The role of STATs in lung carcinogenesis: an emerging target for novel therapeutics

Lung cancer treatment potential and limits associated with the STAT family of transcription factors

Lung cancer is one of the mortal cancers and the leading cause of cancer-related mortality, with a cancer survival rate of fewer than 5% in developing nations. This low survival rate can be linked to things like late-stage detection, quick postoperative recurrences in patients receiving therapy, and chemoresistance developing against various lung cancer treatments. Signal transducer and activator of transcription (STAT) family of transcription factors are involved in lung cancer cell proliferation, metastasis, immunological control, and treatment resistance. By interacting with specific DNA sequences, STAT proteins trigger the production of particular genes, which in turn result in adaptive and incredibly specific biological responses. In the human genome, seven STAT proteins have been discovered (STAT1 to STAT6, including STAT5a and STAT5b). Many external signaling proteins can activate unphosphorylated STATs (uSTATs), which are found inactively in the cytoplasm. When STAT proteins are activated, they can increase the transcription of several target genes, which leads to unchecked cellular proliferation, anti-apoptotic reactions, and angiogenesis. The effects of STAT transcription factors on lung cancer are variable; some are either pro- or anti-tumorigenic, while others maintain dual, context-dependent activities. Here, we give a succinct summary of the various functions that each member of the STAT family plays in lung cancer and go into more detail about the advantages and disadvantages of pharmacologically targeting STAT proteins and their upstream activators in the context of lung cancer treatment.

Alveolar macrophage secretion of vesicular SOCS3 represents a platform for lung cancer therapeutics

Lung cancer remains the leading cause of cancer-related death in the United States. Although the alveolar macrophage (AM) comprises the major resident immune cell in the lung, few studies have investigated its role in lung cancer development. We recently discovered a potentially novel mechanism wherein AMs regulate STAT-induced inflammatory responses in neighboring epithelial cells (ECs) via secretion and delivery of suppressors of cytokine signaling 3 (SOCS3) within extracellular vesicles (EVs). Here, we explored the impact of SOCS3 transfer on EC tumorigenesis and the integrity of AM SOCS3 secretion during development of lung cancer. AM-derived EVs containing SOCS3 inhibited STAT3 activation as well as proliferation and survival of lung adenocarcinoma cells. Levels of secreted SOCS3 were diminished in lungs of patients with non-small cell lung cancer and in a mouse model of lung cancer, and the impaired ability of murine AMs to secrete SOCS3 within EVs preceded the development of lung tumors. Loss of this homeostatic brake on tumorigenesis prompted our effort to "rescue" it. Provision of recombinant SOCS3 loaded within synthetic liposomes inhibited proliferation and survival of lung adenocarcinoma cells in vitro as well as malignant transformation of normal ECs. Intratumoral injection of SOCS3 liposomes attenuated tumor growth in a lung cancer xenograft model. This work identifies AM-derived vesicular SOCS3 as an endogenous antitumor mechanism that is disrupted within the tumor microenvironment and whose rescue by synthetic liposomes can be leveraged as a potential therapeutic strategy for lung cancer.

The Expression Levels of IL-4/IL-13/STAT6 Signaling Pathway Genes and SOCS3 Could Help to Differentiate the Histopathological Subtypes of Non-Small Cell Lung Carcinoma

Background

The interleukin (IL)-4/IL-13/signal transducer and activator of transcription (STAT) 6 signaling pathway and the SOCS3 gene, one of its main regulators, constitute an important link between the inflammation process in the epithelial cells and inflammatory-related tumorigenesis. The present study is the first to evaluate IL-4, IL-13, STAT6, and SOCS3 mRNA expression in non-small cell lung carcinoma (NSCLC) histopathological subtypes.

Methods

Gene expression levels were assessed using TaqMan^® probes by quantitative reverse transcription PCR (qRT-PCR) in lung tumor samples and unchanged lung tissue samples.

Results

Increased expression of IL-4, IL-13, and STAT6 was observed in all histopathological NSCLC subtypes (squamous cell carcinoma [SCC], adenocarcinoma [AC], and large cell carcinoma [LCC]). Significantly higher expression of IL-13 and STAT6 (p = 0.019 and p = 0.008, respectively) was found in SCC than in LCC. No statistically significant differences were found for IL-4. Significantly higher SOCS3 expression was found in LCC than in AC (p = 0.027). A negative correlation (rho = –0.519) was observed for the STAT6 and SOCS3 genes in SCC (p = 0.005). No associations were found between gene expression and tumor staging (post-operative Tumor Node Metastasis [pTNM], American Joint Committee on Cancer [AJCC]), patients’ age, sex, or history of smoking.

Conclusions

As the number of LCC cases in our study was quite low, the statistically significant results obtained should be confirmed in a larger group of patients, particularly as the relationships identified between increased IL-4, IL-13, and STAT6 mRNA expression and decreased SOCS3 expression suggest that these genes may serve as potential diagnostic markers for differentiating between NSCLC histopathological subtypes.

The Antitumor Effect of C-terminus of Hsp70-Interacting Protein via Degradation of c-Met in Small Cell Lung Cancer

Background

The mesenchymal-epithelial transition factor (MET) receptor can be overexpressed in solid tumors, including small cell lung cancer (SCLC). However, the molecular mechanism regulating MET stability and turnover in SCLC remains undefined. One potential mechanism of MET regulation involves the C-terminus of Hsp70-interacting protein (CHIP), which targets heat shock protein 90-interacting proteins for ubiquitination and proteasomal degradation. In the present study, we investigated the functional effects of CHIP expression on MET regulation and the control of SCLC cell apoptosis and invasion.

Methods

To evaluate the expression of CHIP and c-Met, which is a protein that in humans is encoded by the MET gene (the MET proto-oncogene), we examined the expression pattern of c-Met and CHIP in SCLC cell lines by western blotting. To investigate whether CHIP overexpression reduced cell proliferation and invasive activity in SCLC cell lines, we transfected cells with CHIP and performed a cell viability assay and cellular apoptosis assays.

Results

We found an inverse relationship between the expression of CHIP and MET in SCLC cell lines (n=5). CHIP destabilized the endogenous MET receptor in SCLC cell lines, indicating an essential role for CHIP in the regulation of MET degradation. In addition, CHIP inhibited MET-dependent pathways, and invasion, cell growth, and apoptosis were reduced by CHIP overexpression in SCLC cell lines.

Conclusion

CHIP is capable of regulating SCLC cell apoptosis and invasion by inhibiting MET-mediated cytoskeletal and cell survival pathways in NCI-H69 cells. CHIP suppresses MET-dependent signaling, and regulates MET-mediated SCLC motility.

STAT3 targeting by polyphenols: Novel therapeutic strategy for melanoma

Melanoma or malignant melanocytes appear with the low incidence rate, but very high mortality rate worldwide. Epidemiological studies suggest that polyphenolic compounds contribute for prevention or treatment of several cancers particularly melanoma. Such findings motivate to dig out novel therapeutic strategies against melanoma, including research toward the development of new chemotherapeutic and biologic agents that can target the tumor cells by different mechanisms. Recently, it has been found that signal transducer and activator of transcription 3 (STAT3) is activated in many cancer cases surprisingly. Different evidences supply the aspect that STAT3 activation plays a vital role in the metastasis, including proliferation of cells, survival, invasion, migration, and angiogenesis. This significant feature plays a vital role in various cellular processes, such as cell proliferation and survival. Here, we reviewed the mechanisms of the STAT3 pathway regulation and their role in promoting melanoma. Also, we have evaluated the emerging data on polyphenols (PPs) specifically their contribution in melanoma therapies with an emphasis on their regulatory/inhibitory actions in relation to STAT3 pathway and current progress in the development of phytochemical therapeutic techniques. An understanding of targeting STAT3 by PPs brings an opportunity to melanoma therapy. © 2016 BioFactors, 43(3):347-370, 2017.

IFNs-signaling effects on lung cancer: an up-to-date pathways-specific review

IFNs have found important applications in clinical medicine, including the treatment of lung malignancies. The biological effect of the IFN-receptor signaling is regulated essentially by three factors: the expression profile of the IFN itself, the profile of the receptor, and the expression of target genes. IFNs initiate their signaling by binding to specific receptors. The activated IFNs can directly induce gene transcription and/or multiple downstream signaling that both induce diverse cellular responses including the cell cycle arrest and the apoptosis in tumor cells. We provided evidence that IFN-γ enhances the pro cell death effects of Fas/CD95 in human neoplastic alveolar epithelial cell line, A549. We also found that p27 protein plays a pivotal role in the inducing cell death of IFNγ-CH-11-treated A549 cells, since it is involved in the Ras/Raf signaling pathway. This article discusses recent insights into these possible additional functions of IFNs in lung cancer treatment.

SIAH2 antagonizes TYK2-STAT3 signaling in lung carcinoma cells

The Janus tyrosine kinases JAK1-3 and tyrosine kinase-2 (TYK2) are frequently hyperactivated in tumors. In lung cancers JAK1 and JAK2 induce oncogenic signaling through STAT3. A putative role of TYK2 in these tumors has not been reported. Here, we show a previously not recognized TYK2-STAT3 signaling node in lung cancer cells. We reveal that the E3 ubiquitin ligase seven-in-absentia-2 (SIAH2) accelerates the proteasomal degradation of TYK2. This mechanism consequently suppresses the activation of STAT3. In agreement with these data the analysis of primary non-small-cell lung cancer (NSCLC) samples from three patient cohorts revealed that compared to lung adenocarcinoma (ADC), lung squamous cell carcinoma (SCC) show significantly higher levels of SIAH2 and reduced STAT3 phosphorylation levels. Thus, SIAH2 is a novel molecular marker for SCC. We further demonstrate that an activation of the oncologically relevant transcription factor p53 in lung cancer cells induces SIAH2, depletes TYK2, and abrogates the tyrosine phosphorylation of STAT1 and STAT3. This mechanism appears to be different from the inhibition of phosphorylated JAKs through the suppressor of cytokine signaling (SOCS) proteins. Our study may help to identify molecular mechanisms affecting lung carcinogenesis and potential therapeutic targets.

Low-dose gamma-irradiation inhibits IL-6 secretion from human lung fibroblasts that promotes bronchial epithelial cell transformation by cigarette-smoke carcinogen

Despite decades of research in defining the health effects of low-dose (<100 mGy) ionizing photon radiation (LDR), the relationship between LDR and human cancer risk remains elusive. Because chemical carcinogens modify the tumor microenvironment, which is critical for cancer development, we investigated the role and mechanism of LDR in modulating the response of stromal cells to chemical carcinogen-induced lung cancer development. Secretion of proinflammatory cytokines such as interleukin-6 (IL-6), CXCL1 and CXCL5 from human lung fibroblasts was induced by cigarette-smoke carcinogen benzo[a]pyrene diol epoxide (BPDE), which was inhibited by a single dose of LDR. The activation of NF-κB, which is important for BPDE-induced IL-6 secretion, was also effectively suppressed by LDR. In addition, conditioned media from BPDE-treated fibroblasts activated STAT3 in the immortalized normal human bronchial epithelial cell line Beas-2B, which was blocked with an IL-6 neutralizing antibody. Conditioned medium from LDR-primed and BPDE-treated fibroblast showed diminished capacity in activating STAT3. Furthermore, IL-6 enhanced BPDE-induced Beas-2B cell transformation in vitro. These results suggest that LDR inhibits cigarette smoke-induced lung carcinogenesis by suppressing secretion of cytokines such as IL-6 from fibroblasts in lung tumor-prone microenvironment.

Molecular networks in respiratory epithelium carcinomas

Current anti-cancer research is focused on cell surface receptors targeting, mainly epidermal growth factor receptor and vascular endothelial growth factor receptor, against which a few targeted agents are now available in clinical practice. Recent improvements of our understanding on the intracellular networks that participate in respiratory epithelium carcinogenesis have further elucidated the role of a variety of molecules that represent attractive targets for novel therapeutic strategies. The aim of this review is to explore the potential therapeutic opportunities of the manipulation of these pathways.

Targeting MET as a strategy to overcome crosstalk-related resistance to EGFR inhibitors

The hepatocyte growth factor (HGF)-mesenchymal-epithelial transition factor (MET) pathway has a key role in carcinogenesis; it is implicated in proliferation, inhibition of apoptosis, angiogenesis, migration, invasiveness, and metastasis. All of these molecular events are driven through membrane and intracellular coplayers and several downstream effector proteins. MET has been shown to cross react with epithelial growth factor receptor (EGFR) proteins and possibly substitutes their activity, thus conferring resistance to EGFR-targeting drugs. Therefore, identification of MET inhibitors might lead to new treatments for MET-triggered neoplasia and improve the sensitivity of molecularly targeted antineoplastic compounds that are currently in use. In this Review, we outline current data regarding the HGF-MET pathway during carcinogenesis and the strategies for therapeutic targeting of this pathway. We also discuss the rationale and future perspectives of the combinatorial blockade of HGF-MET and EGFR signalling cascades in cancer treatment.

Silibinin inhibits cytokine-induced signaling cascades and down-regulates inducible nitric oxide synthase in human lung carcinoma A549 cells

Recently, we reported that silibinin inhibits primary lung tumor growth and progression in mice and down-regulates inducible nitric oxide synthase (iNOS) expression in tumors; however, the mechanisms of silibinin action are largely not understood. Also, the activation of signaling pathways inducing various transcription factors are associated with lung carcinogenesis and their inhibition could be an effective strategy to prevent and/or treat lung cancer. Herein, we used human lung epithelial carcinoma A549 cells to explore the potential mechanisms and observed strong iNOS expression by cytokine mixture (containing 100 units/mL IFN-gamma + 0.5 ng/mL interleukin-1beta + 10 ng/mL tumor necrosis factor-alpha). We also examined the cytokine mixture-activated signaling cascades, which could potentially up-regulate iNOS expression, and then examined the effect of silibinin (50-200 mumol/L) on these signaling cascades. Silibinin treatment inhibited, albeit to different extent, the cytokine mixture-induced activation of signal transducer and activator of transcription 1 (Tyr(701)), signal transducer and activator of transcription 3 (Tyr(705)), activator protein-1 family of transcription factors, and nuclear factor-kappaB. The results for activator protein-1 were correlated with the decreased nuclear levels of phosphorylated c-Jun, c-Jun, JunB, JunD, phosphorylated c-Fos, and c-Fos. Further, silibinin also strongly decreased cytokine mixture-induced phosphorylation of extracellular signal-regulated kinase 1/2 but only marginally affected JNK1/2 phosphorylation. Silibinin treatment also decreased constitutive p38 phosphorylation in the presence or absence of cytokine mixture. Downstream of these pathways, silibinin strongly decreased cytokine mixture-induced expression of hypoxia-inducible factor-1alpha without any considerable effect on Akt activation. Cytokine mixture-induced iNOS expression was completely inhibited by silibinin. Overall, these results suggest that silibinin could target multiple cytokine-induced signaling pathways to down-regulate iNOS expression in lung cancer cells and that could contribute to its overall cancer preventive efficacy against lung tumorigenesis.

Preconditioning mediated by sublethal oxygen-glucose deprivation-induced cyclooxygenase-2 expression via the signal transducers and activators of transcription 3 phosphorylation

The signal transducers and activators of transcription (STATs) were found to be essential for cardioprotection. However, their role in preconditioning (PC) neuroprotection remains undefined. Previously, our studies showed that PC mediated a signaling cascade that involves activation of epsilon protein kinase C (varepsilonPKC), extracellular signal-regulated kinase (ERK1/2), and cyclooxygenase-2 (COX-2) pathways. However, the intermediate pathway by which ERK1/2 activates COX-2 was not defined. In this study, we investigated whether the PC-induced signaling pathway requires phosphorylation of STAT isoforms for COX-2 expression. To mimic PC or lethal ischemia, mixed cortical neuron/astrocyte cell cultures were subjected to 1 and/or 4 h of oxygen-glucose deprivation (OGD), respectively. The results indicated serine phosphorylation of STAT3 after PC or varepsilonPKC activation. Inhibition of either varepsilonPKC or ERK1/2 activation abolished PC-induced serine phosphorylation of STAT3. Additionally, inhibition of STAT3 prevented PC-induced COX-2 expression and neuroprotection against OGD. Therefore, our findings suggest that PC signaling cascade involves STAT3 activation after varepsilonPKC and ERK1/2 activation. Finally, we show that STAT3 activation mediates COX-2 expression and ischemic tolerance.

Understanding signaling cascades in melanoma

Understanding regulatory pathways involved in melanoma development and progression has advanced significantly in recent years. It is now appreciated that melanoma is the result of complex changes in multiple signaling pathways that affect growth control, metabolism, motility and the ability to escape cell death programs. Here we review the major signaling pathways currently known to be deregulated in melanoma with an implication to its development and progression. Among these pathways are Ras, B-Raf, MEK, PTEN, phosphatidylinositol-3 kinase (PI3Ks) and Akt which are constitutively activated in a significant number of melanoma tumors, in most cases due to genomic change. Other pathways discussed in this review include the [Janus kinase/signal transducer and activator of transcription (JAK/STAT), transforming growth factor-beta pathways which are also activated in melanoma, although the underlying mechanism is not yet clear. As a paradigm for remodeled signaling pathways, melanoma also offers a unique opportunity for targeted drug development.