Integrin splicing and cancer stem cell fate

 描述(申请人提供)：这项建议将检验一项新的假设，即乳腺癌干细胞(CSCs)的起源和功能由一个前馈环路控制，该环路支持河马转导系统TAZ的激活。此循环的连接点是 α6β1整合素，α6Bβ1。α6亚基的两个变体(α6A和α6B)在细胞质结构域上存在唯一的不同。共同的mRNA的选择性剪接产生了这些变体。α6Aβ1整合素信号通路阻止TAZ激活。第一个目标是基于α6Aβ1与极性/肿瘤抑制蛋白Scribble相互作用以及Scribble与TAZ结合并阻止其核定位的发现，探讨相关机制。因此，第一个目的将检验这样的假设，即α6Aβ1整合素与乳腺上皮细胞表面的Scribble相互作用，并有助于其锚定在质膜上，这种相互作用是由存在于α6A细胞质结构域中的PDZ结合结构域介导的。据推测，α6A整合素/Scribble复合体隔离TAZ，阻止其核定位和激活。第二个目的将评估一种假说，即TAZ促进肿瘤干细胞发生的机制之一是抑制导致α6Bβ1发生和α6Aβ1丢失的mR NA剪接因子ESRP1mRNA，并形成LM511基质。此外，推测TAZ调控血管内皮生长因子转录并诱导血管内皮细胞生长因子信号转导，而血管内皮细胞生长因子信号转导途径使BMI1介导的ESRP1被抑制。TAZ还促进作为α6Bβ1配体的LM511基质的形成。因此，建立了一个涉及TAZ和支持CSCs的LM511/α6Bβ1信号的前馈环。第三个特定目的将确定α6Aβ1和α6Bβ1信号在激活TAZ的能力上的不同，重点是Jun末端激酶(Jnk)的作用。需要解决的特定假设是，α6Aβ1信号促进JNK激活和JNK介导的一种新的丝氨酸(S90)上的TA Z的磷酸化，从而导致TA Z失活。相反，LM511/α6Bβ1信号通路阻止了JNK1的激活，并阻止了JNKJNK介导的TAPZ磷酸化使TAPZ激活。这一假设推断，JNK抑制在TAZ激活和干细胞特性获得中具有因果作用，这一点将得到评估。这一建议具有丰富的创新性和重要意义 所获得的结果将对我们理解乳腺CSCs的生物学产生重大影响，并揭示新的治疗干预机制。

 DESCRIPTION (provided by applicant): This proposal will examine the novel hypothesis the genesis and function of breast cancer stem cells (CSCs) are governed by a feed forward loop that sustains activation of the Hippo transducer TAZ. The nexus of this loop is a splice variant of the α6β1 integrin, α6Bβ1. Two variants of the α6 subunit exist (α6A and α6B) that differ onl in their cytoplasmic domains. Alternative splicing of a common mRNA generates these variants. α6Aβ1 integrin signaling prevents TAZ activation. The first aim will pursue the mechanism involved based on the findings that α6Aβ1 interacts with the polarity/tumor suppressor protein Scribble and that Scribble associates with TAZ and prevents its nuclear localization. Thus, the first aim will test the hypothesis that the α6Aβ1 integrin interacts with Scribble on the surfaceof mammary epithelial cells and contributes to its anchoring on the plasma membrane, an interaction mediated by the PDZ-binding domain present in the α6A cytoplasmic domain. It is postulated that the α6A integrin/Scribble complex sequesters TAZ preventing its nuclear localization and activation. The second aim will assess the hypothesis that one mechanism by which TAZ promotes the genesis of CSCs is to repress the mRNA splicing factor ESRP1 resulting in the genesis of α6Bβ1 and loss of α6Aβ1, and the formation of a LM511 matrix. Moreover, it is postulated that TAZ regulates VEGF transcription and induces VEGF signaling, and that VEGF signaling enables the BMI1-mediated repression of ESRP1. TAZ also promotes the formation of a LM511 matrix that functions as the ligand for α6Bβ1. Consequently, a feed forward loop is established involving TAZ and LM511/α6Bβ1 signaling that sustains CSCs. The third specific aim will determine how α6Aβ1 and α6Bβ1 signaling differ in their ability to actiate TAZ focusing on the role of Jun-terminal kinase (JNK). The specific hypothesis to be addressed is that α6Aβ1 signaling promotes JNK activation and JNK-mediated phosphorylation of TAZ on a novel serine (S90), which contributes to TAZ inactivation. LM511/α6Bβ1 signaling, in contrast, prevents JNK activation and JNK-mediated TAZ phosphorylation enabling TAZ activation. This hypothesis infers that JNK inhibition has a causal role in TAZ activation and the acquisition of stem cell properties, which will be evaluated. This proposal is rich in innovation and significance and the results to be obtained will have a major impact on our understanding of the biology of breast CSCs and reveal new mechanisms for therapeutic intervention.