Muscadine Grape Skin Extract Induces an Unfolded Protein Response-Mediated Autophagy in Prostate Cancer Cells: A TMTBased Quantitative Proteomic Analysis

Funding Source

U.S. Department of Education, National Institutes of Health

Grant Number

8G12MD007590, 5 G12 RR003062,G12MD007595,P031S130068,P20MD002285-01,G12MD007583


Department of Chemistry

Document Type


Publication Date



Muscadine grape skin extract (MSKE) is derived from muscadine grape (Vitis rotundifolia), a common red grape used to produce red wine. Endoplasmic reticulum (ER) stress activates the unfolded protein response (UPR) that serves as a survival mechanism to relieve ER stress and restore ER homeostasis. However, when persistent, ER stress can alter the cytoprotective functions of the UPR to promote autophagy and cell death. Although MSKE has been documented to induce apoptosis, it has not been linked to ER stress/UPR/autophagy. We hypothesized that MSKE may induce a severe ER stress response-mediated autophagy leading to apoptosis. As a model, we treated C4-2 prostate cancer cells with MSKE and performed a quantitative Tandem Mass Tag Isobaric Labeling proteomic analysis. ER stress response, autophagy and apoptosis were analyzed by western blot, acridine orange and TUNEL/Annexin V staining, respectively. Quantitative proteomics analysis indicated that ER stress response proteins, such as GRP78 were greatly elevated following treatment with MSKE. The up-regulation of pro-apoptotic markers PARP, caspase-12, cleaved caspase-3, -7, BAX and down-regulation of anti-apoptotic marker BCL2 was confirmed by Western blot analysis and apoptosis was visualized by increased TUNEL/ Annexin V staining upon MSKE treatment. Moreover, increased acridine orange, and LC3B staining was detected in MSKE-treated cells, suggesting an ER stress/autophagy response. Finally, MSKE-mediated autophagy and apoptosis was antagonized by co-treatment with chloroquine, an autophagy inhibitor. Our results indicate that MSKE can elicit an UPR that can eventually lead to apoptosis in prostate cancer cells.


DOI: 10.1371/journal.pone.0164115

PubMed ID: 27755556

Funding text

NIH grants 8G12MD007590 (formerly NIH/NCRR Grant Number 5 G12 RR003062) (VOM), P20MD002285-01 (VOM), G12MD007595 (GW). This project was also supported by the NIH Research Centers in Minority Institutions (RCMI) Program and Biomedical Proteomics Facility Grant G12MD007583 (NMB) and Title V grant number P031S130068 from the U.S. Department of Education (LAC)