高表达VMP1的可降低肝癌细胞的转移以及侵袭[25]。研究发现，由低氧诱导的miR-210能够促进HCC的转移和侵袭，当下调miR-210的表达后，在低氧条件下HCC的转移及侵袭均显著下降。综合得出，miR-210与VMP1的作用相反，提示低氧诱导的miR-210能够通过与VMP1直接结合影响HCC的转移和侵袭。另外，VMP1能够逆转由miR-210介导的HCC的转移及侵袭, 在高表达miR-210的HCC中转染VMP1后，与空转染组比较HCC的转移及侵袭均明显下降。但是将miR-210的反义寡核苷酸转染到Huh-7细胞中后发现，由低氧导致的VMP1 表达的下调作用得到逆转，由此表明，在低氧环境下VMP1表达的下调是由上调的miR-210介导的[25]。总之，低氧环境下，miR-210可以通过下调VMP1的表达促进肿瘤细胞的侵袭转移（图 2）。
图2.低氧诱导的miR-210在实体肿瘤中的调控机制
4.2低氧/miR-210 /VEGF通路
Foekens[36]等用生物信息学分析38例乳腺癌患者发现，miR-210与低氧/VEGF信号通路偶联（图 2）。VEGF广泛表达于肾癌，乳腺癌，黑素瘤，肝癌，胃癌，膀胱癌，子宫内膜癌及胚胎组织性肿瘤及非肿瘤的病理过程中，与转化生长因子B（TGF-B），血小板源性生长因子（PDGF），NO及一些重金属离子有关，VEGF受缺血和缺氧环境的调节。研究发现，瘤体组织VEGF的表达水平与其微血管密度及恶性程度成正相关，并明显高于非肿瘤组织。这表明VEGF通过促进血管生成的方式促进肿瘤生成，尤其在高度血管化肿瘤中。近期研究
发现，低氧诱导的胰腺癌患者的血清中同时检测到VEGF和miR-210的大量表达[37]。当给予VEGF的抑制剂后不但可以阻断VEGF的表达，也能够阻断miR-210的表达，由此表明，低氧诱导的miR-210的大量表达与低氧相关下游靶点VEGF密切相关[37]。但是，两者在肿瘤发生过程中究竟哪一个占主导作用目前还不清楚。
4.3 低氧/ROS/miR-210/ ROS通路
目前研究发现，低氧诱导的miR-210的表达可以被活性氧的清除剂N-乙酰半胱氨酸（NAC）所衰减，表明低氧增加的miR-210的表达主要由活性氧（reactive oxygen species, ROS）介导产生。ROS 可双向调控某些肿瘤细胞的凋亡和增殖。最新研究发现，低浓度的ROS 更广泛的生理意义在于其对转录因子的激活以及对细胞增殖、分化的促进。研究表明，低氧诱导ROS通路的活化能够促进miR-210的表达（图 2），进而影响脂肪组织来源干细胞（Adipose tissue-derived stem cells, ASCs）的转移和增殖[38]。而miR-210可以通过下调铁硫簇支架蛋白（iron–sulfur cluster scaffold homolog 1/2, ISCU1/2）以及非受体型蛋白酪氨酸磷酸酶2（protein tyrosine phosphatase, non-receptor type 2, PTPN2）的表达反馈调节ROS的表达，也就是说，ROS与miR-210两者在肿瘤细胞的增殖及转移过程中能够形成前馈回路[38]。这对肿瘤细胞在侵袭以及转移的过程中具有非常重要的意义。
4.4 miR-210/FGFRL1/G1-G0通路
在ESCC中，miR-210能够通过下调FGFRL1的表达阻滞细胞周期G1/G0期，抑制ESCC的增殖。但是miR-210通过FGFRL1阻碍细胞周期进程达到抑制癌细胞增殖的作用只是部分的
[23]
，暗示着miR-210还可能通过其他的靶标基因抑制癌细胞的增殖（图 2）。
4.5 miR-210/ISCU1/2/ETC通路
铁硫簇支配蛋白1/2（iron-sulfur cluster assembly proteins1/2, ISCU1/2）是一类重要的蛋白，以铁硫复合物为辅基，参与细胞电子传递过程，在细胞氧化还原反应中发挥重要作用。采用生物信学分析发现miR-210与ISCU2的3’-UTR端靶向结合，且在低氧条件下，上调的miR-210能够抑制ISCU2的表达，进而抑制线粒体的电子传递（electron transport chain, ETC）及三羧酸循环。尽管miR-210/ISCU1/2调节机制在各种细胞中均存在，但是其生物能量利用率仍受细胞环境影响[39]，例如，相对于非转化细胞，肿瘤细胞中糖酵解速率增加，氧化磷酸化速率减弱，该过程受miR-210/ISCU1/2机制调控[40,41]，尤其是在HIF高表达的肾肿瘤细胞中。因此，研究低氧环境中miR-210/ISCU1/2/ET对肿瘤细胞代谢过程的调控机制复杂，有待深入研究。
5 展望
近年关于miR-210在低氧环境中对实体肿瘤发生发展的研究十分广泛，miR-210在肿瘤细胞的增殖、转移以及侵袭过程中具有多种作用与功能。对于研究miR-210的手段多采用计算机预测靶基因3’-UTR与miR-210的种子序列的互补性、微阵列分析技术和AGO蛋白免疫沉淀法（argonaute protein immunoprecipitation, miRNP-IP）以及miR-210的定量分析法，这些都将为全面研究miR-210的功能提供重要的实验方法。miR-210的肿瘤机制研究也已经扩展到炎症方面，因此，深入探讨miR-210的调控机制将为实体肿瘤的临床治疗提供更广阔前景。
参考文献
[1] Siegel R,Naishadham D,Jemal A. Cancer statistics,2013, CA Cancer J Clin[J]. 2013 ,63(1): 11-30.
[2] Xie X, Lu J，Kulbokas EJ,et al. Systematic discovery of regulatory motifs in human promoters and 3’- UTRs by comparison of several mammals.Nature[J],2005,434(7031):338-345.
[3] Fasanaro P, D'Alessandra Y, Di Stefano V, et al. MicroRNA-210 modulates endothelial cell response to hypoxia and inhibits the receptor tyrosine kinase ligand Ephrin-A3. J Biol Chem[J],2008, 283(23):15878-15883.
[4] Lawson ND, Vogel AM, Weinstein BM, et al. Sonic hedgehog and vascular endothelial growth factor act upstream of the Notch pathway during arterial endothelial differentiation [J]. Dev Cell, 2002,3 (1):127-136.
[5] Guimbellot, J. S., Erickson, et al,Correlation of microRNA levels during hypoxia with predicted target mRNAs through genomewide microarray analysis. BMC Med Genomics[J]. 2009 ,25,10.1186/1755-8794-2-15.
[6] Scapoli L, Palmieri A, Lo Muzio L, et al. MicroRNA expression profiling of oral carcinoma identifies new markers of tumor progression. Int J Immunopathol Pharmacol[J], 2011,23(4): 1229-1234.
[7] PuissegurMP,Mazure NM, Bertero T, et al. miR-210 is overexpressed in late stages of lung cancer and mediates mitochondrial alterations associated with modulation of HIF-1 activity. Cell Death and Differentiation [J],2011,18(3): 465-478.
[8] Devlin C, Greco S, Martelli F,et al,miR-210: More than a silent player in hypoxia. IUBMB Life[J]. 2011 Feb;63(2):94-100.
[9] S Grosso J Doyen, SK Parks,et al,MiR-210 promotes a hypoxic phenotype and increases radioresistance in human lung cancer cell lines. Cell Death and Disease[J] ,2013,4, e544; [10] Roa WH, Kim JO, Razzak R,et al,Sputum microRNA profiling: a novel approach for the early detection of non-small cell lung cancer. Clin Invest Med[J]. 2012 ,Oct 6;35(5):E271 [11] Eilertsen M, Andersen S, Al-Saad S,et al, Positive prognostic impact of miR-210 in non-small cell lung cancer.Lung Cancer[J]. 2013,Nov 14. (13)00516-3.
[12] Li ZH, Zhang H, Yang ZG, et al,Prognostic significance of serum microRNA-210 levels in nonsmall-cell lung cancer.J Int Med Res[J]. 2013 ,Oct;41(5):1437-44.
[13] Chaput N, Andre F, Schartz NE,et al, Exosomes and anti-tumour immunotherapy.Bull Cancer[J]. 2003, 90(8-9):695-8.
[14] Hamish W King, Michael Z Michael and Jonathan M Gleadle .Hypoxic enhancement of exosome release by breast cancer cells. BMC Cancer[J], 2012, 12:421.
[15] Tadokoro H, Umezu T, Ohyashiki K, et al,Exosomes derived from hypoxic leukemia cells enhance tube formation in endothelial cells. J Biol Chem[J]. 2013 Nov 29;288(48):34343-51. [16] Toyama T,Kondo N,EndoY,et al,High Expression of MicroRNA-210 is an Independent Factor Indicating a Poor Prognosis in Japanese Triplenegative Breast Cancer Patients. Jpn J Clin Oncol [J], 2012,42 (4):256-263
[17]ChenWY, LiuWJ, ZhaoYP, etal,Induction, modulation and potential targets of miR-210 in pancreatic cancer cells. Hepatobiliary Pancreat Dis Int[J]. 2012,11(3):319-24.
[18] Ho AS, Huang X, Cao H, et al,Circulating miR-210 as a Novel Hypoxia Marker in Pancreatic Cancer.Transl Oncol[J]. 2010 Apr;3(2):109-13.
[19] White NM, Bao TT, Grigull J, et al.miRNA profiling for clear cell renal cell carcinoma: biomarker discovery and identification of potential controls and consequences of miRNA dysregulation. J Urol [J],2011;186(3):1077-83
[20] Redova M, Poprach A, Besse A, et al,MiR-210 expression in tumor tissue and in vitro effects of its silencing in renal cell carcinoma.Tumour Biol[J]. 2013,34(1):481-91.
[21] Zhao A, Li G, Péoc'h M, et al,Serum miR-210 as a novel biomarker for molecular diagnosis of clear cell renal cell carcinoma. Exp Mol Pathol[J]. 2013,94(1):115-20.
[22] Tsuchiya S.The role of microRNA-210 in esophageal squamous cell carcinoma.Yakugaku Zasshi[J]. 2012;132(9):1069-73.
[23] Tsuchiya S, Fujiwara T, Sato F, et al,MicroRNA-210 Regulates Cancer Cell Proliferation through Targeting Fibroblast Growth Factor Receptor-like 1 (FGFRL1). J Biol Chem[J].2011, 7;286(1):420-8.
[24] Scapoli L, Palmieri A, Lo Muzio L, et al, MicroRNA expression profiling of oral carcinoma identifies new markers of tumor progression.Int J Immunopathol Pharmacol[J]. 2010 Oct-Dec;23(4):1229-34.
[25] Ying Q, Liang L, Guo W,et al,Hypoxia-Inducible MicroRNA-210 Augments the Metastatic Potential of Tumor Cells by Targeting Vacuole Membrane Protein 1 in Hepatocellular Carcinoma. Hepatology[J]. 2011,54(6):2064-75.
[26] ?zata DM, Caramuta S, Velázquez-Fernández D, et al, The role of microRNA deregulation in the pathogenesis of adrenocortical carcinoma.Endocr Relat Cancer[J]. 2011 Oct 27;18(6):643-55.
[27] Chen J, Wang W, Zhang Y, et al,Predicting distant metastasis and chemoresistance using plasma miRNAs.Med Oncol[J]. 2014 Jan;31(1):799.
[28] Cui J, Eldredge JB, Xu Y, et al,MicroRNA expression and regulation in human ovarian carcinoma cells by luteinizing hormone.PLoS One[J]. 2011;6(7):21730.
[29] Lai NS, Dong QS, Ding H,et al,MicroRNA-210 overexpression predicts poorer prognosis in glioma patients.J Clin Neurosci[J]. 2013 Sep 11. 0967-5868(13)00482-7.
[30] Ragusa M, Caltabiano R, Russo A,et al, MicroRNAs in vitreus humor from patients with ocular diseases.Mol Vis[J]. 2013;19:430-40.
[31] Dusetti NJ, Jiang Y, Vaccaro MI, et al. Cloning and expression of the rat vacuole membrane protein1 (VMP1), a new gene activated in pancreas with acute pancreatitis,which promotes vacuole formation. Biochem Biophys Res Commun[J] ,2002;290:641-649.
[32] Vaccaro MI, Grasso D, Ropolo A, et al, VMP1 expression correlates with acinar cell cytoplasmic vacuolization in arginine-induced acute pancreatitis. Pancreatology[J] ,2003;3:69-74 [33] Jiang PH, Motoo Y, Vaccaro MI,et al, Expression of vacuole membrane protein 1 (VMP1) in spontaneous chronic pancreatitis in the WBN/Kob rat. Pancreas[J], 2004,29:225-230.
[34] Vaccaro MI, Ropolo A, Grasso D,et al, A novel mammalian trans-membrane protein reveals an alternative initiation pathway forautophagy. Autophagy[J], 2008;4:388-390.
[35] Pardo R, Lo Re ′ A, Archange C, et al. Gemcitabine induces the VMP1-mediated autophagy
pathway to promote apoptotic death in human pancreatic cancer cells.Pancreatology[J] 2010,10:19-26.
[36] Foekens JA, Sieuwerts AM, Smid M, et al,Four miRNAs associated with aggressiveness of lymph node-negative, estrogen receptor-positive human breast cancer. Proc Natl Acad Sci U S A[J], 2008,105:13021-13026.
[37] Bin Bao, Shadan Ali, Aamir Ahmad,Hypoxia-Induced Aggressiveness of Pancreatic Cancer Cells Is Due to Increased Expression of VEGF, IL-6 and miR-21, Which Can Be Attenuated by CDF Treatment. PLoS One[J]. 2012,7(12):e50165.
[38] Kim JH, Park SG, Song SY, et al, Reactive oxygen species-responsive miR-210 regulates proliferation and migration of adipose-derived stem cells via PTPN2. Cell Death Dis[J]. 2013, 11;4:e588.
[39] Gee HE, Ivan C, Calin GA,et al,HypoxamiRs and Cancer: From Biology to Targeted Therapy[J]. ,Antioxid Redox Signal. 2013 Nov 22.
[40] Chan SY, Zhang YY, Hemann C, et al. MicroRNA-210 controls mitochondrial metabolism during hypoxia by repressing the iron-sulfur cluster assembly proteins ISCU1/2. Cell Metab[J], 2009,10 (4):273-284.
[41] Huang X, Zuo J. Emerging roles of miR-210 and other non-coding RNAs in the hypoxic response. Acta Biochim Biophys Sin (Shanghai).2014 [Epub ahead of print].