Neural cell adhesion molecule (
NCAM) is a type of
cell surface glycoprotein and a member of the
immunoglobulin superfamily. It has been reported that
NCAM may be associated with perineural invasion by malignant salivary gland
tumors such as
adenoid cystic carcinoma. We have previously demonstrated that
NCAM is constitutively expressed in the human salivary gland tumor cell line HSG, in vitro. In the present study, we have aimed to clarify the hypothesis that
NCAM-mediated inhibition of salivary gland
tumor proliferation is caused by homophilic binding and involves the prevention of signal transduction for perineural invasion using HSG cells.
NCAM mRNA and
protein expression was found to decrease in a dose-dependent manner upon treatment with the anti-
NCAM antibody (MAb
NCAM) for 24 h. The MTT assay showed a significant reduction in the number of viable HSG cells. Confocal
laser microscopy showed that HSG cells underwent apoptosis
after treatment with MAb
NCAM. The activation of
caspases 3, 7 and 9 was observed in HSG cells
after treatment with MAb
NCAM, thus confirming that apoptosis was induced by the activated
caspases. Apaf-1 activity was also detected in HSG cells in a dose-dependent manner
after treatment with MAb
NCAM. The up-regulation of TGF-beta1-mediated
NCAM expression appeared to lead to the activation of homophilic
NCAM binding, further accelerating HSG cell proliferation. In addition, the localization of
NCAM in
adenoid cystic carcinomas (ACCs) was examined using an immunohistochemical method.
NCAM was slightly to moderately positive in 9 of 13 cases (69.2%) of ACC. These findings suggest that
NCAM is associated not only with a cell-to-cell adhesion mechanism, but also with
tumorigenesis, including growth, development and perineural invasion in human salivary gland
tumors.