Loxl2 and Loxl3 Paralogues Play Redundant Roles during Mouse Development.

Lysyl oxidase-like 2 (LOXL2) and 3 (LOXL3) are members of the lysyl oxidase family of enzymes involved in the maturation of the extracellular matrix. Both enzymes share a highly conserved catalytic domain, but it is unclear whether they perform redundant functions in vivo. In this study, we show that mice lacking Loxl3 exhibit perinatal lethality and abnormal skeletal development. Additionally, analysis of the genotype of embryos carrying double knockout of Loxl2 and Loxl3 genes suggests that both enzymes have overlapping functions during mouse development. Furthermore, we also show that ubiquitous expression of Loxl2 suppresses the lethality associated with Loxl3 knockout mice.

Loxl3 Promotes Melanoma Progression and Dissemination Influencing Cell Plasticity and Survival.

Malignant melanoma is a highly aggressive tumor causing most skin cancer-related deaths. Understanding the fundamental mechanisms responsible for melanoma progression and therapeutic evasion is still an unmet need for melanoma patients. Progression of skin melanoma and its dissemination to local or distant organs relies on phenotypic plasticity of melanoma cells, orchestrated by EMT-TFs and microphthalmia-associated TF (MITF). Recently, melanoma phenotypic switching has been proposed to uphold context-dependent intermediate cell states benefitting malignancy. LOXL3 (lysyl oxidase-like 3) promotes EMT and has a key role in human melanoma cell survival and maintenance of genomic integrity. To further understand the role of Loxl3 in melanoma, we generated a conditional Loxl3-knockout (KO) melanoma mouse model in the context of BrafV600E-activating mutation and Pten loss. Melanocyte-Loxl3 deletion increased melanoma latency, decreased tumor growth, and reduced lymph node metastatic dissemination. Complementary in vitro and in vivo studies in mouse melanoma cells confirmed Loxl3's contribution to melanoma progression and metastasis, in part by modulating phenotypic switching through Snail1 and Prrx1 EMT-TFs. Importantly, a novel LOXL3-SNAIL1-PRRX1 axis was identified in human melanoma, plausibly relevant to melanoma cellular plasticity. These data reinforced the value of LOXL3 as a therapeutic target in melanoma.

E2A Modulates Stemness, Metastasis, and Therapeutic Resistance of Breast Cancer.

Cancer stem cells (CSC) are considered responsible for tumor initiation, therapeutic resistance, and metastasis. A comprehensive knowledge of the mechanisms governing the acquisition and maintenance of cancer stemness is crucial for the development of new therapeutic approaches in oncology. E2A basic helix-loop-helix (bHLH) transcription factors are associated with epithelial-mesenchymal transition (EMT) and tumor progression, but knowledge of their functional contributions to cancer biology is still limited. Using a combination of in vivo and in vitro analyses in a novel PyMT-E2A conditional knockout mouse model and derived primary tumor cell lines, we report here an essential role of E2A in stemness, metastasis, and therapeutic resistance in breast cancer. Targeted deletion of E2A in the mammary gland impaired tumor-initiating ability and dedifferentiation potential and severely compromised metastatic competence of PyMT-driven mammary tumors. Mechanistic studies in PyMT-derived cell lines indicated that E2A actions are mediated by the upregulation of Snai1 transcription. Importantly, high E2A and SNAIL1 expression occurred in aggressive human basal-like breast carcinomas, highlighting the relevance of the E2A-Snail1 axis in metastatic breast cancer. In addition, E2A factors contributed to the maintenance of genomic integrity and resistance to PARP inhibitors in PyMT and human triple-negative breast cancer cells. Collectively, these results support the potential for E2A transcription factors as novel targets worthy of translational consideration in breast cancer. SIGNIFICANCE: These findings identify key functions of E2A factors in breast cancer cell stemness, metastasis, and drug resistance, supporting a therapeutic vulnerability to targeting E2A proteins in breast cancer.

Lysyl oxidase-like 3 is required for melanoma cell survival by maintaining genomic stability.

Lysyl oxidase-like 3 (LOXL3) is a member of the lysyl oxidase family comprising multifunctional enzymes with depicted roles in extracellular matrix maturation, tumorigenesis, and metastasis. In silico expression analyses followed by experimental validation in a comprehensive cohort of human cell lines revealed a significant upregulation of LOXL3 in human melanoma. We show that LOXL3 silencing impairs cell proliferation and triggers apoptosis in various melanoma cell lines. Further supporting a pro-oncogenic role in melanoma, LOXL3 favors tumor growth in vivo and cooperates with oncogenic BRAF in melanocyte transformation. Upon LOXL3 depletion, melanoma cells display a faulty DNA damage response (DDR), characterized by ATM checkpoint activation and inefficient ATR activation leading to the accumulation of double-strand breaks (DSBs) and aberrant mitosis. Consistent with these findings, LOXL3 binds to proteins involved in the maintenance of genome integrity, in particular BRCA2 and MSH2, whose levels dramatically decrease upon LOXL3 depletion. Moreover, LOXL3 is required for efficient DSB repair in melanoma cells. Our results reveal an unexpected role for LOXL3 in the control of genome stability and melanoma progression, exposing its potential as a novel therapeutic target in malignant melanoma, a very aggressive condition yet in need for more effective treatment options.

Lysyl Oxidase-like Protein LOXL2 Promotes Lung Metastasis of Breast Cancer.

The lysyl oxidase-like protein LOXL2 has been suggested to contribute to tumor progression and metastasis, but in vivo evidence has been lacking. Here we provide functional evidence that LOXL2 is a key driver of breast cancer metastasis in two conditional transgenic mouse models of PyMT-induced breast cancer. LOXL2 ablation in mammary tumor cells dramatically decreased lung metastasis, whereas LOXL2 overexpression promoted metastatic tumor growth. LOXL2 depletion or overexpression in tumor cells does not affect extracellular matrix stiffness or organization in primary and metastatic tumors, implying a function for LOXL2 independent of its conventional role in extracellular matrix remodeling. In support of this likelihood, cellular and molecular analyses revealed an association of LOXL2 action with elevated levels of the EMT regulatory transcription factor Snail1 and expression of several cytokines that promote premetastatic niche formation. Taken together, our findings established a pathophysiologic role and new function for LOXL2 in breast cancer metastasis. Cancer Res; 77(21); 5846-59. ©2017 AACR.