Hanqun Liu1 • Yuxuan Yong3 • Xingjian Li1 • Panghai Ye1 • Kai Tao2 • Guoyou Peng1 • Mingshu Mo1 • Wenyuan Guo1 • Xiang Chen1 • Yangfu Luo1 • Yuwan Lin1 • Jiewen Qiu2 • Zhiling Zhang1 • Liuyan Ding1 • Miaomiao Zhou1 • Xinling Yang3 • Lin Lu1 • Qian Yang4 • Pingyi Xu1
1 Department of Neurology, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou 510120, China
2 Department of Neurosurgery, Tangdu Hospital, The Fourth Military Medical University, Xi’an 710038, China
3 Department of Neurology, The Second Affiliated Hospital of Xinjiang Medical University, Ürümqi 830054, China
4 Department of Experiment Surgery, Tangdu Hospital, The Fourth Military Medical University, Xi’an 710038, China
Abstract
Previous studies suggest that the reduction of SMAD3 (mothers against decapentaplegic homolog 3) has a great impact on tumor development, but its exact pathological function remains unclear. In this study, we found that the protein level of SMAD3 was greatly reduced in human-grade IV glioblastoma tissues, in which LAMP2A (lysosome-associated membrane protein type 2A) was significantly up-regulated. LAMP2A is a key rate-limiting protein of chaperone-mediated autophagy (CMA), a lysosome pathway of protein degradation that is activated in glioma. We carefully analyzed the amino-acid sequence of SMAD3 and found that it contained a pentapeptide motif biochemically related to KFERQ, which has been proposed to be a targeting sequence for CMA. In vitro, we confirmed that SMAD3 was degraded in either serum-free or KFERQ motif deleted condition, which was regulated by LAMP2A and interacted with HSC70 (heat shock cognate 71 kDa protein). Using isolated lysosomes, amino-acid residues 75 and 128 of SMAD3 were found to be of importance for this process, which affected the CMA pathway in which SMAD3 was involved. Similarly, down-regulating SMAD3 or up-regulating LAMP2A in cultured glioma cells enhanced their proliferation and invasion. Taken together, these results suggest that excessive activation of CMA regulates glioma cell growth by promoting the degradation of SMAD3. Therefore, targeting the SMAD3–LAMP2A-mediated CMA-lysosome pathway may be a promising approach in anti-cancer therapy.
Keywords
Glioma; SMAD3; Chaperone-mediated; Autophagy; Cell growth
