Vanlandewijck Michael, Dadras Mahsa Shahidi, Lomnytska Marta, Mahzabin Tanzila, Lee Miller Martin, Busch Christer, Brunak Søren, Heldin Carl-Henrik, Moustakas Aristidis
Ludwig Institute for Cancer Research, Science for Life Laboratory, Uppsala University, Uppsala, Sweden.
Integrated Cardio Metabolic Center, Novum, Karolinska Institute, Huddinge, Sweden.
Oncotarget. 2017 Dec 31;9(5):5716-5735. doi: 10.18632/oncotarget.23788. eCollection 2018 Jan 19.
The multifunctional cytokine transforming growth factor β (TGFβ) controls homeostasis and disease during embryonic and adult life. TGFβ alters epithelial cell differentiation by inducing epithelial-mesenchymal transition (EMT), which involves downregulation of several cell-cell junctional constituents. Little is understood about the mechanism of tight junction disassembly by TGFβ. We found that one of the newly identified gene targets of TGFβ, encoding the serine/threonine kinase salt-inducible kinase 1 (SIK), controls tight junction dynamics. We provide bioinformatic and biochemical evidence that SIK can potentially phosphorylate the polarity complex protein Par3, an established regulator of tight junction assembly. SIK associates with Par3, and induces degradation of Par3 that can be prevented by proteasomal and lysosomal inhibition or by mutation of Ser885, a putative phosphorylation site on Par3. Functionally, this mechanism impacts on tight junction downregulation. Furthermore, SIK contributes to the loss of epithelial polarity and examination of advanced and invasive human cancers of diverse origin displayed high levels of SIK expression and a corresponding low expression of Par3 protein. High mRNA expression also correlates with lower chance for survival in various carcinomas. In specific human breast cancer samples, aneuploidy of tumor cells best correlated with cytoplasmic SIK distribution, and SIK expression correlated with TGFβ/Smad signaling activity and low or undetectable expression of Par3. Our model suggests that SIK can act directly on the polarity protein Par3 to regulate tight junction assembly.
多功能细胞因子转化生长因子β（TGFβ）在胚胎期和成年期均调控体内稳态及疾病发生。TGFβ通过诱导上皮-间质转化（EMT）改变上皮细胞分化，这一过程涉及多种细胞间连接成分的下调。目前对TGFβ导致紧密连接解体的机制了解甚少。我们发现，TGFβ新确定的基因靶点之一编码丝氨酸/苏氨酸激酶盐诱导激酶1（SIK），它可控制紧密连接的动态变化。我们提供了生物信息学和生物化学证据，表明SIK可能磷酸化极性复合物蛋白Par3，Par3是已确定的紧密连接组装调节因子。SIK与Par3结合，并诱导Par3降解，蛋白酶体和溶酶体抑制或Par3上假定的磷酸化位点Ser885突变可阻止这种降解。在功能上，这一机制影响紧密连接的下调。此外，SIK导致上皮极性丧失，对多种来源的晚期侵袭性人类癌症进行检测发现，SIK表达水平高，而Par3蛋白表达相应较低。高mRNA表达也与各种癌症较低的生存几率相关。在特定的人类乳腺癌样本中，肿瘤细胞的非整倍性与细胞质中SIK的分布最相关，SIK表达与TGFβ/Smad信号活性以及Par3低表达或未检测到的表达相关。我们的模型表明，SIK可直接作用于极性蛋白Par3以调节紧密连接组装。
