title: Calpain-dependent clearance of the autophagy protein p62/SQSTM1 is a contributor to ΔPK oncolytic activity in melanoma.
abstract: Oncolytic virotherapy is a promising strategy for reducing tumor burden through selective virus replication in rapidly proliferating cells. However, the lysis of slowly replicating cancer stem cells (CSCs), which maintain neoplastic clonality, is relatively modest and the potential contribution of programmed cell death pathways to oncolytic activity is still poorly understood. We show that the oncolytic virus ΔPK lyses CSC-enriched breast cancer and melanoma 3D spheroid cultures at low titers (0.1 pfu/cell) without resistance development and it inhibits the 3D growth potential (spheroids and agarose colonies) of melanoma and breast cancer cells. ΔPK induces calpain activation in both melanoma and breast cancer 3D cultures as determined by the loss of the p28 regulatory subunit, and 3D growth is restored by treatment with the calpain inhibitor PD150606. In melanoma, ΔPK infection also induces light chain 3 (LC3)-II accumulation and p62/SQSTM1 clearance, both markers of autophagy, and 3D growth is restored by treatment with the autophagy inhibitor chloroquine (CQ). However, expression of the autophagy-required protein Atg5 is not altered and CQ does not restore p62/SQSTM1 expression, suggesting that the CQ effect may be autophagy-independent. PD150606 restores expression of p62/SQSTM1 in ΔPK-infected melanoma cultures, suggesting that calpain activation induces anti-tumor activity through p62/SQSTM1 clearance.
authors.affiliation: Department of Pharmacology, University of Maryland School of Medicine, Baltimore, MD, USA.
authors.forename: A
authors.initials: A
authors.lastname: Colunga
authors.affiliation: Department of Pharmacology, University of Maryland School of Medicine, Baltimore, MD, USA.
authors.forename: D
authors.initials: D
authors.lastname: Bollino
authors.affiliation: Department of Pharmacology, University of Maryland School of Medicine, Baltimore, MD, USA.
authors.forename: A
authors.initials: A
authors.lastname: Schech
authors.affiliation: Department of Pharmacology, University of Maryland School of Medicine, Baltimore, MD, USA.
authors.forename: L
authors.initials: L
authors.lastname: Aurelian
mesh_terms: D000179:Acrylates / Q000008:administration & dosage; D048868:Adaptor Proteins, Signal Transducing / Q000096:biosynthesis*; D017209:Apoptosis / Q000187:drug effects; D001343:Autophagy / Q000187:drug effects; D002154:Calpain / Q000008:administration & dosage; D045744:Cell Line, Tumor; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects / Q000235:genetics; D006801:Humans; D008545:Melanoma / Q000235:genetics* / Q000628:therapy / Q000821:virology; D014411:Neoplastic Stem Cells / Q000473:pathology / Q000821:virology; D050130:Oncolytic Virotherapy; D050504:Oncolytic Viruses / Q000187:drug effects / Q000235:genetics*; D000071456:Sequestosome-1 Protein; D018874:Spheroids, Cellular / Q000187:drug effects / Q000473:pathology; D014779:Virus Replication / Q000187:drug effects / Q000235:genetics
chemical_list: D000179:Acrylates; D048868:Adaptor Proteins, Signal Transducing; C100442:PD 150606; C099718:SQSTM1 protein, human; D000071456:Sequestosome-1 Protein; D002154:Calpain