The Role of Angiopoietin-Like 4 in Head and Neck Squamous Cell Carcinoma Progression and Dissemination

Abstract

Dysregulation of cellular signaling and behavior are instrumental in promoting tumor cell metabolism, proliferation, tissue invasion and metastasis. Extensive investigations in human cancer development have identified various of these alterations within tumors and their microenvironments that have helped guide the direction of drug development in cancer. Different types of molecular-based therapies for this disease are designed to modulate or interact with cell surface receptors (monoclonal antibodies), intracellular cascades (small molecule tyrosine kinase inhibitors) as well as microenvironment components related to the functionality of the extracellular matrix, tumor vasculature and immune response. To design these cancer molecular-based therapies, an improved understanding of the molecular underpinnings leading to tumor formation and growth is essential. The overall aim of our investigation is the identification of the molecular mechanisms associated with the induction of tumor cell migration and proliferation induced by Angiopoietin-like 4 (ANGPTL4), a pro-tumorigenic and pro- angiogenic factor, in head and neck cancer squamous cell carcinoma (HNSCC). HNSCC accounts for approximately 900,000 cases and over 400,000 deaths annually, with around 54,000 new cases and 11,000 deaths per year in the United States. Unfortunately, the clinical management of this tumor remains challenging and there is an urgent need for novel therapeutic alternatives. Our studies, divided into two research aims, use in vitro cell- based models together with signal transduction and cell and molecular biology methods. Our results demonstrate that: 1) ANGPTL4 is upregulated in human-derived dysplastic oral keratinocytes (DOKs) and HNSCC cell lines, but not in normal oral keratinocytes (NOKs), suggesting an early and sustained role for ANGPTL4 in disease progression. ANGPTL4 is a molecular marker in biopsies from patients with mild-moderate or moderate oral epithelial dysplasia, primary HNSCC and metastatic HNSCC. ANGPTL4 is necessary and sufficient to promote cell migration in DOKs and HNSCCs lines. Binding of ANGPTL4 to neuropilin-1 (NRP1) leads to paxillin (PXN) phosphorylation and cell migration in an ABL1-dependent manner, exposing the ANGPTL4/NRP1/ABL1/PXN cascade as a vulnerable target for HNSCC treatment. 2) Epidermal Growth Factor (EGF)- and Hypoxia-inducible Factor-1 (HIF-1)-mediated pathways cooperate in the upregulation of ANGPTL4 in normal and dysplastic oral keratinocytes and HNSCC cells. Besides EGF, the EGF ligand, amphiregulin leads to an increase in ANGPTL4 and is upregulated in HNSCC lesions. ANGPTL4 activates the HNSCC molecular markers p38 MAPK, AKT and mTOR in NOKs; these kinases may act as potential intracellular regulators of the autocrine signals and paracrine secretions that ANGPTL4 activates to promote HNSCC tumorigenesis. Collectively, our findings are clinically relevant and suggest that ANGPTL4 and its associated signaling molecules are potential therapeutic targets in HNSCC clinical management.