PAK2通过调控细胞骨架影响食管鳞癌迁移和侵袭机制研究

Our study found p21-activated kinase2(PAK2) was highly expressed in esophageal squamous cell carcinoma(ESCC) compared with normal esophageal tissue. And the high expression of PAK2 was associated with the depth of invasion and lymph node metastasis of ESCC. We have analyzed the level of PAK2 and cell motility and invasiveness in several ESCC cell lines. Our results revealed a significant correlation of elevated PAK2 with high rate of migration and invasion of ESCC cell lines. Furthmore, downregulation of PAK2 could suppress ESCC cell migration and invasion. Further investigation found PAK2 could induce MLC phosphorylation which was a part of cytoskeleton. Thus, we could make a conclusion that Pak2 may mediate ESCC cell migration and invasion through regulation of cytoskeleton dynamics. However the precise mechanisms of molecular changes that contribute to this remain unknown. .PAK2 is a member of the PAK family of serine/threonine-specific protein kinase. There are six p21 activated kinases(Paks) in mammals, which are divided into group Ⅰ(Pak1 to Pak3)and group Ⅱ(Pak4 to Pak6). Paks are activated in response to different receptor signaling pathways, including growth factor receptors, G-protein-coupled receptors, and integrin receptors, to regulate cell shape and motility as well as cell survival, cell growth, and programmed cell death. .Dynamic changes of the cytoskeleton are critical for normal cell motility. During malignant transformation, the signaling pathways controlling these cytoskeletal dynamics are altered, and an increase in cell motility allows cancer cells to invade surrounding tissues and metastasize. Pak functions as a downstream effector of GTPases such as Rac and Cdc42 in the regulation of cytoskeleton and stimulates cell motility and invasion. Several targets of Pak that are implicated in regulating cytoskeletal dynamics, including LIM kinase(LIM-k), myosin light chain(MLC) kinase(MLCk), MLC, Op18/stathmin, p41 Arc (Arp2/3), filamin, and cortactin have been identified..Although the overall incidence of ESCC is decreasing in most country, it is still the fourth most common malignancy and the fourth leading cause of cancer-related death in China. Despite the advance in diagnosis and treatment, the prognosis for patients with invasion and metastasis remains dismal. Changes in the expression of specific genes in ESCC plays important roles in diverse cellular functions, such as cell adhesion, signal transduction, development, migration, invasion and metastasis etc. .The aim of this project was to investigate the detailed mechanisms that how Pak2 mediate ESCC cell migration and invasion through regulation of cytoskeleton dynamics in vitro and in vivo. A better understanding of molecular changes during ESCC migration and invasion may lead to new paradigms and possible improvements in cancer diagnosis, treatment and prevention.

我国食管癌的发病率和死亡率均较高，多数患者在发现时已存在局部侵犯和远处转移。p21活化激酶2（PAK2）是一个丝氨酸/苏氨酸蛋白激酶，参与调控细胞骨架重组、细胞周期进程与细胞凋亡等。申请者发现PAK2在食管癌中表达升高，并与肿瘤的侵润深度和淋巴结转移呈正相关；体外研究证实在除外PAK1和PAK3的影响下，PAK2与食管癌细胞的迁移和侵袭呈正相关，这种作用是PAK2特异的。细胞骨架的改变在肿瘤的侵袭和转移中发挥重要作用，目前已知LIMK、MLCK、merlin、filmin A、p41-ARC和Op18/stathmin等与细胞骨架相关蛋白均为Paks的底物，其与PAK1的关系目前研究较为明确，而PAK2对细胞骨架的调控作用机制尚不明确。通过细胞模型和动物模型，筛选研究PAK2对食管癌细胞可能产生的细胞骨架动力学的调控作用和具体分子生物学机制，进而阐明PAK2对食管癌的侵袭和转移调控机制。

p21活化激酶2（PAK2）是一个丝氨酸/苏氨酸蛋白激酶，参与调控细胞骨架重组、细胞周期进程与细胞凋亡过程。我们发现PAK2在食管癌中高表达，并与肿瘤的侵润深度和淋巴结转移成正相关，这种作用是PAK2特异的。肿瘤细胞的上皮-间质转化（EMT）及细胞骨架改变在肿瘤的迁移和侵袭过程中起到重要作用。我们发现TGF-β能够诱导食管鳞癌细胞EMT，进而促进食管鳞癌细胞的侵袭和迁移，而在这过程中PAK2起到关键作用，发现具体通路为TGF-β—AKT—PAK2。在LIMK、MLCK、merlin等细胞骨架相关蛋白的筛选中，我们发现PAK2能够激活MLCK，进而磷酸化MLC，从而引起细胞骨架的改变；最终影响食管鳞癌细胞的迁移和侵袭。结合细胞实验和动物实验，本研究发现PAK2在食管鳞癌中的具体作用路径为TGF-β—AKT—PAK2—MLCK—MLC，最终通过改变细胞骨架而促进食管鳞癌的侵袭和迁移。