FOXM1-mediated activation of phospholipase D1 promotes lipid droplet accumulation and reduces ROS to support paclitaxel resistance in metastatic cancer cells
Graphical abstract
Introduction
Metastasis is the ultimate challenge in tumor therapy, and most metastatic tumors react poorly to chemotherapy. Paclitaxel is one of the most widely used chemotherapeutic drugs for the treatment of solid carcinoma, such as breast cancer, non-small-cell lung cancer, gastric cancer, and cervical carcinoma. The widely accepted mechanism is that paclitaxel stabilizes tubulin dimers and interferes with microtubular disassembly, which leads to cellular apoptosis [1].
Recently, some studies have suggested that paclitaxel directly affects mitochondria by inducing the generation of reactive oxygen species (ROS), such as superoxide or hydrogen peroxide. In addition, cancer cells have developed mechanisms for potentially quenching excess ROS to maintain redox homeostasis [2,3]. ROS are generated in the electron transport chain, mainly in mitochondria. Excessive ROS-induced oxidative stress can disturb endoplasmic reticulum (ER) homeostasis and provoke the unfolded protein response (UPR) [4,5], which can activate caspase-12-mediated apoptosis [6]. In this regard, blocking the pathway that regulates redox homeostasis in metastatic cancer cells may be effective in sensitizing cancer cells to paclitaxel.
The lipid droplet (LD), an organelle that is abundant in certain types of cancer, has attracted attention due to its unique structure, crucial roles in lipid metabolism, and functions in chemoresistance. An LD stores neutral lipids, such as triglyceride (TG), in the core, which is surrounded by a phospholipid monolayer mainly composed of phosphatidylcholine (PC) [7]. LDs function as a lipid buffering system in response to metabolic changes and interact with other subcellular compartments, such as ROS. LDs formed in glia niche have been found to limit the levels of ROS and inhibit the oxidation of polyunsaturated fatty acids (PUFAs), protecting glia and neuroblasts from peroxidation chain reaction [8]. However, whether LDs participate in paclitaxel resistance and how they protect cells from ROS remains to be uncovered. ROS can attack lipids containing carbon–carbon double bond (s), especially in PUFAs, and lead to the production of lipid peroxyl radicals and lipid hydro-peroxides [9], a process known as lipid peroxidation. Thus, we hypothesize that the degree of unsaturation of lipid could alleviate ROS-induced ER stress.
PC metabolism is vital for LD expansion, partly due to the localized activation in the LD monolayer of CTP: phosphocholine cytidylyltransferase (CCTα), the key enzyme in the Kennedy pathway for PC synthesis [10]. Moreover, lysophosphatidylcholine acyltransferase 2 (LPCAT2), which participates in remodification of the fatty acid composition of PC in the Lands cycle [11,12], promotes LD production to support chemoresistance by maintaining ER homeostasis in colorectal cancer [13]. Furthermore, phosphatidic acid (PA), the product of PC hydrolysis, also has been reported to promote the formation of LD, for its ability to influence the structure of membranes and facilitate the budding reaction [14,15]. Two isoforms of phospholipase D (PLD), PLD1 and PLD2, are vital for the hydrolysis of PC to yield choline and the second-messenger signaling lipid PA [16]. PLD1 mainly localizes to peri-nuclear regions (ER, Golgi apparatus, and endosomes), while PLD2 localizes primarily to the plasma membrane [17,18]. Increased expression of PLD1 promotes LD formation [15,19].
Activation of oncogenes effects metabolic reprogramming in cancer, resulting in enhanced nutrient uptake to support biosynthesis and homeostasis [20]. Since cancer cells can harness lipids to support proliferation, invasion and metastasis [21,22], lipid metabolism has been leveraged as a novel target for chemoresistance. The cancer stem-like cell maintaines low ROS levels and drug resistance by coupling FOXM1-dependent Prx3 expression and fatty acid oxidation-mediated NADPH regeneration [23]. Here, we explored the metabolic reprogramming of lipids under the regulation of FOXM1 in paclitaxel resistance and uncovered potential roles of special metabolites in balancing cellular homeostasis when cancer cells are confronted with elevated ROS induced by paclitaxel.
Section snippets
Cell culture and viability assays
Breast cancer cell lines MCF7 and 4T1 were obtained from the China Center for Type Culture Collection (Wuhan, China). MCF7 and its derived metastatic cells MCF7-LMs were cultured in DMEM, supplemented with 0.01 mg/ml insulin (Sigma, St Louis, MO). 4T1 and its derived metastatic cells 4T1-LMs and 4T1-LuMs were maintained in RPMI-1640 medium. All culture mediums were supplemented with 10% fetal bovine serum (Gibco, Grand Island, NY) and 100 IU/ml penicillin and streptomycin.
Paclitaxel
Results
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High abundance of FOXM1 in cancer cells conferred them paclitaxel resistance in vitro and in vivo.
In our previous studies, we successfully isolated liver metastatic cancer cells (MCF7-LMs, 4T1-LMs) and lung metastatic cancer cells (4T1-LuMs) in mice models (Fig. S1A) as described elsewhere [[33], [34], [35]]. The detailed procedure is described in Materials and Methods. First, we investigated the sensitivity of metastatic cancer cells to paclitaxel treatment in vitro. When treated with
Discussion
Despite numerous reports highlighting the mechanisms of paclitaxel resistance in breast cancer, few studies have focused on the role of intracellular metabolic rewriting in chemoresistant metastatic cancer cells. Here, we provide evidence for FOXM1-mediated LD accumulation as a key driver of paclitaxel resistance in metastatic cancer cells. Moreover, increased LD accumulation protects metastatic cancer cells from excessive ROS and maintains ER homeostasis when cells were treated with
Conclusion
Our work provides the evidence for lipid droplet accumulation, which is dependent on FOXM1-induced activation of PLD1, in maintaining ER homeostasis in metastatic cancer cells treated with paclitaxel. Inhibition of PLD1 and/or LDs may be a promising adjuvant to reduce chemoresistance and improve treatment outcomes for patients with poor responses to current chemotherapy.
Author contributions
B.Z. and X.C. conceived and designed the study. X.Z., C·H., Y·Y., S.J. and J.Z. performed the experiments. C.H. performed the molecular docking. X.Z., C·H., W.Z. and H.L. analyzed the data. X.Z. and C.H. drafted the manuscript. B.Z. and X.C. revised and edited the article. All authors have read and approved the final manuscript.
Funding information
This work was supported by the National Natural Science Foundation of China (Grant No. 81572427, 81874189) and the State Key Project on Infection Diseases of China (2018ZX10723204-003).
Author disclosure statement
The authors declare no conflict of interest.
Acknowledgements
We would like to thank Guangxin Wang, Fang Zhou and Yan Wang at The Analysis and Testing Center of Institute of Hydrobiology, Chinese Academy of Sciences for their assistance with confocal images acquisition.
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2023, Advances in Biological RegulationCitation Excerpt :Therefore, both Aldolase A and PLD1 have predictive value for the survival of lung cancer patients (Chang et al., 2022). Along the same line, PLD1 promotes lipid droplet accumulation to support resistance of metastatic cancer cells (Zhang et al., 2022) and in response to nutrient removal (Hussain et al., 2021). PA was recently shown to be produced at mitochondria-associated endoplasmic reticulum membrane subdomains, where the lipid transfer proteins ORP5 and ORP8 control the biogenesis of these primary organelles for energy storage (Guyard et al., 2022).
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These authors contributed equally to this work.