Parathyroid hormone-related peptide (PTHrP) is associated with several human cancers such as colon carcinoma. This disease is a complex multistep process that involves enhanced cell cycle progression and migration. Recently we obtained evidence that in the human colorectal adenocarcinoma Caco2 cells, exogenous PTHrP increases the proliferation and positively modulates cell cycle progression via ERK1/2, p38 MAPK and PI3K. The purpose of this study was to explore if the serine/threonine kinase RSK, which is involved in the progress of many cancers and it is emerging as a potential therapeutic target, mediates PTHrP effects on cancer colon cells. Western blot analysis revealed that PTHrP increases RSK phosphorylation via ERK1/2 signaling pathway but not through p38 MAPK. By performing subcellular fractionation, we found that the peptide also induces the nuclear localization of activated RSK, where many of its substrates are located. RSK participates in cell proliferation, in the upregulation of cyclin D1 and CDK6 and in the downregulation of p53 induced by PTHrP. Wound healing and transwell filter assays revealed that cell migration increased after PTHrP treatment. In addition, the hormone increases the protein expression of the focal adhesion kinase FAK, a regulator of cell motility. We observed that PTHrP induces cell migration and modulates FAK protein expression through ERK/RSK signaling pathway but not via p38 MAPK pathway. Finally, studies revealed that the hormone activates RSK in xenografts tumor. Taken together, our findings provide new insights into the deregulated cell cycle and migration that is characteristic of tumor intestinal cells.

Parathyroid hormone-related peptide (PTHrP) is distributed in most fetal and adult tissues, and its expression correlates with the severity of colon carcinoma. Recently we obtained evidence that in Caco-2 cells, a cell line from human colorectal adenocarcinoma, exogenous PTHrP increases the number of live cells, via ERK1/2, p38 MAPK, and PI3-kinase and induces the expression of cyclin D1, a cell cycle regulatory protein. In this study, we further investigated the role of PTHrP in the regulation of the cell cycle progression in these intestinal cells. Flow cytometry analysis revealed that PTHrP treatment diminishes the number of cells in the G0/G1 phase and increases the number in both S and G2/M phases. The hormone increases the expression of CDK6 and diminishes the amount of negative cell cycle regulators p27Kip1, p15INK4B, and p53. However, PTHrP does not modify the expression of cyclin D3, CDK4, and p16INK4A. In addition, inhibitors of ERK1/2 (PD98059), p38 MAPK (SB203580), and PI3Kinase (LY294002) reversed PTHrP response in Caco-2 cells. Taken together, our results suggest that PTHrP positively modulates cell cycle progression and changes the expression of proteins involved in cell cycle regulation via ERK1/2, p38 MAPK, and PI3K signaling pathways in Caco-2 cells.

Parathyroid Hormone-related Protein (PTHrP) is normally produced in many tissues and is recognized for its endocrine, paracrine, autocrine and intracrine modes of action. PTHrP is also implicated in different types of cancer and its expression correlates with the severity of colon carcinoma. Using the human colon cell line Caco-2 we recently obtained evidence that PTHrP, through a paracrine pathway, exerts a protective effect under apoptotic conditions. However, if exogenous PTHrP is able or not to induce the proliferation of these intestinal tumor cells is not known. We found that PTHrP treatment increases the number of live Caco-2 cells. The hormone induces the phosphorylation and nuclear translocation of ERK 1/2, α p38 MAPK, and Akt, without affecting JNK phosphorylation. In addition, PTHrP-dependent ERK phosphorylation is reverted when PI3K activity was inhibited. Following MAPKs nuclear translocation, the transcription factors ATF-1 and CREB were activated in a biphasic manner. In addition PTHrP induces the translocation into the nucleus of β-catenin, protein that plays key role in maintaining the growth and proliferation of colorectal cancer, and increases the amount of both positive cell cycle regulators c-Myc and Cyclin D. Studies with ERK1/2, α p38 MAPK, and PI3K specific inhibitors showed that PTHrP regulates Caco-2 cell proliferation via these signaling pathways. In conclusion, the results obtained in this work expand our knowledge on the role of exogenous PTHrP in intestinal tumor cells and identify the signaling pathways that are involved in the mitogenic effect of the hormone on Caco-2 cells.

No abstract