| ObjectivesGliomas are the most common and aggressive malignant brain tumors and are associated with high mortality and incidence in humans.Glioblastomas(GBM)account for almost 75%of malignant primary brain tumors and are characterized by a low five-year survival rate and high recurrence.Despite rigorous multi-modal therapy,including surgery,chemotherapy and radiotherapy,patients with malignant glioma survive an average of 12-15 months following primary diagnosis.Therefore,new molecular biomarkers are urgently needed for diagnosis and targeted therapy.Dysregulated Hippo signaling has been found to underlie the development of many cancers,including gliomas,indicating that this pathway may be an attractive therapeutic target for the disease in humans.In our previous studies,we found that prostate transmembrane protein,androgen induced 1(PMEPA1),ubiquitin specific protease 39(USP39)and actin-like 6A(ACTL6A)play a vital role in the progression of human gliomas through regulation of Hippo signaling.Other studies have demonstrated that some cytoskeleton-associated proteins modulate Hippo signaling to control cell fate decisions and regulate cell growth.Cytoskeleton-associated protein 4(CKAP4)is a type II transmembrane protein originally observed in the ER,but it also binds to microtubules.It has since been found in the cell surface membrane of vascular smooth muscle cells,bladder epithelial cells,and type Ⅱ pneumocytes,where it functions as a receptor for several ligands,including surfactant protein A(SP-A),tissue plasminogen activator(TPA),anti-proliferating factor(APF),and Dickkopf1(DKK1)protein.Studies have shown that CKAP4 plays an important role in the development of several types of cancer,including lung cancer,hepatocellular carcinoma,pancreatic cancer,esophageal cancer and oral squamous cell carcinoma.However,the role of CKAP4 in the development of human glioma remains unknown.In this study,we demonstrate that CKAP4 is upregulated in human gliomas and contributes to malignant progression of gliomas as an oncogene through suppression of Hippo signaling.Materials and MethodsFirstly,GEPIA,TOGA,CCGA and other public databases were used to evaluate the expression of CKAP4 in gliomas of different grades.Next,IHC,Western and PCR experiments were performed on glioma specimens to verify the results in the database.Furthermore,CKAP4 expression level in glioma cells was knocked down to observe the effect on the proliferation,invasion and migration of tumor cells.Then,CKAP4 expression level in glioma cells was overexpressed to verify the effect on the function of tumor cells.Then,the effect of CKAP4 knockdown and overexpression on tumor in vivo was observed by establishing tumor in situ expression model.Finally,to find out the pathway through which CKAP4 affects tumor function,so as to develop specific drugs for the treatment of glioma.ResultsThe expression level of CKAP4 in human glioma is increased compared with normal brain tissue,which is correlated with the increase of tumor grade.And the tumor with high expression of CKAP4 is associated with poor survival of patients.CKAP4 knockout in GBM cell lines,LN229 and U251,inhibited the proliferation of gliomas in vitro and mouse brain tumor models in situ.In contrast,overexpression of CKAP4 enhanced these malignant properties of U87MG in vitro and in vivo models.By functional analysis of luciferase reporter gene construction under the control of YAP/TaZ promoter,increased CKAP4 expression leads to activation of YAP/PDZ-binding motif(TaZ)and TEAD-dependent transcription complex(downstream target of Hippo signaling).ConclusionCKAP4 may act as an oncogene and promote the development of glioma by inhibiting Hippo signaling. |
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