Molecular Mechanisms Of Protein Acetylation On Regulating The Small GTPase Arf6 Signal Transduction

As an important component of tumor microenvironment,chemokines play a key role in the process of inflammation,angiogenesis,immune response and so on.It also can mediate tumor growth,tumor invasion and metastasis.Chemokines are important regulatory factors in the development of tumor.CCL18 belongs to the CC subgroup chemokines,and was firstly identified in the lung tissues.CCL18 was mainly secreted by dendritic cells and tumor associated macrophage(TAM).TAM is an important immune cell in tumor microenvironment,which can promote angiogenesis and tumor development.The secretion of CCL18 by TAM was negatively correlated with the prognosis of tumor patients.CCL18 has become an important marker of tumor associated macrophages.Recent research found that,CCL18 released by breast TAMs promotes the invasiveness of cancer cells by triggering integrin clustering and enhancing their adherence to extracellular matrix.Binding of CCL18 to PITPNM3 can activate Akt-LIMK-cofilin signal pathway,which promotes actin-based cytoskeletal remodeling.Also,binding of CCL18 to PITPNM3 can induce the epithelial-mesenchymal transition(EMT)via PI3K-Akt-GSK3p-Snail signal pathway,thus promoting the invasion and metastasis of breast cancer cells.We indentify ACAP4,a new effctor of CCL 18 pathways in our research.When treated with CCL 18,ACAP4 could be acetylated by PCAF and we also indentified the acetylated site was Lysine 311(K311)in MDA-MB-31 cells.Further research indicated that acetylation of K311 of ACAP4 could decrease the interaction between ACAP4 and PtdIns(4.5)P2,which can also lower the ACAP4 distribution in plasma-membrane(PM).Therefore,dynamic acetylation of ACAP4 can switch the conversion of ACAP4 distribution between PM and cytosol.Early studies indicated that Acapin,a new ACAP4 binding partner,can competitively bind ACAP4 with Arf6,thus promoting the release of Arf6 GTPase activity inhibition by ACAP4.In our study,we found that ACAP4’s mimic acetylation could increase the interaction between ACAP4 and Acapin,but not alter the direct binding between ACAP4 and Arf6.In addition,competitive binding between Acapin and acetylated ACAP4 can hinder the regulation of the Arf6 GTPase activity by ACAP4,thus playing an important role in breat cancer cells migration.Now,we are researching the function of acetylation on cell migration regulated by CCL 18.Also,we are continuing to conduct animal experiments to evaluate the effect of PCAF on the tumor metastasis elicited by CCL18.Reversible protein phosphorylation has emerged as a key regulatory mechanismof kinetochore-microtubule attachment.The AuroraB-PP1 axis is crucial for kinetochore-microtubule attachment and chromosome bi-orientation.As a component of the CPC,Aurora B kinase plays a major role in the correction of erroneous attachments,through the phosphorylation of the KMN network.In the case of erroneous attachment,tension is not applied between sister kinetochores and thus the inter-kinetochore distance is short.Once sister kinetochores achieve a bipolar attachment,the kinetochores are stretched by the pulling forces exerted by attached microtubules emanating from the opposite poles.Thus,Aurora B at the inner centromere is closer to the KMN network in the application of tension,making the KMN network more phosphorylated.Phosphorylation of the KMN network reduces the affinity of the network for microtubules,which facilitates the establishment of amphitelic attachment by destabilizing erroneous attachments.The protein phosphatase 1(PP1),which stabilizes kinetochore-microtubule interactions and silences the spindle checkpoint by dephosphorylating Aurora B kinase targets when chromosome bi-orientation is achieved.Glycogen synthase kinase 3(GSK3),as a multifunctional protein kinase,plays an important role in the kinetochore-microtubule attachment,but the regulation mechanism has not been well elucidated.In our study,we identified PP1γ as a new substrate of GSK3(3.GSK3β can phosphorylate the protein phosphotase PPlγ at its carboxyal-terminal T307 and T311 sites.Phosphorylation of T307/311 of PP1γ can promote its binding with Aurora B,thus increasing the phosphorylation leve of Aurora B at T232.Our research suggested existence of GSK3β-PP1γ-Aurora B signal axis and provided further insights to study the potential mechanism of kinetochore-microtubule attachment regulated by GSK3β.