Inactivation or loss of TTP promotes invasion in head and neck cancer via transcript stabilization and secretion of MMP9, MMP2, and IL-6.
OBJECTIVE
Invasion is the critical step in progression of a precancerous lesion to squamous cell carcinoma of the head and neck (HNSCC). Invasion is regulated by multiple proinflammatory mediators. Tristetraprolin (TTP) is an mRNA-degrading protein that regulates multiple proinflammatory 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.


METHODS
Using complementary approaches, we modulated TTP and altered expression of interleukin (IL)-6 and matrix metalloproteinase (MMP) 2/9, which were quantified by ELISA and zymogram. Invasion was evaluated in vitro using the oral-cancer-equivalent (OCE) three-dimensional 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 HNSCC, 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'-untranslated region (UTR). High IL-6 and MMP9 are prognostic for poor clinical outcomes in patients with HNSCC.


CONCLUSIONS
Targeting the rap1-p38-TTP cascade is an attractive novel treatment strategy in HNSCC to concurrently suppress multiple mediators of invasion.
Periodontics and Oral Medicine, Oral Maxillofacial Surgery, University of Michigan School of Dentistry, Ann Arbor, Michigan 48109, USA.
Elizabeth A
EA
Van Tubergen
Rajat
R
Banerjee
Min
M
Liu
Robert
R
Vander Broek
Emily
E
Light
Shiuhyang
S
Kuo
Stephen E
SE
Feinberg
Amanda L
AL
Willis
Gregory
G
Wolf
Thomas
T
Carey
Carol
C
Bradford
Mark
M
Prince
Francis P
FP
Worden
Keith L
KL
Kirkwood
Nisha J
NJ
D'Silva
D020413:3' Untranslated Regions / Q000235:genetics; D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D002294:Carcinoma, Squamous Cell / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D002465:Cell Movement; D049109:Cell Proliferation; D002642:Chick Embryo; D049033:Chorioallantoic Membrane / Q000378:metabolism; D006258:Head and Neck Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D047468:Immunoprecipitation; D015850:Interleukin-6 / Q000235:genetics / Q000378:metabolism*; D008156:Luciferases / Q000378:metabolism; D020778:Matrix Metalloproteinase 2 / Q000235:genetics / Q000378:metabolism*; D020780:Matrix Metalloproteinase 9 / Q000235:genetics / Q000378:metabolism*; D009361:Neoplasm Invasiveness; D009367:Neoplasm Staging; D020871:RNA Stability; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D046888:Tissue Array Analysis; D051816:Tristetraprolin / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D048051:p38 Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism; D020827:rap1 GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism
D020413:3' Untranslated Regions; D015850:Interleukin-6; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D051816:Tristetraprolin; C497552:ZFP36 protein, human; D008156:Luciferases; D048051:p38 Mitogen-Activated Protein Kinases; C522361:MMP2 protein, human; D020778:Matrix Metalloproteinase 2; C579270:MMP9 protein, human; D020780:Matrix Metalloproteinase 9; D020827:rap1 GTP-Binding Proteins