Role of p21-activated kinases in thyroid cancer

进行性转移性甲状腺乳头状癌（PTC）患者预后不良。尽管在开发新疗法方面取得了进展，但完全缓解一直难以实现，非持久缓解是报告的最佳结局。局部浸润和远处转移是PTC死亡的两个预测因素。我们专注于定义这些特征的关键调节因子，以确定新的靶点来改善治疗。我们发现p21激活激酶（PAK）信号在侵袭性PTC的侵袭性前沿被激活，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联，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BRAF高度调节，BRAF敲低抑制PAK活性。此外，这种作用不依赖于MEK。我们随后确定PAK与BRAF过表达和内源性系统物理相互作用，并且该复合物发生在有丝分裂中，与调节细胞分裂和生长的作用一致。我们已经在体内证明甲状腺中BRAF V600 E的急性激活与磷酸化PAK水平的增加相关。最后，我们在对BRAF抑制产生耐药性的患者的肿瘤样本中鉴定了PAK上游调节因子的获得性突变。这些数据表明PAK是BRAF的关键下游靶标，BRAF在RAS/RAF/ERK通路激活的肿瘤的PTC进展中起重要的功能作用。该项目的假设是PAK是BRAF下游的一个关键信号节点，参与体内甲状腺癌肿瘤发生和进展;可以阐明相互作用的机制，并且可以利用它来开发用于进行性甲状腺癌患者和其他BRAF突变肿瘤患者的改善的主要和次要治疗。

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.