摘要
雌激素受体(ER)是核受体超级家族成员之一,它包括两种亚型:α和β。两种亚型在结构上基本相似: 一级结构上,从N 端到C 末端,它们均由Α、Β、C、D、E 和F 共6 个部分组成,含两个转录激活区AF1 和AF2。AF1 具有雌激素不依赖的转录激活功能,位于A/B 区;AF2 具有雌激素依赖的转录激活功能,位于E/F 区。AF1 和AF2 的有效转录激活均依赖于与其它蛋白质的相互作用。越来越多的证据表明,ER 除主要在细胞核中发挥作用外,它们也有一部分存在于细胞膜上。与胞内受体相比,膜受体只占2-3%。雌激素可以通过膜上的蛋白质即膜ER 快速激活细胞内的第二信号系统,间接调节一系列基因转录,在多种细胞类型中快速发挥生物学效应。膜ER 可能直接或间接地与G 蛋白偶联受体作用激活多种信号通路,产生cAMP, 激活PLC 和IP3,促进级联反应,增强ERK、JNK和P38 MAPK 活性。另外,膜ER 与核ER 功能互补,使细胞在雌激素作用下既可以快速改变蛋白质活性,又可以持久调节蛋白的合成及功能。目前认为ER 是乳腺癌内分泌治疗的靶标和预后指标之一。乳腺癌内分泌的治疗主要是通过降低ER 转录活性而实现。因此调节ER 转录活性的蛋白因子的发现和相应的功能研究对于有效开发治疗与雌激素相关疾病的药物具有重大意义。
有研究表明,CTGF 在乳腺癌、胰腺癌和黑色素瘤中过度表达。CTGF 是一种富含半胱氨酸的分泌性多肽,其分子量为36～38kD,属于即早基因CCN 家族。作为分泌蛋白,CCN 蛋白可以充当桥梁将胞外基质蛋白与细胞表面分子在结构与功能上联系起来,并通过与其它信号分子的串话,促进有丝分裂、细胞粘附、细胞凋亡、细胞迁移,并调控血管发生、肿瘤生长等生物学过程。作为细胞生长关键性调节因子,CTGF 参与乳腺癌的发生和发展过程。本实验以ERβAF1 为诱饵蛋白,通过酵母双杂交方法筛选出CTGF。首次发现分泌蛋白CTGF 与ER存在直接相互作用,并且体外GST pull-down实验进一步证实CTGF 与ERα、ERβ全长都存在相互作用。通过与CTGF 高度同源的NOV 蛋白比较,发现CTGF 与ER 的结合具有高度特异性。由这些结果我们推测,CTGF 可能是ER 信号途径的新型调节因子。另外,分泌蛋白CTGF 也可能通过特异性受体-膜ER 参与MAPK信号通路,在乳腺癌的发展过程中发挥重要的作用。
Estrogen receptor (ER) is one of the members of the nuclear receptorsuperfamily. Mammalian ER is encoded by two genes:a and ?. Both ERa and ER?can be subdivided into six regions (A-F), which contain two transactivation functionregions, called AF1 and AF2, respectively. AF1 locates in the A/B region, which hasligand-independent transactivation function. AF2 locates in the E/F region, withligand-dependent transactivation function. The effective transactivation of AF1 andAF2 depends on their interaction with other proteins. It has become widely acceptedthat both ERa and ER?can be expressed at the plasma membrane in addition to inthe nucleus, although at a lower density(2-3%) compared with the density in thenucleus. At the membrane, the cross talk with signaling molecules facilitates E2/ER torapidly initiate signal transduction and trigger downstream signaling cascades thatcontribute to important functions. These functions include cell growth andsurvival,migration , and new blood vessel formation. In some instances these resultfrom the initiation of gene transcription, direct stimulation of signaling via G proteinactivation, cAMP generation, phospholipase C activation ,IP3 generation andactivation of extracellular-regulated kinase(ERK), c-Jun N-terminal kinase(JNK) andP38 MAPK(mitogen-activated protein kinase). Furthermore, the nuclear and theplasma membrane form of the ER are believed to be functional complementation,mediating cellular effects rapidly and enduringly. ER plays an important role in thedevelopment of breast cancer. Recently ER is thought to act as a target of the therapyof breast cancer and good index of prognosis. Until now, the endocrine therapy ofmammary carcinoma is acquired mainly by decreasing ER transcriptional activity.Therefore, it is of great significance to discover and characterize the proteins thatmodulateER activityin developing the drugs of diseases related to estrogen.
Some evidences have shown that CTGF (connective tissue growth factor) isoverexpressed in pancreatic cancer, breast cancer, and melanoma. CTGF encodes a36-38 kDa cysteine-rich secreted polypeptide that is a member of an immediate earlygene family known as the CCN family. Functioning as matricellular protein, CCNproteins can bridge the functional and physical gap between ECM-associated proteinsand cell surface molecules. Moreover, CCN family proteins can regulate disparatefundamental biological processes, including mitosis, cell adhesion, apoptosis, growth,differentiation, angiogenesis, embtyogenesis, and tumorigenesis by the cross talk withmultiple signal transduction pathways. As a secretory protein, CTGF may play an
引文
1. Nilsson S, Gustafsson JA. Estrogen receptor transcription and transactivation: basic aspects of estrogen action [J]. Breast Cancer Res., 2000, 2:360-366
2. Klinge CM. Estrogen receptor interaction with estrogen response elements [J]. Nucleic Acids Res., 2001, 29:2905-2919
3. Klinge CM. Estrogen receptor interaction with co-activators and co-repressors [J]. Steroids., 2000, 65:227-251
4. Katzenellenbogen BS, Katzenellenbogen JA. Estrogen receptor transcription and trans-activation: Estrogen receptor alpha and estrogen receptor beta: regulation by selective estrogen receptor modulators and importance in breast cancer [J]. Breast Cancer Res., 2000, 2:335-344
5. Aranda A, Pascual A. Nuclear hormone receptors and gene expression [J]. Physiol. Rev., 2001, 81:1269-1304
6. Kuiper GG, Enmark E, Pelto-Huikko M et al. Cloning of a novel receptor expressed in rat prostate and ovary [J]. Proc. Natl. Acad. Sci. U. S. A., 1996, 93:5925-5930
7. Kuiper GG, Carlsson B, Grandien K et al. Comparison of the ligand binding specificity and transcript tissue distribution of estrogen receptors alpha and beta. Endocrinology [J]. Endocrinology., 1997, 138:863-870
8. Krust A, Green S, Argos P et al. The chicken oestrogen receptor sequence: homology with v-erbA and the human oestrogen and glucocorticoid receptors [J]. EMBO J., 1986, 5:891-897
9. Mangelsdorf DJ, Thummel C, Beato M et al. The nuclear receptor superfamily: the second decade [J]. Cell., 1995, 83:835-839
10. Mosselman S, Polman J, Dijkema R.?ER-?: identification and characterization of a novel human estrogen receptor[J]. FEBS Lett., 1996, 392:49-53
11. Razandi M, et al. Cell membrane and nuclear estrogen receptors (ERs) originate from a single transcript: studies of ERa and ER? expressed in Chinese hamster ovary cells [J]. Mol.Endocrinol.,1999,13:307–319
12. Cheng C C, Shapiro D J. Activation of the p38 mitogen-actived protein kinase pathway by estrogen or by 4-hydroxytamoxifen is coupled to estrogen receptor-induced apoptosis [J]. J Bio Chem., 2000,275: 479-86
13. Sauve F, McBroom LD, Gallant J, et al. CIA, a novel estrogen receptor coactivator with a bifunctional nuclear receptor interacting determinant [J]. Mol Cell Biol., 2001, 21(1):343-353
14. Ko L, Cardona GR, Henrion-Caude A, et al. Identification and characterization of a tissue-specific coactivator, GT198, that interacts with the DNA-binding domains of