Expression of SV-40 T antigen in the small intestinal epithelium of transgenic mice results in proliferative changes in the crypt and reentry of villus-associated enterocytes into the cell cycle but has no apparent effect on cellular differentiation programs and does not cause neoplastic transformation

Abstract

Abstract. The mouse intestinal epithelium represents a unique mammalian system for examining the relationship between cell division, commitment, and differentiation. Proliferation and differentiation are rapid, perpetual, and spatially well-organized processes that occur along the crypt-to-villus axis and involve clearly defined cell lineages derived from a common multipotent stem cell located near the base of each crypt. Nucleotides -1178 to +28 of the rat intestinal fatty acid binding protein gene were used to establish three pedigrees of transgenic mice that expressed SV-40 large T antigen (TAg) in epithelial cells situated in the uppermost portion of small intestinal crypts and in already committed, differentiating enterocytes as they exited these crypts and migrated up the villus. T antigen production was associated with increases in crypt cell proliferation but had no apparent effect on commitment to differentiate along enterocytic, enteroendocrine, or Paneth cell lineages. Singleand multilabel-immunocytochemical studies plus RNA blot hybridization analyses suggested that the differentiation programs of these lineages were similar in transgenic mice and their normal litterrnates. This included enterocytes which, based on the pattern of [3H]thymidine and 5-bromo-2'-deoxyuridine labeling and proliferating nuclear antigen expression, had reentered the cell cycle during their migration up the villus. The state of cellular differentiation and/or TAg production appeared to affect the nature of the cell cycle; analysis of the ratio of S-phase to M-phase cells (collected by metaphase arrest with vincristine) and of the intensities of labeling of nuclei by [3H]thymidine indicated that the duration of S phase was longer in differentiating, villus-associated enterocytes than in the less well-differentiated crypt epithelial cell population and that there may be a block at the G2/M boundary. Sustained increases in crypt and villus epithelial cell proliferation over a 9-mo period were not associated with the development of gut neoplasms-suggesting that tumorigenesis in the intestine may require that the initiated cell have many of the properties of the gut stem call including functional anchorage.T HE manner in which epithelial cell renewal occurs in the mouse intestine provides a unique opportunity to address questions about the relationships between cell division and differentiation programs in a mammalian system. The opportunity arises because of three features: (a) Address reprint requests to Jeffrey Gordon, Department of Molecular Biology and Pharmacology, Box 8103, Washington University, 660 So. Euclid Ave., St. Louis, MO 63110.Gfinter H. Schmidt's present address is A.B.C. Cambridge, Ltd., Cambridge, England. proliferation and differentiation in the gut are spatially well organized along the crypt-to-villus axis; (b) the processes occur rapidly (completed in •3 d) and perpetually; and (c) cell lineage relationships are well known and involve derivation from a single, active multipotent stem cell.Each adult sma...

Transforming functions of Simian Virus 40

“…For instance, expression of full length SV40 LT in postmitotic, villus-associated enterocytes causes them to reenter the cell cycle without an apparent e ect on their state of di erentiation (Hauft et al, 1992) and a similar phenomenon is observed upon expression of LT in secretory cells of the colon (Asa et al, 1996;Lopez et al, 1995), pancreas (Lopez et al, 1995), retinal (Penna et al, 1998) and smooth muscle cells (March et al, 1999;Herring et al, 1999). However, some exceptions have been noticed: in adult animals where brain cells were forced to express LT under the control of the FGF1 promoter, tumors were produced which lacked terminal di erentiation markers for astrocytes or neurons, but expressed high levels of markers for proliferating cells.…”

“…For instance, SV40 T antigen has been expressed in several di erentiated cell subpopulations of the small intestine and, although all of them originate from common precursor stem cells, the consequences of this expression are extremely di erent. While hyperplasia and dysplasia of the small intestine result from the production of T antigen in enterocytic cells (Hauft et al, 1992;Kim et al, 1994), no apparent pathology is detected in the small bowel in transgenic mice expressing the T antigen in secretory cells (Asa et al, 1996;Lee et al, 1992, Lopez et al, 1995. Expression of T antigen in Paneth cells results in a loss of the mature cell type and leads to an ampli®cation of cells showing an intermediate morphology between Paneth and goblet cells (Garabedian et al, 1997).…”

The immune response to sporadic colorectal cancer in a novel mouse model

“…However, according to a recent study showing that crypts contain four to six stem cells (Barker et al, 2007), all of the stem Vil-Cre  LoxP-Tag mice developed multiple adenocarcinomas of the intestine and colon at an average age of 6 months showing for the first time that Tag is able to efficiently transform epithelial cells of the colon and intestine leading to adenocarcinoma. Development of colon carcinoma in previous studies was not successful, probably because the promoter was not active in the putative stem cell region (Hauft et al, 1992, Gum et al, 2001. This hypothesis is supported by a recent published study, in which a stem cell-specific loss of Apc resulted in progressively growing colon cancer, in contrast to the deletion of Apc in short-lived transitamplifying cells (Barker et al, 2009).…”

“…One postulates that colon carcinoma derives from these stem cells, which remain anchored to the base of the crypt during the fast epithelial turnover and accumulate mutations by high proliferative activity. According to this, it is not surprising that previous attempts to induce transformation of the differentiated cell population by Tag were not successful (Hauft et al, 1992;Gum et al, 2001Gum et al, , 2004.…”

“…The localization of the oncogene in the crypt of Lieberku¨hn influences tumorigenesis (Hauft et al, 1992;Janssen et al, 2002). The crypts contain a population of pluripotent stem cells (Cheng and Leblond, 1974;Yen and Wright, 2006), which give rise to mature cells (Cheng and Leblond, 1974;Yen and Wright, 2006).…”