ABSTRACT
Tumor recurrence following treatment remains a major clinical challenge. Evidence from xenograft models and human trials indicates selective enrichment of cancer-initiating cells (CICs) in tumors that survive therapy. Together with recent reports showing that CIC gene signatures influence patient survival, these studies predict that targeting self-renewal, the key 'stemness' property unique to CICs, may represent a new paradigm in cancer therapy. Here we demonstrate that tumor formation and, more specifically, human colorectal CIC function are dependent on the canonical self-renewal regulator BMI-1. Downregulation of BMI-1 inhibits the ability of colorectal CICs to self-renew, resulting in the abrogation of their tumorigenic potential. Treatment of primary colorectal cancer xenografts with a small-molecule BMI-1 inhibitor resulted in colorectal CIC loss with long-term and irreversible impairment of tumor growth. Targeting the BMI-1-related self-renewal machinery provides the basis for a new therapeutic approach in the treatment of colorectal cancer.
Subject(s)
Colorectal Neoplasms/drug therapy , Heterocyclic Compounds, 2-Ring/pharmacology , Neoplasm Recurrence, Local/metabolism , Neoplastic Stem Cells/metabolism , Polycomb Repressive Complex 1/metabolism , Thiazoles/pharmacology , Animals , Blotting, Western , Bromodeoxyuridine , Cell Line, Tumor , Flow Cytometry , Genetic Vectors/genetics , Heterocyclic Compounds, 2-Ring/therapeutic use , Humans , Luciferases , Mice, Inbred NOD , Mice, SCID , Polycomb Repressive Complex 1/antagonists & inhibitors , RNA Interference , RNA, Small Interfering/genetics , Thiazoles/therapeutic useABSTRACT
There is increasing evidence that some cancers are hierarchically organized, sustained by a relatively rare population of cancer-initiating cells (C-ICs). Although the capacity to initiate tumors upon serial transplantation is a hallmark of all C-ICs, little is known about the genes that control this process. Here, we establish that ID1 and ID3 function together to govern colon cancer-initiating cell (CC-IC) self-renewal through cell-cycle restriction driven by the cell-cycle inhibitor p21. Regulation of p21 by ID1 and ID3 is a central mechanism preventing the accumulation of excess DNA damage and subsequent functional exhaustion of CC-ICs. Additionally, silencing of ID1 and ID3 increases sensitivity of CC-ICs to the chemotherapeutic agent oxaliplatin, linking tumor initiation function with chemotherapy resistance.
Subject(s)
Colonic Neoplasms/genetics , Cyclin-Dependent Kinase Inhibitor p21/genetics , Inhibitor of Differentiation Protein 1/genetics , Inhibitor of Differentiation Proteins/genetics , Neoplasm Proteins/genetics , Neoplastic Stem Cells/metabolism , Animals , Antineoplastic Agents/pharmacology , Blotting, Western , Cell Cycle/drug effects , Cell Cycle/genetics , Cell Proliferation/drug effects , Colonic Neoplasms/drug therapy , Colonic Neoplasms/pathology , Cyclin-Dependent Kinase Inhibitor p21/metabolism , Gene Expression Regulation, Neoplastic , Humans , Inhibitor of Differentiation Protein 1/metabolism , Inhibitor of Differentiation Proteins/metabolism , Mice , Mice, Inbred NOD , Mice, SCID , Microscopy, Confocal , Neoplasm Proteins/metabolism , Neoplastic Stem Cells/drug effects , Neoplastic Stem Cells/pathology , Organoplatinum Compounds/pharmacology , Oxaliplatin , RNA Interference , Reverse Transcriptase Polymerase Chain Reaction , Spheroids, Cellular/drug effects , Spheroids, Cellular/metabolism , Spheroids, Cellular/pathology , Tumor Cells, Cultured , Xenograft Model Antitumor AssaysABSTRACT
Mus81 (methyl methansulfonate UV sensitive clone 81) and Eme1 (essential meiotic endonuclease 1, also known as MMS4) form a heterodimeric endonuclease that is critical for genomic stability and the response to DNA crosslink damage and replication blockade. However, relatively little is known as to how this endonuclease is regulated following DNA damage. Here, we report mammalian Eme1 interacts with Np95, an E3 ubiquitin ligase that participates in chromatin modification, replication-linked epigenetic maintenance and the DNA damage response. Np95 and Eme1 co-localize on nuclear chromatin following exposure of cells to camptothecin, an agent that promotes the collapse of replication forks. The observed co localization following DNA damage was found to be dependent on an intact RING finger, the structural motif that encodes the E3 ubiquitin ligase activity of Np95. Taken together, these findings link Mus81-Eme1 with the replication-associated chromatin modifier functions of Np95 in the cellular response to DNA damage.
