Expression of μ-protocadherin is negatively regulated by the activation of the β-catenin signaling pathway in normal and cancer colorectal enterocytes.

L Montorsi,E Tagliafico,A Rossi,B Calabretta,C Gemelli,S Ferrari,T Zanocco-Marani,F Ferrarini,A Grande,G Manco,S Parenti,L Losi

doi:10.1038/cddis.2016.163

Abstract

Mu-protocadherin (MUCDHL) is an adhesion molecule predominantly expressed by colorectal epithelial cells which is markedly downregulated upon malignant transformation. Notably, treatment of colorectal cancer (CRC) cells with mesalazine lead to increased expression of MUCDHL, and is associated with sequestration of β-catenin on the plasma membrane and inhibition of its transcriptional activity. To better characterize the causal relationship between β-catenin and MUCDHL expression, we performed various experiments in which CRC cell lines and normal colonic organoids were subjected to culture conditions inhibiting (FH535 treatment, transcription factor 7-like 2 siRNA inactivation, Wnt withdrawal) or stimulating (LiCl treatment) β-catenin activity. We show here that expression of MUCDHL is negatively regulated by functional activation of the β-catenin signaling pathway. This finding was observed in cell culture systems representing conditions of physiological stimulation and upon constitutive activation of β-catenin in CRC. The ability of MUCDHL to sequester and inhibit β-catenin appears to provide a positive feedback enforcing the effect of β-catenin inhibitors rather than serving as the primary mechanism responsible for β-catenin inhibition. Moreover, MUCDHL might have a role as biomarker in the development of CRC chemoprevention drugs endowed with β-catenin inhibitory activity.

Highlights

An important clue supporting the possibility that regulation of MUCDHL expression is a downstream event of the β-catenin signaling pathway came from the observation that MUCDHL downregulation always accompanies adenomatous polyposis coli (APC) inactivation in colorectal cancer (CRC)
Immuno-histochemical data obtained in our laboratory showed that 11 out of 21 analyzed CRC cases were negative for MUCDHL and APC expression, whereas the remaining exhibited a double positivity for the same proteins (Figure 1)
To further support the hypothesis that expression of MUCDHL is negatively regulated by active β-catenin, we treated the CaCo2 and HCT116 CRC cell lines with the FH535 compound, which inhibits the β-catenin pathway through complete silencing of the β-catenin-regulated transcription factor 7-like 2 (TCF4) transcription factor

Summary

Introduction

Upregulation of MUCDHL may represent the cause or the effect of β-catenin inhibition, respectively. In both cases MUCDHL would, once expressed, sequester and inhibit βcatenin on the plasma membrane, with different biological consequences. To better understand the correlation between β-catenin activity and MUCDHL expression, we performed experiments in which the β-catenin signaling pathway was inhibited in CRC cell lines using a chemical inhibitor or a siRNA-based approach and showed that MUCDHL expression is upregulated by both treatments.

Methods

Results

Conclusion