PubMed · 368546
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G E Feurle. 1979-02-02. [Gastrointestinal hormones. Current knowledge].. https://pubmed.ncbi.nlm.nih.gov/368546/
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The inappropriate activation of androgen receptor (AR) by nonsteroids is considered a potential mechanism in the emergence of hormone-refractory prostate tumors, but little is known about the properties of these "pseudoactivated" AR. Here, we present the first comprehensive analysis closely examining the properties of AR activated by the neuropeptide bombesin that distinguish it from androgen-activated AR. We show that bombesin-activated AR (a) is required for bombesin-induced growth of LNCaP cells, (b) has a transcriptional profile overlapping with, but not identical to, androgen-activated AR, (c) activates prostate-specific antigen by preferentially binding to its proximal promoter, and (d) assembles a distinct coactivator complex. Significantly, we found that Src kinase is critical for bombesin-induced AR-mediated activity and is required for translocation and transactivation of AR. Additionally, we identify c-Myc, a Src target gene, to be activated by bombesin and a potential coactivator of AR-mediated activity specific to bombesin-induced signaling. Because Src kinase is often activated by other nonsteroids, such as other neuropeptides, growth factors, chemokines, and cytokines, our findings have general applicability and provide rationale for investigating the efficacy of the Src kinase pathway as a target for the prevention of relapsed prostate cancers.
Bombesin receptor subtype-3 (BRS-3) is an orphan G protein-coupled receptor having sequence homologies to gastrin-releasing peptide and neuromedin B receptors. [d-Phe6, beta-Ala11, Phe13, Nle14]bombesin(6-14) is known to act as a synthetic receptor agonist for BRS-3. To characterize BRS-3-mediated biological responses, we examined the effect of BRS-3 activation by [d-Phe6, beta-Ala11, Phe13, Nle14]Bn(6-14) on the adhesion of the small cell lung cancer NCI-N417 cells that express native BRS-3. We found that the BRS-3 agonist stimulated adhesion of NCI-N417 cells in laminin-coated culture wells. The adhesion of the cells to laminin induced by BRS-3 activation was accompanied by an increase in vinculin-like immunoreactivity and diminished in the presence of an anti-beta1 integrin antibody, suggesting that the receptor activation stimulates focal adhesion formation. We suggest that BRS-3 may be involved in invasion and metastasis of certain cancer cells, like small cell lung cancer cells, upon attachment to laminin.
The neuropeptides bombesin and endothelin-1 stimulate prostate cancer (PC) cell migration and invasion (J Clin Invest, 2000; 106: 1399-1407). The intracellular signaling pathways that direct this cell movement are not well delineated. The monomeric GTPase RhoA is required for migration in several cell types including neutrophils, monocytes and fibroblasts. We demonstrate that bombesin-stimulated PC cell migration occurs via the heterotrimeric G-protein-coupled receptors (G-protein) G alpha 13 subunit leading to activation of RhoA, and Rho-associated coiled-coil forming protein kinase (ROCK). Using siRNA to suppress expression of the three known G-protein alpha-subunit-associated RhoA guanine nucleotide exchange factors (GEFs), we also show that two of these RhoA GEFs, PDZ-RhoGEF and leukemia-associated RhoGEF (LARG), link bombesin receptors to RhoA in a non-redundant manner in PC cells. We next show that focal adhesion kinase, which activates PDZ-RhoGEF and LARG, is required for bombesin-stimulated RhoA activation. Neutral endopeptidase (NEP) is expressed on normal prostate epithelium whereas loss of NEP expression contributes to PC progression. We also demonstrate that NEP inhibits neuropeptide activation of RhoA. Together, these results establish a contiguous signaling pathway from the bombesin receptor to ROCK in PC cells, and they implicate NEP as a major regulator of neuropeptide-stimulated RhoA in these cells. This work also identifies members of this signaling pathway as potential targets for rational pharmacologic manipulation of neuropeptide-stimulated migration of PC cells.