Bortezomib reverses the proliferative and antiapoptotic effect of neuropeptides on prostate cancer cells

Objectives: Neuropeptides are important signal initiators in advanced prostate cancer, partially acting through activation of nuclear factor kappa B. Central to nuclear factor kappa B regulation is the ubiquitin‐proteasome system, pharmacological inhibition of which has been proposed as an anticancer strategy. We investigated the putative role of the proteasome inhibitor bortezomib in neuropeptides signaling effects on prostate cancer cells. Methods: Human prostate cancer cell lines, LNCaP and PC‐3, were used to examine cell proliferation, levels of proapoptotic (caspase‐3, Bad) and cell cycle regulatory proteins (p53, p27, p21), as well as total and phosphorylated Akt and p44/42 mitogen‐activated protein kinase proteins. Furthermore, 20S proteasome activity, subcellular localization of nuclear factor kappa B and transcription of nuclear factor kappa B target genes, interleukin‐8 and vascular endothelial growth factor, were assessed. Results: Neuropeptides (endothelin‐1, bombesin) increased cell proliferation, whereas bortezomib decreased proliferation and induced apoptosis, an effect maintained after cotreatment with neuropeptides. Bad, p53, p21 and p27 were downregulated by neuropeptides in PC‐3, and these effects were reversed with the addition of bortezomib. Neuropeptides increased proteasomal activity and nuclear factor kappa B levels in PC‐3, and these effects were prevented by bortezomib. Interleukin‐8 and vascular endothelial growth factor transcripts were induced after neuropeptides treatment, but downregulated by bortezomib. These results coincided with the ability of bortezomib to reduce mitogen‐activated protein kinase signaling in both cell lines. Conclusions: These findings are consistent with bortezomib‐mediated abrogation of neuropeptides‐induced proliferative and antiapoptotic signaling. Thus, the effect of the drug on the neuropeptides axis needs to be further investigated, as neuropeptide action in prostate cancer might entail involvement of the proteasome.