Expression of midkine in the early stage of carcinogenesis in human colorectal cancer

Targeting Bmi1 for Enhancing Anoikis Sensitivity and Inhibiting Metastasis in Colorectal Cancer

BACKGROUND/AIM

Patients diagnosed with advanced metastatic colorectal cancer (CRC) confront a bleak prognosis characterized by low survival rates. Anoikis, the programmed apoptosis resistance exhibited by metastatic cancer cells, is a crucial factor in this scenario.

MATERIALS AND METHODS

We employed bulk flow cytometry and RT-qPCR assays, conducted in vivo experiments with mice and zebrafish, and analyzed patient tissues to examine the effects of the B cell-specific Moloney murine leukemia virus insertion site 1 (Bmi1)-midkine (MDK) axis on the cellular response to anoikis. Bmi1 is pivotal in tumorigenesis. This study elucidated the involvement of Bmi1 in conferring anoikis resistance in CRC and explored its downstream targets associated with metastasis.

RESULTS

Elevated levels of Bmi1 expression correlated with distant metastasis in CRC. Suppression of Bmi1 significantly diminished the metastatic potential of CRC cells. Inhibition of Bmi1 led to an increase in the proportion of apoptotic SW620 cells detached from the matrix. This effect was further enhanced by the addition of irinotecan, a topoisomerase I inhibitor. Furthermore, Bmi1 was found to synergize with MDK in modulating CRC viability, with consistent expression patterns observed in in vivo models and clinical tissue specimens. In summary, Bmi1 acted as a regulator of CRC metastatic capability by conferring anoikis resistance. Additionally, it collaborated with MDK to facilitate invasion and distant metastasis.

CONCLUSION

Targeting Bmi1 may offer a promising adjunctive therapeutic strategy when administering traditional chemotherapy regimens to patients with advanced CRC.

Spatial and single-cell colocalisation analysis reveals MDK-mediated immunosuppressive environment with regulatory T cells in colorectal carcinogenesis

BACKGROUND

Cell-cell interaction factors that facilitate the progression of adenoma to sporadic colorectal cancer (CRC) remain unclear, thereby hindering patient survival.

METHODS

We performed spatial transcriptomics on five early CRC cases, which included adenoma and carcinoma, and one advanced CRC. To elucidate cell-cell interactions within the tumour microenvironment (TME), we investigated the colocalisation network at single-cell resolution using a deep generative model for colocalisation analysis, combined with a single-cell transcriptome, and assessed the clinical significance in CRC patients.

FINDINGS

CRC cells colocalised with regulatory T cells (Tregs) at the adenoma-carcinoma interface. At early-stage carcinogenesis, cell-cell interaction inference between colocalised adenoma and cancer epithelial cells and Tregs based on the spatial distribution of single cells highlighted midkine (MDK) as a prominent signalling molecule sent from tumour epithelial cells to Tregs. Interaction between MDK-high CRC cells and SPP1+ macrophages and stromal cells proved to be the mechanism underlying immunosuppression in the TME. Additionally, we identified syndecan4 (SDC4) as a receptor for MDK associated with Treg colocalisation. Finally, clinical analysis using CRC datasets indicated that increased MDK/SDC4 levels correlated with poor overall survival in CRC patients.

INTERPRETATION

MDK is involved in the immune tolerance shown by Tregs to tumour growth. MDK-mediated formation of the TME could be a potential target for early diagnosis and treatment of CRC.

FUNDING

Japan Society for the Promotion of Science (JSPS) Grant-in-Aid for Science Research; OITA Cancer Research Foundation; AMED under Grant Number; Japan Science and Technology Agency (JST); Takeda Science Foundation; The Princess Takamatsu Cancer Research Fund.

Midkine (MDK) growth factor: a key player in cancer progression and a promising therapeutic target

Midkine is a heparin-binding growth factor, originally reported as the product of a retinoic acid-responsive gene during embryogenesis, but currently viewed as a multifaceted factor contributing to both normal tissue homeostasis and disease development. Midkine is abnormally expressed at high levels in various human malignancies and acts as a mediator for the acquisition of critical hallmarks of cancer, including cell growth, survival, metastasis, migration, and angiogenesis. Several studies have investigated the role of midkine as a cancer biomarker for the detection, prognosis, and management of cancer, as well as for monitoring the response to cancer treatment. Moreover, several efforts are also being made to elucidate its underlying mechanisms in therapeutic resistance and immunomodulation within the tumor microenvironment. We hereby summarize the current knowledge on midkine expression and function in cancer development and progression, and highlight its promising potential as a cancer biomarker and as a future therapeutic target in personalized cancer medicine.

Diagnostic impact of high serum midkine level in patients with gastric cancer

AIM

We evaluated the diagnostic impact of serum midkine (s-MK) levels in patients with gastric cancer using a monoclonal antibody enzyme-linked immunosorbent assay system (ELISA) to detect s-MK levels.

METHODS

Serum samples were obtained from 131 patients with gastric cancer including stage I (n = 71), stage II (n = 28), stage III (n = 16), and stage IV (n = 16) before surgery. Serum samples were analyzed using ELISA to detect soluble midkine. A cut-off value was fixed at 421 pg/mL, and the sample divided into two groups: a high s-MK group and a low s-MK group. Clinicopathological factors and prognosis were compared between these two groups using univariate and multivariate analyses. Comparison of two groups was analyzed by Fisher's exact probability test. Statistical significance was considered at P < 0.05.

RESULTS

High s-MK was significantly associated with high carcinoembryonic antigen (CEA) (P < 0.01). Positive rate of s-MK was higher than the positive rates of CEA in patients with stage I/II gastric cancer. Combination with CEA + CA19-9 + s-MK increased the positive rates of patients with stage I/II gastric cancer. No other clinicopathological factors were associated with s-MK. Although the high s-MK group showed worse overall survival than the low s-MK group, the difference was not statistically significant.

CONCLUSION

s-MK level is increased even during early-stage gastric cancer. Combined with s-MK, the positive rate of CEA + CA19-9 was increased in patients with stage I/II gastric cancer.

Influence of Menopause on Inflammatory Cytokines during Murine and Human Bone Fracture Healing

Postmenopausal females display a chronic inflammatory phenotype with higher levels of circulating pro-inflammatory cytokines. Furthermore, the inflammatory response to injury may be altered under estrogen-deficiency, because it was shown previously that estrogen-deficient mice displayed increased levels of the inflammatory cytokines Midkine (Mdk) and Interleukin-6 (IL-6) in the early fracture hematoma. Because a balanced immune response to fracture is required for successful bone regeneration, this might contribute to the delayed fracture healing frequently observed in osteoporotic, postmenopausal fracture patients. In this study, we aimed to investigate whether further cytokines in addition to Mdk and IL-6 might be affected by estrogen-deficiency after fracture in mice and whether these cytokines are also relevant during human fracture healing. Additionally, we aimed to investigate whether serum from male vs. female fracture patients affects osteogenic differentiation of human mesenchymal stem cells (MSCs). To address these questions, female mice were either sham-operated or ovariectomized (OVX) and subjected to standardized femur osteotomy. A broad panel of pro- and anti-inflammatory cytokines was determined systemically and locally in the fracture hematoma. In a translational approach, serum was collected from healthy controls and patients with an isolated fracture. Mdk and IL-6 serum levels were determined at day 0, day 14 and day 42 after fracture. Subgroup analysis was performed to investigate differences between male and female fracture patients after menopause. In an in vitro approach, human MSCs were cultured with the collected patient serum and osteogenic differentiation was assessed by qPCR and alkaline-phosphatase staining. Our results suggest an important role for the pro-inflammatory cytokines Mdk and IL-6 in the response to fracture in estrogen-deficient mice among all of the measured inflammatory mediators. Notably, both cytokines were also significantly increased in the serum of patients after fracture. However, only Mdk serum levels differed significantly between male and female fracture patients after menopause. MSCs cultivated with serum from female fracture patients displayed significantly reduced osteogenic differentiation, which was attenuated by Mdk-antibody treatment. In conclusion, our study demonstrated increased Mdk levels after fracture in OVX mice and female fracture patients after menopause. Because Mdk is a negative regulator of bone formation, this might contribute to impaired osteoporotic fracture healing.

Lentivirus-mediated RNAi knockdown of insulin-like growth factor-1 receptor inhibits the growth and invasion of hepatocellular carcinoma via down-regulating midkine expression

The insulin-like growth factor-1 receptor (IGF-1R) overexpression contributes to the development of a variety of cancers. The present study explored the role of IGF-1R in the development and progression of hepatocellular carcinoma (HCC) and the possibility of IGF-1R silencing by lentivirus-mediated RNA interference (RNAi) as a therapeutic target for HCC. We showed that IGF-1R mRNA was up-regulated in Huh7 and Hep3B cells and human HCC tissues, and that IGF-1R knockdown by RNAi led to decreased proliferation, apoptosis induction, and decreased migration and invasion of Huh7 and Hep3B cells. Further, the in vivo study indicated that IGF-1R knockdown markedly diminished the tumorigenesis and metastasis of Huh7 xenograft. Moreover, the intratumoral administration of lentivirus-IGF-1R siRNA led to significant tumor growth inhibition in an established Huh7 xenograft model. Mechanistic investigations showed that midkine was found to be the most significantly down-regulated protein in Huh7 cells with IGF-1R knockdown, and ectopic overexpression of midkine significantly rescued inhibition of Huh7 cell proliferation, migration, and invasion caused by IGF-1R suppression. Collectively, these data suggest that IGF-1R inhibition by RNAi can significantly suppress HCC growth and invasion at least partially through down-regulating midkine expression, and IGF-1R is a potential target for HCC gene therapy.

Dual inhibition of P-glycoprotein and midkine may increase therapeutic effects of anticancer drugs

Multidrug resistance (MDR) to chemotherapy may significantly affect the outcome of cancer treatment. ATP-dependent drug efflux pumps, including P-glycoprotein (P-gp), contribute to the resistance of various chemotherapeutic agents. Overexpression of P-gp in tumor cells induces chemoresistance via pumping the anticancer drugs out of the cells. In addition to taking part in many biological processes such as development, reproduction and repair, midkine (MK) also plays important roles in the pathogenesis of malignant diseases as well as in the regulation of MDR. Although, the mechanisms of action of P-gp and MK are different, overexpression of both proteins prevents the accumulation of many chemotherapeutics in tumor cells, leading to decreased therapeutic effects of anticancer drugs. Therefore, identification of the result of dual inhibition of P-gp and MK in overcoming chemoresistance may enhance the likelihood for a more efficient chemotherapy.

Suppression of midkine gene promotes the antitumoral effect of cisplatin on human gastric cancer cell line AGS in vitro and in vivo via the modulation of Notch signaling pathway

Midkine (MK) is reported to be associated with the clinical stages and distant metastases in gastric cancer, and to positively regulate the proliferation of human gastric cancer cells. However, the possible mechanisms of MK in the development of gastric cancer are still not fully clarified. In this study, the therapeutic effect of MK inhibition in gastric cancer in vivo and in vitro was investigated, by knock-down of MK expression with a small interfering RNA (siRNA). MK was expressed in gastric carcinoma tissues and cancer cells. The cytotoxic effect of cisplatin on AGS cells in vitro was attenuated by recombinant human MK, but was promoted by suppressing MK expression via downregulating the Notch signaling pathway-related proteins (Notch 1, Notch 2, Delta-like 1 and Jagged 1). Suppression of MK expression also promoted the inhibitory effect of cisplatin on AGS cells in vivo. In concusion, suppression of midkine gene promoted the antitumoral effect of cisplatin on human gastric cell line AGS in vitro and in vivo via Notch signaling pathway.

Midkine is overexpressed in acute pancreatitis and promotes the pancreatic recovery in L-arginine-induced acute pancreatitis in mice

BACKGROUND AND AIM

Midkine (MK) is involved in the pathogenesis of numerous malignancies, but the expression and effect of MK in acute pancreatitis (AP) have not been well studied and documented.

METHODS

In this study, the expression of MK was assayed in mice with L-arginine-induced AP. A recombinant human MK (rhMK) was introduced in this study to test the effect of MK on the L-arginine-induced AP. Serum amylase and lipase were assayed. Pancreas tissue samples were also collected for the evaluation of histological injury. Western blot and immunochemical staining of α-amylase and proliferating cell nuclear antigen were applied for the study of acinar regeneration in the pancreas.

RESULTS

The elevation of MK expression was found in mice with AP induced by L-arginine. After rhMK administration, rhMK did not affect the severity of acute pancreatic injury in acute phase in L-arginine-induced pancreatitis in mice, in accordance with changes of serum amylase and lipase and the histological evaluation. But during the recovery phase, the area of remaining acinar cells was increased and the fibrosis was reduced in rhMK-treated mice. Furthermore, the expression of proliferating cell nuclear antigen and α-amylase was also upregulated after rhMK treatment.

CONCLUSION

Midkine is over-expressed during AP in the animal model. Recombinant MK could promote the recovery of L-arginine-induced pancreatitis in mice. Therefore, MK may be involved in the regeneration of acinar cells in AP, and rhMK may be a possible therapeutic intervention for the repairment of AP.

Midkine is up-regulated in both cancerous and inflamed bowel, reflecting lymph node metastasis in colorectal cancer and clinical activity of ulcerative colitis

Midkine is a multifunctional cytokine and growth factor displaying proinflammatory and pro-tumorigenic activity. Its association with bowel diseases has not been fully elucidated. Our purpose was to delineate midkine expression pattern by RT-qPCR in inflamed/cancerous bowel (n=208) and whole blood (n=150) in colorectal cancer (CRC), Crohn's disease (CD), and ulcerative colitis (UC) and to evaluate midkine dynamics in early postoperative period following colorectal surgery. The expression of midkine was significantly up-regulated in stage III CRC and independently associated with lymph node metastasis. The expression of midkine in whole blood was up-regulated solely in N1 CRC. Midkine expression in cancer-free tissue (CRC) was also elevated and dependent on CRC advancement. In IBD, inflammation increased the bowel expression of midkine solely in UC, in a manner proportional to the disease clinical activity. Large and small bowel differed with respect to the expression of midkine in quiescent tissue (higher in small bowel) and to its correlation pattern with chemokines (in a large bowel) and angiogenic factors and cell cycle regulators (in a small bowel). Circulating midkine and its expression in whole blood dropped directly following colorectal surgery; however, the concentration of midkine in serum was restored on postoperative day three. Midkine is involved in bowel inflammation in UC and lymph node metastasis in CRC, rendering midkine an attractive target for their treatment. Owing to midkine elevation in early postoperative period and its overexpression in tumor-adjacent tissue, targeting midkine might be considered also as a prevention of CRC recurrence following curative tumor resection.

Midkine: A Novel Biomarker to Predict Malignancy in Patients with Nodular Thyroid Disease

Background. Midkine (MK), a new heparin-binding growth factor, plays important roles in a variety of biological phenomena such as carcinogenesis, inflammation, and angiogenesis. In this study, we aimed to evaluate serum midkine (SMK) and nodular midkine (NMK) levels in patients with thyroid nodules to predict malignancy and whether there was any association between. Methods. A total of 105 patients (74 women, 31 men) with thyroid nodules were enrolled. The levels of SMK and NMK were measured. Any possible correlation between SMK, NMK, and biochemical, cytopathological, or radiological variables was investigated. Results. Both SMK and NMK were found to be higher in hypoechoic nodules with an irregular border and without a halo (p < 0.05). Serum MK levels were significantly higher in nodules with microcalcifications than nodules with macrocalcification or without calcification (p = 0.001). SMK levels were found to be correlated with NMK levels (SMK 0.63 ng/ml versus 1.04 ng/mL and NMK 0.55 ng/mL versus 0.55 ng/mL, r (2) = 0.54, p < 0.001). Conclusion. Both SMK and NMK can predict tumorigenesis of highly malignant/suspicious thyroid cytopathology and also well correlated with sonographic features of thyroid nodules. We suggest that MK levels may serve as an alternative biomarker, in conjunction with the cytopathological results in preoperative assessment of thyroid nodules.

The clinical and prognostic significance of midkine in breast cancer patients

Midkine overexpression has been shown to be a tumor biomarker in several types of human cancer, but little is known about the clinical significance of midkine in breast cancer patients. The aim of this study was to analyze the expression of midkine in breast cancer and its correlation with clinicopathological characteristics, including breast cancer patient's survival. The expression status of midkine in breast cancer from Gene Expression Omnibus (GEO accession number: GDS3853) was observed initially. Furthermore, the expression of midkine messenger RNA (mRNA) and protein was examined in breast cancer and normal mammary tissues through real-time PCR and immunohistochemistry. Moreover, the relationship of midkine protein expression with clinical characteristics of 170 breast cancer patients was analyzed by immunohistochemistry. In our results, midkine was up-expressed in breast cancer tissues compared with normal mammary tissues in microarray data (GDS3853). Midkine mRNA and protein expression was significantly increased in breast cancer tissues than in normal mammary tissues. By immunohistochemistry, high levels of midkine protein were positively associated with the status of clinical stage, T classification, N classification, and M classification in breast cancer patients. Furthermore, midkine overexpression was an independent poor prognostic indicator for the survival of patients with breast cancer. In conclusion, overexpression of midkine protein serves as an unfavorable prognostic biomarker in breast cancer patients.

Midkine proteins in cardio-vascular disease. Where do we come from and where are we heading to?

Midkine is a recently identified new growth factor/cytokine with pleiotropic functions in the human organism. First discovered in the late eighties, midkines have now become the subject of numerous studies in cardiovascular, neurologic, renal diseases and also various types of cancers. We summarize here the most important functions of midkine in cardiovascular diseases, emphasizing its role in inflammation and its antiapoptotic and proangiogenetic effects. Midkine has multiple roles in the organism, with the specific feature of being either beneficial or harmful depending on which tissue it acts on. Even though midkine has been shown to have cardiac protective effects against acute ischemia/reperfusion injury and to inhibit cardiac remodeling, it also promotes intimal hyperplasia and vascular stenosis. As such, different therapeutic strategies are currently being evaluated, consisting of administering either midkine proteins or midkine inhibitors depending on the desired outcome. More data is gathering to suggest that these novel therapies could become an adjunctive to standard cardiovascular therapy. Nonetheless, much is still to be learned about midkine. The encouraging results up till now require further studying in order to fully understand the complete profile of its mechanism of action and the clinical safety and efficacy of novel therapeutic opportunities offered by midkine molecular targeting.

Inhibitory effect of midkine-binding peptide on tumor proliferation and migration

BACKGROUND

To investigate the inhibitory effect of midkine-binding peptides on human umbilical vein endothelial cells (HUVECs) proliferation and angiogenesis of xenograft tumor.

METHODS

The midkine-binding peptides were panned by Ph.D.-7(™) Phage Display Peptide Library Kit, and the specific binding activities of positive clones to target protein were examined by phage ELISA. The effect of midkine-binding peptides on proliferation of HUVECs was confirmed by MTT test. The xenograft tumor model was formed in BALB/c mice with the murine hepatocarcinoma cells H22 (H22). Microvessel density (MVD) was analyzed by immunohistochemistry of factor VIII staining.

RESULTS

Midkine-binding peptides have the inhibitory effects on tumor angiogenesis, a proliferation assay using human umbilical vein endothelial cells (HUVECs) indicated that particular midkine-binding peptides significantly inhibited the proliferation of the HUVECs. Midkine-binding peptides were also observed to efficiently suppress angiogenesis induced by murine hepatocarcinoma H22 cells in BALB/c nude mice.

CONCLUSION

The midkine-binding peptides can inhibit solid tumor growth by retarding the formation of new blood vessels. The results indicate that midkine-binding peptides may represent potent anti-angiogenesis agents in vivo.

Measuring midkine: the utility of midkine as a biomarker in cancer and other diseases

Midkine (MK) is a pleiotropic growth factor prominently expressed during embryogenesis but down-regulated to neglible levels in healthy adults. Many published studies have demonstrated striking MK overexpression compared with healthy controls in various pathologies, including ischaemia, inflammation, autoimmunity and, most notably, in many cancers. MK expression is detectable in biopsies of diseased, but not healthy, tissues. Significantly, because it is a soluble cytokine, elevated MK is readily apparent in the blood and other body fluids such as urine and CSF, making MK a relatively convenient, accessible, non-invasive and inexpensive biomarker for population screening and early disease detection. The first diagnostic tests that quantify MK are just now receiving regulatory clearance and entering the clinic. This review examines the current state of knowledge pertaining to MK as a biomarker and highlights promising indications and clinical settings where measuring MK could make a difference to patient treatment. I also raise outstanding questions about reported variants of MK as well as MK's bio-distribution in vivo. Answering these questions in future studies will enhance our understanding of the significance of measured MK levels in both patients and healthy subjects, and may reveal further opportunities for measuring MK to diagnose disease. MK has already proven to be a biomarker that can significantly improve detection, management and treatment of cancer, and there is significant promise for developing further MK-based diagnostics in the future.

Involvement of midkine in neuroblastoma tumourigenesis

Midkine is highly expressed in various cancers, including neuroblastoma, one of the most malignant paediatric solid tumours known. Also, it has been shown to be useful as a tumour marker, a prognosis factor and a target of molecular therapy. Several molecular tools (e.g. siRNA, antibodies and RNA aptamer) have been used to establish a midkine-targeted therapy. The involvement of midkine in tumourigenesis has been demonstrated in vivo in a mouse neuroblastoma model, where targeting it with an RNA aptamer was shown to be an effective treatment for xenografted tumours. Chemoresistance is one of the notable phenotypes regulated by midkine in various cancer cell types. In pancreatic tumours and glioma cells, midkine is expressed in chemoresistant cells and is involved in the survival of these cells in the presence of anticancer drugs. In contrast to these tumours, midkine was found to be expressed in every neuroblastoma cell line tested and the knockdown of midkine alone was sufficient to suppress their growth. These results indicate that neuroblastoma cells are highly dependent on midkine and that a midkine-targeted therapy could exert a significant effect in these cells. However, to achieve a midkine-targeted therapy for high-risk neuroblastoma patients, the further refinement of the RNA aptamer or antibody as tools and the elucidation of midkine signalling are immediate issues that need to be resolved. Regarding the latter, although it has been shown that Notch2 functions as a receptor in neuroblastoma cells, it is likely that other receptors (e.g. anaplastic lymphoma kinase) are also involved in midkine signalling.

LINKED ARTICLES

This article is part of a themed section on Midkine. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-4.

The signal peptide of the tumor-shared antigen midkine hosts CD4+ T cell epitopes

BACKGROUND

The CD4 T cell response to the tumor antigen Midkine was unknown.

RESULTS

Most of the T cell response to Midkine relies on T cell epitopes contained in its signal peptide.

CONCLUSION

The signal peptide of Midkine is accessible to HLA class II pathway for CD4 T cell presentation.

SIGNIFICANCE

It is a new function for signal peptides to contribute to tumor-specific CD4 T cell response. Because of the key role of CD4 T cell response in immunity to tumors, we investigated the CD4(+) T cell response to the recently identified tumor antigen Midkine (MDK). By weekly stimulations of T lymphocytes harvested from seven HLA-DR-typed healthy donors, we derived CD4(+) T cell lines specific for eight MDK peptides. Most of the T cell lines reacted with the peptides 9-23 and 14-28, located in and overlapping the MDK signal peptide, respectively. Accordingly, the MDK signal peptide appeared to be rich in good binders to common HLA-DR molecules. The peptide 9-23-specific T cell lines were specifically stimulated by autologous dendritic cells loaded with lysates of MDK-transfected cells or with lysates of tumor cells naturally expressing the MDK protein. One T cell line was stimulated by HLA-compatible MDK-transfected tumor cells. By contrast, the peptide 14-28-specific T cell lines were not stimulated in any of these conditions. Our data demonstrate that CD4(+) T cell epitopes present in the signal peptide can be accessible to recognition by CD4(+) T cells and may therefore contribute to tumor immunity, whereas a peptide overlapping the junction between the signal peptide and the mature protein is not.

In-depth characterization of the secretome of colorectal cancer metastatic cells identifies key proteins in cell adhesion, migration, and invasion

Liver metastasis in colorectal cancer is the major cause of cancer-related deaths. To identify and characterize proteins associated with colon cancer metastasis, we have compared the conditioned serum-free medium of highly metastatic KM12SM colorectal cancer cells with the parental, poorly metastatic KM12C cells using quantitative stable isotope labeling by amino acids in cell culture (SILAC) analyses on a linear ion trap-Orbitrap Velos mass spectrometer. In total, 1337 proteins were simultaneously identified in SILAC forward and reverse experiments. For quantification, 1098 proteins were selected in both experiments, with 155 proteins showing >1.5-fold change. About 52% of these proteins were secreted directly or using alternative secretion pathways. GDF15, S100A8/A9, and SERPINI1 showed capacity to discriminate cancer serum samples from healthy controls using ELISAs. In silico analyses of deregulated proteins in the secretome of metastatic cells showed a major abundance of proteins involved in cell adhesion, migration, and invasion. To characterize the tumorigenic and metastatic properties of some top up- and down-regulated proteins, we used siRNA silencing and antibody blocking. Knockdown expression of NEO1, SERPINI1, and PODXL showed a significant effect on cellular adhesion. Silencing or blocking experiments with SOSTDC1, CTSS, EFNA3, CD137L/TNFSF9, ZG16B, and Midkine caused a significant decrease in migration and invasion of highly metastatic cells. In addition, silencing of SOSTDC1, EFNA3, and CD137L/TNFSF9 reduced liver colonization capacity of KM12SM cells. Finally, the panel of six proteins involved in invasion showed association with poor prognosis and overall survival after dataset analysis of gene alterations. In summary, we have defined a collection of proteins that are relevant for understanding the mechanisms underlying adhesion, migration, invasion, and metastasis in colorectal cancer.

Midkine promotes neuroblastoma through Notch2 signaling

Midkine is a heparin-binding growth factor highly expressed in various cancers, including neuroblastoma, the most common extracranial pediatric solid tumor. Prognosis of patients with neuroblastoma in which MYCN is amplified remains particularly poor. In this study, we used a MYCN transgenic model for neuroblastoma in which midkine is highly expressed in precancerous lesions of sympathetic ganglia. Genetic ablation of midkine in this model delayed tumor formation and reduced tumor incidence. Furthermore, an RNA aptamer that specifically bound midkine suppressed the growth of neuroblastoma cells in vitro and in vivo in tumor xenografts. In precancerous lesions, midkine-deficient MYCN transgenic mice exhibited defects in activation of Notch2, a candidate midkine receptor, and expression of the Notch target gene HES1. Similarly, RNA aptamer-treated tumor xenografts also showed attenuation of Notch2-HES1 signaling. Our findings establish a critical role for the midkine-Notch2 signaling axis in neuroblastoma tumorigenesis, which implicates new strategies to treat neuroblastoma.

Midkine mRNA level in peripheral blood mononuclear cells is a novel biomarker for primary non-small cell lung cancer: a prospective study

BACKGROUND AND OBJECTIVES

Midkine (MK) mRNA was highly expressed in various human cancer tissues and cells. The present study aimed to investigate whether MK mRNA level in peripheral blood mononuclear cells (PBMC) could serve as a diagnostic biomarker for patients having primary non-small cell lung cancer (NSCLC).

METHODS

MK mRNA level in PBMC from 87 patients with primary NSCLC, 35 patients with lung benign lesion (LEL), and 30 healthy volunteers was analyzed by real-time quantitative RT-PCR. The levels of serum carcinoembryonic antigen, carbohydrate antigen 125 (CA125), and neuron-specific enolase were detected by chemiluminescent microparticle enzyme immunoassay.

RESULTS

PBMC MK mRNA level was significantly higher in patients with primary NSCLC than that in other groups (P < 0.001), while there was no significant difference between LEL patients and healthy volunteers (P > 0.05). Higher MK mRNA level was correlated with clinical stages (P = 0.026), differentiation (P = 0.025), and lymph node metastasis (P = 0.022) of NSCLC. Using a cutoff of 0.0063, the sensitivity and specificity of MK mRNA levels to differentiate between patients with NSCLC and patients with LEL were 57.47 and 93.33 %,and it were 56.32 and 93.33 % for patients with NSCLC and healthy volunteers, respectively. Furthermore, multivariate analysis indicated that PBMC MK mRNA level above the cutoff value presented a chance of 11-fold higher for NSCLC occurrence.

CONCLUSIONS

MK mRNA level in PBMC may be a potential non-invasive molecular marker for the diagnosis of primary NSCLC.

Novel functional proteins interact with midkine in hepatic cancer cells

BACKGROUND

Midkine is a heparin-binding growth factor that promotes the proliferation, survival, migration and differentiation of various target cells. Midkine plays an important role in tumorigenesis and tumor progression, and is overexpressed in many human malignant tumors. Patients with high tumor midkine expression frequently have a worse prognosis than those with low expression. The present study was designed to investigate the interaction network of midkine in hepatic cancer cells, and to elucidate its role in hepatocellular carcinoma.

METHODS

DNA encoding full-length midkine was cloned into pDBLeu vector to serve as bait in yeast two-hybrid screening to identify interacting proteins. Candidate proteins were examined on SC-Leu-Trp-His+3-AT (20 mmol/L) plates and assayed for X-gal activity, then sequenced and classified according to the GenBank. Finally, identified proteins were expressed by the in vitro expression system pCMVTnT, and protein interactions were confirmed by co-immunoprecipitation.

RESULTS

Using the yeast two-hybrid system, we found 6 proteins that interacted with midkine: NK-kappa-B inhibitor alpha (I-κ-B-alpha), Dvl-binding protein naked cuticle 2, granulin, latent active TGF-beta binding protein 3, latent active TGF-beta binding protein 4, and phospholipid scramblase 1. In vitro co-immunoprecipitation demonstrated that all identified proteins directly interacted with midkine.

CONCLUSION

The identification of midkine-interacting proteins in hepatic cancer cells indicates that midkine is a multifunctional factor that may participate in cell migration, differentiation, and proliferation, and is also associated with the multicellular response feedback during the development of hepatocellular carcinoma.

Midkine in the pathology of cancer, neural disease, and inflammation

Midkine (MK) is a heparin-binding growth factor involved in various cellular processes such as cellular proliferation, survival, and migration. In addition to these typical growth factor activities, MK exhibits several other activities related to fibrinolysis, blood pressure, host defense and other processes. Many cell-surface receptors have been identified to account for the multiple biological activities of MK. The expression of MK is frequently upregulated in many types of human carcinoma. Moreover, blood MK levels are closely correlated with patient outcome. Knockdown and blockade of MK suppress tumorigenesis and tumor development. Thus, MK serves as a tumor marker and a molecular target for cancer therapy. Furthermore, there is growing evidence that MK plays pivotal roles in neural and inflammatory diseases. Understanding of the mechanisms of action of MK is expected to create new therapeutic options for several human diseases.

Tumor location determines midkine level and its association with the disease progression in colorectal cancer patients: a pilot study

PURPOSE

The purpose of this study was to evaluate midkine, multipotential cytokine, and growth factor in colorectal cancer (CRC) stratified by tumor location.

METHODS

Midkine was assessed immunoenzymatically in paired cancerous and noncancerous tissues from 53 CRCs and referred to CRC stage, tumor location, and size, and circulating cytokine levels.

RESULTS

Midkine was higher in cancerous versus noncancerous tissue in 98 % cases (424.2 vs. 31.1 pg/mg, p < 0.0001). Mean fold increase was 30.1; in 72.5 %, the relative increase was over fivefold. Midkine upregulation was more pronounced in colon than in rectum (fold increase: 36.6 vs. 12.7, p = 0.005) due to higher midkine level in noncancerous rectal than colonic tissue (45.5 vs. 26.2 pg/mg, p = 0.074). Tumor location affected midkine association with CRC stage. Midkine fold change was higher in advanced stages of rectal cancers (16.8 vs. 5.3, respectively in III/IV vs. I/II, p = 0.013), while it tended to be lower in colonic ones (25.3 vs. 47.8, p = 0.134). In addition, fold change in midkine level was higher in rectal N1 than N0 cancers (17.3 vs. 16.5, p = 0.032), while it tended to be lower in colonic cancers (23.6 vs. 50.1, p = 0.085). Midkine negatively correlated with tumor size (r = 0.40, p = 0.017), while it tended to positively correlate with its serum levels (r = 0.45, p = 0.081).

CONCLUSIONS

Midkine is differently expressed in tumors arising from colonic and rectal mucosa, where it may play diverse roles in carcinogenesis. High midkine expression in noncancerous rectal mucosa might contribute to, a characteristic for rectal cancers, higher incidence of local recurrence. Divergent expression of midkine and its association pattern ought to be taken into account while designing midkine-directed therapies for CRC.

Decreased therapeutic effects of noscapine combined with imatinib mesylate on human glioblastoma in vitro and the effect of midkine

BACKGROUND

Glioblastoma (GBM) develops resistance to the advances in chemotherapy leading to poor prognosis and life quality. Consequently, new treatment modalities are needed. Our aims were to investigate the effects of combined noscapine (NOS) and imatinib mesylate (IM) on human GBM in vitro and the role of midkine (MK) in this new combination treatment.

METHODS

Monolayer and spheroid cultures of T98G human GBM cell line were used to evaluate the effects of IM (10 μM), Nos (10 μM) and their combination on cell proliferation and apoptotic indexes, cell cycle, the levels of antiapoptotic MK, MRP-1, p170, PFGFR-α, EGFR, bcl-2 proteins, apoptotic caspase-3 levels, morphology (SEM) and ultrastructure (TEM) for 72 hrs. Results were statistically analyzed using the Student's t-test.

RESULTS

The combination group induced highest decrease in cell proliferation and apoptotic indexes, caspase-3 levels, MRP-1 and PDGFR-α levels. The decrease in p170 levels were lower than IM but higher that NOS. The highest increases were in EGFR, MK, bcl-2 and cAMP levels in the combination group. The G0+G1 cell cycle arrest at the end of 72nd hr was the lowest in the combination group. Apoptotic appearence was observed rarely both in the morphologic and ultrastructural evaluation of the combination group. In addition, autophagic vacuoles which were frequently observed in the IM group were observed rarely.

CONCLUSIONS

The combination of Nos with IM showed antagonist effect in T98G human GBM cells in vitro. This antagonist effect was correlated highly with MK levels. The effects of NOS on MRP-1, MK and receptor tyrosine kinase levels were firstly demonstrated in our report. In addition, we proposed that MK is one of the modulator in the switch of autophagy to cell death or survival/resistance.

Preparation and preliminary characterization of rabbit monoclonal antibodies against human midkine

We prepared rabbit monoclonal antibodies that target human midkine (MK). The MK gene was amplified by PCR from the plasmid pEGFP-MK and subcloned into the prokaryotic expression vector pGEX-1λT to generate an N-terminally glutathione S-transferase (GST)-tagged fusion protein construct. Expression of the GST-MK fusion protein was achieved by IPTG induction in Escherichia coli cells. The expressed protein was purified using the GST system. After verifying purification, the fusion protein was used to immunize rabbits to prepare monoclonal antibodies against human MK by the rabbit hybridoma technique. The hybridomas generated were screened by an enzyme-link immunoassay (ELISA) for specificity, which was further characterized by Western blotting and ELISA. SDS-PAGE analysis showed that the purified protein corresponds to the calculated molecular weight. The GST-MK fusion protein was prepared. At least one hybridoma cell line secreting anti-MK MAb was obtained. Western blotting analysis confirmed the identity of the MAb. The titer of the MAbs measured by an indirect ELISA was 1:64,000. The affinity constant, which was measured by a non-competitive ELISA, was found to be 3.0 × 10(9) M(-1). Western blotting and immunohistochemistry analysis showed that the produced MAbs bind to the MK protein in cancerous tissues. The GST-MK fusion protein was successfully expressed and purified. The MAbs against MK were subsequently prepared, which should further aid research and the application of MK MAbs in clinical settings.

Premature ligand-receptor interaction during biosynthesis limits the production of growth factor midkine and its receptor LDL receptor-related protein 1

Protein production within the secretory pathway is accomplished by complex but organized processes. Here, we demonstrate that the growth factor midkine interacts with LDL receptor-related protein 1 (LRP1) at high affinity (K(d) value, 2.7 nm) not only at the cell surface but also within the secretory pathway during biosynthesis. The latter premature ligand-receptor interaction resulted in aggregate formation and consequently suppressed midkine secretion and LRP1 maturation. We utilized an endoplasmic reticulum (ER) retrieval signal and an LRP1 fragment, which strongly bound to midkine and the LRP1-specialized chaperone receptor-associated protein (RAP), to construct an ER trapper. The ER trapper efficiently trapped midkine and RAP and mimicked the premature ligand-receptor interaction, i.e. suppressed maturation of the ligand and receptor. The ER trapper also diminished the inhibitory function of LRP1 on platelet-derived growth factor-mediated cell migration. Complementary to these results, an increased expression of RAP was closely associated with midkine expression in human colorectal carcinomas (33 of 39 cases examined). Our results suggest that the premature ligand-receptor interaction plays a role in protein production within the secretory pathway.

Midkine: a promising molecule for drug development to treat diseases of the central nervous system

Midkine (MK) is a heparin-binding cytokine, and promotes growth, survival, migration and other activities of target cells. After describing the general properties of MK, this review focuses on MK and MK inhibitors as therapeutics for diseases in the central nervous system. MK is strongly expressed during embryogenesis especially at the midgestation period, but is expressed only at restricted sites in adults. MK expression is induced upon tissue injury such as ischemic brain damage. Since exogenously administered MK or the gene transfer of MK suppresses neuronal cell death in experimental systems, MK has the potential to treat cerebral infarction. MK might become important also in the treatment of neurodegenerative diseases such as Alzheimer's disease. MK is involved in inflammatory diseases by enhancing migration of leukocytes, inducing chemokine production and suppressing regulatory T cells. Since an aptamer to MK suppresses experimental autoimmune encephalitis, MK inhibitors are promising for the treatment of multiple sclerosis. MK is overexpressed in most malignant tumors including glioblastoma, and is involved in tumor invasion. MK inhibitors may be of value in the treatment of glioblastoma. Furthermore, an oncolytic adenovirus, whose replication is under the control of the MK promoter, inhibits the growth of glioblastoma xenografts. MK inhibitors under development include antibodies, aptamers, glycosaminoglycans, peptides and low molecular weight compounds. siRNA and antisense oligoDNA have proved effective against malignant tumors and inflammatory diseases in experimental systems. Practical information concerning the development of MK and MK inhibitors as therapeutics is described in the final part of the review.

Midkine expression in malignant salivary gland tumors and its role in tumor angiogenesis

The aims of this study were to investigate midkine (MK) expression patterns in salivary gland tumors (SGTs) and to evaluate the correlation between MK expression and the degree of malignancy. We performed immunohistochemistry to examine MK expression in specimens of adenoid cystic carcinoma (ACC), mucoepidermoid carcinoma (MEC), and pleomorphic adenoma (PA). In addition, we performed immunohistochemistry for CD31 and measured microvessel density (MVD), which is an indicator of angiogenesis. Immunohistochemistry showed that MK protein expression was significantly higher in specimens of malignant SGTs (ACC [P<0.01] and MEC [P<0.001]) than in benign SGT (PA) samples. Furthermore, MVD values tended to be higher in cases that exhibited high expression of MK, which indicated a significant correlation between the degree of MK expression and MVD (P<0.001). These results suggest that MK may play important roles in malignant transformation and tumor angiogenesis in SGTs.

Midkine: a novel prognostic biomarker for cancer

Since diagnosis at an early stage still remains a key issue for modern oncology and is crucial for successful cancer therapy, development of sensitive, specific, and non-invasive tumor markers, especially, in serum, is urgently needed. Midkine (MK), a plasma secreted protein, was initially identified in embryonal carcinoma cells at early stages of retinoic acid-induced differentiation. Multiple studies have reported that MK plays important roles in tumor progression, and is highly expressed in various malignant tumors. Because increased serum MK concentrations also have been reported in patients with various tumors, serum MK may have the potential to become a very useful tumor marker. Here, we review and discuss the possibility and usefulness of MK as a novel tumor marker.

Midkine in plasma as a novel breast cancer marker

Midkine, a heparin-binding growth factor, is up-regulated in many types of cancer. The aim of this study was to measure plasma midkine levels in patients with breast cancer and to assess its clinical significance. We examined plasma midkine levels in 95 healthy volunteers, 11 patients with ductal carcinoma in situ (DCIS), 111 patients with primary invasive breast cancer without distant metastasis (PIBC), and 25 patients with distant metastatic breast cancer (MBC), using an automatic immunoasssay analyzer (TOSOH AIA system). In PIBC, we studied the correlation between plasma midkine levels and clinicopathological factors. Immunoreactive midkine was detectable in the plasma of healthy volunteers, and a cut-off level of 750 pg/mL was established. In breast cancer patients, plasma midkine levels were increased above normal values. These elevated levels of midkine were seen in one (9.1%) of 11 patients with DCIS, 36 (32.4%) of 111 patients with PIBC, and 16 (64.0%) of 25 patients with MBC. Increased levels of midkine were correlated with menopausal status (P = 0.0497) and nuclear grade (P = 0.0343) in PIBC. Cancer detection rates based on midkine levels were higher than those based on three conventional markers including CA15-3 (P < 0.0001), CEA (P = 0.0077), and NCCST-439 (P < 0.0001). Detection rates of breast cancer using a combination of two conventional tumor markers (CA15-3/CEA, CA15-3/NCCST-439, or CEA/NCCST-439) with midkine is significantly higher than those using combination of three conventional tumor markers. Midkine may be a useful novel tumor marker for detection of breast cancer, superior to conventional tumor markers.

Midkine mRNA is overexpressed in pancreatic cancer

PURPOSE

Midkine (MK) has been reported to be a possible molecular marker for the diagnosis of pancreatic cancer. We investigated the feasibility of quantitative analysis of MK mRNA by quantitative real-time RT-PCR (qRT-PCR) as a promising tool for the diagnosis of pancreatic cancer.

RESULTS

We found that pancreatic cancer tissues expressed significantly higher levels of MK mRNA than intraductal pancreatic mucinous neoplasm (IPMN) and non-neoplastic pancreatic tissues (P < 0.05); in contrast, we did not find any differences in MK mRNA expression between IPMN and non-neoplastic pancreatic tissues. Additionally, we observed that poorly differentiated carcinoma samples expressed higher levels of MK mRNA than well-differentiated carcinoma samples, although a significant difference was not observed.

CONCLUSIONS

The present data suggests that quantitative analysis of MK mRNA provides an objective and sensitive evaluation and may be a promising modality for the diagnosis of pancreatic cancer and the prediction of its prognosis.

Midkine is highly expressed in neuroblastoma tissues

PURPOSE

Neuroblastoma (NBL) is a tumor from neural crest cells, and is the most frequent solid tumor in children. Midkine (MK) is a pleiotropin analogon, which is frequently expressed in neuronal and epithelial tumors and is a marker for a poor clinical outcome. The aims of this study were to assess MK expression in NBL and investigate the correlation with clinical outcome.

METHODS

Fifty-six specimens of NBL were stained for MK on a tissue microarray by immunohistochemistry (IHC). Fresh frozen tumor tissues were used for RNA isolation, and RT-PCR analysis for MK-mRNA expression was performed. Survival data, risk factors and disease stages were correlated with MK status assessed by IHC and RT-PCR analysis.

RESULTS

MK-mRNA expression was found in the majority of the tumor tissues (75%), whereas MK protein could be detected only in 46% of the NBL by IHC. No correlation of MK status with survival, risk factors or disease stage was observed.

CONCLUSION

A majority of NBL express MK-mRNA, whereas not all MK mRNA positive tumors showed also a positive MK IHC staining. The high expression of MK-mRNA expression might present a promising target for new adenovirus-based gene therapeutic approaches for the treatment of NBL.

Plasma midkine level is a prognostic factor for human neuroblastoma

Neuroblastoma is the third-most-common solid tumor of childhood. To date, no reliable blood marker for neuroblastoma has been established. The growth factor midkine is highly expressed in human carcinomas and its knockdown leads to tumor growth suppression in animal models. The present study evaluated the plasma midkine level in human neuroblastoma patients. Plasma samples were obtained from patients found through mass screening, as well as from sporadic neuroblastoma patients. The total number of cases examined was 756. Among them, prognostic information was available for 175 sporadic cases and 287 mass-screening cases. Midkine levels were significantly higher in neuroblastoma patients, including both mass-screening cases and sporadic cases, than in non-tumor controls (P < 0.0001). The midkine level was significantly correlated with the statuses of MYCN amplification, TRKA expression, ploidy, stage and age (P < 0.0001, < 0.0001, = 0.004, < 0.0001 and < 0.0001, respectively), which are known prognostic factors for neuroblastoma. There was a striking correlation between high plasma midkine level and poor prognosis (P < 0.0001). Within sporadic cases, the midkine level was also strikingly higher than in non-tumor controls (P < 0.0001), and correlated with the statuses of MYCN amplification and stage (P = 0.0005 and = 0.003, respectively). There was a significant correlation between high plasma midkine level and poor prognosis (P = 0.04). Taken together, the present data indicate that plasma midkine level is a prognostic factor for human neuroblastoma.

Midkine as a prognostic biomarker in oral squamous cell carcinoma

The aim of this study was to evaluate serum midkine (S-MK) concentrations as a prognostic tumour marker in oral squamous cell carcinoma (OSCC). We measured S-MK concentrations in patients with OSCC and healthy volunteers. In addition, we performed real-time quantitative reverse transcription-PCR analysis and immunohistochemistry with fresh tumour samples. To determine whether S-MK concentrations have prognostic value, we performed survival analyses with clinical information by using the log-rank test. Serum midkine concentrations were significantly higher in patients with OSCC than in healthy controls (P<0.001). Serum midkine concentrations were also significantly increased in early-stage OSCC compared with those of healthy individuals (P<0.001). In addition, immunohistochemistry allowed identification of overexpressed MK protein in OSCC tissues. MK mRNA showed higher expression in OSCC samples compared with normal mucosal samples. Patients in high S-MK groups showed a significantly lower 5-year survival rate compared with patients in low S-MK groups (P<0.05). The increased S-MK concentrations in early-stage OSCC were strongly associated with poor survival. Serum midkine concentrations may thus be a useful marker not only for cancer screening but also for predicting prognosis of OSCC patients.

Midkine and its clinical significance in endometrial carcinoma

Midkine (MK) is a secreted heparin-binding growth factor. Several types of human cancer have increased MK expression with elevated serum levels. The purpose of this study was to determine whether MK was expressed in endometrial carcinoma and to evaluate the clinicopathological significance of serum MK in patients with endometrial carcinoma. Immunohistochemical expression of MK was evaluated in 85 endometrial carcinoma samples and 33 controls. MK expression was significantly higher in the carcinomas than in normal endometrium (P < 0.001). Interestingly, MK expression was highest at the margins of invasion and low in the superficial areas of the tumor samples. Using ELISA, we compared serum MK concentration in 120 endometrial carcinoma patients with the concentration in 46 patients with benign gynecologic tumors. Serum MK value in patients with cancer was significantly higher than that in the patients with benign diseases (P = 0.01). Patients with positive lymph node metastasis or recurrence, or cancer death, had a higher serum MK level (P = 0.008, P = 0.009, respectively). In conclusion, MK immunoreactivity in endometrial carcinoma is significantly higher than in normal endometrium. Additionally, preoperative serum MK levels are significantly correlated with prognosis and the presence of lymph node metastasis. Thus, MK may be a useful serum biomarker for identifying high risk patients of endometrial carcinoma.

Midkine and LDL-receptor-related protein 1 contribute to the anchorage-independent cell growth of cancer cells

The growth factor midkine (MK) is highly associated with cancer progression. Knockdown of MK expression strikingly suppresses tumor growth in nude mice. Thus, MK is a candidate target for cancer treatment. LDL-receptor-related protein 1 (LRP1) is a receptor for MK. We found that among the four ligand-binding domains of LRP1, the N-terminal half of the second domain (designated as MK-TRAP) had the strongest affinity to MK. MK-TRAP bound to MK, but not to HB-GAM/pleiotrophin, basic fibroblast growth factor or platelet-derived growth factor (PDGF)-BB. Exogenous MK-TRAP inhibited the binding between MK and LRP1. G401 cells that transiently or stably overexpress MK-TRAP showed decreased cell growth in monolayer culture and reduced colony formation in soft agar, which could be rescued by exogenous MK administration. MK-TRAP collected from conditioned medium also inhibited anchorage-independent growth of G401 cells and CMT-93 cells. Anti-MK antibody also inhibited the anchorage-independent growth. CMT-93 cells stably expressing MK-TRAP formed smaller tumors in a xenograft nude mouse model than control cells. Moreover, GST-RAP, a potent inhibitor of LRP1, inhibited the anchorage-independent growth of control G401 cells but not that of MK-TRAP stable transformants. Collectively, these data demonstrate a crucial role of MK-LRP1 signaling in anchorage-independent cell growth.

Midkine expression in colorectal tumors: correlation with Ki-67 labeling in sporadic, but not ulcerative colitis-associated ones

Midkine (MK) is a heparin-binding growth factor encoded by a retinoic acid responsive gene. To investigate the possible contribution of MK to genesis of colorectal carcinomas, an immunohistochemical examination of protein expression was conducted in sporadic and ulcerative colitis (UC)-associated tumors. MK expression significantly differed among normal mucosa, adenomas with low-grade dysplasia (LGD), adenomas with high-grade dysplasia (HGD) and invasive adenocarcinomas: MK expression was increased along with tumor progression. UC-associated lesions (regenerative mucosa of UC, UC-associated dysplasia and UC-associated adenocarcinoma) had similar variations. MK expression in UC-associated lesions was significantly higher than in normal mucosa, although there was no significant difference among UC-associated lesions. However, in UC-associated dysplasia, MK expression did not differ between the upper and lower halves, in contrast to adenoma with LGD and HGD, in which MK expression was significantly higher in the upper than lower halves, corresponding to cell proliferative zone. Furthermore, correlations with Ki-67 and single-strand DNA labeling, respectively, reflecting cellular proliferative activity and apoptosis, were noted in sporadic but not UC-associated lesions. These results suggest that MK is involved in genesis/development of sporadic colorectal tumors as well as of UC-associated tumors, but might contribute differently to genesis/development in these two types of tumors.

Clinical significance of midkine expression in pancreatic head carcinoma

Midkine (MK) is a heparin-binding growth factor and a product of a retinoic acid-responsive gene. Midkine is overexpressed in many carcinomas and thought to play an important role in carcinogenesis. However, no studies have been focussed on the role of MK in pancreatic carcinoma. This study sought to evaluate the clinical significance of MK expression in pancreatic head carcinoma, including the relationship between immunohistochemical expression and clinicopathologic factors such as prognosis. Immunohistochemical expression of MK and CD34 was evaluated in pancreatic head carcinoma specimens from 75 patients who underwent surgical resection. Midkine was expressed in 53.3% of patients. Midkine expression was significantly correlated with venous invasion, microvessel density, and liver metastasis (P=0.0063, 0.0025, and 0.0153, respectively). The 5-year survival rate was significantly lower for patients positive for MK vs patients negative for MK (P=0.0073). Multivariate analysis revealed that MK expression was an independent prognostic factor (P=0.0033). This is the first report of an association between MK expression and pancreatic head carcinoma. Midkine may play an important role in the progression of pancreatic head carcinoma, and evaluation of MK expression is useful for predicting malignant properties of pancreatic head carcinoma.

Midkine is an autocrine activator of signal transducer and activator of transcription 3 in 3T3-L1 cells

Mitotic clonal expansion is believed to be necessary for 3T3-L1 adipocyte formation. Signal transducer and activator of transcription 3 (STAT3), a mitogenic signaling protein, is activated through tyrosine phosphorylation during the proliferative phases of adipogenesis. We hypothesize that this signaling protein plays a key role in mitotic clonal expansion and differentiation. Here we determined that the adipocyte differentiation cocktail containing isobutylmethylxanthine, dexamethasone, and insulin (MDI) induced STAT3 tyrosine phosphorylation indirectly through the synthesis of an autocrine/paracrine factor. We further determined that the factor has heparin binding properties and identified the factor as midkine, a pleiotrophic growth factor previously associated with neuronal development and oncogenesis. Recombinant midkine induced STAT3 tyrosine phosphorylation in a time- and dose-dependent manner and stimulated the proliferation of postconfluent 3T3-L1 cells. Midkine neutralizing antibodies inhibited differentiation-induced STAT3 tyrosine phosphorylation as well as adipogenesis. These results show that MDI-induced synthesis and release of midkine explains the delayed activation of STAT3 during adipogenesis and that the midkine-STAT3 signaling pathway plays a necessary role in mitotic clonal expansion and differentiation.

Midkine as a prognostic marker for gastrointestinal stromal tumors

PURPOSE

Midkine (MK), a heparin-binding growth factor, has an important role in cancer progression. The outcome of patients with gastrointestinal stromal tumors (GISTs) is correlated with tumor size and mitotic count. The aim of this study was to determine MK expression in GISTs.

METHODS

Midkine was detected in 31 (55%) of 57 surgically resected GISTs by immunohistochemistry with a rabbit antibody against MK and peroxidase method.

RESULTS

A significant worse outcome of MK-positive patients was found (P < 0.05; log rank test). Multivariate Cox regression analysis showed an independent prognostic impact (relative risk for overall survival 3.64; P < 0.05). Interestingly, MK expression was significantly associated with mitotic rate (P < 0.05; Chi-squared test), but not with tumor size (P = 0.97).

CONCLUSIONS

Taken together, MK is a prognostic marker for GIST patients. MK might also be a useful peripheral tumor marker since it can be detected in peripheral serum. Future studies should involve higher GIST patient numbers including tumor and serum samples for detection of MK.

Truncated midkine correlates with sensitivity to anticancer drugs and malignancy in human tumor cell line

Midkine (MK) is a heparin binding growth factor having functions of neurite-outgrowth, mitogenesis and tissue repair. This molecule is involved in tumor growth and metastasis. The MK molecule consists of five exons, but there is a truncated isoform, lacking exon 3. We established SW13 cells transfected with the human truncated MK cDNA. These cells were induced to undergo apoptosis by anticancer agents, cisplatin, etoposide (ETP), mitomycin C (MMC) and paclitaxel (PAX). Truncated midkine (tMK) suppressed cell death and helped the cells to be viable. When the cells were cultured on dishes coated with extracellular matrix molecules, spontaneous detachment occurred in the tMK expressing cells. Also tMK enhanced cell invasion. These results suggest that expression of tMK has cell-protective functions and plays important roles in carcinogenesis and malignancy. Furthermore, it is suggested that tMK has a greater ability of malignant transformation than full-length MK. Whether tMK is expressed or not will be useful information for improving cancer chemotherapy.

Construction of a fusion protein expression vector MK-EGFP and its subcellular localization in different carcinoma cell lines

AIM: To construct an expression plasmid encoding human wild-type midkine (MK) and enhanced green fluorescence protein (EGFP) fusion protein (MK-EGFP), and to analyze the subcellular localization of MK in different carcinoma cell lines.

METHODS: Two kinds of MK coding sequences with or without signal peptide were cloned into plasmid pEGFP-N2, and the recombinant plasmids constructed were introduced into HepG2, MCF7 and DU145 cells, respectively, by transfection. With the help of laser scanning confocal microscopy, the expression and subcellular localization of MK-GFP fusion protein could be detected.

RESULTS: Compared with the GFP control, in which fluorescence was detected diffusely over the entire cell body except in the nucleolus, both kinds of fusion protein MK-GFP were localized exclusively to the nucleus and accumulated in the nucleolus in the three kinds of cancer cell lines.

CONCLUSION: This study reveals the specific nucleolar translocation independent of signal peptide, which may be involved in the mechanism that MK works. It provides valuable evidence for further study on the functions of MK in nucleus and its possible mechanisms, in which ribosomal RNA transcription and ribosome assembly are involved.

Expression of midkine and its clinical significance in esophageal squamous cell carcinoma

AIM: To investigate the expression of midkine in eso-phageal squamous cell carcinoma (ESCC) and analyze its relationship with clinicopathological features.

METHODS: RT-PCR and immunocytochemical staining were used to detect the expression of midkine mRNA and protein in EC109 cells, respectively. Then the expression of midkine in 66 cases of ESCC samples were detected by immunohistochemistry using monoclonal antibodies against human midkine.

RESULTS: Midkine was expressed in EC109 cell by RT-PCR and immunocytochemistry. The immunoreactivity was detected in 56.1 % (37/66) of the ESCC samples. The expression of midkine was found in cytoplasm of tumor cells. Notably, the intensity of midkine was stronger at the area abundant in vessels and the in-vading border of the tumors. Midkine was more in-tensely expressed in well differentiated tumors (76.9 %) than in moderately and poorly differentiated tumors (43.1 % and 41.2 %, respectively) (P < 0.05). There was no statistically significant correlation between midkine expression and gender, age, clinical stage, lymph node metastasis or survival in ESCC.

CONCLUSION: Midkine is overexpressed in ESCC. It may play a role in tumor angiogenesis and invasion. The expression of midkine is correlated with tumor cell differentiation in ESCC. The more poorly tumor cells differentiate, the weaker midkine expresses.

Midkine regulates pleiotrophin organ-specific gene expression: evidence for transcriptional regulation and functional redundancy within the pleiotrophin/midkine developmental gene family

Midkine (MK) and the highly related cytokine pleiotrophin (PTN) constitute the PTN/MK developmental gene family. The Mk and Ptn genes are essential for normal development of the catecholamine and renin-angiotensin pathways and the synthesis of different collagens. It is not known whether the Ptn and Mk genes regulate each other or whether PTN and MK are functionally redundant in development. We have now compared the levels of expression of Ptn and Mk in genetically deficient Mk -/- and Ptn -/- mice and found highly significant increases in Ptn gene expression in spinal cord, dorsal root ganglia, eye, heart, aorta, bladder, and urethra, but not in brain, bone marrow, testis, and lung of Mk -/- mice compared with wild type mice; a remarkable approximately 230-fold increase in Ptn expression levels was found in heart of Mk -/- mice and highly significant but lesser increases were found in six other organs. Differences in levels of Mk gene expression in Ptn -/- mice could not be detected in any of the organs tested. The data demonstrate that MK regulates Ptn gene expression with a high degree of organ specificity, suggesting that Ptn gene expression follows Mk gene expression in development, that the increase in Ptn gene expression is compensatory for the absence of MK in Mk -/- mice, that PTN and MK share a high degree of functional redundancy, and that MK may be very important in the development of heart in mouse.