Role of the LOXL2 enzyme in the pro-invasive behaviour of melanoma cells and matrix remodelling of the tumour stroma
Cutaneous melanoma is an aggressive, heterogeneous and highly metastatic skin cancer. Despite successful therapies targeting the BRAFV600E oncogenic pathway or immune checkpoints, many patients relapse and remain in therapeutic failure. Innate or acquired resistances are due to genetic mutations or non-genetic phenotypic reprogramming and plasticity. Recent studies based on single cell RNA-seq analysis of cutaneous melanoma have identified tumor cell subpopulations that are classified according to their differentiation state and transcriptional signature. Upon microenvironment and therapeutic pressures, melanoma cells can switch from a melanocytic state to dedifferentiated states associated with increased expression of tyrosine kinase receptors (RTK) and mesenchymal or neural crest stem cell-like markers. Such adaptive plasticity was described as a driver of resistance to targeted therapies. Tumor progression is influenced by alterations in the biochemical and biophysical properties of the tumor microenvironment. Increased collagen fiber deposition and crosslinking are indeed known to stiffen tumors, promote malignant progression and confer resistance to treatments. Our study relies on original observations from the team that dedifferentiated cells produce an abundant extracellular matrix (ECM) enriched in the lysyl oxidase-like 2 LOXL2, a collagen crosslinking enzyme also known to drive the epithelial-to-mesenchymal transition in breast cancer. Its role in melanoma biology remains poorly explored. We hypothesized that LOXL2 production by melanoma cells could influence their mesenchymal properties as well as ECM remodeling and tumor stiffness observed in vivo during adaptive response and therapeutic resistance.
We first showed that LOXL2 is preferentially expressed by dedifferentiated melanoma cells and that its expression is associated with poor prognosis in melanoma. LOXL2 is induced by the combination of BRAF and MEK inhibitors or hypoxia, cues known to promote the transition towards a dedifferentiated phenotype, and regulated by the cell plasticity transcription factor ZEB1. Interestingly, LOXL2 induction by the targeted therapy is reversed by inhibition of the RTK and AKT pathways. We then investigated the specific contribution of LOXL2 to the dedifferentiated mesenchymal phenotype using loss-of-function approaches. We revealed that LOXL2 plays a role in focal adhesion formation and mesenchymal cell morphology, and promotes melanoma cell migration, invasion and metastasis. Mechanistically, comparative proteomic analysis identified the plasminogen activator inhibitor 2, PAI-2, a member of the serpin family, as a potential effector of LOXL2-mediated migration. Finally, we showed that targeting LOXL2 in dedifferentiated cells and melanoma-associated fibroblasts impairs their ability to contract a collagen matrix and assemble an organized ECM, suggesting the implication of LOXL2 in the dialogue between melanoma cells and the tumoral matrix.
Taken together, these results establish an original link between LOXL2, melanoma cell phenotypic diversity and stromal matrix remodeling. Our study reveals that, in addition to its conventional role in collagen remodeling, LOXL2 exerts a tumor cell-autonomous pro-invasive action in melanoma. In addition, my work provides a better understanding of the ECM biomechanical signals that affect tumor cell plasticity and adaptation to anti-melanoma therapies, and highlights the value of targeting LOXL2 in the treatment of metastatic and resistant disease.
Melanoma, phenotypic transition, LOXL2, ECM remodeling, migration
- Dr Gilles PAGÈS, DR Inserm, Institut de Recherche sur le Cancer et le Vieillissement (IRCAN), Université Côte d’Azur
- Pr Samia MOURAH, DR Inserm, Hôpital Saint Louis, Université Paris Cité
- Dr Julie CARAMEL, CR Inserm, Centre de Recherche en Cancérologie de Lyon (CRCL), Université Claude Bernard Lyon 1
- Dr Emmanuel DONNADIEU, DR CNRS, Institut Cochin, Université de Paris
- Dr Sophie TARTARE-DECKERT, DR Inserm, C3M, Université Côte d’Azur
- Dr Marcel DECKERT, DR Inserm, C3M, Université Côte d’Azur