CDK10 suppresses metastasis of lung adenocarcinoma through inhibition of the ETS2/c-Raf/p-MEK/p-ERK signaling loop

The repertoire of aberrant signaling underlying the pathogenesis of lung adenocarcinoma remains largely uncharacterized, which precludes an efficient therapy for these patients, especially when distant metastasis occurs. Cyclin-dependent kinase 10 (CDK10) has been reported to modulate the progression of malignant tumors; however, contradictory effects have been found among different types of malignant tumors. In the present study, we found that CDK10 was downregulated in lung adenocarcinoma compared with the paired adjacent normal lung tissue, and lower expression level of CDK10 was associated with more frequent N2 staged lymph node and distant metastasis, higher TNM stage, and shorter overall survival. Further study indicated that CDK10 inhibited the migration and invasion abilities with no impact on the proliferation of lung adenocarcinoma cells. Mechanistically, CDK10 could bind to and promote the degradation of ETS2, a transcription factor for C-RAF and MMP2/9, thereby inactivating the downstream c-Raf/p-MEK/p-ERK pathway that drives epithelial-mesenchymal transition and impairing the expression of matrix metalloproteinases involved in cell invasion. In addition, the p-MEK/p-ERK pathway conducts a positive feedback regulation on the expression of ETS2. Knockdown of CDK10 in human lung adenocarcinoma cells significantly promoted the formation of metastatic foci in lungs in a xenograft mouse model. In conclusion, CDK10 suppresses metastasis of lung adenocarcinoma by disrupting the ETS2/c-Raf/p-MEK/p-ERK/ETS2 signaling and MMP2/9, providing a new therapeutic target for the treatment of lung adenocarcinoma with metastasis.

NDRG1 promotes endothelial dysfunction and hypoxia-induced pulmonary hypertension by targeting TAF15

Background

Pulmonary hypertension (PH) represents a threatening pathophysiologic state that can be induced by chronic hypoxia and is characterized by extensive vascular remodeling. However, the mechanism underlying hypoxia-induced vascular remodeling is not fully elucidated.

Methods and Results

By using quantitative polymerase chain reactions, western blotting, and immunohistochemistry, we demonstrate that the expression of N-myc downstream regulated gene-1 (NDRG1) is markedly increased in hypoxia-stimulated endothelial cells in a time-dependent manner as well as in human and rat endothelium lesions. To determine the role of NDRG1 in endothelial dysfunction, we performed loss-of-function studies using NDRG1 short hairpin RNAs and NDRG1 over-expression plasmids. In vitro, silencing NDRG1 attenuated proliferation, migration, and tube formation of human pulmonary artery endothelial cells (HPAECs) under hypoxia, while NDRG1 over-expression promoted these behaviors of HPAECs. Mechanistically, NDRG1 can directly interact with TATA-box binding protein associated factor 15 (TAF15) and promote its nuclear localization. Knockdown of TAF15 abrogated the effect of NDRG1 on the proliferation, migration and tube formation capacity of HPAECs. Bioinformatics studies found that TAF15 was involved in regulating PI3K-Akt, p53, and hypoxia-inducible factor 1 (HIF-1) signaling pathways, which have been proved to be PH-related pathways. In addition, vascular remodeling and right ventricular hypertrophy induced by hypoxia were markedly alleviated in NDRG1 knock-down rats compared with their wild-type littermates.

Conclusions

Taken together, our results indicate that hypoxia-induced upregulation of NDRG1 contributes to endothelial dysfunction through targeting TAF15, which ultimately contributes to the development of hypoxia-induced PH.

EphrinA3 is a key regulator of malignant behaviors and a potential prognostic factor in lung adenocarcinoma

BACKGROUND

As a member of the Ephrin protein family that elicits short distance cell-cell signaling, EphrinA3 has been shown to promote or inhibit tumorigenesis depending on tumor types, but its roles and the underlying mechanisms in lung adenocarcinoma (LUAD) have not been reported.

MATERIALS AND METHODS

The TCGA database and Kaplan-Meier Plotter database were used to analyze the differential expression of EphrinA3 between LUAD and para-carcinoma tissues, and its effect on overall survival of LUAD patients. CCK-8 assay, Edu assay, and flow cytometry were used to probe the effect of EphrinA3 on the proliferation of LUAD cells, and transwell assay was employed to examine its effect on migration and invasion. In addition, the effect of EphrinA3 on the growth of LUAD was further evaluated using a xenograft tumor model.

RESULTS

EphrinA3 was expressed highly in LUAD, and its expression level was negatively correlated with the prognosis of LUAD patients. In addition, EphrinA3 promoted proliferation, migration, and invasion of LUAD cells, and accelerated tumor growth in a xenograft LUAD model. The reported EphrinA3 receptors, EphA1 and EphA10, were expressed in clinical LUAD tissues and co-localized with EphrinA3 in LUAD cells. Mechanistically, EphrinA3/Eph signaling activated AKT, ERK, and p38MAPK, induced epithelial-mesenchymal transition (EMT), and upregulated matrix metalloproteases-2 and -9 (MMP-2/-9).

CONCLUSION

EphrinA3 expression was negatively correlated with prognosis of patients with LUAD. EphrinA3 promoted proliferation, migration, and invasion of LUAD cells. EphrinA3 enhanced the phosphorylation of ERK and AKT, and potentiates EMT and MMP expression in LUAD cells.

Mxi1-0 Promotes Hypoxic Pulmonary Hypertension Via ERK/c-Myc-dependent Proliferation of Arterial Smooth Muscle Cells

Background: Hypoxic pulmonary hypertension (HPH) is a challenging lung arterial disorder with remarkably high incidence and mortality, and so far patients have failed to benefit from therapeutics clinically available. Max interacting protein 1–0 (Mxi1-0) is one of the functional isoforms of Mxi1. Although it also binds to Max, Mxi1-0, unlike other Mxi1 isoforms, cannot antagonize the oncoprotein c-Myc because of its unique proline rich domain (PRD). While Mxi1-0 was reported to promote cell proliferation via largely uncharacterized mechanisms, it is unknown whether and how it plays a role in the pathogenesis of HPH.

Methods: GEO database was used to screen for genes involved in HPH development, and the candidate players were validated through examination of gene expression in clinical HPH specimens. The effect of candidate gene knockdown or overexpression on cultured pulmonary arterial cells, e.g., pulmonary arterial smooth muscle cells (PASMCs), was then investigated. The signal pathway(s) underlying the regulatory role of the candidate gene in HPH pathogenesis was probed, and the outcome of targeting the aforementioned signaling was evaluated using an HPH rat model.

Results: Mxi1 was significantly upregulated in the PASMCs of HPH patients. As the main effector isoform responding to hypoxia, Mxi1-0 functions in HPH to promote PASMCs proliferation. Mechanistically, Mxi1-0 improved the expression of the proto-oncogene c-Myc via activation of the MEK/ERK pathway. Consistently, both a MEK inhibitor, PD98059, and a c-Myc inhibitor, 10058F4, could counteract Mxi1-0-induced PASMCs proliferation. In addition, targeting the MEK/ERK signaling significantly suppressed the development of HPH in rats.

Conclusion: Mxi1-0 potentiates HPH pathogenesis through MEK/ERK/c-Myc-mediated proliferation of PASMCs, suggesting its applicability in targeted treatment and prognostic assessment of clinical HPH.

PTPL1 suppresses lung cancer cell migration via inhibiting TGF-β1-induced activation of p38 MAPK and Smad 2/3 pathways and EMT

Epithelial-mesenchymal transition (EMT) enables dissemination of neoplastic cells and onset of distal metastasis of primary tumors. However, the regulatory mechanisms of EMT by microenvironmental factors such as transforming growth factor-β (TGF-β) remain largely unresolved. Protein tyrosine phosphatase L1 (PTPL1) is a non-receptor protein tyrosine phosphatase that plays a suppressive role in tumorigenesis of diverse tissues. In this study we investigated the role of PTPL1/PTPN13 in metastasis of lung cancer and the signaling pathways regulated by PTPL1 in terms of EMT of non-small cell lung cancer (NSCLC) cells. We showed that the expression of PTPL1 was significantly downregulated in cancerous tissues of 23 patients with NSCLC compared with adjacent normal tissues. PTPL1 expression was positively correlated with overall survival of NSCLC patients. Then we treated A549 cells in vitro with TGF-β1 (10 ng/mL) and assessed EMT. We found that knockdown of PTPL1 enhanced the migration and invasion capabilities of A549 cells, through enhancing TGF-β1-induced EMT. In nude mice bearing A549 cell xenografts, knockdown of PTPL1 significantly promoted homing of cells and formation of tumor loci in the lungs. We further revealed that PTPL1 suppressed TGF-β-induced EMT by counteracting the activation of canonical Smad2/3 and non-canonical p38 MAPK signaling pathways. Using immunoprecipitation assay we demonstrated that PTPL1 could bind to p38 MAPK, suggesting that p38 MAPK might be a direct substrate of PTPL1. In conclusion, these results unravel novel mechanisms underlying the regulation of TGF-β signaling pathway, and have implications for prognostic assessment and targeted therapy of metastatic lung cancer.

Protein tyrosine phosphatase L1 represses endothelial-mesenchymal transition by inhibiting IL-1β/NF-κB/Snail signaling

Endothelial-mesenchymal transition (EnMT) plays a pivotal role in various diseases, including pulmonary hypertension (PH), and transcription factors like Snail are key regulators of EnMT. In this study we investigated how these factors were regulated by PH risk factors (e.g. inflammation and hypoxia) in human umbilical vein endothelial cells (HUVECs). We showed that treatment with interleukin 1β (IL-1β) induced EnMT of HUVECs via activation of NF-κB/Snail pathway, which was further exacerbated by knockdown of protein tyrosine phosphatase L1 (PTPL1). We demonstrated that PTPL1 inhibited NF-κB/Snail through dephosphorylating and stabilizing IκBα. IL-1β or hypoxia could downregulate PTPL1 expression in HUVECs. The deregulation of PTPL1/NF-κB signaling was validated in a monocrotaline-induced rat PH (MCT-PH) model and clinical PH specimens. Our findings provide novel insights into the regulatory mechanisms of EnMT, and have implications for identifying new therapeutic targets for clinical PH.

Cefminox, a Dual Agonist of Prostacyclin Receptor and Peroxisome Proliferator-Activated Receptor-Gamma Identified by Virtual Screening, Has Therapeutic Efficacy against Hypoxia-Induced Pulmonary Hypertension in Rats

Prostacyclin receptor (IP) and peroxisome proliferator-activated receptor-gamma (PPARγ) are both potential targets for treatment of pulmonary arterial hypertension (PAH). Expression of IP and PPARγ decreases in PAH, suggesting that screening of dual agonists of IP and PPARγ might be an efficient method for drug discovery. Virtual screening (VS) of potential IP-PPARγ dual-targeting agonists was performed in the ZINC database. Ten of the identified compounds were further screened, and cefminox was found to dramatically inhibit growth of PASMCs with no obvious cytotoxicity. Growth inhibition by cefminox was partially reversed by both the IP antagonist RO113842 and the PPARγ antagonist GW9662. Investigation of the underlying mechanisms of action demonstrated that cefminox inhibits the protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling pathway through up-regulation of the expression of phosphatase and tensin homolog (PTEN, which is inhibited by GW9662), and enhances cyclic adenosine monophosphate (cAMP) production in PASMCs (which is inhibited by RO113842). In a rat model of hypoxia-induced pulmonary hypertension, cefminox displayed therapeutic efficacy not inferior to that of the prostacyclin analog iloprost or the PPARγ agonist rosiglitazone. Our results identified cefminox as a dual agonist of IP and PPARγ that significantly inhibits PASMC proliferation by up-regulation of PTEN and cAMP, suggesting that it has potential for treatment of PAH.