Study of ß-catenin signaling pathway modulated by PTHrP in cell and animal colorectal cancer models

Abstract

Colorectal cancer (CRC) is a complex disease and a major cause of cancer-related deaths worldwide. One of the main obstacles in treating advanced CRC is chemotherapy resistance. In previous studies, we demonstrated that parathyroid hormone-related peptide (PTHrP) acts as a pro-tumor cytokine in CRC-derived cells, capable of modulating several mitogenic pathways and inducing β-catenin nuclear localization. Furthermore, we observed that PTHrP favors the communication between tumor cells and their microenvironment, promoting a more aggressive tumor phenotype. Using different CRC models, the first goal of this work was to further explore, how PTHrP is able to modulate the complex β-catenin signaling pathway, whereas the second aim was to examine whether this modulation by PTHrP is associated with resistance to chemotherapy agents commonly used in CRC treatment, particularly platinum-based compounds. The findings obtained in vitro by subcellular fractionation, Western blot analysis and immunocytochemistry technique, suggest that PTHrP induces the phosphorylation of β-catenin at Ser552 and its nuclear accumulation. Through viability assays, we found that PTHrP, either directly or indirectly through tumor microenvironment-derived endothelial cells, is associated with reduced oxaliplatin sensitivity in HCT116 cells from CRC. Pharmacological inhibition studies further support the involvement of β-catenin signaling in this effect. In vivo, the impact of PTHrP on the oxaliplatin response was model-dependent. In HCT116 xenografts generated in N:NIH(S)_nu mice, in contrast to our in vitro findings, oxaliplatin-treated animals showed no significant differences between mice with and without PTHrP within the experimental timeframe. However, we observed that PTHrP reduces oxaliplatin sensitivity in murine CT-26 intestinal tumor cells. In a CT-26 syngeneic murine model, PTHrP was associated with reduced oxaliplatin efficacy and increased β-catenin immunoreactivity. Overall, our findings provide consistent in vitro evidence supporting an association between PTHrP, β-catenin signaling, and decreased oxaliplatin sensitivity in CRC cells. However, in vivo results suggest a more complex and context-dependent role, highlighting the need for further studies to clarify the mechanistic contribution of β-catenin and the extent to which PTHrP drives chemoresistance in diverse settings.