Smad4-Mediated Signaling Inhibits Intestinal Neoplasia by Inhibiting Expression of β-Catenin

Abstract

Background & Aims Mutational inactivation of APC is an early event in colorectal cancer (CRC) progression that affects the stability and increases the activity of β-catenin, a mediator of Wnt signaling. CRC progression also involves inactivation of signaling via transforming growth factor (TGF)β and bone morphenogenic protein (BMP), which are tumor suppressors. However, the interactions between these pathways are not clear. We investigated the effects of loss of the transcription factor Smad4 loss on levels of β-catenin mRNA and Wnt signaling. Methods We used microarray analysis to associate levels of Smad4 and β-catenin mRNA in colorectal tumor samples from 250 patients. We performed oligonucleotide-mediated knockdown of Smad4 in human embryonic kidney (HEK293T) and in HCT116 colon cancer cells and transgenically expressed Smad4 in SW480 colon cancer cells. We analyzed adenomas from (APCΔ1638/+) and (APCΔ1638/+)x(K19CreERT2Smad4lox/lox) mice using laser-capture microdissection. Results In human CRC samples, reduced levels of Smad4 correlated with increased levels of β-catenin mRNA. In Smad4-depleted cell lines, levels of β-catenin mRNA and Wnt signaling increased. Inhibition of BMP or depletion of Smad4 in HEK293T cells increased binding of RNA polymerase II to the β-catenin gene. Expression of Smad4 in SW480 cells reduced Wnt signaling and levels of β-catenin mRNA. In mice with heterozygous disruption of Apc(APCΔ1638/+), Smad4-deficient intestinal adenomas had increased levels of β-catenin mRNA and expression of Wnt target genes, compared with adenomas from APCΔ1638/+mice that expressed Smad4. Conclusions Transcription of β-catenin is inhibited by BMP signaling to Smad4. These findings provide important information about the interaction among TGF-β, BMP, and Wnt signaling pathways in CRC progression.

Smad4 sensitizes colorectal cancer to 5-fluorouracil through cell cycle arrest by inhibiting the PI3K/Akt/CDC2/survivin cascade

“…Smad4 deficiency in CRC cells promoted tumor progression. This evidence is consistent with our previous results (10) and a recent study (22). In addition, we showed for the first time in the present study that Smad4 sensitizes CRC to chemotherapy through downregulation of the PI3K/Akt/CDC2/survivin cascade.…”

Histone methyltransferase SETD2 modulates alternative splicing to inhibit intestinal tumorigenesis

“…The Wnt pathway involves various feedback loops that balance the opposing processes of cell proliferation and differentiation. Studies indicate that, even in the presence of heterozygousactivating mutations downstream of the FRZ receptor, mutationdriven Wnt-signaling activation can be further enhanced in APC min/+ mice and cells (40)(41)(42)(43)(44)(45). Our results highlighted that SETD2 fine-tuned Wnt signaling to safeguard ISCs or progenitor cells in the intestine, whereas downregulation facilitated inherently more proliferative and progenitor traits in ISCs in the Apc-mutated background ( Figure 8E).…”

SMAD4 Suppresses AURKA-Induced Metastatic Phenotypes via Degradation of AURKA in a TGFβ-Independent Manner

“…However, reactivation of SMAD4 was not sufficient for restoring a TGFb growth inhibitory response in SW480 cells (3,4), suggesting that the role of SMAD4 in tumor suppression and understanding its underlying molecular mechanisms require additional investigation. According to previous studies, SMAD4 elicits its antitumor effects by blocking b-catenin signaling (6,11) which is amplified by AURKA (26). Therefore, we examined whether the downregulation of b-catenin signaling by SMAD4 is mechanistically associated with the function of AURKA.…”

“…One of the mechanisms by which SMAD4 suppresses tumor progression is by modulating the WNT/b-catenin signaling pathway (5,6). Aberrant activation of b-catenin as a key effector of the WNT signaling cascade could lead to cancer development (7)(8)(9)(10).…”

“…Recent evidence has revealed that the restoration of SMAD4 in SMAD4-deficient SW480 colon carcinoma cells resulted in suppression of WNT/b-catenin signaling activity and migration capacity in human colon carcinoma cells (11). In HEK293T cells, inhibition of bone morphogenetic protein signaling or loss of SMAD4 can similarly augment b-catenin levels through a transcriptional mechanism, resulting in stimulation of WNT signaling (6). However, the molecular mechanism by which SMAD4 negatively regulates b-catenin signaling has not been identified.…”