Role of the serine-threonine kinase PAK1 in prolactin-dependent signaling

描述（由申请方提供）：在正常乳腺发育中，激素催乳素（PRL）对肺泡增殖和分化至关重要。越来越多的证据支持PRL参与乳腺癌，乳腺癌是女性癌症的主要类型，也是女性癌症死亡的第二大原因（仅次于肺癌）。2002年，预计将诊断出203 500个新的乳腺癌病例，预计将有39 600名妇女死于这种疾病。催乳素受体（PRLR）在80%的人类乳腺癌中被检测到，并且在乳腺癌细胞中过表达。正常和肿瘤乳腺上皮细胞合成催乳素和催乳素受体，因此催乳素可作为人乳腺癌细胞的自分泌生长因子。这些结果表明，需要一个更完整的了解催乳素受体信号的生长促进，抗凋亡途径。酪氨酸（Tyr）激酶JAK 2被鉴定为PRLR结合的信号分子。识别被招募到PRLR-JAK 2的蛋白质并剖析随后被激活的信号通路最终将为理解PRL作用提供基础。初步数据表明，丝氨酸-苏氨酸激酶PAK 1与JAK 2结合并被JAK 2磷酸化。二维肽图谱鉴定了PAK 1的三个Tyr（s），其被JAK 2磷酸化。JAK 2对PAK 1的Tyr磷酸化也显示出保护细胞免于凋亡。该基金提出了一个假设，即PAK 1是JAK 2的底物，在对PRL的反应中，PAK 1被JAK 2依赖的Tyr磷酸化激活，并增强PRL依赖的细胞存活。Aim 1将验证PRL在体内促进PAK 1的Tyr磷酸化。Aim 2将决定PAK 1的JAK 2磷酸化是否改变PAK 1激酶活性和/或PAK 1结合PAK 1靶标的能力。在Aim 3中，将确定PAK 1的JAK 2 Tyr磷酸化对PRL依赖性细胞存活的影响。由于PAK 1和PRL都与乳腺癌有关，因此拟议的研究可能最终填补上游PRL-PRLR-JAK 2事件和下游PAK 1依赖性功能之间的现有空白，以了解人类乳腺癌的机制。JAK 2对PAK 1的Tyr磷酸化可能代表了寻找人类乳腺癌病因和治疗的新分子靶点。

DESCRIPTION (provided by applicant): In normal mammary development, the hormone prolactin (PRL) is critical for alveolar proliferation and differentiation. Increasing evidence supports the involvement of PRL in breast cancer, the leading type of cancer in women and the second leading cause (after lung cancer) of cancer death among women. In 2002, 203,500 new cases of breast cancer were expected to be diagnosed, and 39,600 women were expected to die of the disease. The prolactin receptor (PRLR) is detected in 80% of human breast cancers, and is overexpressed in breast cancer cells. Normal and tumor mammary epithelial cells synthesize PRL and PRLR, thus the PRL could behave as an autocrine growth factor for human breast cancer cells. These results suggest the need for a more complete understanding of PRLR signaling to growth promoting, anti-apoptotic pathways. Tyrosine (Tyr) kinase JAK2 was identified as a PRLR-bound signaling molecule. Identification of the proteins recruited to the PRLR-JAK2 and dissection of the signaling pathways that are subsequently activated will ultimately provide a basis for understanding PRL action. Preliminary data demonstrate that the serine-threonine kinase PAK1 associates with and is Tyr phosphorylated by JAK2. Two-dimensional peptide mapping identified three Tyr(s) of PAK1 which are phosphorylated by JAK2. Tyr phosphorylation of PAK1 by JAK2 was also shown to protect cells from apoptosis. This grant proposes to examine the hypothesis that PAK1 is a substrate for JAK2 and that in response to PRL, PAK1 is activated by JAK2-dependent Tyr phosphorylation and enhances PRL-dependent cell survival. Aim1 will verify that PRL promotes Tyr phosphorylation of PAK1 in vivo. Aim2 will determine whether JAK2 phosphorylation of PAK1 alters PAK1 kinase activity and/or ability of PAK1 to bind PAK1 targets. In Aim3 the effect of JAK2 Tyr phosphorylation of PAK1 on PRL-dependent cell survival will be determined. Because both PAK1 and PRL have been implicated in breast cancer, the proposed studies may ultimately fill out the existing gap between upstream PRL-PRLR-JAK2 events and downstream PAK1-dependent functions in our understanding of the mechanism of human breast cancer. Tyr phosphorylation of PAK1 by JAK2 is likely to represent a novel molecular target in the search for the etiology and treatment of human breast cancer.