Mouse intestinal goblet cells expressing SV40 T antigen directed by the MUC2 mucin gene promoter undergo apoptosis upon migration to the villi

Mucinous colorectal cancers exhibit a characteristic set of molecular genet ic alterations and may be derived from progenitor cells committed to the go blet cell lineage. Previously, we demonstrated that the MUC2 mucin gene pro moter drives transgene reporter expression with high specificity in small i ntestinal goblet cells of transgenic mice. On the basis of these experiment s, we reasoned that the MUC2 promoter could be used to drive SV40 T antigen (Tag) expression in the same cell type, decoupling them from their normal antiproliferative controls, A line of mice was established (MUCTag6) that e xpressed Tag in intestinal goblet cells as determined by RNA blot and immun ohistochemical analysis, These goblet cells were markedly involuted however , most notably in the villi. Endogenous intestinal MUC2 message levels were reduced to about one third the normal level in these mice. However, absorp tive cell lineage markers were comparable with nontransgenics. Bromodeoxyur idine-positive S-phase cells are limited to crypts in nontransgenic intesti ne but are present in both crypts and villi in MUCTag6. In contrast, mitoti c cells were not present in the villi, indicating that MUCTag6 villi goblet cells do not progress into M phase. Apoptotic cells positive for terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling were in creased more than fourfold in MUCTag6 villi (P < 0.001), and apoptotic gobl et cells were evident. Electron microscopic examination of MUCTag6 intestin al villi revealed the presence of degraded cell remnants containing mucin g oblets together with other cell debris, further indicating apoptosis of the goblet cell lineage. Thus, the expression of Tag in intestinal goblet cell s releases them from normal antiproliferative controls, causing their inapp ropriate entry into S phase even after they transverse the crypt/ villus ju nction. They do not, however, progress to M phase. Instead, they undergo ap optosis with a high degree of efficiency in S or G, phase. These experiment s demonstrate that apoptosis effectively blocks inappropriate goblet cell p roliferation in the intestine, supporting ifs proposed role as an antineopl astic mechanism.