[Keyword] MK; gene expression; tumor

    Midkine (MK) is a novel gene Kadomatsu differential hybridization method in 1988 in retinoic acid-induced mouse embryonic tumor cell lines HM  1 cDNA library screening. It with PTN (pleiotropic nutritional factors, also known as heparin binding associated factor) is very similar gene structure, together form the MK family. Both produced by five exons and four introns, wherein the non-translated region of exon Ⅰ, exon II encoding the signal peptide and N-terminal of several amino acid residues, III and Ⅳ encoding the core region of amino acid residues, Ⅴ encoding the C-terminal amino acid residues, just Ⅴ of exon and intron size range. Human MK gene is located in p11.2, the upstream of the gene loci of the retinoic acid response factor, IgG enhancer element, AP 1 and NF  kB binding sites, WT1 (Wilm’s’s tumor suppressor gene product (1)), action sites (5 ‘ GCGGGGGGCG  3’) and the steroid / thyroid hormone receptor binding sites, these sites are associated with the regulation of gene expression, as shown in Figure 1.

    Figure 1 MK gene upstream regulatory sites and a schematic diagram of the exon I

    MK gene expression and tumor

    MK highly expressed in many tumor tissues, Tsutsui Northern Blot method MK Wilm’s tumor, hepatocellular carcinoma, gastric cancer, pancreatic cancer, colon cancer and esophageal cancer relative cancer adjacent tissues have different levels of high expression; O’Brien et al. nuclease protection analysis found that high expression of MK in bladder cancer; Nakanishi used Northern Blot, in situ hybridization and immunohistochemistry technology research showed that MK expression level of ovarian cancer; Miyashiro, etc. RT  PCR, Northern Blot and immunohistochemistry and other methods to detect breast cancer in high expression of MK. Subsequently, in prostate cancer, lung cancer, brain tumor, papillary thyroid tumors, cervical cancer [1] and a large number of the digestive tract, digestive gland tumors also found that a high expression of MK.

    The results show that MK expression levels in recent years, MK expression and tumor development process, and is closely related to the severity of foreign Mishima found by Northern and Western blotting MK expression in highly malignant astrocytoma significant higher than the low-grade malignant tissue; O’Brien found closely related to MK expression levels in bladder cancer and the development of cancer, especially in invasive bladder cancer, the MK high expression of the degree associated with poor prognosis. Domestic Yan Zhengfeng, etc. [2,3] application of immunohistochemistry and Western blotting method study found that increased MK expression of hepatocellular carcinoma (HCC), possible invasion and intrahepatic metastasis and hematogenous spread of HCC; addition Konishi et al [4] The study also found that, in addition to high-frequency, high degree of expression in malignant, MK also highly expressed in precancerous lesions. Immunohistochemical analysis of studies show that 80% of the incubation period of tumor MK highly expressed in the incubation period of prostate tumor and normal prostate tissue of 15 cases, normal tissue did not express or only weak expression of MK thus believe that MK expression level of detection of tissue available During the early diagnosis of the tumor.

    Also present in the blood and urine of cancer patients MK. 2000 Ikematsu [5] MK content of 10 kinds of serum tumor disease study found that MK was significantly increased in the serum of cancer patients, the the MK level higher than 0.5 ng / ml in 87% of cancer patients serum and the control group was only 0.154 ng / ml, and after resection of the tumor, serum MK content decreased. Shimada et al [6] that the increase in serum MK content as diagnostic markers of esophageal cancer. Obata et al [7] reported that MK content in the serum of patients with gastric cancer was significantly increased, and the serum of advanced cancer the MK content is higher than early tumor. MK content Ikematsu et al [8] in 2003 reported that, in the urine of patients with gastric cancer, colorectal cancer, liver cancer, cholangiocarcinoma, pancreatic cancer, brain cancer, bladder cancer, kidney cancer and thyroid cancer and other tumor also significantly increased, II, The positive rate of gastric cancer and colorectal cancer in Phase I. Thus, by detecting the serum or urine of MK level is possible for the diagnosis and staging of Clinical Oncology.

    2 MK expression in the positioning of the product

    It has been reported that they are present in the cytoplasm, and also has been reported that exist in the nucleus, nucleolus positioning of MK cells conclusion is not consistent. Luo Xiangji immuno histochemistry and in situ hybridization studies found positive signal MKmRNA and protein aggregation in the cytoplasm of HCC tumor cells, and blood vessels in HCC cells outside the organization in intensive at MK expression is particularly evident; cells have been found the surface of the MK receptors include members of the syndecan family, proteoglycan-receptor tyrosine kinase f (PTPζ), a transmembrane low density lipoprotein (LDL) receptor-related protein (LRP) and the anaplastic lymphoma kinase (ALK) and the like. 2005, Dai et al [9] was found through the use of GFP as a tracer molecule, MK-specific localization in HepG2 cell’s nucleus and nucleolus, and by point mutation and deletion mutations comparative analysis of successfully determining the positioning of the core region in the MK nucleus the K79R81, K86K87 and the C-terminal tail, MK nucleolar localization, C-terminal is the most critical, followed by N-terminal tail, K79R81 and K86K87.

    The 3 MK tumorigenic molecular mechanisms

    The current study showed that MK and molecular mechanisms of tumor formation associated mainly induce the occurrence of tumor cells, fibrinolysis and cell chemotaxis, promote the formation of tumor blood vessels, enhance the resistance of tumor cells, and deletion MK (tMK) the emergence of several forms of expression.

    3.1 the occurrence of tumor cells including induction of cell transformation, anti-apoptosis and promote mitosis. First, MK can be induced by a variety of cell transformation. The Kadomatsu research that MK-induced transformation of NIH3T3 cells with high proliferative capacity tumor tissue, Stoica, studies have shown [10] MK transformation SW  13 cells in nude mice tumor formation in nude mice, but also reveals MK is achieved by binding to ALK (between anaplastic lymphoma kinase, PTN receptor). Additionally MK also stimulate WI ALK phosphorylation  38 human fibroblast cells in the expression of ALK protein WI  38, derived from the cerebral microvasculature and umbilical cord endothelial cells (HUVEC), neuroblastoma (SH SY  5Y) and glioblastoma (U87MG) cells activate the PI3 kinase and MAP kinase signaling pathways. Secondly, a certain amount of MK can protect G401 cell lines from cisplatin-induced functions death, to prevent degeneration of continuous illumination of the light due to receptor cells. The protective effect on cells alert MK in tumor cells may be provided in the form of anti-apoptotic to promote the formation of tumors. Shibata et al [11] found that MK can be cultured mouse cells engulfed into the nucleus become an essential component of the anti-apoptotic process. And further found that the anti-apoptotic mechanisms MK-regulated cells were associated with PI3K and MAPK signaling pathways. G401 cell lines found MK as an autocrine mitogen original combination with the MK high affinity of the cell surface receptor regulation by the JAK / STAT pathway of cell protein tyrosine phosphorylation induced mitotic . In addition, Sandra [12] MK formation in ameloblastoma may study found that the MK by MAPK and Akt signaling pathways to promote cell division, induced the occurrence of ameloblastoma.

    3.2 fibrinolysis and cell chemotaxis promote fibrinolysis and cell chemotaxis associated with tumor proliferation and metastasis, Kojima material findings, MK urokinase-type plasminogen activator and lowered by up-regulating bovine aortic endothelial cells plasminogen activator inhibitor  1 expression, raise the level of the vascular endothelial plasminogen activating factor (PA) / plasmin enhanced fibrinolysis, and play a key role in the MK molecule C-terminal 43 The amino acid polypeptide. Many studies have found that the MK neutrophils, osteoblasts, osteosarcoma cells, nerve cells, macrophages and smooth muscle cells chemotaxis, and found that in addition to the of of N  Syndecan and PTPζ and related to this role, chondroitin sulfate, especially chondroitin sulfate E plays a crucial role in the MK-mediated cell migration process, the role of PI3K and MAPK signaling pathways related [13].

    3.3 promote blood vessel formation of the formation of blood vessels associated with tumor proliferation and metastasis, Muramaki [14] MK gene introduced into the bladder cancer research, found that the overexpression of the M’s can promote the growth of vascular endothelial cells, thereby stimulating increased activity of blood vessel formation , eventually leading to the occurrence of cancer. Also found expression in breast cancer cells MCF  7 MK induced rabbit corneal strong angiogenic response. In addition, the domestic studies have shown that overexpression in breast cancer [15] and other tumors MK is closely related with the tumor angiogenesis.

    In recent years, the research of gene therapy are also confirmed from the opposite side of MK tumorigenicity, for example, Takei et al [16] found that the antisense DNA of MK can be effectively suppressed cell growth and the growth of the colon cancer cells in nude mice, and MK is achieved by inhibiting the atelocollagen-mediated gene transfer, and MK antisense DNA affect tumor growth in two of the most important factors is the inhibition of cancer cell mitosis and tumor angiogenesis.

    3.4 resistance generated Kang et al [17] the expression of the gene in gastric cancer cell lines with acquired resistance analysis found that in all the resistant cell line, MK is overexpressed, suggesting that expression of MK enhanced resistance to gastric tumor cells.

    3.5 missing type MK (tMK), the expression tMK is found in the 1996 Miyashiro in RT  PCR method of colorectal cancer tissues, the expression of MK. MK found in the study of human tumor tissue tMK are alternative splicing variants, deletions of the functional areas of the main encoding the N-terminal amino acids near exon Ⅲ. Due to its C-terminal functional areas still exist, and thus retain the complete MK mostly biological activity.

    Found tmk only expressed in the tumor tissue and the expression of the high frequency in the gastrointestinal cancer metastatic lymph nodes, but not in the normal tissue, and Paul et al 2001 [18] successfully prepared a tMK monoclonal antibodies, and through immune group found tMK also specifically expressed in Wilm’s tumor cells and, in addition, are found in a variety of other tumors have tMK specific expression. Seen, tMK expression in the tumor specificity makes it a tumor diagnosis, a new logo and a new target for the treatment of tumors. And can be speculated: (1) MK increased the expression of only a basis of cancer, and Do tMK is a critical condition for its truly develop into cancer; (2) tMK developed into cancer tissue metabolism disorders and Expression is cancer self-promotion of the development of the material. Although the Nobata [19] suggest that MK gene intron 3 62 bp G T substitution may improve colon cancer tMK’s expression, but About the MK and tMK between interaction and tumor development The exact mechanism remains unclear.

    4 Conclusion

    Since 1988, people have done a lot of research for MK expression and tumor relations, however MK expression in the cancer patients of different gender, age and race level differences in the studies have not been carried out, therefore, the MK as tumor diagnosis indicators and therapeutic targets, the need for a large number of clinical and basic research.