Tumor-derived CTF1 (cardiotrophin 1) is a critical mediator of stroma-assisted and autophagy-dependent breast cancer cell migration, invasion and metastasis.

Macroautophagy/autophagy is an evolutionarily conserved cellular stress response mechanism. Autophagy induction in the tumor microenvironment (stroma) has been shown to support tumor metabolism. However, cancer cell-derived secreted factors that initiate communication with surrounding cells and stimulate autophagy in the tumor microenvironment are not fully documented. We identified CTF1/CT-1 (cardiotrophin 1) as an activator of autophagy in fibroblasts and breast cancer-derived carcinoma-associated fibroblasts (CAFs). We showed that CTF1 stimulated phosphorylation and nuclear translocation of STAT3, initiating transcriptional activation of key autophagy proteins. Additionally, following CTF1 treatment, AMPK and ULK1 activation was observed. We provided evidence that autophagy was important for CTF1-dependent ACTA2/α-SMA accumulation, stress fiber formation and fibroblast activation. Moreover, promotion of breast cancer cell migration and invasion by activated fibroblasts depended on CTF1 and autophagy. Analysis of the expression levels of CTF1 in patient-derived breast cancer samples led us to establish a correlation between CTF1 expression and autophagy in the tumor stroma. In line with our in vitro data on cancer migration and invasion, higher levels of CTF1 expression in breast tumors was significantly associated with lymph node metastasis in patients. Therefore, CTF1 is an important mediator of tumor-stroma interactions, fibroblast activation and cancer metastasis, and autophagy plays a key role in all these cancer-related events.Abbreviations: ACTA2/α-SMA: actin, alpha 2, smooth muscle CAFs: cancer- or carcinoma-associated fibroblasts CNT Ab.: control antibody CNTF: ciliary neurotrophic factor CTF1: cardiotrophin 1 CTF1 Neut. Ab.: CTF1-specific neutralizing antibody GFP-LC3 MEF: GFP-fused to MAP1LC3 protein transgenic MEF LIF: leukemia inhibitory factor IL6: interleukin 6 MEFs: mouse embryonic fibroblasts MEF-WT: wild-type MEFs OSM: oncostatin M TGFB/TGFß: transforming growth factor beta.

A novel ATG5 interaction with Ku70 potentiates DNA repair upon genotoxic stress.

The maintenance of cellular homeostasis in living organisms requires a balance between anabolic and catabolic reactions. Macroautophagy (autophagy herein) is determined as one of the major catabolic reactions. Autophagy is an evolutionarily conserved stress response pathway that is activated by various insults including DNA damage. All sorts of damage to DNA potentially cause loss of genetic information and trigger genomic instability. Most of these lesions are repaired by the activation of DNA damage response following DNA repair mechanisms. Here we describe, a novel protein complex containing the autophagy protein ATG5 and the non-homologous end-joining repair system proteins. We discovered for the first time that ATG5 interacted with both Ku80 (XRCC5) and Ku70 (XRCC6). This novel interaction is facilitated mainly via Ku70. Our results suggest that this interaction is dynamic and enhanced upon genotoxic stresses. Strikingly, we identified that ATG5-Ku70 interaction is necessary for DNA repair and effective recovery from genotoxic stress. Therefore, our results are demonstrating a novel, direct, dynamic, and functional interaction between ATG5 and Ku70 proteins that plays a crucial role in DNA repair under genotoxic stress conditions.

Study of Protein-protein Interactions in Autophagy Research.

Protein-protein interactions are important for understanding cellular signaling cascades and identifying novel pathway components and protein dynamics. The majority of cellular activities require physical interactions between proteins. To analyze and map these interactions, various experimental techniques as well as bioinformatics tools were developed. Autophagy is a cellular recycling mechanism that allows the cells to cope with different stressors, including nutrient deprivation, chemicals, and hypoxia. In order to better understand autophagy-related signaling events and to discover novel factors that regulate protein complexes in autophagy, we performed protein-protein interaction screens. Validation of these screening results requires the use of immunofluorescence and immunoprecipitation techniques. In this system, specific autophagy-related protein-protein interactions that we discovered were tested in Neuro2A (N2A) and HEK293T cell lines. Details of the technical procedures used are explained in this visualized experiment paper.