Mechanism for oral tumor cell lysyl oxidase like-2 in cancer development: synergy with PDGF-AB

Faranak Mahjour,Vikki Noonan,Neha Shrestha,Alpdogan Kantarci,Philip C Trackman,Vrinda Dambal,Varun Singh

doi:10.1038/s41389-019-0144-0

Abstract

Extracellular lysyl oxidases (LOX and LOXL1–LOXL4) are critical for collagen biosynthesis. LOXL2 is a marker of poor survival in oral squamous cell cancer. We investigated mechanisms by which tumor cell secreted LOXL2 targets proximal mesenchymal cells to enhance tumor growth and metastasis. This study identified the first molecular mechanism for LOXL2 in the promotion of cancer via its enzymatic modification of a non-collagenous substrate in the context of paracrine signaling between tumor cells and resident fibroblasts. The role and mechanism of active LOXL2 in promoting oral cancer was evaluated and employed a novel LOXL2 small molecule inhibitor, PSX-S1C, administered to immunodeficient, and syngeneic immunocompetent orthotopic oral cancer mouse models. Tumor growth, histopathology, and metastases were monitored. In vitro mechanistic studies with conditioned tumor cell medium treatment of normal human oral fibroblasts were carried out in the presence and absence of the LOXL2 inhibitor to identify signaling mechanisms promoted by LOXL2 activity. Inhibition of LOXL2 attenuated cancer growth and lymph node metastases in the orthotopic tongue mouse models. Immunohistochemistry data indicated that LOXL2 expression in and around tumors was decreased in mice treated with the inhibitor. Inhibition of LOXL2 activity by administration of PXS-S1C to mice reduced tumor cell proliferation, accompanied by changes in morphology and in the expression of epithelial to mesenchymal transition markers. In vitro studies identified PDGFRβ as a direct substrate for LOXL2, and indicated that LOXL2 and PDGF-AB together secreted by tumor cells optimally activated PDGFRβ in fibroblasts to promote proliferation and the tendency toward fibrosis via ERK activation, but not AKT. Optimal fibroblast proliferation in vitro required LOXL2 activity, while tumor cell proliferation did not. Thus, tumor cell-derived LOXL2 in the microenvironment directly targets neighboring resident cells to promote a permissive local niche, in addition to its known role in collagen maturation.

Highlights

Oral squamous cell carcinoma (OSCC) accounts for more than 90% of oral cavity cancers and is the sixth most common cancer in the world[1,2]
Histopathology of LOXL2 and Lysyl oxidases (LOXs) expression in human oral cancer biopsies Tissue blocks from three to five biopsies from different donors corresponding to dysplasia, differentiated OSCC, and poorly differentiated oral cancer, respectively, from the Boston University School of Dental Medicine Pathology diagnostic services laboratory were obtained under an approved IRB protocol (#31869)
To independently determine if the other LOX paralogues were expressed in oral cancer, we investigated The Cancer Genome Atlas (TCGA) data set for OSCC of the tongue compared to non-affected tongue tissue from the same 334 subjects, focusing on the relative gene expression of all five LOX paralogues, LOX and LOXL1–LOXL4

Summary

Introduction

Oral squamous cell carcinoma (OSCC) accounts for more than 90% of oral cavity cancers and is the sixth most common cancer in the world[1,2]. Metastasis to cervical lymph nodes in patients with OSCC occurs in almost half of patients[4] and recurrent metastasis occurs in 20–30% of patients after treatment[5,6]. These cancers have a poor 5-year survival rate, and cause significant morbidity due to limiting speech, food intake, and other aspects of oral and systemic health. Lysyl oxidases (LOXs) catalyze the oxidative deamination of the ɛ-amino group of lysine and hydroxylysine residues in the telopeptide regions of procollagens to form peptidyl aldehydes, which results in biosynthetic cross-linking of collagen[7].

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Conclusion