Human plasma membrane-associated sialidase (NEU3) specifically hydrolyzes
gangliosides, and it is up-regulated in
colon cancer and plays an essential role in the expression of malignant phenotypes. To clarify the role of NEU3 in
tumorigenesis in vivo, we examined the susceptibility of NEU3 transgenic mice to induction of colonic
aberrant crypt foci (ACF) by
azoxymethane. Mice were injected with
azoxymethane (i.p., 15 mg/kg/week) for 6 weeks, and 4 weeks later ACF had formed in the NEU3 transgenic mice significantly more than in the control wild-type mice. Enhanced phosphorylation of
epidermal growth factor (
EGF) receptor, Akt and ERK and up-regulation of
Bcl-xL protein were observed in the transgenic colon mucosa, but no changes were found in cell proliferation, suggesting that the increased ACF formation is due to suppression of apoptosis. Immunohistological analysis with anti-cleaved
caspase 3 antibody showed an actual reduction in apoptotic cells in the transgenic mucosa at 6 h after the first
azoxymethane injection, when apoptosis in the colonic crypt occurs. Consistent with our previous observations of human
colon cancer, thin-layer chromatography of the
gangliosides from the transgenic colon mucosa revealed decreased GM3 and increased
lactosylceramide as compared to those from the control mucosa, probably because of catalysis of
gangliosides by NEU3. The results of this study provide the first evidence that NEU3 essentially increases
azoxymethane-induced ACF formation in colon mucosa by suppression of apoptosis, possibly via activation of the
EGF signaling pathway, and thus indicate that up-regulation of NEU3 is important to the promotion stage of colorectal
carcinogenesis in vivo.