Brk signal transduction in breast cancer

描述（由申请人提供）：蛋白酪氨酸激酶（PTK）在正常细胞生长和分化的调节中起关键作用;其过表达可能通过增加对局部作用肽生长因子的敏感性或降低对凋亡信号的敏感性而赋予乳腺癌细胞生长优势。膜受体PTKs活性升高发生在相当一部分乳腺肿瘤中。大多数恶性人乳腺癌的胞质组分中的总可溶性PTK活性也高于良性或正常乳腺组织。事实上，最近已经从恶性人类乳腺组织中克隆了几种新的非受体PTK，并且发现其在迄今为止检查的大多数乳腺癌中具有高度活性和/或过表达。因此，重要的是要确定这些不太好的特点PTKs的作用，作为已知的信号通路的新组件也过表达的人乳腺癌的大部分。从人转移性乳腺肿瘤中克隆了一种新的非受体PTK，称为乳腺肿瘤激酶（Brk），发现其在人乳腺癌和乳腺癌细胞系中过表达，但在正常成人乳腺组织中不表达。虽然Brk与c-Src在功能上有明显区别，但它与c-Src密切相关，包含1个SH 3结构域和1个SH 2结构域。Brk的过表达转化人乳腺上皮细胞。在人乳腺癌细胞中，Brk与Akt/PKB相关，并响应heregulin/c-erbB 2激活而被激活。Brk过表达以细胞类型特异性方式诱导细胞凋亡。我们假设Brk通过作为erbB 2/erbB 3受体家族成员下游和Akt激酶（细胞生长、存活和转化的关键调节因子）近端的信号传导组分，赋予人乳腺癌细胞生长和/或存活优势。我们将1）阐明Brk活性和磷酸化对不同促有丝分裂剂的反应，2）确定Brk与Akt和其他信号分子相互作用的功能意义，3）测定过表达Brk和Brk基因沉默期间细胞生物学和转化的体外和体内读数。通过确定生长因子受体介导的信号事件的变化机制，我们将增加已知参与乳腺癌细胞生长和存活的调节蛋白的库。非受体PTK途径可能被证明是化疗干预的有用靶点。

DESCRIPTION (provided by applicant): Protein tyrosine kinases (PTKs) play a critical role in the regulation of normal cell growth and differentiation; their overexpression may confer a growth advantage to breast cancer cells by increasing sensitivity to locally-acting peptide growth factors, or by decreasing sensitivity to apoptotic signals. Elevated activity of membrane receptor PTKs occurs in a significant portion of breast tumors. Total soluble PTK activity in the cytosolic fractions of a majority of malignant human breast cancers is also higher than that from benign or normal breast tissue. Indeed, several novel non-receptor PTKs have recently been cloned from malignant human breast tissues and found to be highly active and/or overexpressed in a majority of breast cancers examined thus far. It is therefore important to define the role of these less well characterized PTKs as novel components of known signaling pathways also overexpressed in a large proportion of human breast cancers. A novel nonreceptor PTK, termed breast tumor kinase (Brk) was cloned from a human metastatic breast tumor, and found to be overexpressed in human breast carcinomas and breast cancer cell lines, but not in normal adult breast tissue. Although clearly functionally distinct, Brk is closely related to c-Src, and contains 1 SH3-domain and 1 SH2-domain. Overexpression of Brk transforms human mammary epithelial cells. In human breast cancer cells, Brk associated with Akt/PKB and was activated in response to heregulin/c-erbB2 activation. Brk overexpression induced apoptosis in a cell-type specific manner. We hypothesize that Brk confers a growth and/or survival advantage to human breast cancer cells by acting as signaling component downstream of erbB2/erbB3 receptor family members and proximal to Akt kinase, a key regulator of cell growth, survival and transformation. We will 1) elucidate Brk activity and phosphorylation in response to diverse mitogenic agents 2) determine the functional significance of Brk interaction with Akt and other signaling molecules, and 3) assay in vitro and in vivo readouts of cell biology and transformation in cells overexpressing Brk and during Brk gene-silencing. By identifying mechanisms underlying changes in growth factor receptor-mediated signaling events, we will increase the repertoire of regulatory proteins known to be involved in breast cancer cell growth and survival. Non-receptor PTK pathways may prove to be useful targets for chemotherapeutic intervention.