Genetic deficiency of decorin causes intestinal tumor formation through disruption of intestinal cell maturation

Abstract

Decorin is a member of the small leucine-rich proteoglycan gene family and plays an important role in suppressing cancer cell growth and metastasis. To elucidate the importance of decorin in intestinal carcinogenesis, a decorin-deficient (Dcn(-/-)) mouse model was employed. We found that targeted inactivation of decorin was sufficient to cause intestinal tumor formation with 30% of the Dcn(-/-) mice developing intestinal tumors with no other chemical or genetic initiation. Moreover, a high-risk diet amplified and accelerated the tumors initiated by decorin deficiency. Further, tumorigenesis in Dcn(-/-) mice was associated with disruption of intestinal maturation, including decreased cell differentiation and increased proliferation, which were linked to the downregulation of p21(WAF1/cip1), p27(kip1), intestinal trefoil factor and E-cadherin and to the upregulation of beta-catenin signaling. In addition, we found that decorin was highly expressed in the differentiated area of human normal colonic mucosa, but was dramatically reduced in paired colorectal cancer tissues. Taken together, our data demonstrate that decorin acts as a tumor suppressor gene and plays an important role in the maintenance of cell maturation and therefore homeostasis in the intestinal tract.

Fig. 1.

Intestinal tumors formed in Dcn^−/− mice. (a) One adenoma was seen in the intestine of a Dcn^−/− mouse on AIN-76 diet (scale, 2 mm); (b) histopathology of the tumor in (a) is shown in (b) (original magnification, ×20); (c) a large adenocarcinoma was seen in a Dcn^−/− mouse fed western-style diet (scale, 2 mm). Histopathological features of the tumor in (c) are shown in (d) (×20). Note that the layers of the intestinal wall were destroyed with infiltration of the carcinoma.

Fig. 2.

The incidence and frequency of intestinal tumors in Dcn^+/+ or Dcn^−/− mice fed AIN-76A or a western-style diet for 36 weeks. (*P < 0.05; **P < 0.01, compared with Dcn^+/+ mice, by Fisher's exact or Student’s t-test, respectively). N, the number of animals studied in each group.

Fig. 3.

Intestinal cell differentiation [assayed by Alcian blue and ITF staining (a and b)] was decreased, but cell proliferation [proliferative cell nuclear antigen (PCNA) staining (c)] and β-catenin expression (d) were increased in Dcn^−/− mice fed AIN-76A control diet (original magnification, ×20).

Fig. 4.

Gene expression was validated by quantitative real-time reverse transcription–PCR. The relative mRNA levels of p21, p27, Muc2 and β-catenin were analyzed from intestinal epithelial cells of Dcn^+/+ or Dcn^−/− mice fed AIN-76A diet (five animals per group). (*P < 0.05, compared with Dcn^+/+ mice by Mann–Whitney test.).

Fig. 5.

Alterations of protein in Dcn mice fed with AIN-76A diet assayed by western blots. p21, p27, ITF and E-cadherin were significantly reduced and β-catenin, cdk4 and cyclin D1 were increased in Dcn^−/− mouse intestinal epithelial cells. Proteins were extracted from two individual mice of each genetic group. Signal quantification was normalized to β-actin and Dcn^+/+ mouse, and the average fold changes were shown in the columns.

Fig. 6.

Decorin is highly expressed in human normal colon mucosa (right side) and decreased in colon cancer tissues (left side). (original magnification, ×20).