| Research Abstract |
The ability of oral cancer invade surrounding tissues and form metastasis foci at distant sites is main cause of treatment failure. Understanding mechanism of invasion and metastasis is very important for development of new effective treatments. First we thus investigated the expression of various proteins in the tumor tissues to determine what factors are associated with invasive and metastasis potential of oral cancer. Immunohistochemical studies revealed that reduced expressions of E-cadherin and desmosomal proteins, such as desmoglein, desmocollin and desmoplakin, were correlated with mode of invasion and lymph node metastasis. The relationship between expression of sialyl LewisィイD1aィエD1 and metastatic potential was also found. As concerning expression of matrix metalloprotease (MMP), a marked expression of MMP-1, MMP-2, MMP3, MMP-9 and MT1-MMP was frequently observed in invasive and matastatic cases. Especially, more than 80% of tumors with coexpression of MMP-2 and MT1-MMP metast
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asized in cervical lymph nodes. Moreover, an increased expression of MMP-inhibitor, MlMP-1, was observed in cases with an increased expression of MMPs. The involvement of MMPs in invasion and metastasis of oral cancer was confirmed by gelatin zymograpfy. Gelatin zymogram revealed the presence of proMMP-2, active MMP-2 and proMMP-9 in the tumor tissues. Especially, highly invasive cases showed the increased gelatinolytic activities of MMP-2 as well as MMP-9 in the tumors, and the cases with the high levels of MMPs and low levels of TlMP-1 seemed to have a high potential to metastasize.
In order to examine regulation of MMP production with invasiveness, we second performed in vivo study. Invasion of oral cancer cells in an in vitro invasion model was found to be enhanced by various growth factors and cytokines, such as EGF and TNF α. One of mechanism is largely mediated by proteolytic activity in the cells : e.g., EGF and TNF α enhanced productions of urokinase-type plasminogen activator (uPA) and MMP-9, respectively, in the cells as well as their invasiveness. These protease productions are regulated by certain transcription factors, such as AP-1 and NF-κB. Inhibition of the activation of these factors would result a suppression of invasiveness. Our study clearly demonstrated that lactacystin, a specific proteasome inhibitor, could prevent TNF α from enhancing MMP-9 production, NF-κB activation, induction of MMP-9 mRNA and cell migration. Other some agents such as dexamethasone were also found to act as an inhibitor of MMP-9 and uPA transcriptions as well as tumor invasion. Less
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