Interleukin-6- and Cyclic AMP-Mediated Signaling Potentiates Neuroendocrine Differentiation of LNCaP Prostate Tumor Cells

Abstract

Neuroendocrine (NE) differentiation in prostatic adenocarcinomas has been reported to be an early marker for development of androgen independence. Secretion of mitogenic peptides from nondividing NE cells is thought to contribute to a more aggressive disease by promoting the proliferation of surrounding tumor cells. We undertook studies to determine whether the prostate cancer cell line LNCaP could be induced to acquire NE characteristics by treatment with agents that are found in the complex environment in which progression of prostate cancer towards androgen independence occurs. We found that cotreatment of LNCaP cells with agents that signal through cyclic AMP-dependent protein kinase (PKA), such as epinephrine and forskolin, and with the cytokine interleukin-6 (IL-6) promoted the acquisition of an NE morphological phenotype above that seen with single agents. Convergent IL-6 and PKA signaling also resulted in potentiated mitogen-activated protein kinase (MAPK) activation without affecting the level of signal transducer and activator of transcription or PKA activation observed with these agents alone. Cotreatment with epinephrine and IL-6 synergistically increased c-fos transcription as well as transcription from the ␤4 nicotinic acetylcholine receptor subunit promoter. Potentiated transcription from these elements was shown to be dependent on the MAPK pathway. Most importantly, cotreatment with PKA activators and IL-6 resulted in increased secretion of mitogenic neuropeptides. These results indicate that PKA and IL-6 signaling participates in gene transcriptional changes that reflect acquisition of an NE phenotype by LNCaP cells and suggest that similar signaling mechanisms, particularly at sites of metastasis, may be responsible for the increased NE content of many advanced prostate carcinomas.

Androgen signaling and post-transcriptional downregulation of Bcl-2 in androgen-unresponsive prostate cancer

“…15 We sought to mimic androgen ablation in LNCaP cells to address what changes would occur in Bcl-2 and Bax. We grew LNCaP cells in phenol red-free media containing charcoalstripped serum.…”

Neurotensin stimulates mitogenesis of prostate cancer cells through a novel c-Src/Stat5b pathway

“…Although the mechanisms controlling in vivo differentiation of prostatic NE cells are only partially understood, we and others have previously demonstrated acquisition of NE characteristics by stimulating prostate cancer cell lines in vitro with various agents that are naturally present in the tumor microenvironment, such as interleukin-6 and epinephrine (Deeble et al, 2001;Amorino and Parsons, 2004). LNCaP cells acquire NE characteristics in response to androgen withdrawal, IL-6 addition and/or treatment with physiological and pharmacological agents that elevate intracellular cyclic adenosine monophosphate (cAMP), such as epinephrine, isoproterenol, forskolin and dibutyryl cAMP (Qiu et al, 1998;Cox et al, 1999Cox et al, , 2000Deeble et al, 2001).…”

“…LNCaP cells acquire NE characteristics in response to androgen withdrawal, IL-6 addition and/or treatment with physiological and pharmacological agents that elevate intracellular cyclic adenosine monophosphate (cAMP), such as epinephrine, isoproterenol, forskolin and dibutyryl cAMP (Qiu et al, 1998;Cox et al, 1999Cox et al, , 2000Deeble et al, 2001). Removal of differentiating agents results in reversion to the tumor cell phenotype, indicating that the process is reversible.…”

“…Removal of differentiating agents results in reversion to the tumor cell phenotype, indicating that the process is reversible. Differentiation in response to cAMP-elevating agents also results in protein kinase A (PKA) activation (Deeble et al, 2001). Overexpression of the PKA catalytic subunit is sufficient to induce NE differentiation in LNCaP cells, and NE differentiation is inhibited by the expression of a dominant-negative (DN) mutant of the PKA regulatory subunit (Cox et al, 2000).…”

“…Overexpression of the PKA catalytic subunit is sufficient to induce NE differentiation in LNCaP cells, and NE differentiation is inhibited by the expression of a dominant-negative (DN) mutant of the PKA regulatory subunit (Cox et al, 2000). NE-like cells derived from LNCaP cells are nonmitotic and secrete significantly greater amounts of the mitogenic neuropeptides, parathyroid hormone-related peptide (PTHrP) and neurotensin (NT) Deeble et al, 2001), relative to undifferentiated parental LNCaP cells.…”