A NEURAL TRANSCRIPTION FACTOR IN LUNG CANCER EVOLUTION

这项拨款提案侧重于转录因子人类achaete-scute Homolog-1(HASH1)在小细胞肺癌(SCLC)演变中的关键作用。与其他三种主要类型的肺癌不同，小细胞肺癌的区别在于神经和神经内分泌(NE)的表达。HASH1是果蝇Achaete-Scute复合体的人类对应物，DroSingila achaete-Scute复合体是一个保守的碱性螺旋环螺旋转录因子家族，对于从未分化的前体细胞合成原始神经母细胞是必不可少的。在哺乳动物的发育过程中，ASH1(啮齿动物称为MASH1)对于交感肾上腺、肠、嗅觉、视网膜和脑交感神经元的正常分化是必不可少的。我们最近发现，正常胎肺中的ASH1仅限于肺中的NE细胞。此外，ASH1的转基因敲除会导致肺NE细胞完全无法分化，并导致出生时致命的呼吸功能不全。肺损伤模型的初步研究表明，hASH1在肺增生性NE细胞的募集中起着重要作用。在广泛的肺癌表型中，hASH1的表达与NE表型标志物严格一致。我们发现，去除培养的SCLC细胞中的hASH1蛋白会导致NE标志物表达的相应减少，并增加细胞凋亡率。我们研究了一种新的转基因模型，在该模型中，hASH1使用细胞特异性启动子CC10靶向肺Clara细胞。这些小鼠的远端呼吸道出现进行性增生，涉及CC10反应细胞。值得注意的是，hASH1与SV40T抗原有效地合作，促进这些靶细胞的恶性转化和NE肿瘤。综上所述，这些发现表明hASH1可能在小细胞肺癌从肺NE前体细胞进化过程中起关键作用。我们提出的一系列研究现在试图确定：1)hASH1和相关的原神经转录因子如何在肺癌发生的新模型中发挥作用；2)hASH1与肺癌的演变相关的转录靶点是什么；以及3)hASH1通过Notch途径调节在SCLC细胞中可能发生了怎样的变化。这些研究将提供对hASH1在小细胞肺癌发病机制中作用的更全面的了解，潜在地导致在新的治疗策略中利用小细胞肺癌的特定脆弱性。

This grant proposal focuses on the critical role of the transcription factor, human achaete-scute homolog-1 (hASH1) in the evolution of small cell lung cancer (SCLC). Unlike the other three major types of lung cancer, SCLC is distinguished by expression of neural and neuroendocrine (NE) features. HASH1 is a human counterpart to the Drosophila achaete-scute complex, a conserved family of basic helix loop helix transcription factors that are essential for commitment of primitive neuroblasts from undifferentiated precursors. In mammalian development, ASH1 (termed MASH1 in rodents) is essential for normal differentiation of sympathoadrenal, enteric, olfactory, retinal, and brain sympathetic neurons. We have recently shown that ASH1 in the normal fetal lung is restricted to lung NE cells. Furthermore, transgenic knockout of ASH1 results in a complete failure of lung NE cells to differentiate and causes fatal respiratory insufficiency at birth. Preliminary studies from lung injury models suggest an important role for hASH1 in the recruitment of hyperplastic lung NE cells. Across a broad spectrum of lung cancer phenotypes, hASH1 expression is strictly concordant with NE phenotypic markers. We found that depletion of hASH1 protein from cultured SCLC cells resulted in a comparable reduction of NE marker expression, and an increase in apoptotic fraction. We have studied a new transgenic model in which hASH1 is targeted to lung Clara cells, using a cell-specific CC10 promoter. These mice develop progressive hyperplasia of their distal airway involving the CC10-reactive cells. Remarkably, hASH1 cooperates potently with the SV40 T-Antigen to promote malignant transformation and NE tumors in these target cells. Collectively, these findings indicate that hASH1 may be critical in the evolution of SCLC from lung NE precursor cells. Our proposed series of studies now seek to determine: 1) How hASH1 and related proneural transcription factors function in novel models of lung carcinogenesis; 2) What are the transcriptional targets of hASH1, relevant to the evolution of lung cancer, and 3) How hASH1 regulation, via the Notch pathway, may be altered in SCLC cells. These studies will provide a more comprehensive understanding of hASH1 action in SCLC pathogenesis, potentially leading to exploitation of specific vulnerabilities of SCLC tumors in novel treatment strategies.