Abstract 596: DKK3 expression and its function in head and neck squamous cell carcinoma
Authors: Katase Naoki , Gunduz Mehmet , Tsujigiwa Hidetsugu , Ito Satoshi , Fujii Masae , Nagatsuka Hitoshi , Sasaki Akira , Nohno Tsutomu 
Published: May 2015

Abstract
Head and neck squamous cell carcinoma (HNSCC) is frequently occurring malignancy worldwide. It is believed that HNSCC may occur as the result of cumulative abnormalities on cancer related genes. However, the key genes or pathways that might serve an important role in HNSCC biology are yet to be investigated.
Therefore, we previously performed genome wide loss of heterozygosity (LOH) analysis in HNSCC in order to seek specifically affected tumor suppressor genes (TSG). Using several microsatellite markers, we searched frequently deleted allele, and focused on dickkopf WNT signaling pathway inhibitor 3 (DKK3). DKK3 is known as a tumor suppressor, and as indicated in its alternative name, reduced expression in cancer (REIC), its expression was reduced or lost in several kinds of cancer tissues and cells. The expression, function and clinical importance of DKK3 in HNSCC were investigated.
In this study, 90 cases of HNSCC tissue samples, which were obtained from Okayama University hospital with written informed consent, for immunohistochemistry to examine DKK3 protein expression. The protein expression status was scored as positive or negative. Pearson's Chi-square test and Fisher's exact test were used to evaluate the correlation between the DKK3 protein expression and clinicopathological characteristics. Kaplan-Meier analysis was performed to determine the survival analysis. For functional analyses, HNSCC-derived cells were used. Gastric and colorectal cancer cell lines were also used for comparison. DKK3 mRNA expression was checked by RT-PCR, and then RNAi was performed in DKK3-expressing cells in order to inspect the effect of DKK3 knockdown on cell proliferation, migration, and invasion.
DKK3 protein expression was observed 76 cases out of 90 cases (84.4%). The expression was observed in the cytoplasm and cellular membrane of the cancer cells. Small vessels around the cancer nests were also positive. Intriguingly, DKK3 positive patients showed significantly shorter disease free survival (p=0.038) and overall survival (p=0.155). And DKK3 negative patients did not show metastasis. DKK3 mRNA expression was detected only in HNSCC derived cells, whereas that was not observed in gastric or colorectal cancer cells. DKK3 knockdown by siRNA transfection in HNSCC cells resulted in significant reduction of cellular migration and invasion. Western blotting revealed that DKK3 knockdown did not affect on WNT canonical or non-canonical pathways.
It is reported that DKK3 expression was reduced or lost in several cancers because of CpG methylation. However, the expression pattern of DKK3 in HNSCC was quite different. All these data strongly suggest potential role of DKK3 in HNSCC invasion, and potential clinical target for HNSCC invasion or metastasis.
Citation Format: Naoki Katase, Mehmet Gunduz, Hidetsugu Tsujigiwa, Satoshi Ito, Masae Fujii, Hitoshi Nagatsuka, Akira Sasaki, Tsutomu Nohno. DKK3 expression and its function in head and neck squamous cell carcinoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 596. doi:10.1158/1538-7445.AM2014-596