Pivotal role of PKC, Src and Akt in colon cancer cells response to PTHrP: control of mitogenic signaling

MARTÍN, MA. JULIA; GIGOLA, GRACIELA; CARRIQUIBORDE, MARTIN; GENTIL, FLORENCIA; GENTILI, CLAUDIA

Congreso; LXI Reunión Científica Anual de la Sociedad Argentina de Investigación Clínica (SAIC).; 2016

Parathyroid hormone related peptide (PTHrP) is present in the fetus, in most adult tissues and in various tumors. Its expression correlates with the severity of colon carcinoma. Previously we demonstrated that exogenous PTHrP (10-8 M) stimulates Caco-2 cells proliferation through MAPK and PI3K/Akt pathways. The aim of this study was to investigate the molecular mechanisms that modulate the activation of these signaling pathways induced by PTHrP in two tumor intestinal cell lines, Caco-2 and HCT116. We also evaluated if the hormone exerts proliferative effects in vivo. It is known that Src and several isoforms of PKC have a key role in the development and progression of multiple cancers. Western blot analysis revealed that after PTHrP treatment, PKCα levels decreased and increased in Caco-2 cells and HCT116 cells, respectively. Also, Src is phosphorylated/activated by the hormone in Caco-2 cells as well as in HCT116 cells. Furthermore, using specifics inhibitors we observed that PKCδ, Src and Akt signaling pathways modulate the phosphorylation of ERK 1/2 induced by PTHrP in both tumor cell lines. Moreover, the expression of c-Myc oncoprotein induced by PTHrP was reverted when ERK 1/2 signaling pathway was inhibited. Finally, when Akt and PKC signaling pathways were blocked, we observed a reversion on Caco-2 cell proliferation induced by the hormone. On the other hand, xenograft tumor model studies revealed that when a low number of HCT116 cells (1x106) are inoculated into nude mice, the administration of PTHrP (40 ug/kg) promotes the formation and tumor growth. Also, immunohistochemical and western blot analysis of these tumors showed that PTHrP increased the expression of cyclin D1, a positive regulator of cell cycle progression, and c-Myc. Together, the results from in vitro and in vivo studies provide information about the molecular mechanisms that are modulated by exogenous PTHrP in tumor intestinal cells.