Advertisement

Overexpression of autophagy-related gene ATG7 promotes bladder cancer invasion via autophagic removal of pre-mRNA processing protein AUF1 and increased stability of RhoGDI? mRNA in vitro and in vivo

Login to Access Video or Poster Abstract: MP34-12
Sources of Funding: NIH/NCI CA165980, CA177665, CA112557, and NIH/NIEHS ES000260; the Natural Science Foundation of China (NSFC81229002, NSFC81372946) and Key Project of Science and Technology Innovation Team of Zhejiang Province (2013TD10) and the Xinmiao Talent Program of Zhejiang Province (2016R413068)

Introduction

Autophagy is an evolutionarily conserved mechanism that is critical for cellular homeostasis but its involvement in cancer in general has been controversial. Even less is known about the relationship between autophagy and bladder cancer development and progression. Here we explore the role of ATG7, a key autophagy-related regulator, in bladder cancer cell invasion.

Methods

Expression of ATG7 protein in human bladder cancer specimens, cell lines and N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN)-induced mouse invasive bladder cancer specimens were assessed using immunohistochemistry and immunoblotting. After ruling out transcriptional regulation, the possibility of microRNA in ATG7 expression was tested by bioinformatics search for putative miRNAs that could target 3’-UTR of ATG7 mRNA, by assessing the expression of candidate miRNAs in bladder cancer tissues and cell lines and by studying the effects of miRNAs on ATG7 expression with stable transfection. The effects of ATG7 expression on invasion was evaluated after shRNA knockdown. The levels of cell invasion effectors (RhoGDI?, RhoGDI?, Rac1, 2, 3, and RhoA) were also determined. The upstream regulators of RhoGDI? were determined using RNA-IP and verified in xenografted tumors.

Results

ATG7 was markedly and reproducibly upregulated in human muscle-invasive bladder cancers, their cell-line derivatives and mouse invasive bladder cancer induced by BBN. Knockdown of ATG7 in human bladder cancer cell lines UMUC3 and T24 dramatically reduced their invasion. Mechanistic analyses showed that ATG7 overexpression was mediated by miR-190, which was also highly upregulated in bladder cancer tissues and cell lines. miR-190 bound to the 3’-UTR of ATG7 mRNA increasing its stability. A separate mechanism was that ATG7-mediated autophagic response could remove AUF1 protein and reduce AUF1 interaction with RhoGDI? mRNA, leading to increased RhoGDI? mRNA stability which then promotes invasion. Indeed, inhibition of ATG7-mediated autophagy led to AUF1 protein accumulation, RhoGDI? downregulation and decreased cell invasion.

Conclusions

Our results provide the first mechanistic link between autophagy and bladder cancer cell invasion. The signaling axis along ATG7-AUF1- RhoGDI? that is highly operative in bladder cancer cells might be explored further for developing novel diagnostic and therapeutic approaches to manage advanced bladder cancers.

Funding

NIH/NCI CA165980, CA177665, CA112557, and NIH/NIEHS ES000260; the Natural Science Foundation of China (NSFC81229002, NSFC81372946) and Key Project of Science and Technology Innovation Team of Zhejiang Province (2013TD10) and the Xinmiao Talent Program of Zhejiang Province (2016R413068)

Authors
Junlan Zhu
Yang Li
Chuanshu Huang
Xue-Ru Wu
back to top