Homogeneous Polyporus polysaccharide exerts anti-bladder cancer effects via autophagy induction

Abstract

Context Polyporus polysaccharide (PPS), the leading bioactive ingredient extracted from Polyporus umbellatus (Pers.) Fr. (Polyporaceae), has been demonstrated to exert anti-bladder cancer and immunomodulatory functions in macrophages. Objective To explore the effects of homogeneous Polyporus polysaccharide (HPP) on the proliferation and autophagy of bladder cancer cells co‐cultured with macrophages. Materials and methods MB49 bladder cancer cells and RAW264.7 macrophages were co-cultured with or without HPP intervention (50, 100, or 200 μg/mL) for 24 h. The cell counting kit-8 (CCK-8) assay and 5-ethynyl-2″-deoxyuridine (EdU) staining evaluated MB49 cell proliferation. Monodansylcadaverine (MDC) staining and transmission electron microscopy (TEM) observed autophagosomes. Western blotting detected the expression levels of autophagy-related proteins and PI3K/Akt/mTOR pathway proteins. Results HPP inhibited the proliferation of MB49 cells co-cultured with RAW264.7 cells but not MB49 cells alone. HPP altered the expression of autophagy-related proteins and promoted the formation of autophagosomes in MB49 cells in the co-culture system. Autophagy inhibitors 3-methyladenine (3-MA) and chloroquine (CQ) not only antagonized HPP-induced autophagy but also attenuated the inhibitory effects of HPP on MB49 cell proliferation in the co-culture system. HPP or RAW264.7 alone was not sufficient to induce autophagy in MB49 cells. In addition, HPP suppressed the protein expression of the PI3K/Akt/mTOR pathway in MB49 cells in the co-culture system. Discussion and conclusions HPP induced bladder cancer cell autophagy by regulating macrophages in the co-culture system, resulting in the inhibition of cancer cell proliferation. The PI3K/Akt/mTOR pathway was involved in HPP-induced autophagy in the co-culture system.