Signal transduction pathways assosiated with PTHrP-induced proliferation of colon carcinoma cells

MARTÍN, MA. JULIA; CALVO, NATALIA G; RUSSO DE BOLAND, ANA; GENTILI, CLAUDIA R

Baltimore

Congreso; ASBMR Anual Meeting 2013; 2013

American Society for Bone and Minerla Reserch

Parathyroid Hormone-related Peptide (PTHrP, also known as its tumoral analog) was initially identified through its role in humoral hypercalcemia of malignancy, one of the most frequent paraneoplastic syndromes. Subsequently, the protein was found to be distributed in most fetal and adult tissues, including intestinal mucosa. It has been observed that its expression correlates with the severity of colon carcinoma and that its overexpression increases cell proliferation in certain intestinal cell lines. However, so far the role of exogenous PTHrP in Caco-2, a cell line derived from human colorectal adenocarcinoma, is not known. This study examined, whether extracellular PTHrP induces proliferation of Caco-2 cells and whether regulates cell proliferation via the MAP kinases and Akt signaling pathways. Using different cell proliferation assays we found that PTHrP (10-8 M) increased the number of live Caco-2 cells. Furthermore, Western blot analysis revealed that the PTH analog stimulates the phosphorylation of ERKs as well as the α isoform of p38 MAPK and Akt without affecting their protein expression levels and the phosphorylation/activation of JNK. Fluorescence microscopy studies indicated that extracellular PTHrP induces the translocation of ERK1/2, p38α and Akt into the nucleus of these intestinal cells. PTHrP also stimulates the phosphorylation of ATF-1 and CREB transcription factors in a biphasic manner, the second phase being partially dependent on MAP kinases activation. Moreover, the peptide induces the translocation of β-catenin into the nucleus of Caco-2 cells and increases the amounts of positive cell cycle regulators c-Myc and Cyclin D. In addition, use of specific inhibitors of ERK 1/2, p38 MAPK and Akt signaling pathways indicate that both MAPKs and Akt participate in PTHrP-induced colonic cell proliferation The present work provides, to our knowledge, the first evidence demonstrating that exogenous PTHrP induces the proliferation of Caco-2 cells and identifies, at least in part, the signaling pathways that are involved in the mitogenic effect of PTHrP on these intestinal cells.