Over-expressed and truncated midkines promote proliferation of BGC823 cells in vitro and tumor growth in vivo

Increased serum concentrations of estrogen-induced growth factors Midkine and FGF2 in NF1 patients with plexiform neurofibroma

Neurofibromatosis type 1 (NF1) predisposes to the development of dermal and plexiform neurofibromas and serum of NF1 patients stimulates neurofibroma proliferation in vitro. This study aimed to determine whether, in NF1 patients, serum levels of midkine (MK) and fibroblast growth factor 2 (FGF2) were associated with the number and/or type of neurofibromas. In addition, their concentrations were correlated with serum levels of dehydroepiandrosterone sulfate (DHEAS), a neurosteroid secreted by the peripheral nervous system. We performed a case control-study and measured, by ELISA assay, serum concentrations of MK, FGF2, and DHEAS in 20 NF1 patients and 30 controls. We found increased serum levels of MK and FGF2 in NF1 patients between 30 and 50 years old. Their concentrations were significantly higher in NF1 patients with plexiform neurofibromas than in controls (P=0.003 for MK and P=0.008 for FGF2). As an underlying hormonal regulation was suspected, DHEAS serum levels were measured but no difference was observed between patients and controls. We also observed a strong association between MK and FGF2 levels (P=0.0001) in NF1 patients and controls. In conclusion, we point out MK and FGF2 as biomarkers for plexiform neurofibroma in NF1 patients. As both growth factors are estrogen-responsive genes and neurofibromin is a co-repressor of estrogen receptor alpha activity, we suggest that the increased serum levels of MK and FGF2 observed in NF1 patients might be due to estradiol hypersensitivity.

Apoptosis Deregulation and the Development of Cancer Multi-Drug Resistance

Simple Summary

Despite recent therapeutic advances against cancer, many patients do not respond well or respond poorly, to treatment and develop resistance to more than one anti-cancer drug, a term called multi-drug resistance (MDR). One of the main factors that contribute to MDR is the deregulation of apoptosis or programmed cell death. Herein, we describe the major apoptotic pathways and discuss how pro-apoptotic and anti-apoptotic proteins are modified in cancer cells to convey drug resistance. We also focus on our current understanding related to the interactions between survival and cell death pathways, as well as on mechanisms underlying the balance shift towards cancer cell growth and drug resistance. Moreover, we highlight the role of the tumor microenvironment components in blocking apoptosis in MDR tumors, and we discuss the significance and potential exploitation of epigenetic modifications for cancer treatment. Finally, we summarize the current and future therapeutic approaches for overcoming MDR.

Abstract

The ability of tumor cells to evade apoptosis is established as one of the hallmarks of cancer. The deregulation of apoptotic pathways conveys a survival advantage enabling cancer cells to develop multi-drug resistance (MDR), a complex tumor phenotype referring to concurrent resistance toward agents with different function and/or structure. Proteins implicated in the intrinsic pathway of apoptosis, including the Bcl-2 superfamily and Inhibitors of Apoptosis (IAP) family members, as well as their regulator, tumor suppressor p53, have been implicated in the development of MDR in many cancer types. The PI₃K/AKT pathway is pivotal in promoting survival and proliferation and is often overactive in MDR tumors. In addition, the tumor microenvironment, particularly factors secreted by cancer-associated fibroblasts, can inhibit apoptosis in cancer cells and reduce the effectiveness of different anti-cancer drugs. In this review, we describe the main alterations that occur in apoptosis-and related pathways to promote MDR. We also summarize the main therapeutic approaches against resistant tumors, including agents targeting Bcl-2 family members, small molecule inhibitors against IAPs or AKT and agents of natural origin that may be used as monotherapy or in combination with conventional therapeutics. Finally, we highlight the potential of therapeutic exploitation of epigenetic modifications to reverse the MDR phenotype.

Serum midkine as non-invasive biomarker for detection and prognosis of non-small cell lung cancer

Lung cancer continues to be the leading cause for cancer-related deaths in men and women worldwide. Sufficient screening tools enabling early diagnosis are essential to improve patient outcomes. The aim of this study was to evaluate serum midkine (S-MK) both as a diagnostic and prognostic biomarker in non-small cell lung cancer (NSCLC). This single-center analysis included 59 NSCLC patients counting 30 squamous cell cancers and 29 adenocarcinomas. Preoperative S-MK concentration was determined using ELISA. Patients were followed up to five years. S-MK was found to be significantly overexpressed in patients with NSCLC compared to healthy controls (p < 0.001). The discriminative power of S-MK to differentiate NSCLC subjects from controls was fairly high with an area under the receiver operating characteristic curve of 0.83 (p < 0.001). Optimal sensitivity of 92% and reasonable specificity of 68% was reached at a threshold of 416 pg/ml S-MK. Patients with high S-MK concentration showed a significantly shorter overall survival compared to patients with low S-MK expression (p < 0.05). In conclusion, S-MK is overexpressed in patients with NSCLC and serves as an independent prognostic factor for overall survival. S-MK may thus be considered as an additional non-invasive biomarker not only for NSCLC screening but also for outcome prediction.

H. sinensis mycelium inhibits epithelial-mesenchymal transition by inactivating the midkine pathway in pulmonary fibrosis

The medical fungus Hirsutella sinensis has been used as a Chinese folk health supplement because of its immunomodulatory properties. Our previous studies established the antifibrotic action of Hirsutella sinensis mycelium (HSM) in the lung. The epithelial-mesenchymal transition (EMT) is involved in the pathogenesis of idiopathic pulmonary fibrosis. The present study investigates the role of HSM in mediating EMT during the development of pulmonary fibrosis. HSM significantly inhibits bleomycin (BLM)-induced pulmonary fibrosis by blocking the EMT. In addition, the expression levels of midkine are increased in the lungs of the BLM-induced group. Further analysis of the results indicates that the mRNA level of midkine correlated positively with EMT. HSM markedly abrogates the transforming growth factor β-induced EMT-like phenotype and behavior in vitro. The activation of midkine related signaling pathway is ameliorated following HSM treatment, whereas this extract also caused an effective attenuation of the induction of EMT (caused by midkine overexpression) in vitro. Results further confirm that oral medication of HSM disrupted the midkine pathway in vivo. Overall, findings suggest that the midkine pathway and the regulation of the EMT may be considered novel candidate therapeutic targets for the antifibrotic effects caused by HSM.

Midkine derived from cancer-associated fibroblasts promotes cisplatin-resistance via up-regulation of the expression of lncRNA ANRIL in tumour cells

Midkine (MK) is a heparin-binding growth factor that promotes carcinogenesis and chemoresistance. The tumour microenvironment (TME) can affect chemotherapy sensitivity. However, the role of stromal-derived MK, especially in cancer-associated fibroblasts (CAFs), is unclear. Here, we confirmed that MK decreased cisplatin-induced cell death in oral squamous cell carcinoma (OSCC) cells, ovarian cancer cells and lung cancer cells. We also isolated primary CAFs (n = 3) from OSCC patients and found that CAFs secreted increased levels of MK, which abrogated cisplatin-induced cell death. Moreover, MK increased the expression of lncRNA ANRIL in the tumour cells. Normal tissues, matched tumour-adjacent tissues and OSCC tissues were analysed (n = 60) and showed that lncRNA ANRIL was indeed overexpressed during carcinogenesis and correlated with both high TNM stage and lymph node metastasis (LNM). Furthermore, lncRNA ANRIL knockdown in tumour cells inhibited proliferation, induced apoptosis and increased cisplatin cytotoxicity of the tumour cells via impairment of the drug transporters MRP1 and ABCC2, which could be restored by treatment with human MK in a caspase-3/BCL-2-dependent manner. In conclusion, we firstly describe that CAFs in the TME contribute to the high level of MK in tumours and that CAF-derived MK can promote cisplatin resistance via the elevated expression of lncRNA ANRIL.

ERβ-mediated estradiol enhances epithelial mesenchymal transition of lung adenocarcinoma through increasing transcription of midkine

Epithelial-mesenchymal transition (EMT) plays a specific role in the migration of tumor cells. Both estrogen and midkine (MK) have been thought to be important factors in promoting the progression of non-small-cell lung cancer (NSCLC) and can enhance EMT. Some evidence indicated the correlation between estradiol (E2) and MK, but the precise mechanism on their interreaction is unknown. Here, we try to clarify whether and how E2 regulates MK expression to promote EMT. We found that E2 increased MK mRNA expression in lung adenocarcinoma cells LTEP-a2 and A549 in a time-dependent manner. E2-induced MK expression was inhibited by the estrogen receptor (ER) antagonist ICI 182,780 and tamoxifen but not by phosphoinositide-3 kinase and MAPK inhibitors, suggesting a genomic mechanism of E2 on the regulation of MK transcription. Moreover, luciferase reporter and chromatin immunoprecipitation assays exhibited that E2 induced ERβ recruitment to the estrogen response element in the MK promoter. Small interfering RNA to ERα and ERβ revealed that ERβ mainly mediated E2-induced MK transcription. Interestingly, E2 enhanced MK expression in accordance with increase of EMT, whereas knockdown of MK could block EMT under E2 stimulation. Importantly, through analyzing lung adenocarcinoma tissues, there was indeed a correlation among levels of E2, MK, and EMT-related protein expression. Taken together, we reported a previously unrecognized mechanism on E2 in the regulation of MK expression and proved that MK plays a pivotal role in progression of E2-regulated EMT.

A conjugate of an anti-midkine single-chain variable fragment to doxorubicin inhibits tumor growth

Doxorubicin (DOX) was conjugated to a single-chain variable fragment (scFv) against human midkine (MK), and the conjugate (scFv-DOX) was used to target the chemotherapeutic agent to a mouse solid tumor model in which the tumor cells expressed high levels of human MK. The His-tagged recombinant scFv was expressed in bacteria, purified by metal affinity chromatography, and then conjugated to DOX using oxidative dextran (Dex) as a linker. The molecular formula of this immunoconjugate was scFv(Dex)_1.3(DOX)₂₀. In vitro apoptosis assays showed that the scFv-DOX conjugate was more cytotoxic against MK-transfected human adenocarcinoma cells (BGC823-MK) than untransfected cells (55.3 ± 2.4 vs 22.4 ± 3.8%) for three independent experiments. Nude mice bearing BGC823-MK solid tumors received scFv-DOX or equivalent doses of scFv + DOX for 2 weeks and tumor growth was more effectively inhibited by the scFv-DOX conjugate than by scFv + DOX (51.83% inhibition vs 40.81%). Histological analysis of the tumor tissues revealed that the highest levels of DOX accumulated in tumors from mice treated with scFv-DOX and this resulted in more extensive tumor cell death than in animals treated with the equivalent dose of scFv + DOX. These results show that the scFv-DOX conjugate effectively inhibited tumor growth in vivo and suggest that antigen-specific scFv may be competent drug-carriers.

Involvement of midkine expression in the inhibitory effects of low-frequency magnetic fields on cancer cells

Effects of magnetic fields (MFs) on cancer cells may depend on cell type and exposure conditions. Gene expression levels are different among cancer cells. However, the effect of MFs on cancer cells with different gene expressions is still unclear. In this study, the cancer cell lines BGC-823, MKN-45, MKN-28, A549, SPC-A1, and LOVO were exposed to a low-frequency MF. Specific parameters of MFs were determined. Furthermore, the potential of the MF to influence cancer cell growth with midkine (MK) expression was evaluated. Cell proliferation and cell cycle were detected using the CCK-8 assay and flow cytometry. Cell ultrastructure was observed by transmission electron microscopy. BGC-823 cells with over-expression of MK (BGC-MK cells) and stanniocalcin-1 were generated by plasmid construction and transfection. Results showed that exposure to a 0.4-T, 7.5 Hz MF inhibited the proliferation of BGC-823, MKN-28, A549, and LOVO cells, but not MKN-45 and SPC-A1 cells. Moreover, the inhibitory effect of the MF on BGC-MK cells was lower (12.3%) than that of BGC-823 cells (20.3%). Analysis of the cell cycle showed that exposure to the MF led to a significant increase in the S phase in BGC-823 cells, but not in BGC-MK cells. In addition, organelle morphology was modified in BGC-823 cells exposed to the MF. These results suggest that exposure to a 0.4-T, 7.5 Hz MF could inhibit tumor cell proliferation and disturb the cell cycle. The alteration of MK expression in cancer cells may be related to the inhibitory effect of the MF on these cells.

Midkine positively regulates the proliferation of human gastric cancer cells

Midkine (MDK), a heparin-binding growth factor, modulates the proliferation and migration of various cells, is often highly expressed in many malignant tumors, and may act as an oncoprotein. We found that MDK is overexpressed in clinical human gastric cancer tissues relative to its expression in adjacent noncancerous tissues. To further investigate the biological activities of MDK in gastric cancer, we introduced the MDK gene into human SGC7901 gastric cancer cells, where it contributed to the proliferation of SGC7901 cells in vitro and in vivo. Conversely, the knockdown of MDK expression by siRNA resulted in significantly reduced proliferation of BGC823 cells. Our study also shows that MDK activates both the Akt and ERK1/2 pathways and upregulates the expression of several cell-cycle-related proteins, including cyclin A, cyclin D1, Cdk2, Cdk4, and Cdk6, which in part explains the contribution of MDK to gastric cancer cell survival and growth. These results demonstrate that MDK contributes to gastric cancer cell proliferation and suggest that it plays an important role in the development of human gastric cancer.