來(lái)自哈佛醫(yī)學(xué)院（HMS）和麻省總醫(yī)院（HMS）的研究人員在乳腺癌、肝癌和其他種類(lèi)的癌癥中發(fā)現(xiàn)了一種具有潛在促癌作用（cancer-promoting）的基因,。他們發(fā)現(xiàn)這種YAP基因可以轉(zhuǎn)化人乳腺上皮細(xì)胞,，為理解一種首先在果蠅中發(fā)現(xiàn)的細(xì)胞生長(zhǎng)新調(diào)控通路,，是怎樣在人類(lèi)癌癥扮演重要角色的問(wèn)題打開(kāi)了大門(mén)。該研究工作發(fā)表《PNAS》的網(wǎng)絡(luò)版上,。
“我們?cè)谌橄侔┘?xì)胞中篩選與腫瘤發(fā)生相關(guān)的DNA,。確定這些潛在導(dǎo)致癌癥發(fā)生的新基因,，對(duì)研究正常細(xì)胞轉(zhuǎn)化成為癌細(xì)胞的新途徑來(lái)說(shuō)至關(guān)重要,。”該文章的高級(jí)作者,，來(lái)自HMS和MGH的教授Daniel Haber博士說(shuō),。該研究由Haber博士實(shí)驗(yàn)室和HMS細(xì)胞生物學(xué)系Joan Brugge教授領(lǐng)導(dǎo)的實(shí)驗(yàn)室共同完成,。
通過(guò)在BRCA1/p53基因缺失小鼠模型中進(jìn)行的乳腺腫瘤的微陣列分析,，Haber博士領(lǐng)導(dǎo)的研究小組發(fā)現(xiàn)在小鼠乳腺腫瘤中擴(kuò)增的DNA區(qū)域僅僅包含一種已知基因——YAP,。
“在一些人類(lèi)腫瘤細(xì)胞中也發(fā)現(xiàn)了相似的DNA擴(kuò)增區(qū)域，但這些區(qū)域通常包含了其他一些促進(jìn)細(xì)胞生存的已知基因,。”
Haber說(shuō),，“因此,，關(guān)于YAP基因是否在這些癌癥中起作用的問(wèn)題在很大程度上受到了忽視,。我們發(fā)現(xiàn)排除這些擴(kuò)增的DNA區(qū)域中的其它基因，我們能夠?qū)Ｗ⒂赮AP作為候選研究對(duì)象的工作中,。”
YAP基因在文獻(xiàn)中首先是在果蠅實(shí)驗(yàn)中引起人們的注意,，果蠅中的YAP基因，又稱(chēng)為Yorkie (Yki),，作用是促進(jìn)細(xì)胞分裂和細(xì)胞生存,，并受其它幾個(gè)基因調(diào)控,，如：Hippo (Hpo), Salvador (Sav), Warts (Wts), 和Mats,。這些調(diào)控途徑上游基因中任何一個(gè)發(fā)生變異或者Yki基因的過(guò)量表達(dá)將會(huì)引起果蠅眼睛或者翅膀細(xì)胞的過(guò)量生長(zhǎng),。這種促進(jìn)細(xì)胞分裂和細(xì)胞生存的作用的偶聯(lián)是唯一的——其它能促進(jìn)細(xì)胞分裂的基因如Myc,，卻會(huì)促進(jìn)細(xì)胞的死亡,。
“在癌癥模型中用汽車(chē)來(lái)比喻癌癥形成，Myc基因就像用汽油驅(qū)使汽車(chē)前進(jìn)一樣,，驅(qū)動(dòng)細(xì)胞分裂,，但同時(shí)又能對(duì)細(xì)胞分裂輕微‘剎車(chē)’,，所以當(dāng)細(xì)胞分裂中出現(xiàn)錯(cuò)誤的時(shí)候，細(xì)胞分裂之‘車(chē)’能夠很快的停下來(lái)——通過(guò)清除細(xì)胞或者細(xì)胞死亡,。”來(lái)自HMS細(xì)胞生物學(xué)系的研究伙伴,，該文章的第一作者M(jìn)ichael Overholtzer博士說(shuō),，“而Yki基因的活化，就像汽油驅(qū)動(dòng)汽車(chē)前進(jìn)的同時(shí)使剎車(chē)閘失效,。這種作用對(duì)于癌癥細(xì)胞生長(zhǎng)來(lái)說(shuō)求之不得,。因此,，這些發(fā)現(xiàn)于果蠅的基因：Yki(YAP), Hpo, Sav, Wts, 和 Mats,，雖然很多是首先在果蠅中被發(fā)現(xiàn)的,，卻可能是控制著人類(lèi)癌癥的新途徑的發(fā)生,。
對(duì)YAP基因功能的早期研究結(jié)果并不支持它是一種人類(lèi)致癌基因的說(shuō)法,，這是由于它的過(guò)量表達(dá)事實(shí)上促進(jìn)細(xì)胞死亡而不是促進(jìn)細(xì)胞存活。然而,，由于在小鼠乳腺瘤中發(fā)現(xiàn)了YAP基因的擴(kuò)增，Overholtzer和他的同事們決定在Brugge實(shí)驗(yàn)室開(kāi)發(fā)的3D乳腺培養(yǎng)模型中進(jìn)行YAP功能的研究,。
利用這種模型,，他們?cè)谌S的蛋白矩陣而不是二維矩陣上培養(yǎng)細(xì)胞，使得培養(yǎng)的乳腺細(xì)胞的生長(zhǎng)具有人類(lèi)乳腺相似的架構(gòu),。
利用三維培養(yǎng),，研究者們能夠證明YAP基因的過(guò)量表達(dá)戲劇性的改變了細(xì)胞侵入蛋白矩陣的行為。這種入侵行為正常情況下都與強(qiáng)烈促癌基因相關(guān),。研究者進(jìn)一步表明,，在3D培養(yǎng)和其它的分析實(shí)驗(yàn)中，YAP的過(guò)量表達(dá)既能激活細(xì)胞的生長(zhǎng)又能抑制細(xì)胞的死亡,。
此外,，在實(shí)驗(yàn)室的研究中，YAP的過(guò)量表達(dá)能夠?qū)⒎前┑娜橄偌?xì)胞轉(zhuǎn)化成為癌細(xì)胞,，這是通過(guò)YAP表達(dá)的細(xì)胞在軟瓊脂上生長(zhǎng)——一種衡量癌癥潛能的實(shí)驗(yàn)證明,。與Overholtzer和他的同事的工作進(jìn)行的同時(shí)，冷泉港的Scott Lowe博士的實(shí)驗(yàn)室證明了在一種小鼠模型中,，YAP的過(guò)量表達(dá)可以導(dǎo)致肝癌的發(fā)生,。(Cancer Cell, July 2006)。這表明YAP基因確實(shí)是一種新致癌基因,。
“我們下一步想要知道的是YAP基因在人類(lèi)細(xì)胞中是怎樣受Hpo-Sav-Wts通路所控制的”，Overholtzer說(shuō),。“雖然我們?cè)谛∈笕橄倭鲋邪l(fā)現(xiàn)了YAP基因的擴(kuò)增，但實(shí)際上YAP擴(kuò)增子（amplicon）在人類(lèi)癌癥中普遍存在,，例如肺癌、胰腺癌,、卵巢癌和其他癌癥中,。因此YAP基因可能在許多癌癥的發(fā)生中起著重要的作用。
英文原文：
Hunt for DNA Amplified in Cancers Uncovers Important Target Gene
Researchers have discovered a new cancer-promoting role for a gene potentially involved in breast, liver, and other kinds of cancers. Their discovery that the gene YAP can transform mammary epithelial cells opens the door to understanding how a novel cell growth controlling pathway first discovered in fruit flies might be important in human cancers.
“We screened the DNA from breast cancer cells for amplifications that are associated with tumor development. The identification of these new potential cancer-causing genes is critical to uncovering novel pathways that drive the conversion of a normal cell to a cancerous one.” says senior author Daniel Haber, MD, PhD, the Laurel Schwartz professor of medicine at Harvard Medical School (HMS) and Massachusetts General Hospital (MGH) and director of the MGH Cancer Center. This research was conducted jointly by Haber’s lab and the lab of Joan Brugge, PhD, professor and chair of the Department of Cell Biology at HMS and is published in the Aug. 8 online early edition of the Proceedings of the National Academy of Sciences and will appear in the Aug. 15 print edition.
Through microarray analysis of a mammary tumor in a BRCA1/p53 deficient mouse model, Haber’s group discovered an amplified region of DNA in the mouse breast tumor that contained only one known gene, called YAP.
“A similar region of DNA is also amplified in some human tumors, but this amplified region often contains other genes that are known to promote cell survival,” says Haber, who worked with co-authors Jianmin Zhang, PhD, and Gromoslaw Smolen, PhD, both research fellows at MGH. “Thus, whether the YAP gene could play a role in these cancers had been largely ignored. The amplified region we discovered excluded these other genes, which allowed us to focus on YAP as a new candidate.”
The YAP gene has an interesting literature associated with it that comes from the fruit fly Drosophila melanogaster. The Drosophila version of the YAP gene, called Yorkie (Yki), functions to promote both cell division and cell survival and is controlled by several other genes called Hippo (Hpo), Salvador (Sav), Warts (Wts), and Mats. The mutation of any of these upstream genes or the over expression of Yki causes dramatic overgrowth of cells in the Drosophila eye or wing. This coupling of cell division and cell survival is unique – other genes that promote cell division, for example, Myc, also sensitize a cell to death.
“To use the car analogy that is often applied to cancer models, activation of Myc is like stepping on the gas to activate cell division but also lightly tapping on the brakes at the same time, so that should anything go wrong during division, the car can very quickly be stopped, or the cell can be removed by cell death,” says first author Michael Overholtzer, PhD, research fellow in cell biology at HMS. “Yki activation, on the other hand, is like stepping on the gas and disabling the brakes at the same time. Such an activity would be thought to be coveted by cancer cells. Therefore these genes, Yki (YAP), Hpo, Sav, Wts, and Mats, most of which were first discovered in the fruit fly, represent a relatively new and exciting pathway that might control human cancers.”
Earlier studies on YAP function in human cells did not support the notion that YAP might be a cancer causing gene because its over expression actually promoted cell death rather than cell survival (like Yki in Drosophila). Nevertheless, due to the amplification of YAP in a mouse breast tumor, Overholtzer and colleagues decided to examine the functions of YAP in a 3D mammary culture model developed in Brugge’s lab.
In this model, they grew cells in a 3-dimensional protein matrix rather than in 2-dimensions on plastic, which allows mammary cells to adopt architecture in culture that is similar to what occurs in the human breast. They had previously uncovered the effects of other genes using this model that would be missed in more conventional 2D models.
Using these 3D cultures, the authors were able to show that the over expression of YAP caused a dramatic change in cell behavior associated with invasion into the protein matrix. This type of invasive activity is normally associated with strong acting cancer-promoting genes. The authors were further able to show, in 3D cultures and other assays that YAP over expression both activated cell growth and inhibited cell death, just as one might have predicted from the studies of Yki in Drosophila.
Moreover, YAP over expression was able to turn their non-cancerous mammary cells into cancer-like cells in the lab, as evidenced by the ability of YAP expressing cells to grow in soft agar, an assay that measures cancerous potential. Parallel to Overholtzer and colleague’s work, the lab of Scott Lowe, PhD, of Cold Spring Harbor, also showed that YAP over expression could contribute to the development of liver tumors in a mouse model (Cancer Cell, July 2006). Thus, it appears that YAP is indeed a newly identified cancer-causing gene.
“What we would like to understand next is how YAP is controlled by the Hpo-Sav-Wts pathway in human cells”, says Overholtzer. “Also, although we found the YAP amplification in a mouse breast tumor, in human cancers this amplicon is actually much more common in other types such as lung, pancreatic, ovarian, and others. Thus it is possible that YAP plays an important role in the development of many different types of cancer.”
