Role of p21-activated kinases in thyroid cancer

进行性转移性甲状腺乳头状癌（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，非持久反应是报道的最佳结果。局部浸润和远处转移是PTC死亡的两个预测因素。我们专注于确定这些特征的关键调节因子，努力确定新的靶点以改善治疗。我们发现p21活化激酶（PAK）信号在侵袭性ptc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的关系，我们分析了这两种信号分子之间的关系。我们证明PAK活性受到BRAF的高度调控，并且BRAF敲低抑制PAK活性。而且，这种效应与MEK无关。我们随后发现PAK与BRAF过表达和内源性系统相互作用，并且该复合物在有丝分裂中发生，与调节细胞分裂和生长的作用一致。我们已经在体内证明，甲状腺中BRAF V600E的急性激活与磷酸化PAK水平的增加有关。最后，我们在对BRAF抑制产生耐药性的患者的肿瘤样本中发现了PAK上游调节因子的获得性突变。这些数据表明PAK是BRAF的一个关键下游靶点，在RAS/RAF/ERK通路激活的肿瘤的PTC进展中起重要的功能作用。本项目假设PAK是BRAF下游参与甲状腺癌体内肿瘤发生发展的关键信号节点；这一相互作用的机制可以被阐明，并可以利用它为进行性甲状腺癌患者和其他braf突变肿瘤患者开发改进的初级和次级治疗方法。

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.