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We investigated expression of gamma-aminobutyric acid (GABA), glutamate decarboxylase, and matrix metalloproteinase (MMP) in the prostates of patients with cancer or benign prostatic hypertrophy by immunohistochemical study. Marked expression of GABA, glutamate decarboxylase 67, and MMPs was observed in the prostates of cancer patients with metastasis (n = 72) and lymph node metastasis, although only sparse expression was noted in those of cancer patients without metastasis (n = 76) or patients with benign prostatic hypertrophy (n = 152). We then investigated the influence of GABA stimulation on in vitro MMP production and the invasive ability of cancer cells using human prostate cancer cell line C4-2. The production of MMPs increased significantly in cancer cells after a 24-h incubation with GABA. Cell invasion assay using a BioCoat Matrigel Invasion Chamber kit revealed that GABA stimulation significantly promoted the invasive ability of cancer cells and that addition of MMP inhibitor GM6001 significantly decreased GABA-induced migration. This may indicate the involvement of MMP activity in GABA-induced cancer cell invasion. We further analyzed the transmission pathway by performing GABA receptor modulation. The GABA(B) receptor agonist baclofen significantly increased MMP production as well as invasive ability. Moreover, blockade of the GABA(B) receptor pathway using GABA(B) receptor antagonist CGP 35348 significantly inhibited GABA-induced MMP production and invasive ability in cancer cells, whereas GABA(A) receptor modulation did not influence MMP production or the invasive ability of cancer cells. Thus, increased expression of GABA may be implicated in cancer metastasis by promoting MMP production in cancer cells, and the GABA(B) receptor pathway may be involved in the process.

One of the causes of insensitivity to androgen ablation therapy in prostate cancer is thought to be attributable to elevated neuropeptides secreted by neuroendocrine cells in the tumor mass. Calcitonin (CT), one of these neuropeptides, is reported to be associated with the growth of prostate cancer. There is an increase in mitogen-activated protein (MAP) kinase activation as prostate cancer progresses to a more advanced and androgen-independent disease. We examined the effect of CT on signal transduction and the relation between CT and early-response genes in the human androgen-insensitive prostate cancer cell line, DU145. The basal phosphorylation level of extracellular signal-regulated kinase 1/2, which is a key kinase in the mediation of growth factor-induced mitogenesis in prostate cancer cells, was constitutively up-regulated. N-[2-(4-bromocinnamyl) aminoethyl]-5-isoquinoline-sulfonamide (H89), a specific inhibitor of protein kinase A, potentiated the effects of more increased phosphorylation of extracellular signal-regulated kinase 1/2. CT induced the inhibition of this MAP kinase phosphorylation, and this effect was completely abolished by pretreatment with H89. Our findings demonstrate that CT caused the inhibition of constitutive MAP kinase phosphorylation in a protein kinase A-dependent manner in DU145. The transient increase of c-fos expression was detected after CT treatment, whereas expression of c-jun RNA was down-regulated after CT treatment. These results suggest that CT may regulate early-response genes, c-fos and c-jun, via a MAP kinase cascade. In conclusion, these findings suggest that DU145 might be a useful model as a therapeutic approach of neuropeptides in androgen-independent prostatic carcinoma.