Intestinal MUC2 and gastric M1/MUC5AC in preneoplastic lesions induced by 1,2-dimethylhydrazine in rat: a sequential analysis.

Our study was performed to sequentially analyze the expression of the intestinal mucin MUC2 and of the gastric mucin MUC5AC as indicators during progression of preneoplastic biomarkers in rat colon. F344 rats were sacrificed 2, 4, 8, 12, 24 and 36 weeks after injection of 1,2-dimethylhydrazine (DMH, 200 mg/kg, i.p.). The expression of MUC2 and of MUC5AC was studied by immunohistochemistry in preneoplastic lesions classified in two categories: histologically altered foci (HAF) and beta-catenin accumulated crypts (BCAC). HAF appeared 4 weeks after DMH injection. Their crypt multiplicity stagnated with time (3-4 crypts/foci) but gastric MUC5AC mucin was always observed in some goblet cells of the lesions of this category. In contrast, MUC2-immunostaining was not modified compared to the adjacent crypts. Double-immunofluorescence revealed that goblet cells which produced MUC5AC continued to express MUC2. In BCAC, crypt multiplicity and mucin expression strongly evolved with time. These lesions were observed only 8 weeks after DMH-injection. At this stage, 20% of BCAC showed a decreased MUC2 expression and 33% were MUC5AC immunopositive. At the 36-week point, 43% of BCAC had a reduced MUC2 staining and 90% were positive for MUC5AC. This immunopositivity was often observed in all the cells of these lesions. Seldom, some BCAC were depleted at the same time in MUC2 and in MUC5AC. Similar alterations in mucin expression were observed in human colonic pre-neoplastic lesions. These findings suggest that a decrease in MUC2 expression and staining of MUC5AC in non-goblet-like cells predicts histological progression of preneoplastic lesions.

The DHE cell line as a model for studying rat gastro-intestinal mucin expression: effects of dexamethasone.

The expression of mucin genes was evaluated in rat intestinal cell lines in order to establish an in vitro model for investigating the regulation of intestinal mucin expression in this species. Two rat intestinal cancer cell lines (DHE, LGA) and three nontumoral rat intestinal cell lines (IEC6, IEC17, IEC18) were screened. The mRNA expression of rMuc1, rMuc2, rMuc3, rMuc4, and rMuc5AC mucin genes was studied by semiquantitative RT-PCR, real-time RT-PCR and Northern-blot analysis. Results were correlated with immunohistochemical expression of rat gastric and intestinal mucin proteins, and secretion of glycoconjugates was examined by enzyme-linked lectin assay. We showed that mRNA of rMucl and rMuc2 were constitutively expressed in all IEC cell populations but periodic acid Schiff staining of these cells did not reveal the presence of glycoproteins. DHE cells expressed rMuc1-5AC mRNA and LGA expressed the same mucins but the level of rMuc4 was much lower. Mucin mRNA expression also differed in relation with the length of cultivation. Immunocytochemical studies revealed the presence of gastric and intestinal mucins in the two tumoral cell lines. Functional experiments showed that bethanechol, A23187 and PMA stimulated release of glycoconjugates in DHE but not in LGA cells. Treatment of DHE cells with dexamethasone (10(-7) mol/l) enhanced rMuc2 mRNA but decreased rMuc1 and rMuc5AC mRNA. Real-time RT-PCR showed that the expression of rMuc1 and rMuc5AC genes was reduced by more than tenfold after 24 h. The increased expression of rMuc2 gene was confirmed by Northern blot analysis. In conclusion, DHE cells provide a valuable cellular model for research on rat mucin secretion and expression.