Midkine expression in human breast cancers: expression of truncated form

Elevated Midkine Serum Levels Are Associated with Long-Term Survival in Critically Ill Patients

Midkine (Mdk) is a multifunctional protein involved in inflammatory processes. Hence, circulating Mdk is increased in sepsis and has been previously suggested as a potential biomarker in these patients. The aim of this study was to elucidate the role of Mdk serum concentrations in critical illness and sepsis and to verify its value as a prognostic biomarker. Thus, we analyzed the Mdk serum concentrations of 192 critically ill patients on admission to the medical intensive care unit (ICU). While the serum levels of Mdk at admission were similar in septic and nonseptic critical illness (362 vs. 337 ng/L, p = 0.727), we found several interesting correlations of Mdk to laboratory and clinical markers associated with ischemia or hypoxia, e.g., to renal failure and hepatic injury. Mdk serum concentrations at admission did not differ between various causes of sepsis or other critical illness. Most noticeable, we observed upregulated Mdk serum concentrations at admission in patients surviving in the long-term, which was only seen in nonseptic critical illness but not in sepsis. Our study suggests a relevant role of Mdk in critically ill patients in general and highlights the possible protective features of Mdk in critical illness.

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.

Midkine and pleiotrophin concentrations in needle biopsies of breast and lung masses

BACKGROUND/OBJECTIVE

Midkine (MDK) and pleiotrophin (PTN) are two closely related heparin-binding growth factors which are overexpressed in a wide variety of human cancers. We hypothesized that the concentrations of these factors in washout of biopsy needles would be higher in breast and lung cancer than in benign lesions.

METHODS

Seventy subjects underwent pre-operative core needle biopsies of 78 breast masses (16 malignancies). In 11 subjects, fine needle aspiration was performed ex vivo on 7 non-small cell lung cancers and 11 normal lung specimens within surgically excised lung tissue. The biopsy needle was washed with buffer for immunoassay.

RESULTS

The MDK/DNA and the PTN/DNA ratio in most of the malignant breast masses were similar to the ratios in benign masses except one lobular carcinoma in situ (24-fold higher PTN/DNA ratio than the average benign mass). The MDK/DNA and PTN/DNA ratio were similar in most malignant and normal lung tissue except one squamous cell carcinoma (38-fold higher MDK/DNA ratio than the average of normal lung tissue).

CONCLUSIONS

Both MDK and PTN are readily measurable in washout of needle biopsy samples from breast and lung masses and levels are highly elevated only in a specific subset of these malignancies.

Midkine's Role in Cardiac Pathology

Midkine (MDK) is a heparin-binding growth factor that is normally expressed in mid-gestational development mediating mesenchymal and epithelial interactions. As organisms age, expression of MDK diminishes; however, in adults, MDK expression is associated with acute and chronic pathologic conditions such as myocardial infarction and heart failure (HF). The role of MDK is not clear in cardiovascular disease and currently there is no consensus if it plays a beneficial or detrimental role in HF. The lack of clarity in the literature is exacerbated by differing roles that circulating and myocardial MDK play in signaling pathways in cardiomyocytes (some of which have yet to be elucidated). Of particular interest, serum MDK is elevated in adults with chronic heart failure and higher circulating MDK is associated with worse cardiac function. In addition, pediatric HF patients have higher levels of myocardial MDK. This review focuses on what is known about the effect of exogenous versus myocardial MDK in various cardiac disease models in an effort to better clarify the role of midkine in HF.

Quantitative comparison of immunohistochemical and PCR analysis of midkine expression in breast cancer types and serum midkine level

BACKGROUND/AIM

Midkine (MK), a heparin-binding growth factor, has an important role in cancer progression. The aim of this study was to determine MK expression in breast tissue and the preoperative and postoperative serum levels of patients with breast cancer.

MATERIALS AND METHODS

Sixty-one patients with breast cancer participated in our study. The MK serum levels were measured pre- and postoperatively for these patients. We also analyzed breast tissues of the 61 patients immunohistochemically. We examined serum midkine levels in 49 healthy volunteers.

RESULTS

MK expression was observed in 44 (72.1%) of 61 breast cancer patients. In breast cancer patients the serum MK levels (3.68 ± 2.13 ng/mL (mean ± SD)) were significantly higher than in the control group (1.77 ± 0.38 ng/mL) before tumor removal (P = 0.000). After tumor removal, serum MK levels (2.47 ± 1.00 ng/mL) were significantly (P = 0.000) decreased according to preoperative levels. Increased serum levels of MK were related with tumor stages when clinical parameters were analyzed.

CONCLUSION

We found that increased serum MK levels and protein expressions were associated with the carcinogenesis of breast cancer. MK levels decreased after tumor removal. According to our findings, MK might be a useful tumor marker for patients with breast cancer.

Transcriptional factor specificity protein 1 (SP1) promotes the proliferation of glioma cells by up-regulating midkine (MDK)

Midkine (MDK) expression is associated with the proliferation of many cancers, including glioma. However, the upstream signaling that leads to MDK accumulation remains elusive. This study investigates the molecular mechanism that induces MDK overexpression in human glioma. The Repository for Molecular Brain Neoplasia Data was analyzed to identify potential MDK regulators. Expression of MDK and specificity protein 1 (SP1) was compared in glioma specimens. Chromatin immunoprecipitation assay was used to confirm the transcriptional regulation. MDK-force-expressed, SP1-silenced glioma cells were used to test rescue effects in vitro and in vivo. MDK and SP1 expression in gliomas was significantly higher than in adjacent tissues and was positively correlated in glioma clinical samples and cell lines. The promoter of the human MDK gene has a putative SP1 binding site. SP1 binds to the promoter of the MDK gene and directly regulates MDK expression. MDK or SP1 gene silencing inhibited the proliferation of glioma cells and reduced the tumor volume in nude mice. Overexpression of MDK in SP1-silenced cells could partially rescue the SP1 inhibition effects in vivo and in vitro. SP1 directly up-regulated the expression of MDK, and the SP1-MDK axis cooperated in glioma tumorigenesis.

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.

Pancreatic cancer

In recent years, it has become clear that the current standard therapeutic options for pancreatic cancer are not adequate and still do not meet the criteria to cure patients suffering from this lethal disease. Although research over the past decade has shown very interesting and promising new therapeutic options for these patients, only minor clinical success was achieved. Therefore, there is still an urgent need for new approaches that deal with early detection and new therapeutic options in pancreatic cancer. To provide optimal care for patients with pancreatic cancer, we need to understand better its complex molecular biology and thus to identify new target molecules that promote the proliferation and resistance to chemotherapy of pancreatic cancer cells. In spite of significant progress in curing cancers with chemotherapy, pancreatic cancer remains one of the most resistant solid tumour cancers and many studies suggest that drug-resistant cancer cells are the most aggressive with the highest relapse and metastatic rates. In this context, activated Notch signalling is strongly linked with chemoresistance and therefore reflects a rational new target to circumvent resistance to chemotherapy in pancreatic cancer. Here, we have focused our discussion on the latest research, current therapy options and recently identified target molecules such as Notch-2 and the heparin-binding growth factor midkine, which exhibit a wide range of cancer-relevant functions and therefore provide attractive new therapeutic target molecules, in terms of pancreatic cancer and other cancers also.

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.

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.

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.

Promotion of self-renewal of embryonic stem cells by midkine

AIM

To characterize the expression and function of midkine (MK) in an in vitro embryonic stem cell (ESC) culture system.

METHODS

To investigate the potential roles of MK, the expression of MK in ESCs was evaluated by RT-PCR and immunocytochemistry. The effects of MK on the self-renewal of ESCs were measured using alkaline phosphatase assays, immunocytochemistry, RT-PCR and colony-forming assays. The mechanism of the growth-promoting effect of MK in mESCs was assessed by cell cycle analysis and Western blot analysis.

RESULTS

MK is expressed in mouse embryonic stem cells (mESCs), human embryonic stem cells (hESCs) and mouse embryonic fibroblasts (MEFs). MK promotes proliferation and self-renewal of mESCs both in feeder and feeder free culture systems. It also promotes self-renewal and proliferation of hESCs. Further study showed that MK promotes the growth of mESCs by inhibiting apoptosis while accelerating the progression toward the S phase, and enhances mESC self-renewal through PI3K/Akt signaling pathway.

CONCLUSION

MK plays profound roles in ESCs. MK/PTPzeta signaling pathway is a novel pathway in the signal network maintaining pluripotency of ESCs. The results extend our knowledge on pluripotency control of ESCs and the relationship between ESCs and cancers.

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, a heparin-binding cytokine with multiple roles in development, repair and diseases

Midkine is a heparin-binding cytokine or a growth factor with a molecular weight of 13 kDa. Midkine binds to oversulfated structures in heparan sulfate and chondroitin sulfate. The midkine receptor is a molecular complex containing proteoglycans. Midkine promotes migration, survival and other activities of target cells. Midkine has about 50% sequence identity with pleiotrophin. Mice deficient in both factors exhibit severe abnormalities including female infertility. In adults, midkine is expressed in damaged tissues and involved in the reparative process. It is also involved in inflammatory reactions by promoting the migration of leukocytes, induction of chemokines and suppression of regulatory T cells. Midkine is expressed in a variety of malignant tumors and promotes their growth and invasion. Midkine appears to be helpful for the treatment of injuries in the heart, brain, spinal cord and retina. Midkine inhibitors are expected to be effective in the treatment of malignancies, rheumatoid arthritis, multiple sclerosis, renal diseases, restenosis, hypertension and adhesion after surgery.

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 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.

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

AIM: To determine whether midkine (MK) and its truncated form (tMK) contribute to gastric tumorigenesis using in vitro and in vivo models.

METHODS: Human MK and tMK plasmids were constructed and expressed in BGC823 (a gastric adenocarcinoma cell line) to investigate the effect of over-expressed MK or tMK on cell growth and turmorigenesis in nude mice.

RESULTS: The growth of MK-transfected or tMK-transfected cells was significantly increased compared with that of the control cells, and tMK-transfected cells grew more rapidly than MK-transfected cells. The number of colony formation of the cells transfected with MK or tMK gene was larger than the control cells. In nude mice injected with MK-transfected or tMK-transfected cells, visible tumor was observed earlier and the tumor tissues were larger in size and weight than in control animals that were injected with cells without the transfection of either genes.

CONCLUSION: Over-expressed MK or tMK can promote human gastric cancer cell growth in vitro and in vivo, and tMK has greater effect than MK. tMK may be a more promising gene therapeutic target compared with MK for treatment of malignant tumors.

A new targeting approach for breast cancer gene therapy using the human fatty acid synthase promoter

Gene therapy with adenoviral vectors is a promising new approach for the treatment of refractory advanced breast cancer. Strategies to restrict adenoviral-mediated therapeutic gene expression are important to avoid harming normal cells. Fatty acid synthase (FAS) is overexpressed in several human cancers. FAS is highly expressed in infiltrating breast cancer tissue, and always associated with malignant phenotypes and poor prognosis. In this study, expression of the FAS was evaluated in three breast cancer cell lines. A 680 bp-FAS promoter was cloned and its transcriptional activity was analyzed in breast cancer cell lines. We made a recombinant adenovirus construct carrying herpes simplex virus thymidine kinase (HSV-TK) driven by human FAS promoter (Ad-FAS-TK) and analyzed its target cytotoxicity in vitro and in vivo against human breast cancer cells combined with prodrug ganciclovir (GCV). The results show that the expression of FAS varies in the three breast cancer cell lines examined (respectively, SK-Br3>MCF-7>MDA-MB-231), but FAS promoter can initiate relative high transcriptional activities in all three kinds of cancer cells while little in normal fibroblast cells. Furthermore, FAS promoter can drive the therapeutic gene in a wider range of human breast cancers than cerbB2 promoter and exhibit a stronger activity than midkine (MK) promoter. Combination of Ad-FAS-TK and GCV treatment exhibited strong-targeted cytotoxic effect on breast cancer cells but showed little activity in normal fibroblast cells. The tumorigenic capability of breast cancer cells treated with Ad-FAS-TK/GCV was completely inhibited in vitro and in vivo assays. In conclusion, adenoviral-mediated suicide gene therapy controlled by tumor associated-FAS promoter can induce specific cytotoxic effect on human breast cancer cells in vitro and in vivo. So it is a promising target for the development of gene therapy against breast cancers.

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.

Abnormal expression, highly efficient detection and novel truncations of midkine in human tumors, cancers and cell lines

We detected aberrant Midkine (MK) expressions in human insulinoma and pancreatic cancer tissues by immunohistochemistry, revealing its potential role in tumorigenesis/carcinogenesis. With a nested-touchdown PCR program we were able to detect the tMK in all human tumor/cancer tissues and cancer/tumor cell lines. Detection of MK in the peripheral cells and precancerous lesions implies its potential for early cancer/tumor diagnosis. Furthermore, we have discovered two novel truncations of the MK, tMKB and tMKC, respectively, in the disease specimens. Our data not only provide an efficient methodology potentially for clinical application but also shed light on the molecular mechanism underlying the role for MK in tumorigenesis/carcinogenesis.

Molecular basis of pregnancy-induced breast cancer protection

We have postulated that the lifetime protective effect of an early pregnancy against breast cancer is due to the complete differentiation of the mammary gland characterized by a specific genomic signature imprinted by the physiological process of pregnancy. In the present work, we show evidence that the breast tissue of postmenopausal parous women has had a shifting of stem cell 1 to stem cell 2 with a genomic signature different from similar structures derived from postmenopausal nulliparous women that have stem cell 1. Those genes that are significantly different are grouped in major categories on the basis of their putative functional significance. Among them are those gene transcripts related to immune surveillance, DNA repair, transcription, chromatin structure/activators/co-activators, growth factor and signal transduction pathway, transport and cell trafficking, cell proliferation, differentiation, cell adhesion, protein synthesis and cell metabolism. From these data, it was concluded that during pregnancy there are significant genomic changes that reflect profound alterations in the basic physiology of the mammary gland that explain the protective effect against carcinogenesis. The implication of this knowledge is that when the genomic signature of protection or refractoriness to carcinogenesis is acquired by the shifting of stem cell 1 to stem cell 2, the hormonal milieu induced by pregnancy or pregnancy-like conditions is no longer required. This is a novel concept that challenges the current knowledge that a chemopreventive agent needs to be given for a long period to suppress a metabolic pathway or abrogate the function of an organ.

Transiently truncated and differentially regulated expression of midkine during mouse embryogenesis

Midkine (MK) is a retinoic acid response cytokine, mostly expressed in embryonic tissues. Aberrant expression of MK was found in numerous cancers. In human, a truncated MK was expressed specifically in tumor/cancer tissues. Here we report the discovery of a novel truncated form of MK transiently expressed during normal mouse embryonic development. In addition, MK is concentrated at the interface between developing epithelium and mesenchyme as well as highly proliferating cells. Its expression, which is closely coordinated with angiogenesis and vasculogenesis, is spatiotemporally regulated with peaks in extensive organogenesis period and undifferentiated cells tailing off in maturing cells, implying its role in nascent blood vessel (endothelial) signaling of tissue differentiation and stem cell renewal/differentiation. Cloning and sequencing analysis revealed that the embryonic truncated MK, in which the conserved domain is in-frame deleted, presumably producing a novel secreted small peptide, is different from the truncated form in human cancer tissues, whose deletion results in a frame-shift mutation. Our data suggest that MK may play a role in epithelium-mesenchyme interactions, blood vessel signaling, and the decision of proliferation vs differentiation. Detection of the transiently expressed truncated MK reveals its novel function in development and sheds light on its role in carcinogenesis.

Exon skipping of midkine pre-mRNA is enhanced by intronic polymorphism in a colon cancer cell line

A correlation between the polymorphism, heterogeneous G/T at the 62nd site of intron 3 in the midkine gene, and the induction of colorectal cancer has been reported [Cancer Lett. 180 (2002) 159]. The minigene containing exons 2, 3 and 4, as well as intronic sequences flanking exon 3, was transfected into COLO205 colon cancer cells. When the base of the site was G, correctly spliced mRNA was strongly detected. However in case of a G to T substitution, a truncated exon 3 mRNA was strongly detected. In this case, the detection of correctly spliced mRNA was weak. When the minigene was transfected into HCT-15 colon cancer cells, correctly spliced mRNA was strongly detected in the cases of both minigenes. This indicates the possibility that a G to T substitution at the 62nd site of intron 3 in the midkine gene enhances the expression of truncated midkine in colon cancer.

Thyroid transcription factor (TTF) -1 regulates the expression of midkine (MK) during lung morphogenesis

Midkine (MK) is a 13-kDa heparin-binding growth factor that is thought to mediate developmental processes, including vasculogenesis, cell migration, and proliferation in various organs. To determine whether MK plays a role during lung morphogenesis, immunostaining for MK was assessed in mouse lung from embryonic day (E) 13 to postnatal day (PN) 24. MK was detected in mesenchymal and respiratory epithelial cells of the peripheral mouse lung from E13.0 to E15.5. From E18.5 to PN1, MK was observed primarily in epithelial cells lining conducting airways and peripheral lung saccules. By PN10, expression was no longer observed in respiratory epithelial cells but was readily detected in small blood vessels in the alveolar region of the lung. Although most respiratory epithelial cells uniformly expressed MK before E13.0, MK was restricted to subsets of cells by E18.5, colocalizing with the Clara cell secretory protein (CCSP) marker in conducting airways and with pro-SPC, a marker specific for alveolar type II pneumocytes. By PN10, MK was not detected in respiratory epithelial cells of the conducting airways and was closely associated with capillary networks. The sites of intense MK staining in the respiratory epithelial cells correlated with sites of expression of thyroid transcription factor (TTF) -1, a transcription factor regulating formation and gene expression in the lung parenchyma. TTF-1 enhanced transcription of the mouse MK gene promoter, acting on TTF-1 regulatory elements located in the 5'-region of the gene. Furthermore, MK expression was not detected in lungs of TTF-1 null mice. TTF-1 regulates expression of MK in the lung. The temporal/spatial distribution of midkine is consistent with a potential role in paracrine signaling during lung morphogenesis.

Association of an intronic polymorphism in the midkine (MK) gene with human sporadic colorectal cancer

Midkine (MK) is a heparin-binding growth factor specified by a retinoic acid responsive gene. It plays important roles in development and carcinogenesis. The MK gene is located on chromosome 11q11.2 in humans. A heterozygous G to T transition at the 62nd base in intron 3 of this gene has been identified in sporadic colorectal and gastric cancers (Int. J. Mol. Med. 6 (2000) 281). To clarify whether this polymorphism is associated with a cancer risk, a case-control study was conducted. We examined 98 colorectal, 60 gastric, 59 esophagus, 32 lung and 37 breast cancer tissue specimens and their corresponding non-neoplastic tissues. Also, 86 unaffected control specimens were examined. The G/T genotype frequency in colorectal cancers was higher than that in normal samples (11.2 versus 2.3%; P=0.017). Therefore, this genotype could represent a risk factor for tumorigenesis in the colon and rectum of Japanese.

Production and characterization of a bacterial single-chain Fv fragment specific to human truncated midkine

The production (and characterization) of a monoclonal antibody against human truncated midkine (tMK), and the detection of tMK in G401 cells, a Wilms' tumor cell line, as well as in Wilms' tumor patient specimens, have been reported (Paul et al., Cancer Lett. 163 (2001) 245-251). Here we report the molecular cloning and expression of this monoclonal antibody as a single-chain Fv fragment (scFv) in Escherichia coli. The scFv protein, purified by immobilized metal affinity chromatography, showed a specific affinity to recombinant tMK and native tMK in G401 cells as detected by enzyme-linked immunosorbent assay and immunofluorescence microscopy, respectively. The binding of this protein to recombinant tMK was competitive with the parental monoclonal antibody. These results suggest that this scFv can also be used for Wilms' tumor detection.

Molecular cloning, expression and purification of truncated midkine and its growth stimulatory activity on Wilms' tumor (G401) cells

Midkine (MK) is a heparin binding growth factor identified as a product of a retinoic acid-responsive gene; it is frequently expressed at high levels in many human carcinomas. Although the expression of the mRNA encoding truncated MK (tMK) in unique human cancer cells has been reported, the tMK polypeptide itself has not yet been identified. In order to clarify the biological role of tMK, recombinant tMK was expressed in Escherichia coli and purified. Recombinant tMK was purified as a single band in SDS-PAGE under reducing conditions showing an apparent molecular mass of 10 kDa. Purified recombinant tMK showed the same extent of proliferative activity towards Wilms' tumor (G401) cells as full length human MK. These results suggest that the structure of this recombinant tMK is same as the native polypeptide.

Detection of truncated midkine in Wilms' tumor by a monoclonal antibody against human recombinant truncated midkine

Although the expression of a truncated midkine (tMK) mRNA has been detected in many cancer cells, the tMK protein itself has not yet been identified. The expression, purification and characterization of human recombinant tMK were described in the former report. A mouse hybridoma cell line producing an IgG2b monoclonal antibody (mab) against purified recombinant tMK was established. This anti-tMK mab did not cross react with synthetic full length (or c-half) human midkine. A putative native tMK was identified in G401 cells using this mab, and showed the same apparent Mw as the recombinant tMK in SDS-PAGE. This mab was also used in an immunohistochemical study to evaluate the expression of tMK in Wilms' tumor cell line, G401 cells, as well as in Wilms' tumor patient specimens. G401 cells and all Wilms' tumor patient specimens immunoreacted with this anti-tMK mab. We conclude that Wilms' tumor cells express tMK and that this mab is useful for the detection of tMK in the Wilms' tumor.

Overexpression of midkine in lung tumors induced by N-nitrosobis(2-hydroxypropyl)amine in rats and its increase with progression

The expression of midkine (MK) in lung tumors induced by N-nitrosobis(2-hydroxypropyl)amine (BHP) in rats was examined. The animals were administered 2000 p.p.m. of BHP in their drinking water for 12 weeks, then maintained without further treatment until being killed 20-28 weeks after the beginning of the experiment. MK mRNA expression of adenocarcinomas and squamous cell carcinomas assessed by means of the reverse transcriptase-polymerase chain reaction and northern blot analysis was significantly higher than in rat embryonic tissues (positive controls) and contrasted strongly with the lack in normal lungs. MK protein was detected immunohistochemically in 58.3% of alveolar hyperplasias, 92.3% of adenomas and 100% of adenocarcinomas and squamous cell carcinomas. The extent of staining significantly increased along with malignant progression in adenomatous (pre-)neoplastic lesions and tended to become more pronounced with malignant progression in squamous lesions. The results suggest that MK may play some essential roles in the development and progression of lung tumors induced by BHP in rats.

Pleiotrophin and midkine, a family of mitogenic and angiogenic heparin-binding growth and differentiation factors

The heparin-binding polypeptide homologs pleiotrophin and midkine are the only known members of a family of secreted growth/differentiation cytokines. Pleiotrophin and midkine are both developmentally regulated and highly conserved among species. They signal a number of physiological functions involved with angiogenesis, neuorogenesis, cell migration, and mesoderm-epithelial interactions. Constitutive expression of pleiotrophin and midkine in responsive cells support their role as "tumor growth factors" and positive regulators of tumor angiogenesis. Widespread deregulation of pleiotrophin and midkine is found in many known human cancers or their derived cell lines, and the molecular targeting of pleiotrophin to block its signaling in tumor cells has limited tumor growth and metastasis in animal models. Elucidating the molecular mechanisms of pleiotrophin and midkine action in tumorgenesis and tumor angiogenesis may lead to the identification of novel targets for tumor therapy.

Truncated midkine as a marker of diagnosis and detection of nodal metastases in gastrointestinal carcinomas

Midkine (MK) is a growth factor identified as a product of a retinoic acid-responsive gene. A truncated form of MK mRNA, which lacks a sequence encoding the N-terminally located domain, was recently found in cancer cells. We investigated the expression of the truncated MK mRNA in specimens of 47 surgically removed human gastrointestinal organs using polymerase chain reaction. Truncated MK was not detected in all of the 46 corresponding non-cancerous regions. On the other hand, this short MK mRNA was expressed in the primary tumours in 12 of 16 gastric cancers, 8 of 13 colorectal carcinomas, five of nine hepatocellular carcinomas, two of two oesophageal carcinomas and one ampullary duodenal cancer. In addition, truncated MK was detectable in all of the 14 lymph node metastases but in none of three metastatic sites in the liver, suggesting that truncated MK mRNA could become a good marker of nodal metastases in gastrointestinal tract.