Loss of p38δ mitogen-activated protein kinase expression promotes oesophageal squamous cell carcinoma proliferation, migration and anchorage-independent growth

The p38 MAPK Components and Modulators as Biomarkers and Molecular Targets in Cancer

The mitogen-activated protein kinase (MAPK) family is an important bridge in the transduction of extracellular and intracellular signals in different responses at the cellular level. Within this MAPK family, the p38 kinases can be found altered in various diseases, including cancer, where these kinases play a fundamental role, sometimes with antagonistic mechanisms of action, depending on several factors. In fact, this family has an immense number of functionalities, many of them yet to be discovered in terms of regulation and action in different types of cancer, being directly involved in the response to cancer therapies. To date, three main groups of MAPKs have been identified in mammals: the extracellular signal-regulated kinases (ERK), Jun N-terminal kinase (JNK), and the different isoforms of p38 (α, β, γ, δ). In this review, we highlight the mechanism of action of these kinases, taking into account their extensive regulation at the cellular level through various modifications and modulations, including a wide variety of microRNAs. We also analyze the importance of the different isoforms expressed in the different tissues and their possible role as biomarkers and molecular targets. In addition, we include the latest preclinical and clinical trials with different p38-related drugs that are ongoing with hopeful expectations in the present/future of developing precision medicine in cancer.

A Special View of What Was Almost Forgotten: p38δ MAPK

Simple Summary

p38δ MAPK, as well as the other p38 isoforms, was proposed as a drug target for cancer therapy, owing to its critical roles in cellular signaling. However, herein, we show that p38δ inhibition may be therapeutically beneficial for treatment of specific cancer types, such as skin carcinoma, hepatocellular carcinoma (HCC), head and neck squamous cell carcinoma (HNSCC), cholangiocarcinoma (CC), and breast cancer. This review aims to discuss the roles of p38δ in cancer and summarize the findings of molecules with potential to inhibit p38δ in order to guide the search for new target cancer therapies based on p38δ inhibitors.

Abstract

The p38δ mitogen-activated protein kinase is an important signal transduction enzyme. p38δ has recently emerged as a drug target due to its tissue-specific expression patterns and its critical roles in regulation of cellular processes related to cancer and inflammatory diseases, such as cell proliferation, cell migration, apoptosis, and inflammatory responses. However, potent and specific p38δ inhibitors have not been defined so far. Moreover, in cancer disease, p38δ appears to act as a tumor suppressor or tumor promoter according to cancer and cell type studied. In this review, we outline the current understanding of p38δ roles in each cancer type, to define whether it is possible to delineate new cancer therapies based on small-molecule p38δ inhibitors. We also highlight recent advances made in the design of molecules with potential to inhibit p38 isoforms and discuss structural approaches to guide the search for p38δ inhibitors.

Use of signals of positive and negative selection to distinguish cancer genes and passenger genes

A major goal of cancer genomics is to identify all genes that play critical roles in carcinogenesis. Most approaches focused on genes positively selected for mutations that drive carcinogenesis and neglected the role of negative selection. Some studies have actually concluded that negative selection has no role in cancer evolution. We have re-examined the role of negative selection in tumor evolution through the analysis of the patterns of somatic mutations affecting the coding sequences of human genes. Our analyses have confirmed that tumor suppressor genes are positively selected for inactivating mutations, oncogenes, however, were found to display signals of both negative selection for inactivating mutations and positive selection for activating mutations. Significantly, we have identified numerous human genes that show signs of strong negative selection during tumor evolution, suggesting that their functional integrity is essential for the growth and survival of tumor cells.

Association Study of MAP3K1 SNPs and Risk Factors with Susceptibility to Esophageal Squamous Cell Carcinoma in a Chinese Population: A Case-Control Study

Purpose

The aim of this study was to screen the predisposed population and explore possible interactions between genetic polymorphisms and risk factors involved in the tumorigenesis and progression of ESCC (esophageal squamous cell carcinoma), in hope of identifying possible therapeutic targets along the way.

Patients and Methods

Cases (1043) and controls (1315) were enrolled to evaluate the possible association between MAP3K1 SNPs and ESCC risk. Subgroup analyses include MAP3K1 variants, gender, age, smoking and drinking status.

Results

Among all three single locus polymorphisms of MAP3K1, only the heterozygote genotype of rs702689 AG is shown to be associated with increased risk for developing ESCC (OR=1.272, 95% confidence interval=1.061–1.525, p=0.009). Moreover, stratified analysis results observed altered susceptibility among patients with exposure to risk factors combined with certain genetic variant to ESCC.

Conclusion

This study reveals that MAP3K1 rs702689 AG genotype might facilitate the tumorigenesis in ESCC, particularly among women, patients who were over 63y and those who never drink nor smoke.

Identification and Validation of Fibroblast Growth Factor 12 Gene as a Novel Potential Biomarker in Esophageal Cancer Using Cancer Genomic Datasets

Esophageal squamous cell carcinoma (ESCC) has a complex, multifactorial etiology in which environmental, geographical, and genetic factors play major roles. It is the second most common cancer among men and the fourth most common among women in India, with a particularly high prevalence in Northeast India. In this study, an integrative in silico [DAVID, NCG5.0, Oncomine, Cancer Cell Line Encyclopedia, and The Cancer Genome Atlas (TCGA)] approach was used to identify the potential biomarkers by using the available three genomic datasets on ESCC from Northeast India followed by its in vitro functional validation. Fibroblast Growth Factor 12 (FGF12) gene was overexpressed in ESCC. The upregulation of FGF12 was also observed on ESCC of TCGA OncoPrint portal, whereas very low expression of FGF12 gene was mapped in normal esophageal tissue on the GTEx database. Silencing of FGF12 showed significant inhibition in activity of tumor cell proliferation, colony formation, and cell migration. The upregulation of FGF12 showed significantly reduced survival in ESCC patients. The protein interaction analysis of FGF12 found the binding with MAPK8IP2 and MAPK13. High expression of FGF12 along with MAPK8IP2, and MAPK13 proteins correlate with poor survival in ESCC patients. Tissue microarray also showed expression of these proteins in patients with ESCC. These results indicate that FGF12 has a potential role in ESCC and suggest that cancer genomic datasets with application of in silico approaches are instrumental for biomarker discovery research broadly and specifically, for the identification of FGF12 as a putative biomarker in ESCC.

P38 delta MAPK promotes breast cancer progression and lung metastasis by enhancing cell proliferation and cell detachment

The protein p38 mitogen-activated protein kinase delta isoform (p38δ) is a poorly studied member of the MAPK family. Data analysis from The Cancer Genome Atlas (TCGA) database revealed that p38δ is highly expressed in all types of human breast cancers. Using a human breast cancer tissue array, we confirmed elevation in cancer tissue. The breast cancer mouse model, MMTV-PyMT (PyMT), developed breast tumors with lung metastasis; however, mice deleted in p38δ (PyMT/p38δ^−/−) exhibited delayed primary tumor formation and highly reduced lung metastatic burden. At the cellular level, we demonstrate that targeting of p38δ in breast cancer cells, MCF-7 and MDA-MB-231 resulted in a reduced rate of cell proliferation. Additionally, cells lacking p38δ also displayed an increased cell-matrix adhesion and reduced cell detachment. This effect on cell adhesion was molecularly supported by the regulation of the focal adhesion kinase (FAK) by p38δ in the human breast cell lines. These studies define a previously unappreciated role for p38δ in breast cancer development and evolution by regulating tumor growth and altering metastatic properties.

p38γ and p38δ: From Spectators to Key Physiological Players

Although the physiological roles of p38γ and p38δ signalling pathways are largely unknown, new genetic and pharmacological tools are providing groundbreaking information on the function of these two stress-activated protein kinases. Recent studies show the importance of p38γ and p38δ in the regulation of processes as diverse as cytokine production, protein synthesis, exocytosis, cell migration, gene expression, and neuron activity, which have an acute impact on the development of pathologies related to inflammation, diabetes, neurodegeneration, and cancer. These recent breakthroughs are resolving some of the questions that have long been asked regarding the function of p38γ and p38δ in biology and pathology.

p38 MAPK Signaling in Osteoblast Differentiation

The skeleton is a highly dynamic tissue whose structure relies on the balance between bone deposition and resorption. This equilibrium, which depends on osteoblast and osteoclast functions, is controlled by multiple factors that can be modulated post-translationally. Some of the modulators are Mitogen-activated kinases (MAPKs), whose role has been studied in vivo and in vitro. p38-MAPK modifies the transactivation ability of some key transcription factors in chondrocytes, osteoblasts and osteoclasts, which affects their differentiation and function. Several commercially available inhibitors have helped to determine p38 action on these processes. Although it is frequently mentioned in the literature, this chemical approach is not always as accurate as it should be. Conditional knockouts are a useful genetic tool that could unravel the role of p38 in shaping the skeleton. In this review, we will summarize the state of the art on p38 activity during osteoblast differentiation and function, and emphasize the triggers of this MAPK.

p38δ MAPK phenotype: an indicator of chemotherapeutic response in oesophageal squamous cell carcinoma

We recently documented p38δ differential expression and function in oesophageal squamous cell carcinoma (OESCC). This study expands upon these findings and investigates whether p38δ status in OESCC can influence response(s) to cytotoxic drugs. The antiproliferative effect of conventional cisplatin and 5-fluorouracil (CF) treatment was compared with the recently reviewed triple regime of cisplatin, 5-fluorouracil and doxorubicin (ACF). p38δ-positive and p38δ-negative cell lines were employed using cell-growth and clonogenic assays. Key regulators of intrinsic and extrinsic apoptotic pathways were measured. Wound-healing assays and a Boyden chamber were used to investigate the effect of drug treatments on cell migration. Functional networks were analysed in terms of changes in MAPK expression. p38δ-negative OESCC is less sensitive to standard CF chemotherapy compared with p38δ-positive cells. However, following ACF treatment p38δ-negative cells showed markedly decreased proliferation and cell migration, and increased apoptosis. ACF induced apoptosis through the extrinsic pathway involving Fas activation, caspase-8 and caspase-3 cleavage and degradation of PARP. Loss of mitochondrial membrane potential (ΔΨm) was observed but downregulation of multidomain proapoptotic proteins, as well as BH3-only proteins, suggests involvement of pathways other than the mitochondrial pathway. Interestingly, induction of p38 and ERK1/2, but not JNK1/2, was observed following ACF treatment. p38δ-negative OESCC is more resistant to traditional CF treatment compared with p38δ-positive OESCC. In light of these results, p38δ phenotyping of tumour tissue may be of considerable value in deciding on an optimal therapeutic strategy for patients with p38δ-negative OESCC.

Clinicopathological significance of p38β, p38γ, and p38δ and its biological roles in esophageal squamous cell carcinoma

P38β, p38γ, and p38δ have been sporadically and scarcely reported to be involved in the carcinogenesis of cancers, compared with p38α isoform. However, little has been known regarding their clinicopathological significance and biological roles in esophageal squamous cell carcinoma (ESCC). Expression status of p38β, p38γ, and p38δ was assayed using immunohistochemistry with ESCC tissue microarray; ensuing clinicopathological significance was statistically analyzed. To define its biological roles on proliferation, migration and invasion of ESCC cell line Eca109 in vitro, MTT, wound healing, and Transwell assays were employed, respectively. As confirmation, athymic nude mice were taken to verify the effect over proliferation in vivo. It was found that both p38β and p38δ expression, other than p38γ, were significantly higher in ESCC tissues compared with paired normal controls. In terms of prognosis, only p38β expression was observed to be significantly associated with overall prognosis. Clinicopathologically, there was significant association between p38γ expression and clinical stage, lymph nodes metastases, and tumor volume. No significant association was found for p38β and p38δ between its expression and other clinicopathological parameters other than significant difference of expression between ESCC versus normal control. In Eca109, it was observed that p38β, p38γ, and p38δ can promote the cell growth and motility. As verification, over-expression of p38δ can promote, whereas knockdown of p38γ can prevent, the tumorigenesis in nude mice model xenografted with Eca109 cells whose basal level of p38δ was stably over-expressed and p38γ was stably knocked down. Together, our results demonstrate that p38β, p38γ, and p38δ played oncogenic roles in ESCC.

Hypermethylation of MAPK13 Promoter in Oesophageal Squamous Cell Carcinoma Is Associated with Loss of p38δ MAPK Expression

The loss of tumour suppressor gene function is a hallmark of malignant transformation and can occur by a variety of genetic and/or epigenetic alterations. We have previously characterised p38δ mitogen-activated protein kinase (MAPK) as a tumour suppressor in oesophageal squamous cell carcinoma (OESCC) and outlined how loss of p38δ MAPK expression promotes increased proliferation and migration, as well as reduced chemosensitivity. Our aim was to investigate the underlying molecular causes of loss of p38δ MAPK expression in OESCC. Sequence analysis of DNA from p38δ MAPK positive and p38δ MAPK negative OESCC cell lines was used to investigate potential loss of function causing mutations. Epigenetic control of p38δ expression in OESCC was examined using methylation-specific PCR and sequencing of bisulfite-converted DNA. We did not identify any mutations in the MAPK13 sequence in OESCC cell lines which lack p38δ MAPK expression. However, we identified a differential pattern of methylation between p38δ MAPK positive and p38δ MAPK negative cell lines. We outline here for the first time differential MAPK13 promoter methylation in OESCC. Our results suggest that epigenetic alterations are responsible, in part, for the suppression of p38δ MAPK expression and promotion of tumourigenesis in OESCC.

Comparative effects of 4-phenyl-3-butenoic acid and vorinostat on cell growth and signaling

BACKGROUND/AIM

4-phenyl-3-butenoic acid (PBA) is a small-molecule anti-inflammatory agent, which has been shown to inhibit growth, increase gap junction intercellular communication and modulate activation of p38 mitogen-activated protein kinase (p38 MAPK) and c-jun n-terminal kinase (JNK) in tumorigenic cells at concentrations that do not similarly affect non-tumorigenic cells. Vorinostat is an anticancer agent structurally similar to PBA. The purpose of this study was to compare the effects of these two agents on JNK and p38 activation, cell growth and gap junction intercellular communication (GJIC).

MATERIALS AND METHODS

Cell growth, GJIC and western blot analyses were performed utilizing tumorigenic WBras1 and H2009 human carcinoma cells, and non-tumorigenic WBneo3 and human bronchial epithelial (HBE) cells.

RESULTS

Both compounds significantly inhibited WBras1 and H2009 tumorigenic cell growth and increased GJIC in WBras1 cells, as previously reported for PBA. Under similar conditions, both compounds increased phosphorylation of p38 MAPK in tumorigenic but not in non-tumorigenic cells and decreased phosphorylation of JNK in tumorigenic cells. However, a decrease in phosphorylation of JNK occurred in non-tumorigenic WBras1 cells following vorinostat treatment but not PBA treatment. Both compounds showed a selective growth inhibition of H2009 human carcinoma over normal HBE lung cells but, unlike PBA, vorinostat significantly decreased cell growth in WBneo3 cells.

CONCLUSION

Overall, PBA exhibited similar effects to vorinostat in tumorigenic cells, while also showing reduced effects on JNK phosphorylation and growth in non-tumorigenic cells compared to ras-transformed cells.

p38δ MAPK: Emerging Roles of a Neglected Isoform

p38δ mitogen activated protein kinase (MAPK) is a unique stress responsive protein kinase. While the p38 MAPK family as a whole has been implicated in a wide variety of biological processes, a specific role for p38δ MAPK in cellular signalling and its contribution to both physiological and pathological conditions are presently lacking. Recent emerging evidence, however, provides some insights into specific p38δ MAPK signalling. Importantly, these studies have helped to highlight functional similarities as well as differences between p38δ MAPK and the other members of the p38 MAPK family of kinases. In this review we discuss the current understanding of the molecular mechanisms underlying p38δ MAPK activity. We outline a role for p38δ MAPK in important cellular processes such as differentiation and apoptosis as well as pathological conditions such as neurodegenerative disorders, diabetes, and inflammatory disease. Interestingly, disparate roles for p38δ MAPK in tumour development have also recently been reported. Thus, we consider evidence which characterises p38δ MAPK as both a tumour promoter and a tumour suppressor. In summary, while our knowledge of p38δ MAPK has progressed somewhat since its identification in 1997, our understanding of this particular isoform in many cellular processes still strikingly lags behind that of its counterparts.

Identification of p38β as a therapeutic target for the treatment of Sézary syndrome

Cutaneous T-Cell Lymphomas (CTCL) represent a group of hematopoietic malignancies that home to the skin and have no known molecular basis for disease pathogenesis. Sézary syndrome (SS) is the leukemic variant of CTCL. Currently, CTCL is incurable, highlighting the need for new therapeutic modalities. We have previously observed that combined smallmolecule inhibition of protein kinase C (PKC) β and glycogen synthase kinase 3 (GSK3) causes synergistic apoptosis in CTCL cell lines and patient cells. Through microarray analysis of a SS cell line, we surveyed global gene expression following combined PKCβ-GSK3 treatment to elucidate therapeutic targets responsible for cell death. Clinically relevant targets were defined as genes differentially expressed in SS patients that were modulated by combination-drug treatment of SS cells. Gene set enrichment analysis uncovered candidate genes enriched for an immune cell signature, specifically the T-cell receptor and MAPK signaling pathways. Further analysis identified p38 as a potential therapeutic target that is over-expressed in SS patients and decreased by synergistic-inhibitor treatment. This target was verified through small-molecule inhibition of p38 leading to cell death in both SS cell lines and patient cells. These data establish p38 as a SS biomarker and potential therapeutic target for the treatment of CTCL.