Abstract LB-069: Identification and characterization of the intercellular adhesion molecule-2 gene as a novel p53 family target
Authors: Takeda Kousuke , Sasaki Yasushi , Nakagaki Takafumi , Tamura Miyuki , Ohashi Tomoko , Ogi Kazuhiro , Idogawa Masashi , Hiratsuka Hiroyoshi , Tokino Takashi 
Published: August 2015

Background: p53 is one of the most important tumor suppressors, and is mutated in about half of human cancers. In response to DNA damage or other cellular stresses, activated p53 transactivates a number of target genes, which mediate various p53 functions, such as cell cycle arrest, apoptosis, DNA repair and senescence. Recent papers suggest that in addition to these functions, p53 contributes to the regulation of migration and invasion. We found that intercellular adhesion molecule-2 (ICAM2) is a target gene of p53 family, that is, p53, TAp73, and TAp63.

Study Aims: The purpose of this study is to characterize the functional relevance of p53-mediated expression of ICAM2 in human cancer.

Methods and Materials: The effect of p53 family on transcription of ICAM2 was investigated using real-time PCR, immunoblot analysis, and chromatin immunoprecipitation (ChIP) and reporter assays. Cancer cell migration and invasion were examined by wound healing assay and Matrigel invasion assay, respectively. The relationship between ICAM2 expression and p53 mutational status in tumor tissues was examined using the Oncomine utility. To examine whether ICAM2 expression affects prognosis in cancer patients, the PrognoScan databases were interrogated.

Results: ICAM2 expression was upregulated by DNA damage-induced p53 activity, as well as by overexpression of p53 family genes. We found a specific binding site for p53 family proteins in the first intron of the ICAM2 gene by a ChIP assay. A heterologous reporter assay revealed that this binding site is a functional response element, suggesting that ICAM2 is a transcriptional target of the p53 family member genes.

We also found that ectopic expression of ICAM2 inhibited cancer cell migration and invasion. Conversely, inactivation of ICAM2 stimulated cancer cell migration and invasion. Importantly, The inhibitory activity of ICAM2 on cancer cell migration and invasion was abrogated by the addition of neutralizing ICAM2 antibodies. We also demonstrated that silencing endogenous ICAM2 in cancer cells caused a marked increase in extracellular signal-regulated kinase-1/2 (ERK) phosphorylation levels, suggesting that ICAM2 inhibits migration and invasion of cancer cells by suppressing ERK signaling. We found six published cancer microarray data sets, in which the p53 status and ICAM2 expression have been reported. In all these six datasets, patients with mutant p53 show lower expression of ICAM2 mRNA than patients with wild-type p53, although this did not reach statistical significance. Moreover, we have found that low expression of ICAM2 may serve as a poor prognostic factor for certain cancer patients.

Conclusions: We identified ICAM2 as a direct transcriptional target of the p53 family member genes. Our finding suggests that ICAM2 is one of the effectors downstream of p53 to negatively regulate tumor metastasis.

Citation Format: Kousuke Takeda, Yasushi Sasaki, Takafumi Nakagaki, Miyuki Tamura, Tomoko Ohashi, Kazuhiro Ogi, Masashi Idogawa, Hiroyoshi Hiratsuka, Takashi Tokino. Identification and characterization of the intercellular adhesion molecule-2 gene as a novel p53 family target. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-069. doi:10.1158/1538-7445.AM2015-LB-069