ABSTRACT
Colorectal cancer cell (CRC) fate is governed by an intricate network of signaling pathways, some of which are the direct target of DNA mutations, whereas others are functionally deregulated. As a consequence, cells acquire the ability to grow under nutrients and oxygen shortage conditions. We earlier reported that p38alpha activity is necessary for proliferation and survival of CRCs in a cell type-specific manner and regardless of their phenotype and genotype. Here, we show that p38alpha sustains the expression of HIF1alpha target genes encoding for glycolytic rate-limiting enzymes, and that its inhibition causes a drastic decrease in ATP intracellular levels in CRCs. Prolonged inactivation of p38alpha triggers AMPK-dependent nuclear localization of FoxO3A and subsequent activation of its target genes, leading to autophagy, cell cycle arrest and cell death. In vivo, pharmacological blockade of p38alpha inhibits CRC growth in xenografted nude mice and azoxymethane-treated Apc(Min) mice, achieving both a cytostatic and cytotoxic effect, associated with high nuclear expression of FoxO3A and increased expression of its target genes p21 and PTEN. Hence, inhibition of p38alpha affects the aerobic glycolytic metabolism specific of cancer cells and might be taken advantage of as a therapeutic strategy targeted against CRCs.
Subject(s)
Colorectal Neoplasms/metabolism , Forkhead Transcription Factors/metabolism , Hypoxia-Inducible Factor 1, alpha Subunit/metabolism , Mitogen-Activated Protein Kinase 14/antagonists & inhibitors , Animals , Apoptosis , Cell Line, Tumor , Cell Proliferation , Colorectal Neoplasms/genetics , Colorectal Neoplasms/pathology , Cyclin-Dependent Kinase Inhibitor p21/metabolism , Forkhead Box Protein O3 , Forkhead Transcription Factors/genetics , Humans , Hypoxia-Inducible Factor 1, alpha Subunit/genetics , Imidazoles/pharmacology , Male , Mice , Mice, Inbred C57BL , Mice, Nude , Mitogen-Activated Protein Kinase 14/genetics , Mitogen-Activated Protein Kinase 14/metabolism , PTEN Phosphohydrolase/metabolism , Protein Isoforms/genetics , Protein Isoforms/metabolism , Pyridines/pharmacology , RNA, Small Interfering/metabolism , Signal Transduction , Transcription, Genetic , Transplantation, HeterologousABSTRACT
Cancer develops when molecular pathways that control the fine balance between proliferation, differentiation, autophagy and cell death undergo genetic deregulation. The prospects for further substantial advances in the management of colorectal cancer reside in a systematic genetic and functional dissection of these pathways in tumor cells. In an effort to evaluate the impact of p38 signaling on colorectal cancer cell fate, we treated HT29, Caco2, Hct116, LS174T and SW480 cell lines with the inhibitor SB202190 specific for p38alpha/beta kinases. We report that p38alpha is required for colorectal cancer cell homeostasis as the inhibition of its kinase function by pharmacological blockade or genetic inactivation causes cell cycle arrest, autophagy and cell death in a cell type-specific manner. Deficiency of p38alpha activity induces a tissue-restricted upregulation of the GABARAP gene, an essential component of autophagic vacuoles and autophagosomes, whereas simultaneous inhibition of autophagy significantly increases cell death by triggering apoptosis. These data identify p38alpha as a central mediator of colorectal cancer cell homeostasis and establish a rationale for the evaluation of the pharmacological manipulation of the p38alpha pathway in the treatment of colorectal cancer.
