探討酪胺酸去磷酸酶N3調控Bicaudal D之分子機制

Abstract

酪氨酸磷酸化在細胞分化、細胞增生與遷移中扮演重要的角色，其受到蛋白質酪氨酸磷酸酶 (Protein tyrosine kinases；PTKs)與蛋白質酪氨酸去磷酸酶 (protein tyrosine phosphatases；PTPs)相互調節。我們過去發表文獻提出PTPN3參與在調控EGFR內吞的運送過程與肺癌細胞的增生。PTPN3為一非受體型蛋白質酪氨酸去磷酸酶，其中N端有一FERM區域，中間有PDZ區域，而C端有一PTP活性區域。然而，PTPN3仍有許多生物性功能尚未釐清。 為了更近一步探討PTPN3功能，我們利用質譜尋找PTPN3的可能受質，結果發現Bicaudal D蛋白(BICD)是其中一個可能性受質。BICD是動力蛋白(dynein)的接頭蛋白，與小GTP酶Rab6具有交互作用，且藉由徵招動力蛋白-動力激活蛋白(Dynactin)複合物調節內質網和高基氏體間的運送。在此篇論文中，我們發現BICD是會被酪氨酸磷酸化的蛋白，並且PTPN3可以降低BICD酪氨酸磷酸化的程度。此外，實驗結果也顯示Src酪氨酸激酶可以酪氨酸磷酸化BICD的卷曲螺旋功能區域中的酪氨酸。而且也發現BICD酪氨酸突變對於水泡性口炎病毒膜蛋白(VSVG)的順行性運輸無顯著影響。在果蠅方面，發現果蠅Ptpmeg與果蠅BicD具有基因遺傳交互作用。 此外，我們目前也著手探討果蠅BicD一些與Ptpmeg相關的生理功能。

Protein tyrosine phosphorylation plays a critical role in cell signaling and regulates a variety of biological processes, including cell differentiation, migration and proliferation. The molecular switch of tyrosine phosphorylation is coordinated by protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs). Our previous study has shown that PTPN3 is involved in the regulation of EGFR endocytic trafficking and lung cancer cell proliferation. PTPN3 is a non-transmembrane PTP that contains a N-terminal FERM domain, a PDZ domain and the C-terminal PTP domain. However, the biological function of PTPN3 remains largely unknown. Previously, we used substrate trapping approach to find the potential substrates of PTPN3. The results showed that Bicaudal D (BICD) is a potential substrate of PTPN3. BICD, a dynein adaptor protein, interacts with the small GTPase Rab6 and recruits the dynein-dynactin complex to regulate Golgi-ER transport. In this study, we found that the BICD is a tyrosine phosphorylated protein and PTPN3 can down-regulate the phospho-tyrosine level of BICD. Moreover, Src tyrosine kinase can phosphorylate the tyrosine residues in the coiled-coil domain of BICD. Further, our preliminary data showed that BICD-YF mutant does not affect the anterograde transport of VSVG and the Golgi morphology. In Drosophila, we found that dPtpmeg genetically interacts with dBicD. We are currently investigating the function of dPtpmeg-dBicD interaction in Drosophila development.