br Discussion br In this study we found that
In this study, we found that CDH17 expression was elevated in human GC, which is consistent with the findings obtained by Wong et al. (2003) and Ito et al. (2004) in patients with HCC and gastric carcinoma, respectively. We also discovered a relationship among CDH17, the AJCC stage and lymph node metastasis in GC tissues. Furthermore, a significant correlation was observed between the CDH17 protein level and the number of blood and lymph vessels in human GC specimens. Subsequent in vitro experiments showed that aberrant expression of CDH17 could significantly influence malignancy-associated biological characteristics, including tumour cell prolifera-tion, migration and invasion. Finally, our data support a possible me-chanism through which CDH17 activates the canonical NF-κB pathway to influence the MMP-2 level in GC cells. r> CDH17, which is also known as liver–intestine CDH, shows diﬀerent expression patterns between embryonic and adult human tissues and is generally absent in most normal adult human tissues (Nollet et al., 2000; Hertel, 2012; Berndorﬀ et al., 1994). However, CDH17 might exhibit abnormal expression in various tumour types. Previous studies have revealed that CDH17 expression is elevated in a number of human cancers. For example, Takamura et al. (2003) reported that CDH17 is overexpressed in human ducal adenocarcinoma of the pancreas. In 2006 and 2010, similar results for human hepatocellular carcinoma
were reported by Wang et al. (2006) and Lee et al. (2010), respectively. In our study, CDH17 was mainly detected in the cell membrane and 52128-35-5 of GC tissues, whereas negative or low levels of CDH17 protein were detected in the para-carcinoma gastric tissues. Similarly, the level of CDH17 mRNA was significantly higher in the GC tissues than in the matched para-carcinoma tissues. Considering the clinical correlations between CDH17 and GC, determination of the peculiar role of CDH17 in GC has become particularly important. Our research de-monstrates that CDH17 might be a potential indicator of advanced-
stage tumours and lymph node metastasis in patients with GC. This relationship was further verified by the significant correlation observed between the CDH17 protein level and the number of blood and lymph vessels in the human GC specimens. This characteristic indicates that CDH17 might be used prospectively for the assessment of disease se-verity and prognostic outcomes, which suggests that CDH17 can po-tentially be used as a bio-marker.
The biological significance of CDH17 in GC is unclear. In this study, we further examined the changes in malignancy-associated biological behaviours after the overexpression or knockdown of CDH17 in GC cells in vitro. Our data showed that the knockdown of CDH17 expres-sion significantly decreased AGS cell proliferation, migration, and in-vasion, whereas the overexpression of CDH17 significantly promoted
the malignancy-associated biological behaviours of AGS cells. A pre-vious study indicated that the down-regulation of CDH17 using siRNA markedly reduced the invasiveness and metastasis of hepatocellular carcinoma (Ding et al., 2009). Our results were consistent with those obtained in a previous study. Therefore, we suggest that abnormal CDH17 expression plays a key role in the malignancy-associated bio-logical behaviours of AGS cells.
MMPs constitute an enzyme family whose members require the presence of a zinc ion at the active site for catalytic activity, and these enzymes are critical for the maintenance of tissue allostasis (Pagemccaw et al., 2007; Parsons et al., 1998). Several MMPs, parti-cularly MMP-2 and MMP-9, are presumably important in angiogenesis (Belotti et al., 2003; Werb, 2010). Previous studies have indicated that
MMP-2 regulates cell proliferation, migration, diﬀerentiation and apoptosis and is therefore closely related to tumour growth, invasion and metastasis (Liu et al., 2003; Li et al., 2017). We also applied mo-lecular biological technology to measure the changes in the levels of MMP family members in response to CDH17 overexpression or knock-down. We found that the overexpression or knockdown of CDH17 re-sulted in corresponding changes in the MMP-2 levels, supporting the close relationship between these two molecules. These results indicate that CDH17 might play a role in tumour progression through MMP-2.
The gene that encodes MMP-2 is a key target of NF-κB signalling, and NF-κB signalling is critical for tumour proliferation, migration, and invasion. NF-κB is generally bound to IκB in the cytoplasm, and this binding maintains the complex (NF-κB: IκB) in an inactive state. When cells are exposed to appropriate extracellular stimuli, activated signal-ling pathways induce the rapid phosphorylation, ubiquitination and, ultimately, proteolytic degradation of IκB, resulting in the release of NF-κB dimers, which then translocate to the nucleus and regulate target gene transcription (Bonizzi and Karin, 2004; Hayden and Ghosh, 2004). Our data provide the first verification that CDH17 activates the cano-nical NF-κB pathway and subsequently leads to an increase in MMP-2 expression in AGS cells. However, the role of CDH17 in the regulation of NF-κB function is complex because considerable conservation of signalling intermediates, such as TNFR-associated factors (TRAFs), cIAPs and receptor-interacting proteins (RIPs), exists upstream of the IKK complex. These proteins are critical for IKK activation (Meylan et al., 2004; Jiang et al., 2017; Pomerantz and Baltimore, 1999), and we therefore cannot assert that CDH17 directly regulates NF-κB.