NET1-mediated RhoA activation facilitates lysophosphatidic acid-induced cell migration and invasion in gastric cancer

Abstract

The most lethal aspects of gastric adenocarcinoma (GA) are its invasive and metastatic properties. This aggressive phenotype remains poorly understood. We have recently identified neuroepithelial cell transforming gene 1 (NET1), a guanine exchange factor (GEF), as a novel GA-associated gene. Neuroepithelial cell transforming gene 1 expression is enhanced in GA and it is of functional importance in cell invasion. In this study, we demonstrate the activity of NET1 in driving cytoskeletal rearrangement, a key pathological mechanism in gastric tumour cell migration and invasion. Neuroepithelial cell transforming gene 1 expression was increased 10-fold in response to treatment with lysophosphatidic acid (LPA), resulting in an increase in active levels of RhoA and a 2-fold increase in cell invasion. Lysophosphatidic acid-induced cell invasion and migration were significantly inhibited using either NET1 siRNA or a RhoA inhibitor (C3 exoenzyme), thus indicating the activity of both NET1 and RhoA in gastric cancer progression. Furthermore, LPA-induced invasion and migration were also significantly reduced in the presence of cytochalasin D, an inhibitor of cytoskeletal rearrangements. Neuroepithelial cell transforming gene 1 knockdown resulted in AGS cell rounding and a loss of actin filament organisation, demonstrating the function of NET1 in actin organisation. These data highlight the importance of NET1 as a driver of tumour cell invasion, an activity mediated by RhoA activation and cytoskeletal reorganisation.

Neuroepithelial transforming gene 1 functions as a potential prognostic marker for patients with non-small cell lung cancer

“…Neuroepithelial transforming gene 1 (Net-1) is a 54-kDa oncoprotein (5), which has also been recognized as a Ras homolog family member A (RhoA) guanine nucleotide exchange factor (GEF) (6), and which was initially identified in a neuroepithelioma cell line (5). Net-1 is a member of seven transmembrane four superfamily with two distinct isoforms (Net-1 and Net-1A) and has a crucial role in cell signal transduction, proliferation, migration and invasion; it is also indicative of a poor prognosis of cancer patients (7)(8)(9)(10). Overexpression of Net-1 has been documented in a variety of human cancer types, including hepatocellular carcinoma, breast cancer, oesophageal adenocarcinoma, skin squamous cell carcinoma and gastric adenocarcinoma (8,(11)(12)(13)(14).…”

The guanine nucleotide exchange factor Net1 facilitates the specification of dorsal cell fates in zebrafish embryos by promoting maternal β-catenin activation

“…Future studies may determine whether this regulatory cascade similarly functions in the dorsal axis formation of other vertebrate animals. In addition, because upregulated net1 expression and aberrant Wnt/β-catenin signaling are widely implicated in numerous cancers [12,[42][43][44][45][46], it will be important to investigate the functional interaction of Net1 and Wnt/β-catenin signaling in cancer cell proliferation, motility and invasiveness.…”

“…Mammalian Net1 was found to be a RhoA-specific GEF that is upregulated in many carcinomas to enhance cell migration and invasion [42][43][44][45][46], but its function during embryonic development has not been fully described. Zebrafish net1, which encodes a protein sharing a similar domain architecture and a high sequence identity with its human and mouse orthologs (57.17% and 57.66%, respectively), was first identified as a dorsally expressed gene at the onset of gastrulation [32].…”

A GEF activity-independent function for nuclear Net1 in Nodal signal transduction and mesendoderm formation

“…Net1, the protein product of NET1, was originally isolated from neuroepithelioma cells and acts as a RhoA-specific guanine nucleotide exchange factor (GEF) to enhance cancer cell migration and invasion (Alberts and Treisman, 1998;Chan et al, 1996;Murray et al, 2008;Tu et al, 2010). In addition, this gene is expressed in a dorsoventral-gradient in the blastoderm margin at the onset of gastrulation and has important functions during early embryonic development (Liu et al, 2011).…”