This study was conducted in ac cordance with the Helsinki Declaration and was a

In INNO-406 Bafetinib agreement with previous studies in human pancrea tic cancer cells we found that neuroten sin induced ERK activation and DNA synthesis in the colon cancer cells HCT116 was mainly dependent on PKC and did not involve EGFR transactivation. Thus, the stimulatory effect of neurotensin and TPA on DNA synthesis was of the same magnitude, and stimulation of both DNA synthesis and ERK phosphorylation by neu rotensin was inhibited by pretreatment with the PKC blocker GF109203X. Furthermore, while neurotensin sti mulated Akt phosphorylation in an EGFR dependent manner, TPA did not induce phosphorylation of Akt in HCT116 cells. In prostate cancer cells, neurotensin also stimulated ERK phosphorylation in a PKC dependent manner, but in these cells activation of PKC mediated transactivation of the EGFR.<br><br> We did not find that EGF stimulated DNA synthesis Lapatinib Tykerb significantly in HCT116 cells. A plausible explanation is the autocrine production of TGFa and other ligands, leading to constitutive activation of EGFR in HCT116 cells. It was previously reported that while exo genous addition of EGF had no effect on DNA synth esis, due to the production of TGFa, the EGFR was not saturated by the autocrine ligand and could be further activated by exogenous EGF, resulting in integrin a2 expression, cell adhesion, and micromotion. It is likely that basal DNA synthesis reflects the effect of this constitutive EGFR activation, consistent with the finding that inhibition of EGFR activity with gefitinib reduced both basal and neurotensin stimulated DNA synthesis.<br><br> However, neurotensin still enhanced DNA synthesis compared to its corresponding control. While neurotensin induced phosphorylation of ERK and stimulation of DNA synthesis in HCT116 cells were dependent on PKC, we found phosphorylation of Akt induced by neurotensin to be independent of PKC. Moreover, the lack of effect purchase Lonafarnib of TPA on phosphorylation of Akt further strengthens the notion that PKC is not involved in activation of Akt in HCT116 cells. Instead, neurotensin induced phosphorylation of Akt was depen dent on EGFR activation, and this effect was mimicked by elevation of intracellular Ca2 induced by thapsigar gin. Our results thus strongly suggest that neurotensin induced phosphorylation of ERK and Akt is mediated by different pathways. In contrast, phosphorylation of both ERK and Akt induced by neurotensin was mediated by PKC dependent EGFR transactivation in prostate cancer cells.<br><br> Furthermore, in HT29 cells, both ERK and Akt phosphorylation induced by neurotensin was abol ished by pretreatment with gefitinib or cetuxi mab. These observations are in line with previous studies in HT29 cells, demonstrating that activation of PAR1 and PAR2 receptors led to transacti vation of the EGFR through matrix metalloproteinase dependent release of TGFa. The different time course of ERK and Akt phosphorylation in HCT116 cells also supports the involvement of different pathways. Conflicting results have been reported on the effect of neurotensin on EGFR phosphorylation in different cells. Thus, while neurotensin did not induce transac tivation of the EGFR in Panc 1 cells, PKC depen dent transactivation of the EGFR mediated the mitogenic effect of neurotensin on prostate cancer cells.