Non-canonical roles of Mitotic Arrest Deficient 1 (Mad1) in tumor promotion

乳腺癌是世界范围内女性最常见的恶性肿瘤。有丝分裂阻滞缺陷1 （Mad 1）通常在乳腺癌中上调，在乳腺癌中它作为预后不良的标志物， Mad 1的上调足以在原位乳腺癌模型中发生肿瘤。Mad 1被识别， 其特征在于其在有丝分裂中的功能，在有丝分裂中，其用于防止染色体错误分离/染色体 不稳定性（CIN）。CIN与促进原发性和转移性肿瘤有关。然而，Mad 1 在整个间期表达，我们最近表明，Mad 1的非典型间期函数 在使p53肿瘤抑制因子不稳定中，Mad 1上调促进原位乳腺肿瘤的发生是至关重要的 增长此外，我们确定了一个以前未被识别的池Mad 1定位到高尔基体。 在高尔基体，Mad 1在新合成的蛋白质的成熟和分泌中执行另一个非典型功能。 α5整合素是一种重要的转移促进因子和预后不良的标志物。因此，Mad 1上调导致 三种肿瘤和转移促进表型：CIN、p53不稳定和α5整合素分泌。要求1 将确定Mad 1上调的哪些功能对于肿瘤促进是必要的和足够的， 功能突变体的分离、竞争实验、特异性抑制剂和新的CRISPR/Cas9编辑 小鼠模型。目的2将定义Mad 1在新合成的细胞分泌中发挥作用的机制。 α5整联蛋白，这将为抑制α5整联蛋白促进转移的活性提供新的机会。在一起， 所提出的实验将确定Mad 1的肿瘤促进活性的机制基础， α5整合素生物合成运输途径，这将扩大我们对乳腺癌的基本理解 癌症并揭示新的治疗靶点。

Breast cancer is the most commonly diagnosed malignancy in women worldwide. Mitotic Arrest Deficient 1 (Mad1) is commonly upregulated in breast cancer where it serves as a marker of poor prognosis, and upregulation of Mad1 is sufficient for tumorigenesis in orthotopic breast cancer models. Mad1 was identified and characterized for its function in mitosis, where it serves to prevent chromosome missegregation/chromosomal instability (CIN). CIN has been implicated in promoting both primary and metastatic tumors. However, Mad1 is expressed throughout interphase and we have recently shown that a non-canonical interphase function of Mad1 in destabilizing the p53 tumor suppressor is critical for Mad1 upregulation to promote orthotopic mammary tumor growth. Additionally, we identified a previously unrecognized pool of Mad1 that localizes to the Golgi apparatus. At the Golgi, Mad1 performs another non-canonical function in the maturation and secretion of newly synthesized α5 integrin, a critical metastasis promoter and marker of poor prognosis. Thus, Mad1 upregulation results in three tumor- and metastasis-promoting phenotypes: CIN, p53 destabilization and α5 integrin secretion. Aim 1 will determine which functions of Mad1 upregulation are necessary and sufficient for tumor promotion using separation of function mutants, competition experiments, specific inhibitors, and novel CRISPR/Cas9 edited mouse models. Aim 2 will define the mechanisms by which Mad1 functions in the secretion of newly synthesized α5 integrin, which will provide novel opportunities to inhibit α5 integrin activity in promoting metastasis. Together, the proposed experiments will identify the mechanistic basis of the tumor promoting activity of Mad1 and define the α5 integrin biosynthetic trafficking pathway, which will expand our fundamental understanding of breast cancer and reveal novel therapeutic targets.