Characterization of the Subcellular Distribution of Phospho-ß-catenin in Colorectal Cancer.

BACKGROUND/AIM: ß-Catenin is a multifunctional protein, which is localized to different subcellular compartments of the normal colon epithelium. The hyperactivation of Wnt pathway results in the nuclear accumulation of ß-catenin and induction of colorectal carcinogenesis. Although N-terminally hypo-phosphorylated ß-catenin (active ß-catenin) is known as the transcriptionally active form, phospho-S33/S37/T41-ß-catenin (phospho-ß-catenin) can also accumulate in the nucleus. In this study, we aimed to characterize the subcellular distribution of phospho-ß-catenin and the other forms of ß-catenin in normal colon epithelium and colorectal cancer (CRC). MATERIALS AND METHODS: Phosphorylated, hypo-phosphorylated, and the total pool of ß-catenin were evaluated in colon epithelium and CRC using immunohistochemistry, immunofluorescence staining, and western blotting. Tissue microarrays were used to determine the expression pattern of phospho-ß-catenin in CRC samples. RESULTS: Almost 11% (49/452) of CRCs expressed moderate to high levels of phospho-ß-catenin in the nucleus. In addition, hypo-phosphorylated and phosphorylated forms of ß-catenin localized to different subcellular regions in normal colon epithelium and CRC. Immunoblotting experiments suggested that truncated phospho-ß-catenin forms can be found in CRCs. CONCLUSION: Phospho-ß-catenin accumulates in the nucleus and different molecular weight ß-catenin proteins are present in colon cancer cells. To elaborate on the functional significance of nuclear phospho-ß-catenin, further studies should be performed.

Effect of casein kinase 1α inhibition on autophagy flux and the AKT/phospho-ß-catenin (S552) axis in HCT116, a RAS-mutated colorectal cancer cell line.

The Wnt/ß-catenin pathway, which interferes with cell proliferation, differentiation, and autophagy, is commonly dysregulated in colorectal cancer (CRC). Mutation of the RAS oncogene is the most prevalent genetic alteration in CRC and has been linked to activation of protein kinase B (AKT) signaling. Phosphorylation of ß-catenin at Ser 552 by AKT contributes to ß-catenin stability, transcriptional activity, and increase of cell proliferation. Casein kinase 1 alpha (CK1α) is an enzyme that simultaneously regulates Wnt/ß-catenin and AKT. The link of the AKT and Wnt pathway to autophagy in RAS-mutated CRC cells has not well identified. Therefore, we investigated how pharmacological CK1α inhibition (D4476) is involved in regulation of autophagy, Wnt/ß-catenin, and AKT pathways in RAS-mutated CRC cell lines. qRT-PCR and immunoblotting experiments revealed that phospho-AKT (S473) and phospho-ß-catenin (S552) are constitutively increased in RAS-mutated CRC cell lines, in parallel with augmented CK1α expression. The results also showed that D4476 significantly reduced the AKT/phospho-ß-catenin (S552) axis concomitantly with autophagy flux inhibition in RAS-mutated CRC cells. Furthermore, D4476 significantly induced apoptosis in RAS-mutated CRC cells. In conclusion, our results indicate that CK1α inhibition reduces autophagy flux and promotes apoptosis by interfering with the AKT/phospho-ß-catenin (S552) axis in RAS-mutated CRC cells.

Relaxin 2/RXFP1 Signaling Induces Cell Invasion via the ß-Catenin Pathway in Endometrial Cancer.

Relaxin is known to play an important role in animal pregnancies, including those of humans. It is suggested that relaxin induces aggressive cell growth and invasiveness in several types of cancer, including endometrial cancer. However, the mechanisms of relaxin remain largely unclear. In this study, we examined the effects of relaxin 2 (RLN2), the major circulating relaxin in humans, on human endometrial carcinoma cell lines. RLN2 treatment induced invasion in HEC-1B and Ishikawa cells. RLN2-induced cell invasion was significantly decreased by transfection of relaxin receptor 1 (RXFP1) siRNAs. The ß-catenin inhibitor, XAV939, also significantly inhibited the RLN2-induced cell invasions. Both a decrease of cadherin expression and an increase of ß-catenin phosphorylation were observed in response to the RLN2 treatment in HEC-1B and Ishikawa cells. We then examined RLN2 and RXFP1 expression in 80 human endometrioid endometrial carcinoma tissues. RLN2 immunoreactivity was detected in the human endometrial carcinoma cells and had a correlative tendency with histological grade and RXFP1. These results suggest that adherens junctions in cancer cells are weakened by the breakdown of the cadherin/catenin complex, which is induced by ß-catenin phosphorylation via RLN2/RXFP1 signaling.