Lysyl oxidase‐like 2 (LOXL2) belongs to the family of lysyl oxidases, and as such promotes crosslinking of collagens and elastin by oxidative deamination of lysine residues. In endothelial cells (ECs), LOXL2 is involved in crosslinking and scaffolding of collagen IV. Additionally, several reports have shown a role for LOXL2 in other processes, including regulation of gene expression, tumor metastasis, and epithelial‐to‐mesenchymal transition (EMT). Here, we demonstrate an additional role for LOXL2 in the regulation of angiogenesis by modulation of endothelial‐to‐mesenchymal transition (EndMT). LOXL2 knockdown in ECs results in decreased migration and sprouting, and concordantly, LOXL2 overexpression leads to an increase in migration and sprouting, independent of its catalytic activity. Furthermore, LOXL2 knockdown resulted in a reduced expression of EndMT markers, and inhibition of transforming growth factor‐β (TGF‐β)‐mediated induction of EndMT. Interestingly, unlike in EMT, overexpression of LOXL2 alone is insufficient to induce EndMT. Further investigation revealed that LOXL2 expression regulates protein kinase B (PKB)/Akt and focal adhesion kinase (FAK) signaling, both pathways that have been implicated in the regulation of EMT. Altogether, our studies reveal a role for LOXL2 in angiogenesis through the modulation of EndMT in ECs, independent of its enzymatic crosslinking activity.

Surgical removal of colorectal cancer (CRC) liver metastases generates areas of tissue hypoxia. Hypoxia imposes a stem-like phenotype on residual tumor cells and promotes tumor recurrence. Moreover, in primary CRC, gene expression signatures reflecting hypoxia and a stem-like phenotype are highly expressed in the aggressive Consensus Molecular Subtype 4 (CMS4). Therapeutic strategies eliminating hypoxic stem-like cells may limit recurrence following resection of primary tumors or metastases.Here we show that expression of DNA repair genes is strongly suppressed in CMS4 and inversely correlated with hypoxia-inducible factor-1 alpha (HIF1α) and HIF-2α co-expression signatures. Tumors with high expression of HIF signatures and low expression of repair proteins showed the worst survival. In human tumors, expression of the repair proteins RAD51, KU70 and RIF1 was strongly suppressed in hypoxic peri-necrotic tumor areas. Experimentally induced hypoxia in patient derived colonospheres in vitro or in vivo (through vascular clamping) was sufficient to downregulate repair protein expression and caused DNA damage. Hypoxia-induced DNA damage was prevented by expressing the hydroperoxide-scavenging enzyme glutathione peroxidase-2 (GPx2), indicating that reactive oxygen species mediate hypoxia-induced DNA damage. Finally, the hypoxia-activated prodrug Tirapazamine greatly augmented DNA damage and reduced the fraction of stem-like (Aldefluorbright) tumor cells in vitro, and in vivo following vascular clamping.We conclude that decreased expression of DNA repair proteins and increased DNA damage in hypoxic tumor areas may be therapeutically exploited with hypoxia-activated prodrugs, and that such drugs reduce the fraction of Aldefluorbright (stem-like) tumor cells.

BackgroundAldehyde dehydrogenase 1A1 (ALDH1A1) encodes an enzyme that oxidizes aldehydes to their corresponding carboxylic acids. In colorectal cancer ALDH1A1 marks cancer stem cells and plays putative roles in tumor progression and drug resistance. However, the potential value of ALDH1A1 as a diagnostic marker or target for therapy remains unclear. Here, we have analyzed ALDH1A1 mRNA and protein levels in relation to clinical, histopathological and molecular tumor features in large series of human colorectal cancer.MethodsALDH1A1 protein levels were determined by immunohistochemistry in a series of primary colorectal tumors and their corresponding liver metastases (n = 158). ALDH1A1 mRNA levels were analyzed in several large patient cohorts of colorectal cancer. ALDH1A1 mRNA and protein levels were then related to overall survival and to clinical, histopathological and molecular tumor features.ResultsHigh levels of ALDH1A1 were associated with a poorly differentiated histology and a right-sided tumor location, but not to a mesenchymal-like molecular subtype. Liver metastases contained significantly higher levels of ALDH1A1 compared to the corresponding primary tumors. Radio- and/or chemotherapy prior to tumor resection was associated with increased ALDH1A1 levels regardless of the molecular subtype. Finally, ALDH1A1 protein expression in primary tumors and metastases correlated with shorter overall survival.ConclusionsALDH1A1 expression is associated with features of poor prognosis, including a poorly differentiated histology and ‘right-sidedness’ of the primary tumor, and with shorter overall survival. ALDH1A1 is also highly expressed in therapy-surviving tumors and in liver metastases. These results warrant further research into the potential value of targeting ALDH1A1 in order to improve the efficacy of standard treatment and thereby preventing tumor recurrence.