Altered phenotype of HT29 colonic adenocarcinoma cells following expression of the DCC gene

Abstract

On 18q, frequently deleted in late stage colorectal cancers, a gene, Deleted in Colon Cancer (DCC), has been identi®ed and postulated to play a role as a tumor suppressor gene. DCC is retained in the majority of mucinous tumors, which produce high levels of mucins, and seems to be preferentially expressed in intestinal goblet cells. To investigate whether DCC is related to mucin expression and can modulate the transformed phenotype, we introduced a full-length DCC cDNA into HT29 cells, which can be induced in vitro to express MUC2, the gene that encodes the major colonic mucin. Expression of DCC did not modulate constitutive or induced expression of MUC2, nor did DCC induce a mature goblet cell phenotype. However, HT29 clones expressing high and low levels of DCC protein showed a signi®cant decrease in cell proliferation and tumorigenicity. Furthermore, increased shedding and an elevated rate of spontaneous apoptosis were associated with higher levels of expression of DCC. In summary, while restoration of DCC expression in a human colon carcinoma cell line did not in¯uence expression of di erentiation markers, DCC expression did a ect the growth and tumorigenic properties of the cells suggesting that DCC can modulate the malignant phenotype of colon cancer.

Receptors that mediate cellular dependence

“…25 Interestingly, in that study, tumorigenic reversion was associated with loss of DCC expression and loss or rearrangement of the transfected DCC expression vector. 25 Several more recent studies also indicate that restoration of DCC expression can suppress tumorigenic growth properties in vitro or in nude mice, 26,27 supporting a role for DCC in tumor suppression. Therefore, one of the roles of DCC may be to induce apoptosis in colorectal cancer cells that grow outside the ligand field.…”

“…20 DCC expression is absent or markedly reduced in over 50% of colorectal tumors, and in multiple other tumor types, such as gastric carcinoma, pancreatic carcinoma, esophageal carcinoma, prostatic carcinoma, carcinoma of the bladder, carcinoma of the breast, male germ cell tumors, neuroblastomas, gliomas, and some leukemias. 21,22 Since the initial description, however, DCC has been an 'odd' tumor suppressor candidate: although in vitro studies have supported DCC's potential role as a tumor suppressor gene, [23][24][25][26][27] point mutations have rarely been identified in DCC coding sequences; 28 mice heterozygous for DCC-inactivating mutations 29 do not display the expected tumor predisposition phenotype; and other known and candidate tumor suppressor genes 30 have been identified in the same region of chromosome 18q as DCC. Reconciliation of these apparently paradoxical data has been suggested by recent work from Mazelin et al, 31 who found that a netrin receptor (or receptors) functions not as a classical tumor suppressor but rather as a conditional tumor suppressor.…”

Dependence receptors: a new paradigm in cell signaling and cancer therapy

“…This hypothesis was supported by the fact that DCC expression is lost or reduced in various cancers (Mehlen and Fearon, 2004) and that its loss of expression is associated with poor prognosis (Shibata et al, 1996;Sun et al, 1999). In addition, restoration of DCC expression can suppress tumorigenic property in vitro and in nude mice (Klingelhutz et al, 1993;Velcich et al, 1999). The DCC extracellular domain shares structural features with certain types of cell-adhesion molecules, such as NCAM (Cho et al, 1994) (Figure 2 and Table 1), but its intracellular domain shows little similarity with known proteins; hence in spite of the above-mentioned studies on cancers, little was known about the precise biological role of DCC.…”

“…Loss of DCC expression is often associated with poor prognosis and advanced cancer or metastasis (Shibata et al, 1996;Saito et al, 1999), suggesting a role of DCC loss in cancer progression rather than in cancer initiation. Moreover, restoration of DCC expression can suppress tumorigenic growth properties in vitro or in nude mice (Klingelhutz et al, 1993;Velcich et al, 1999;Kato et al, 2000;Rodrigues et al, 2007). On the other hand, the fact that only 10-15% of colon cancers carry mutations in DCC and the lack of a tumor predisposing effect of DCC inactivation in mouse models (Fazeli et al, 1997) led some investigators to conclude that DCC had little or no biological role in colon cancer, and that its inactivation was an epiphenomenon.…”

Mouse models for colorectal cancer

“…The Mcc and Dcc gene mutations, whose human counterparts are implicated in CRC, do not show a cancer susceptibility phenotype (Fazeli et al, 1997;Velcich et al, 1999). Dcc, although implicated in apoptosis, has yet to show a physiological function in the GI tract, with its ligand being expressed in the brain.…”