AUTOCRINE TGF-A-- FUNCTION AND CONTROL IN COLON CANCER

这是CA548o7的竞争性更新，本项目上一个周期的目标包括a)自分泌TGF - α功能的测定和b)结肠癌中TGF - α表达的控制机制。已取得的成就包括确定自分泌TGF α：在早期和晚期结肠癌中主要在从限制细胞生长的环境条件重新进入循环状态的过程中起作用。生长因子剥夺)，在积极循环的种群中似乎没有显著作用（例如，组织培养中的指数增长）。晚期结肠癌细胞系与早期细胞的不同之处在于，它们完全独立于外源性生长因子，从生长停滞中重新开始DNA合成，而早期细胞需要外源性胰岛素样生长因子1受体（IGFIR）配体来重新进入细胞周期。我们发现，晚期恶性细胞的生长因子独立性源于生长阻滞细胞中不适当的TGF α表达（而不是过度表达）和EGF受体（EGFR）激活。这具有产生组成EGFR激活的作用，这是一个长期与转化相关的事件。早期细胞在生长停滞时不表达TGF - α或表现出显著的EGFR激活。早期细胞中的IGFIR激活再生了自分泌TGF α：表达和EGFR激活事件，我们已经证明这些细胞中的DNA合成是必要的。最后，我们发现自分泌TGF~在早期细胞中抑制自分泌TGF~的表达。抑制TGF~功能导致生长受阻细胞中自分泌TGF α：表达增强和EGFR激活，同时获得对外源生长因子的独立性，恶性进展到晚期表型。外源性TGFj3处理也阻断了早期细胞中IGFIR介导的TGF α: mRNA的诱导。这些结果产生了几个问题。我们将解决的第一个问题是IGFIR激活刺激TGF α：从生长停滞状态重新表达的机制。更新项目要解决的第二个问题是TGFj3抑制TGF α表达的机制。项目上一个周期的结果表明，TGF α的不适当表达提供了生长因子独立性，但他们没有解决不适当的TGF α表达是如何实现这一点的。因此，这个问题也会在更新项目中解决。

This is the competing renewal for CA548o7 Objectives during the past cycle of this project included the determination of a) autocrine TGF alpha function and b) mechanisms controlling TGF alpha expression in colon cancers. Accomplishments have included the determination that autocrine TGF alpha: in both early and late stage colon cancers functions primarily in the process of re-entering the cycling state from environmental conditions which limit cell growth (e.g.. growth factor deprivation) and does not appear to have a significant role in actively cycling populations (e.g., exponential growth in tissue culture). Late stage colon cancer cell lines differ from early stage cells in that they are completely independent of exogenous growth factors for re-initiation of DNA synthesis from growth arrest whereas early stage cells require an exogenous insulin-like growth factor l receptor (IGFIR) ligand for cell cycle re-entry. We have found that the growth factor independence of late stage malignant cells arises from inappropriate TGF alpha: expression (not overexpression) and EGF receptor (EGFR) activation in growth arrested cells. This has the effect of producing constitutive EGFR activation, an event long associated with transformation. Early stage cells do not express TGF ALPHA: or show significant EGFR activation at growth arrest. IGFIR activation in early stage cells regenerates their autocrine TGF ALPHA: expression and EGFR activation events which we have shown to be necessary for DNA synthesis in these cells. Finally, we have found that autocrine TGF~ represses autocrine TGF~ expression in early stage cells. Inhibition of TGF~ function leads to enhanced expression of autocrine TGF ALPHA: and EGFR activation in growth arrested cells along with the acquisition of independence from exogenous growth factors and malignant progression to a late stage phenotype. Exogenous TGFj3 treatment also blocks IGFIR mediated induction of TGF ALPHA: mRNA in early stage cells. Several issues arise from these results. The first issue we will address is the mechanism by which IGFIR activation stimulates TGF ALPHA: re- expression from the growth arrested state. The second issue that will be addressed in the renewal project is the mechanism by which TGFj3 suppresses TGF alpha expression. The results from the last cycle of the project have shown that inappropriate expression of TGF alpha provides growth factor independence, but they have not addressed how inappropriate TGF alpha expression carries this out. Therefore, this issue will also be addressed in the renewal project.