Ganoderma lucidum polysaccharides induce cytotoxicity in colorectal cancer cells through inducing autophagosome accumulation and inhibiting autophagic flux

Abstract

Ganoderma lucidum (G. lucidum), a traditional Chinese medicine, has been used in cancer prevention for many years. As one of the main components of G. lucidum, G. lucidum polysaccharides (GLPs) showed significant anti‐cancer activity. Previous studies in our laboratory show that GLPs extracted from sporoderm‐broken spores of G. lucidum, significantly inhibited the proliferation and induced apoptosis in colorectal cancer (CRC) cells in vivo and in vitro. However, whether GLPs regulate autophagy in CRC cells is unknown. In the present study, we found that GLPs enhance the level of LC3B and activating autophagy initiation both in HCT116 and HT29 CRC cells as determined by Western blot, transmission electron microscope, and confocal microscope. However, autophagy initiation induced by GLPs was accompanied by impaired degradation of SQSTM1/p62, which suggesting autophagic flux inhibition in CRC cells by GLPs. mRFP‐GFP‐LC3B adenovirus translocation and colocalization analyses confirmed that autophagosome‐lysosome fusion is blocked by GLPs treatment. Furthermore, GLPs inhibited autophagic degradation by inhibiting lysosomal acidification and downregulating the expression of cathepsin B and cathepsin D. Next, we found GLPs induced expression of MAPK/Erk in both CRC cells. Erk inhibitor PD98059 inhibited GLPs‐induced apoptosis and LC3B expression in CRC cells suggesting that Erk activation is partially, at least, responsible for GLPs‐induced autophagy initiation. Importantly, further analysis using flow cytometry revealed that GLPs induced autophagosome accumulation is required for GLP‐induced cytotoxicity. Similar results were obtained using a xenograft mouse model, in which GLPs reduced tumor growth and increased the levels of LC3B and p62 in tumors. Moreover, the levels of cathepsin B and cathepsin D were decreased in tumors from GLP treated mice in vivo. Collectively, these data demonstrate that GLPs inhibit CRC cell proliferation and induce apoptosis through regulation of autophagosome accumulation and autophagic flux inhibition, which may be dependent, at least in part, on MAPK/Erk activation.Support or Funding InformationSupported by Science and Technology Planning Project of Zhejiang Province (Grant No. 2019C02100) and National Natural Science Foundation of China (Grant No. 81473397).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.