Induction of STK11-dependent cytoprotective autophagy in breast cancer cells upon honokiol treatment

Dipali Sharma,Sheetal Parida,Nethaji Muniraj,Marey Shriver,Jack L Arbiser,Neeraj K Saxena,Kathleen Gabrielson,Sumit Siddharth,Juhyung Woo,Edward Gabrielson,Justin Elsey,Arumugam Nagalingam

doi:10.1038/s41420-020-00315-w

Dipali Sharma, Sheetal Parida + Show 10 more

Open Access

https://doi.org/10.1038/s41420-020-00315-w

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Abstract

Cancer cells hijack autophagy pathway to evade anti-cancer therapeutics. Many molecular signaling pathways associated with drug-resistance converge on autophagy induction. Honokiol (HNK), a natural phenolic compound purified from Magnolia grandiflora, has recently been shown to impede breast tumorigenesis and, in the present study, we investigated whether breast cancer cells evoke autophagy to modulate therapeutic efficacy and functional networks of HNK. Indeed, breast cancer cells exhibit increased autophagosomes-accumulation, MAP1LC3B-II/LC3B-II-conversion, expression of ATG proteins as well as elevated fusion of autophagosomes and lysosomes upon HNK treatment. Breast cancer cells treated with HNK demonstrate significant growth inhibition and apoptotic induction, and these biological processes are blunted by macroautophagy/autophagy. Consequently, inhibiting autophagosome formation, abrogating autophagosome-lysosome fusion or genetic-knockout of BECN1 and ATG7 effectively increase HNK-mediated apoptotic induction and growth inhibition. Next, we explored the functional impact of tumor suppressor STK11 in autophagy induction in HNK-treated cells. STK11-silencing abrogates LC3B-II-conversion, and blocks autophagosome/lysosome fusion and lysosomal activity as illustrated by LC3B-Rab7 co-staining and DQ-BSA assay. Our results exemplify the cytoprotective nature of autophagy invoked in HNK-treated breast cancer cells and put forth the notion that a combined strategy of autophagy inhibition with HNK would be more effective. Indeed, HNK and chloroquine (CQ) show synergistic inhibition of breast cancer cells and HNK-CQ combination treatment effectively inhibits breast tumorigenesis and metastatic progression. Tumor-dissociated cells from HNK-CQ treated tumors exhibit abrogated invasion and migration potential. Together, these results implicate that breast cancer cells undergo cytoprotective autophagy to circumvent HNK and a combined treatment with HNK and CQ can be a promising therapeutic strategy for breast cancer.

Highlights

Despite tremendous progress in encouraging regular screenings, identifying breast lesions at earlier stages and Official journal of the Cell Death Differentiation AssociationMuniraj et al Cell Death Discovery (2020)6:81 multiple oncogenic signaling pathways simultaneously may prove more useful than targeting single nodes
We report a stimulation of autophagic flux in breast cancer cells upon HNK treatment and suppressing autophagy with inhibition of autophagosome formation using 3-methyladenine, blockade of autophagosomelysosome fusion with bafilomycin A1 (Baf), or CRISPR/ Cas9-mediated knockout of beclin 1 (BECN1) and autophagy related 7 (ATG7) effectively potentiates HNK induced growth inhibition and apoptotic induction
Breast cancer cells exhibit increased accumulation of intracellular autophagosomes and autophagy markers upon HNK treatment We examined whether breast cancer cells invoke autophagic response upon treatment with HNK

Summary

Introduction

Muniraj et al Cell Death Discovery (2020)6:81 multiple oncogenic signaling pathways simultaneously may prove more useful than targeting single nodes. Macroautophagy (referred as autophagy hereafter) is generally utilized by normal cells to avoid accumulation of damaged proteins or organelles, reduce ER stress and lower reactive oxygen species (ROS) production but cancer cells hijack this process to survive cancer therapy[3]. Multiple pathways including PIK3CA/AKT and AMPK/TSC1/ 2 signaling networks regulate autophagy[9]. Autophagic induction in response to hypoxia, DNA-damage or chemotherapy leads to the development of chemoresistance[10,11,12]. In light of the importance of autophagic induction in evading/reducing drug efficacy, it is imperative to investigate whether breast cancer cells induce autophagy in response to a proposed/established cancer therapy

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