It was previously reported that while exo selleck chem Imatinib Mesylate genous addition of EGF had no effect on DNA synth esis, Inhibitors,Modulators,Libraries 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 Inhibitors,Modulators,Libraries reduced both basal and neurotensin stimulated DNA synthesis. 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 Inhibitors,Modulators,Libraries lack of effect 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 Inhibitors,Modulators,Libraries 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. 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 Inhibitors,Modulators,Libraries 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. We found that neurotensin induced selleck chem phosphoryla tion of the EGFR and the adaptor protein Shc in HCT116 cells, and that inhibiting the EGFR with cetuxi mab or gefitinib strongly reduced neurotensin induced phosphorylation of Akt. These results strongly suggest that the EGFR is transactivated by neurotensin in HCT116 cells and that this transactivation is involved in mediating the Akt phosphorylation stimulated by neuro tensin.