pools of small hairpin RNAs (shRNAs) were directly and stably delivered into mouse livers to screen for genes modulating liver regeneration. Our studies identify the dual-specific kinase MKK4 as a master regulator of liver regeneration. MKK4 silencing robustly increased the regenerative capacity of hepatocytes in mouse models of liver regeneration and acute and chronic liver failure. Mechanistically, induction of MKK7 and a JNK1-dependent activation of the AP1 transcription factor ATF2 and the Ets factor ELK1 are crucial for increased regeneration of hepatocytes with MKK4 silencing.

Time-dependent transcriptional profiling links gene expression to mitogen-activated protein kinase kinase 4 (MKK4)-mediated suppression of omental metastatic colonization

Although metastasis is the most lethal attribute of cancer, critical gaps in our knowledge of how cancer cells effectively colonize distant sites remain. For example, little is known about the cellular and molecular events that occur during the timecourse of metastatic colonization. To address this we are using the mitogen-activated protein kinase kinase 4 (MKK4) metastasis suppressor as a tool to identify these events. Specifically, we report a microarray expression-based strategy to identify genes whose transcription is altered in SKOV3ip.1 human ovarian cancer cells that express ectopic MKK4 throughout the course of in vivo metastatic colonization. The majority of genes identified fell into the categories of cytokinesis, cytoskeleton remodeling, and cell adhesion, and their expression was repressed in MKK4-expressing cells relative to vector controls. The greatest transcriptional divergence was concomitant with impaired proliferation at 14 days post injection (dpi). Specifically, 763 genes were differentially expressed (FDR < 0.05) between lesions that expressed ectopic MKK4 and paired controls. In contrast, only seven genes were differentially expressed at the experimental endpoint, when MKK4-expressing and control cells had formed macroscopic metastases. Application of our cohort of differentially expressed genes to three independent clinical datasets demonstrated a strong correlation between our findings and metastatic phenotypes in patient samples. Our results highlight the dynamic nature of metastatic colonization and reinforce the importance of examining both molecular and cellular phenotypes over time when studying metastasis formation.

Building on the foundation of daring hypotheses: using the MKK4 metastasis suppressor to develop models of dormancy and metastatic colonization

The identification of a novel metastasis suppressor function for the MAP Kinase Kinase 4 protein established a role for the stress-activated kinases in regulating the growth of disseminated cancer cells. In this review, we describe MKK4's biological mechanism of action and how this information is being used to guide the development of new models to study cancer cell dormancy and metastatic colonization. Specifically, we describe the novel application of microvolume structures, which can be modified to represent characteristics similar to those that cancer cells experience at metastatic sites. Although MKK4 is currently one of many known metastasis suppressors, this field of research started with a single daring hypothesis, which revolutionized our understanding of metastasis, and opened up new areas of exploration for basic research. The combination of our increasing knowledge of metastasis suppressors and such novel technologies provide hope for possible clinical interventions to prevent suffering from the burden of metastatic disease.