Inactivation or Loss of TTP Promotes Invasion in Head and Neck Cancer via Transcript Stabilization and Secretion of MMP9, MMP2, and IL-6

Abstract

Purpose Invasion is the critical step in progression of a pre-cancerous lesion to squamous cell carcinoma of the head and neck (SCCHN). Invasion is regulated by multiple pro-inflammatory mediators. Tristetraprolin (TTP) is an mRNA degrading protein that regulates multiple pro-inflammatory mediators. TTP may serve as an excellent treatment target. Rap1 is a ras-like oncoprotein that induces critical signaling pathways. In this study, the role of rap1 in TTP-mediated invasion was investigated. Experimental Design Using complementary approaches we modulated TTP and altered expression of IL-6 and MMP2/9, which were quantified by ELISA and zymogram. Invasion was evaluated in vitro using the Oral-Cancer-Equivalent (OCE) 3D model and in vivo in the chick chorioallantoic membrane (CAM). The role of rap1 and p38 were established using knockdown strategies. Results Downregulation of TTP significantly increased invasion via secretion of MMP9/2 and IL-6. In the novel OCE and CAM invasion models of SCCHN, cells with downregulated TTP destroyed the basement membrane to invade the underlying connective tissue. Rap1 induces p38 mitogen activated protein kinase (p38)-mediated inactivation of TTP. Inactive TTP enhances transcript stability via binding to the 3′-UTR. High IL-6 and MMP9 are prognostic for poor clinical outcomes in SCCHN patients. Conclusions Targeting the rap1-p38-TTP cascade is an attractive novel treatment strategy in SCCHN to concurrently suppress multiple mediators of invasion.

Systematic Analysis of AU-Rich Element Expression in Cancer Reveals Common Functional Clusters Regulated by Key RNA-Binding Proteins

“…TTP has been shown to significantly reduce tumor cell migration and invasion while HuR increases these activities (4,5,21,48,49). The combined impact on mitosis and tumor invasion due to lack of TTP in breast cancer cells and patients may confirm the putative tumor suppressor role of TTP, including its anti-invasive role.…”

Mechanisms of Invasion in Head and Neck Cancer

“…Its activity is increased by EGFR 32,37,42,54,100-102 and integrins, 75 and its inhibition reduces invasion. 81,103,104 In addition, MMP-9 can degrade type IV collagen, 105-107 a key constituent of the basement membrane, and thus has the potential for an important role in enabling HNSCC cells to become Figure 1. Signaling pathways in head and neck squamous cell carcinoma invasion involving the epidermal growth factor receptor (EGFR).…”

“…103,104 Although MMP-2 and MMP-9 are secreted MMPs, the transmembrane protease membranetype 1 MMP (MT1-MMP) also has a significant role. MT1-MMP, together with the tissue inhibitor of metalloproteinases 2, 111,112 is important in the activation of secreted proteases, such as MMP-2, 113 and suppression of MT1-MMP reduces overall matrix degradation activity 114 and invasion.…”

Matrix metalloproteinases in head and neck cancer: current perspectives

“…79,80 MMP2 and MT1-MMP have also been implicated in HNSCC invasion. 81 Moreover, MT1-MMP, along with TIMP2, has been shown to contribute to secreted protease activation, such as MMP2. 82,83 In addition, EMMPRIN is another protein that has been proposed to increase the protease activity of MMPs, cathepsin B, and uPAR, in order to enhance HNSCC invasion.…”