Autophagic flux disruption contributes to Ganoderma lucidum polysaccharide-induced apoptosis in human colorectal cancer cells via MAPK/ERK activation

Abstract

Targeting autophagy may serve as a promising strategy for cancer therapy. Ganoderma lucidum polysaccharide (GLP) has been shown to exert promising anti-cancer effects. However, the underlying mechanisms remain elusive. Whether GLP regulates autophagy in cancer has never been reported. In this study, GLP induced the initiation of autophagy in colorectal cancer (CRC) HT-29 and HCT116 cells, as evidenced by enhanced level of LC3-II protein, GFP-LC3 puncta, and increased formation of double membrane vacuoles. However, GLP treatment caused marked increase of p62 expression. Addition of late stage autophagy inhibitor, chloroquine (CQ), further enhanced LC3-II and p62 level, as well as increased autophagosome accumulation, suggesting a blockage of autophagic flux by GLP in CRC cells. We then found GLP blocked autophagosome and lysosome fusion as determined by mRFP-GFP-LC3 colocalization analysis. Mechanistic study revealed that GLP-induced disruption of autophagosome-lysosome fusion is due to reduced lysosome acidification and lysosomal cathepsin activities. Cell viability and flow cytometry assays revealed that GLPinduced autophagosome accumulation is responsible for GLP-induced apoptosis in CRC cells. In line with this, inhibition of autophagy initiation by 3-methyladenine (3-MA), an early stage autophagy inhibitor, attenuated GLPinduced apoptosis. In contrast, suppression of autophagy at late stage by CQ enhanced the anti-cancer effect of GLP. Furthermore, we demonstrated that GLP-induced autophagosome accumulation and apoptosis is mediated via MAPK/ERK activation. Finally, GLP inhibited tumor growth and also inhibited autophagic flux in vivo. These results unveil new molecular mechanism underlying anti-cancer effects of GLP, suggesting that GLP is a potent autophagy inhibitor and might be useful in anticancer therapy.

Hydroxysafflor yellow�A induces autophagy in human liver cancer cells by regulating Beclin�1 and ERK expression

“…During the process of autophagosome-to-autolysosome formation, the Beclin 1 complex and ERK1/2 serve an important role in regulating autophagy (38). The results of the present study indicated an increase in LC3-II and a decrease in p62 content following HYSA treatment of Hep-G2 cells, suggesting an induction of autophagy.…”

Eckol Inhibits Particulate Matter 2.5-Induced Skin Keratinocyte Damage via MAPK Signaling Pathway

“…MAPK signaling pathway plays a role in many systems of cell proliferation, migration, and apoptosis [23]. Many drugs are used to modulate MAPK signaling pathway to induce cell apoptosis in cells, such as lung cancer [40], human colorectal cancer [41], and cervical cancer HeLa cells [42]. Finally, we checked MAPK signaling pathway-related proteins, ERK, p38, and JNK.…”

Erastin triggers autophagic death of breast cancer cells by increasing intracellular iron levels

“…3MA and Baf-A1 are often used to inhibit autophagy activation ( 5 ). 3MA inhibits autophagy initiation ( 23 ), and Baf-A1 disturbs the fusion of autophagosomes with lysosomes ( 24 ). The inhibitory effects of 3MA or Baf-A1 on autophagy activation are also decided by their concentrations and treatment times.…”

“…The inhibitory effects of 3MA or Baf-A1 on autophagy activation are also decided by their concentrations and treatment times. Higher concentrations of 3MA or Baf-A1 and longer incubation times lead to obvious changes in the baseline level of autophagy-related proteins ( 23 , 24 ). In the present study, the cells were incubated with 5 mmol/l 3MA and 1.5 µmol/l Baf-A1 for 25 h, which did not exhibit marked inhibition on the baseline levels of autophagy-related proteins ( Fig.…”