ABSTRACT
For cancer cells to survive during extracellular matrix (ECM) detachment, they must inhibit anoikis and rectify metabolic deficiencies that cause non-apoptotic cell death. Previous studies in ECM-detached cells have linked non-apoptotic cell death to reactive oxygen species (ROS) generation, although the mechanistic underpinnings of this link remain poorly defined. Here, we uncover a role for receptor-interacting protein kinase 1 (RIPK1) in the modulation of ROS and cell viability during ECM detachment. We find that RIPK1 activation during ECM detachment results in mitophagy induction through a mechanism dependent on the mitochondrial phosphatase PGAM5. As a consequence of mitophagy, ECM-detached cells experience diminished NADPH production in the mitochondria, and the subsequent elevation in ROS levels leads to non-apoptotic death. Furthermore, we find that antagonizing RIPK1/PGAM5 enhances tumour formation in vivo. Thus, RIPK1-mediated induction of mitophagy may be an efficacious target for therapeutics aimed at eliminating ECM-detached cancer cells.
Subject(s)
Epithelial Cells/enzymology , Extracellular Matrix/metabolism , Mammary Glands, Human/enzymology , Mitochondria/enzymology , Mitophagy , Neoplasms/enzymology , Receptor-Interacting Protein Serine-Threonine Kinases/metabolism , Animals , Cell Adhesion , Cell Movement , Cell Proliferation , Cell Survival , Epithelial Cells/pathology , Extracellular Matrix/pathology , Female , HCT116 Cells , HeLa Cells , Humans , Mammary Glands, Human/pathology , Mice, Nude , Mitochondria/pathology , Mitochondrial Proteins/genetics , Mitochondrial Proteins/metabolism , NADP/metabolism , Neoplasm Metastasis , Neoplasms/genetics , Neoplasms/pathology , Phosphoprotein Phosphatases/genetics , Phosphoprotein Phosphatases/metabolism , Reactive Oxygen Species/metabolism , Receptor-Interacting Protein Serine-Threonine Kinases/genetics , Signal Transduction , Tumor BurdenABSTRACT
Immunotoxins are chimeric proteins comprising a specific cellular targeting domain linked to a cytotoxic factor. Here we describe the design and use of a novel, peptide-based immunotoxin that can initiate selective cytotoxicity on ErbB2-positive cells. ErbB2 is a receptor tyrosine kinase that is overexpressed in the tumor cells of approximately 30% of breast cancer patients. Immunotoxin candidates were designed to incorporate a targeting ligand with affinity for ErbB2 along with a membrane lysin-based toxin domain. One particular peptide candidate, NL1.1-PSA, demonstrated selective cytotoxicity towards ErbB2-overexpressing cell lines. We utilized a bioengineering strategy to show that recombinant NL1.1-PSA immunotoxin expression by Escherichia coli also conferred selective cytotoxicity towards ErbB2-overexpressing cells. Our findings hold significant promise for the use of effective immunotoxins in cancer therapeutics.
