MELK as Functional Marker for Mammary Tumors

描述（由申请方提供）：本提案的目的是确定敲低母体胚胎亮氨酸拉链激酶（MELK）表达是否会抑制体内乳腺肿瘤形成。与正常组织相比，MELK在人类乳腺癌中过表达。用siRNA敲低MELK转录物的水平抑制了几种类型的肿瘤（包括乳腺肿瘤）的体外生长。然而，MELK在体内乳腺肿瘤发生中的作用尚未得到证实。我们将使用竞争性移植试验来检验我们的假设，即MELK功能是体内乳腺肿瘤发生所必需的。目标1.确定MELK功能是否是体内多发性T细胞瘤（PyMT）诱导的乳腺肿瘤发生所必需的。我们将从MMTV-PyMT小鼠中分离乳腺肿瘤细胞，并使用表达MELK shRNA和红色荧光蛋白mCherry的慢病毒敲低MELK转录物。对照细胞将用与eGFP MELK shRNA共表达的乱序shRNA感染，受shRNA感染的肿瘤细胞将与对照细胞混合并移植到同基因清洁的乳腺脂肪垫中以产生肿瘤。将分析所得肿瘤中是否存在MELK shRNA感染的供体细胞。如果MELK shRNA在体内抑制肿瘤的发展，我们预计不会发现或很少发现这样的细胞。目的2：确定体内Wnt诱导的乳腺肿瘤的发展是否需要MELK功能。在MMTV-Wnt模型中诱导的乳腺肿瘤比PyMT肿瘤显著更异质，并且在大多数人乳腺癌中更典型。我们将使用MMTV-Wnt 1转基因小鼠来测试该模型中的MELK假设，与PyMT模型所述的完全相同。在这两种情况下，我们将：1）建立原发性肿瘤的有限稀释移植效率; 2）分离肿瘤细胞，用MELK shRNA或乱序对照shRNA慢病毒感染它们，并将它们移植到清除的乳房脂肪垫中; 3）使用荧光显微镜、FACS和Q-PCR的组合分析移植动物中形成的肿瘤中MELK shRNA（mCherry/red）感染的细胞和内源性MELK转录物的存在。迫切需要有效的乳腺癌抑制剂。如果MELK功能是体内乳腺肿瘤生长的先决条件，则小鼠肿瘤细胞和动物模型可用于筛选和验证在乳腺肿瘤模型中特异性抑制MELK功能的化合物（例如，PI实验室开发的特异性激酶抑制剂）。鉴于人和小鼠MELK激酶结构域之间的高度同源性，在小鼠模型中验证的化合物将成为开发靶向人乳腺癌的临床相关抑制剂的先导。项目简介：美国女性乳腺癌的终生风险为1/8，每年约有20万例新确诊病例。迫切需要有效的乳腺癌抑制剂。一个候选基因，母体胚胎亮氨酸拉链激酶（MELK），在大多数乳腺癌中过表达，特别是在侵袭性，低分化肿瘤。尽管有迹象表明，敲低MELK抑制培养物中的肿瘤细胞生长，但缺少MELK在肿瘤发生中的体内作用的证据。我们的假设是MELK功能是体内乳腺肿瘤发生所必需的。在目标1中，我们将使用最好的乳腺肿瘤模型之一，多瘤中T（PyMT）诱导的肿瘤。在目标2中，我们将利用最近建立的Wnt诱导的肿瘤模型。我们已经表明MELK表达在体内标记PyMT肿瘤，并且敲低MELK表达在体外抑制乳腺肿瘤细胞系的生长。PyMT诱导的肿瘤是同质的，并且可以非常有效地在体内移植，使得PyMT模型成为测试我们的假设的最有利的模型。PyMT诱导的肿瘤类似于人类乳腺肿瘤的子集。然而，其他人类肿瘤更异质，并且更好地被Wnt诱导的肿瘤模型捕获。Wnt诱导的肿瘤是异质性的，可能起源于祖细胞室，因此保留了乳腺祖细胞的一些特征。我们的初步数据表明，乳腺端芽含有这些祖细胞表达高水平的MELK。因此，MELK表达可能保留在转化细胞中，并在Wnt 1诱导的乳腺肿瘤的肿瘤起始中发挥功能性作用。在两种小鼠肿瘤模型中，我们将进行一组类似的实验。首先，我们将建立原发性肿瘤的移植效率;其次，我们将用抑制性小发夹RNA（MELK shRNA）或乱序对照shRNA感染肿瘤，并将这些肿瘤移植到乳腺脂肪垫中。第三，我们将使用荧光显微镜和流式细胞术的组合来分析移植动物中形成的肿瘤，以确定MELK shRNA感染的供体细胞是否形成肿瘤。如果MELK shRNA在体内抑制肿瘤形成，我们预计不会发现这些细胞。如果MELK功能是体内乳腺肿瘤生长的先决条件，则小鼠肿瘤细胞和动物模型可用于筛选和验证在乳腺肿瘤模型中特异性抑制MELK功能的化合物（例如，PI实验室开发的特异性激酶抑制剂）。鉴于人和小鼠MELK激酶结构域之间的高度同源性，在小鼠模型中验证的化合物将作为开发靶向人乳腺癌的临床相关抑制剂的先导。

DESCRIPTION (provided by applicant): The goal of this proposal is to determine if knocking down Maternal Embryonic Leucine zipper Kinase (MELK) expression will inhibit mammary tumor formation in vivo. MELK is overexpressed in human breast cancers compared to normal tissue. Knocking down levels of MELK transcript with siRNA inhibits the in vitro growth of several types of tumors, including mammary tumors. However, the role of MELK in mammary tumorigenesis in vivo has not been demonstrated. We will use a competitive transplantation assay to test our hypothesis that MELK function is required for mammary tumorigenesis in vivo. Aim1. Determine if MELK function is required for development of Polyoma Middle T (PyMT) induced mammary tumors in vivo. We will isolate mammary tumor cells from MMTV-PyMT mice and knock down MELK transcripts using lentivirus expressing MELK shRNA and the red fluorescent protein mCherry. Control cells will be infected with scrambled shRNA co-expressed with eGFP MELK shRNA-infected tumor cells will be admixed with control cells and transplanted into syngenic cleared mammary fat pads to generate tumors. The resulting tumors will be analyzed for the presence of donor cells infected with MELK shRNA. We expect to find no/few such cells if MELK shRNA inhibits tumor development in vivo. Aim 2: Determine if MELK function is required for development of Wnt-induced mammary tumors in vivo. Mammary tumors induced in the MMTV-Wnt model are significantly more heterogeneous than are PyMT tumors and are more typical of the majority of human breast cancers. We will use MMTV-Wnt1 transgenic mice to test the MELK hypothesis in this model exactly as described for the PyMT model. In both cases we will: 1) establish limited dilution transplantation efficiency of primary tumors; 2) isolate tumor cells, infect them with MELK shRNA or scrambled control shRNA lentivirus and transplant them into cleared mammary fat pads; 3) analyze tumors formed in transplanted animals using a combination of fluorescence microscopy, FACS and Q- PCR for the presence of MELK shRNA (mCherry/red) infected cells and endogenous MELK transcripts. There is a crucial need for potent inhibitors of breast cancers. If MELK function is a prerequisite for mammary tumor growth in vivo, mouse tumor cells and animal models can be used to screen and validate compounds that specifically inhibit MELK function in mammary tumor models (e.g., specific kinase inhibitors that have been developed in the PI's laboratory). Given the very high homology between human and mouse MELK kinase domains, compounds validated in a mouse model will be the leads for developing clinically relevant inhibitors to target human breast cancer. PROJECT NARRATIVE: The lifetime risk of breast cancer for women in the USA is 1 in 8, with about 200,000 new cases diagnosed each year. There is a crucial need for potent inhibitors of breast cancers. A candidate gene, Maternal Embryonic Leucine zipper Kinase (MELK), is overexpressed in most breast cancers, particularly in aggressive, poorly differentiated tumors. Despite indications that knocking down MELK inhibits tumor cell growth in culture, evidence for an in vivo role for MELK in tumorigenesis is missing. Our hypothesis is that MELK function is required for mammary tumorigenesis in vivo. In Aim 1 we will use one of the best established mammary tumor models, Polyoma Middle T (PyMT) induced tumors. In Aim 2 we will take advantage of the more recently established Wnt-induced tumor model. We have shown that MELK expression marks PyMT tumors in vivo and that knocking down MELK expression inhibits growth of a mammary tumor cell line in vitro. PyMT-induced tumors are homogeneous and can be very efficiently transplanted in vivo making the PyMT model the most favorable one in which to test our hypothesis. PyMT-induced tumors resemble a subset of human breast tumors. However, other human tumors are more heterogeneous and better captured by the Wnt-induced tumor model. Wnt-induced tumors are heterogeneous and likely initiated in the progenitor compartment, thus retaining some features of mammary gland progenitor cells. Our preliminary data suggest that mammary gland end buds containing those progenitor cells express high levels of MELK. Thus, MELK expression may be retained in transformed cells and play a functional role in tumor initiation in Wnt1-induced mammary tumors. In both mouse tumor models we will perform a similar set of experiments. First, we will establish the transplantation efficiency of primary tumors; second, we will infect tumors with inhibitory small hairpin RNAs (MELK shRNAs) or a scrambled control shRNA and transplant those tumors into mammary fat pads. Third, we will analyze tumors formed in transplanted animals using a combination of fluorescence microscopy and flow cytometry to determine if donor cells infected with MELK shRNA form tumors. If MELK shRNA inhibits tumor formation in vivo we expect not to find these cells. If MELK function is a prerequisite for mammary tumor growth in vivo, mouse tumor cells and animal models can be used to screen and validate compounds specifically inhibiting MELK function in mammary tumor models (e.g., specific kinase inhibitors that have been developed in the PI's laboratory). Given the very high homology between human and mouse MELK kinase domains, compounds validated in a mouse model will serve as the leads for developing clinically relevant inhibitors to target human breast cancers.