Abstract 4594: Cytoplasmic LOXL2 regulates actin cytoskeletal organization in esophageal squamous cell carcinoma progression

Background: Lysyl oxidase-like 2 (LOXL2), a copper-dependent enzyme of the lysyl oxidase family, promotes tumor progression and metastasis. We previously revealed that the tumor-promoting role of LOXL2 is mediated by perturbing the architecture of the actin cytoskeleton in esophageal squamous cell carcinoma (ESCC). However, the molecular mechanisms underlying LOXL2-driven ESCC progression remain elusive, and the cytoskeletal proteins that directly interact with LOXL2 remain uncharacterized. Methods: Knockdown LOXL2 in ESCC cells was used by a lentivirus shRNA targeting LOXL2 and analyzed by RNA-sequencing and bioinformatics analysis. Proteomic analysis following by co-immunoprecipitation and immunofluorescence were applied for identification and validation of interacting partners of LOXL2 and its splicing isoform L2Δ13. Cell migration and invasion were measured by wound healing and transwell assays. By risk score calculations, immunohistochemistry of tissue microarrays were adopted to evaluate the prognosis of ESCC patients. Results: We found that knockdown of LOXL2 in ESCC cells suppresses cell migration and invasion, whereas re-expressions of LOXL2 and its non-enzymatic splicing isoform L2Δ13 rescue these cell behaviors. Silencing of LOXL2 inhibits filopodia formation, and induces changes in the expression of cytoskeleton-associated genes. Our interactome analysis identified four actin-binding proteins, i.e. ezrin (EZR), facsin (FSCN1), heat shock protein beta-1 (HSPB1) and tropomodulin-3 (TMOD3), as novel interactors of LOXL2 and L2Δ13. These novel LOXL2/L2Δ13 interaction networks carry important prognostic values in ESCC, as molecular signatures of combinations of LOXL2/L2Δ13 and their cytoskeletal interactors are associated with clinical outcome in ESCC patients. Mechanistically, the ezrin-LOXL2 interaction promotes PKCα-stimulated phosphorylation of ezrin at Thr 567 (T567), an essential residue for ezrin activation, which enhances cell motility and cell invasion in ESCC. Correlating with this, double-high expression of LOXL2 and phosphorylated ezrin-T567 predicts significantly shorter overall survival in ESCC patients. Conclusion: In conclusion, our findings have uncovered a novel molecular mechanism underlying the tumor-promoting role of cytoplasmic LOXL2, which may open new avenues for the therapeutic targeting of LOXL2 in ESCC. (This study is supported by the Natural Science Foundation of China (No. 81472613) and Li Ka Shing Foundation). Citation