vasoactive-intestinal-peptide and nickel-chloride

Vascular endothelial growth factor (VEGF) is a main factor promoting neovascularization (angiogenesis) of solid tumours as prostate carcinoma. Hypoxia stimulates VEGF gene expression by activating the hypoxia-inducible factor-1 (HIF-1alpha). In the present study, the hypoxia-mimicking agent Ni(2+) induced vasoactive intestinal peptide (VIP) expression at both mRNA and peptide levels but it did not modify the expression of VIP receptors (VPAC(1), VPAC(2) and PAC(1) receptors) in androgen-dependent human LNCaP prostate cancer cells. VIP increased the mRNA levels of VPAC(1) and PAC(1) receptors whereas it decreased VPAC(2) receptor mRNA level. These features support that hypoxia up-regulation of VIP gene expression in prostatic carcinoma may lead to VIP regulation of the expression of its receptors by means of autocrine/paracrine mechanisms. Either VIP or hypoxia mimetics with Ni(2+) increased VEGF expression whereas both conditions together resulted in an additive response. It suggests two independent mechanisms for the observed pro-angiogenic activities of VIP and hypoxia. VIP did not stimulate HIF-1alpha mRNA expression but increased the translocation of HIF-1alpha from the cytosolic compartment to the cell nucleus. Moreover, VIP was unable to modify the expression of the HIF-1alpha inhibitor FIH-1 discarding the possibility of an indirect effect of VIP on HIF-1 transactivation.

Topics: Cell Hypoxia; Cell Line, Tumor; Gene Expression Regulation, Neoplastic; Humans; Hypoxia-Inducible Factor 1, alpha Subunit; Male; Mixed Function Oxygenases; Nickel; Prostatic Neoplasms; Receptors, Vasoactive Intestinal Peptide; Repressor Proteins; RNA, Messenger; Transcription Factors; Vascular Endothelial Growth Factor A; Vasoactive Intestinal Peptide

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) are hypothalamic factors believed to play a role in the regulation of anterior pituitary cell function. However, little is known about the expression of PACAP/VIP receptor (PVR) subtypes in such cells. Three PVR subtypes have recently been cloned: the PACAP-selective PVR1, and PVR2 and PVR3, which exhibit similar affinities for PACAP and VIP. In the present study we used the reverse transcription-polymerase chain reaction with PVR-specific primers to identify the PVR messenger RNAs (mRNAs) expressed in the somatotroph-like GH4C1 and the gonadotroph-like alpha T3-1 cell lines. In parallel, the effects of PACAP and VIP on intracellular signaling were studied. GH4C1 cells were found to express mRNA only for the PVR3, and neither PVR1 nor PVR2 mRNA was found. PACAP and VIP stimulated Ca2+ influx responses in individual GH4C1 cells and were equipotent in stimulating cAMP production (EC50, 15 nM) in GH4C1 cell populations, but failed to stimulate inositol phospholipid (PI) turnover, results consistent with the expression of a PVR3. In contrast, alpha T3-1 cells expressed mRNA for PVR1 and PVR3, but not PVR2. The predominant splice variant forms of PVR1 observed were PVR1s and PVR1hop, although the other forms (PVR1hiphop and PVR1hip) were also seen at much lower levels. PACAP stimulated a Ca2+ store-dependent Ca2+ spike and a sustained Ca2+ influx in individual alpha T3-1 cells, whereas VIP only stimulated Ca2+ influx. PACAP (EC50, 3 nM) was approximately 1000-fold more potent than VIP (EC50, approximately 3 microM) in stimulating cAMP production. PACAP also stimulated PI turnover (EC50, approximately 20 nM), whereas VIP stimulated PI turnover only at very high (10 microM) concentrations. These results are indicative of the expression of a PVR1. Rat anterior pituitary tissue expressed mRNAs for PVR1, PVR3, and low levels of PVR2. The coexpression of different PVRs in the same cell type and the differential expression of PVRs in different cell types would allow for a complex regulation of anterior pituitary gland function by PACAP and VIP.

Topics: Animals; Base Sequence; Calcium; Cell Line; Clone Cells; Cyclic AMP; DNA Primers; Dose-Response Relationship, Drug; Gene Expression; Kinetics; Liver; Molecular Sequence Data; Neuropeptides; Neurotransmitter Agents; Nickel; Phosphatidylinositols; Pituitary Adenylate Cyclase-Activating Polypeptide; Pituitary Gland, Anterior; Polymerase Chain Reaction; Rats; Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide; Receptors, Pituitary Hormone; Receptors, Vasoactive Intestinal Peptide; Tumor Cells, Cultured; Vasoactive Intestinal Peptide