Role of p21-activated kinases in thyroid cancer

进行性转移性乳头状甲状腺癌(PTC)患者预后较差。尽管在开发新疗法方面取得了进展，但完全反应一直难以捉摸，非持久反应是最好的报道结果。大体局部侵袭和远处转移是PTC死亡的两个预测因素。我们一直专注于定义这些功能的关键调控因素，以努力确定改善治疗的新靶点。我们发现p21激活的激酶(PAK)信号在侵袭性甲状腺癌的侵袭前沿被激活，并确定它在体外调节人甲状腺癌细胞的运动和增殖。由于BRAF激活与肿瘤侵袭性之间存在关联，我们分析了这两个信号分子之间的关系。我们发现PAK活性受BRAF的高度调控，而BRAF基因敲除抑制了PAK活性。此外，这种效应不依赖于MEK。我们随后发现，PAK与BRAF在物理上相互作用，既有过度表达，也有内源性系统，并且该复合体出现在有丝分裂中，与调节细胞分裂和生长的作用一致。我们已经在体内证明，BRAF V600E在甲状腺中的急性激活与磷酸化PAK水平的增加有关。最后，我们在肿瘤样本中发现了PAK上游调节因子的获得性突变，这些突变来自对BRAF抑制产生抗药性的患者。这些数据表明，PAK是BRAF的关键下游靶点，在RAS/RAF/ERK通路激活的肿瘤的PTC进展中发挥着重要的功能作用。这个项目的假设是，PAK是BRAF下游的一个关键信号节点，参与体内甲状腺癌的发生和发展；这种相互作用的机制可以被阐明，并且它可以被用来为进展性甲状腺癌患者和其他BRAF突变肿瘤患者开发改进的一级和二级治疗方法。

Patients with progressive metastatic papillary thyroid cancer (PTC) have a poor prognosis. Despite advances in developing new therapies complete responses have been elusive and non-durable responses are the best reported outcomes. The presence of gross local invasion and distant metastases are two predictors of death from PTC. We have focused on defining key regulators of these features in an effort to identify novel targets to improve treatment. We identified that the p21 activated kinase (PAK) signaling is activated in the invasive fronts of aggressive PTCs and determined that it regulated human thyroid cancer cell motility and proliferation in vitro. Because of the association between BRAF activation and tumor aggressiveness we analyzed the relationship between these two signaling molecules. We demonstrated that PAK activity was highly regulated by BRAF and that BRAF knock down inhibited PAK activity. Moreover, this effect was independent of MEK. We subsequently identified that PAK physically interacts with BRAF both overexpression and endogenous systems and that the complex occurs in mitosis consistent with a role in regulation cell division and growth. We have shown in vivo that acute activation of BRAF V600E in the thyroid is associated with increased levels of phosphorylated PAK. Finally, we have identified acquired mutations in upstream regulators of PAK in tumor samples from patients who developed resistance to BRAF inhibition. These data point to PAK being a critical downstream target of BRAF which plays an important functional role in PTC progression for tumors with RAS/RAF/ERK pathway activation. The hypotheses of this project is that PAK is a critical signaling node downstream of BRAF involved in thyroid cancer tumorigenesis and progression in vivo; that the mechanism of the interaction can be elucidated, and that it can be exploited to develop improved primary and secondary therapies for patients with progressive thyroid cancer and other patients with BRAF-mutated tumors.