Down-regulation of trypsinogen expression is associated with growth retardation in {alpha}1,6-fucosyltransferase-deficient mice: attenuation of proteinase-activated receptor 2 activity

Alpha1,6-fucosyltransferase (Fut8</it>) plays important roles in physiological and pathological conditions. Fut8</it>-deficient (Fut8−/−</it>) mice exhibit growth retardation, earlier postnatal death, and emphysema-like phenotype. To investigate the underlying molecular mechanism by which growth retardation occurs, we examined the mRNA expression levels of Fut8−/−</it> embryos (18.5 days postcoitum [dpc]) using a cDNA microarray. The DNA microarray and real-time polymerase chain reaction (PCR) analysis showed that a group of genes, including trypsinogens 4, 7, 8, 11, 16, and 20, were down-regulated in Fut8−/−</it> embryos. Consistently, the expression of trypsinogen proteins was found to be lower in Fut8−/−</it> mice in the duodenum, small intestine, and pancreas. Trypsin, an active form of trypsinogen, regulates cell growth through a G-protein-coupled receptor, the proteinase-activated receptor 2 (PAR-2). In a cell culture system, a Fut8</it> knockdown mouse pancreatic acinar cell carcinoma, TGP49-Fut8</it>-KDs, showed decreased growth rate, similar to that seen in Fut8−/−</it> mice, and the decreased growth rate was rescued by the application of the PAR-2-activating peptide (SLIGRL-NH<inf>2</inf>). Moreover, epidermal growth factor (EGF)-induced receptor phosphorylation was attenuated in TGP49-Fut8</it>-KDs, which was highly associated with a reduction of trypsinogens mRNA levels. The addition of exogenous EGF recovered c-fos, c-jun, and trypsinogen mRNA expression in TGP49-Fut8</it>-KDs. Again, the EGF-induced up-regulation of c-fos and c-jun mRNA expression was significantly blocked by the protein kinase C (PKC) inhibitor. Our findings clearly demonstrate a relationship between Fut8</it> and the regulation of EGF receptor (EGFR)-trypsin-PAR-2 pathway in controlling cell growth and that the EGFR-trypsin-PAR-2 pathway is suppressed in TGP49-Fut8</it>-KDs as well as in Fut8−/−</it> mice.