ABSTRACT
Autophagy is a highly conserved process of cellular self-digestion that involves the formation of autophagosomes for the delivery of intracellular components and dysfunctional organelles to lysosomes. This process is induced by different signals including starvation, mitochondrial dysfunction, and DNA damage. The molecular link between autophagy and DNA damage is not well understood yet. Importantly, tumor cells utilize the mechanism of autophagy to cope with genotoxic anti-cancer drug therapy. Another mechanism of drug resistance is provided to cancer cells via the execution of the EMT program. One of the critical transcription factors of EMT is Zeb1. Here we demonstrate that Zeb1 is involved in the regulation of autophagy in several breast cancer cell models. On the molecular level, Zeb1 likely facilitates autophagy through the regulation of autophagic genes, resulting in increased LC3-II levels, augmented staining with Lysotracker, and increased resistance to several genotoxic drugs. The attenuation of Zeb1 expression in TNBC cells led to the opposite effect. Consequently, we propose that Zeb1 augments the resistance of breast cancer cells to genotoxic drugs, at least partially, via autophagy. Collectively, we have uncovered a novel function of Zeb1 in the regulation of autophagy in breast cancer cells.
Subject(s)
Autophagy , Breast Neoplasms/pathology , Drug Resistance, Neoplasm , Mutagens/toxicity , Zinc Finger E-box-Binding Homeobox 1/metabolism , Autophagy/drug effects , Autophagy/genetics , Basic Helix-Loop-Helix Leucine Zipper Transcription Factors/genetics , Basic Helix-Loop-Helix Leucine Zipper Transcription Factors/metabolism , Biomarkers, Tumor/metabolism , Breast Neoplasms/genetics , Cell Line, Tumor , DNA Damage , Drug Resistance, Neoplasm/drug effects , Drug Resistance, Neoplasm/genetics , Epithelial-Mesenchymal Transition/drug effects , Epithelial-Mesenchymal Transition/genetics , Female , Gene Expression Regulation, Neoplastic/drug effects , Humans , Microtubule-Associated Proteins/metabolism , Tumor Suppressor Protein p53/metabolism , Up-Regulation/drug effects , Up-Regulation/genetics , Zinc Finger E-box-Binding Homeobox 1/geneticsABSTRACT
Autophagy is a special catabolic cellular program that is induced in response to deprivation of nutrients and energy starvation. During the execution of this program, cellular components, including aggregates, as well as damaged organelles and some proteins are encapsulated in special vesicles known as autophagosomes and subsequently are degraded after fusion of autophagosomes with lysosomes. Importantly, at late stages of tumorigenesis cancer cells employ autophagy to sustain proliferation in unfavorable conditions, including anti-cancer drug therapy. E3 ubiquitin ligases play an important role in controlling autophagy. Here we demonstrate that the E3 ligase, a p53-induced RING-H2 protein (Pirh2), is involved in the regulation of autophagy in non-small cell lung cancer cells. Knockdown of Pirh2 decreased the expression of genes involved in all steps of autophagy. Concomitantly, Pirh2 knockdown cell lines exhibited much less of the processed form of LC3 compared to the respective cell lines with normal levels of Pirh2. These results were confirmed by the immune fluorescence microscopy using LC3 antibody and the LysoTracker dye. In agreement with the protective role of autophagy, cells with attenuated expression of Pirh2 were more sensitive to the treatment with doxorubicin. Collectively, we have uncovered a novel function of Pirh2 in the regulation of autophagy in lung cancer cells.
