Pituitary adenylate cyclase activating polypeptide-mediated intracrine signaling in the testicular germ cells.
Pituitary adenylate cyclase activating polypeptide (PACAP) is found not only in the brain, but is also abundantly expressed in the testicular germ cells. However, the physiological role of testicular PACAP remains unknown. Autoradiographic studies showed a considerable number of PACAP-specific binding sites in the seminiferous tubules. Immunohistochemistry demonstrated PAC1-receptor (R)-like immunoreactivity (li) in the cytoplasm of round spermatids, aggregated in the acrosome and coexpressed with PACAP-li. Spermatid-enriched fractions were examined for the subcellular localization of PACAP binding sites and PAC1-R-li. The highest levels of PACAP binding sites and PAC1-R-li were found in the cytosolic, followed by the nuclear, and the lowest levels in the membrane fraction. The testicular cytosolic PAC1-R-like protein showed a specific competitive inhibition in the radio-receptor assay for PACAP38 and 27, with a Ki of 0.069 nM and 0.179 nM, respectively. The addition of PACAP to the cytosol of spermatids only slightly activated adenylate cyclase, while it markedly stimulated the expression and activation of ERK-type mitogen-activated protein kinase (MAPK). In the PAC1-R-like protein-depleted cytosol, a PAC1-R-specific agonist, maxadilan, did not activate MAPK, but PACAP and VIP still did. Because VPAC2-R, which binds both PACAP and VIP, is expressed in the testis, the findings suggest that cytosolic VPAC2-R-like proteins are also present and coupled to MAPK. The MAPK activation does not seem to require a heterotrimeric G-protein. Because PACAP and its receptors are coexpressed in the cytoplasm of spermatids, endogenous PACAP may directly interact with the cytosolic PAC1-R-like protein without the ligand being released into the extracellular space. This possibility is supported by the observation that cytosolic endogenous PACAP in spermatids was co-immunoprecipitated with the cytosolic PAC1-R. This mechanism may be called "intracrine," and its physiological significance is discussed.
Li
Min
M
U.S.-Japan Biomedical Research Laboratories, Department of Medicine, Tulane University School of Medicine, New Orleans, Louisiana 70112, USA.
Funahashi
Hisayuki
H
Mbikay
Majambu
M
Shioda
Seiji
S
Arimura
Akira
A
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D001665:Binding Sites / Q000502:physiology; D001667:Binding, Competitive / Q000502:physiology; D015153:Blotting, Western; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D007150:Immunohistochemistry; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D020928:Mitogen-Activated Protein Kinases / Q000502:physiology; D009479:Neuropeptides / Q000502:physiology*; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D051381:Rats; D051236:Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide; D051237:Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide, Type I; D011979:Receptors, Pituitary Hormone / Q000502:physiology*; D051239:Receptors, Vasoactive Intestinal Peptide, Type II; D015398:Signal Transduction / Q000502:physiology; D013087:Spermatids / Q000502:physiology*; D013347:Subcellular Fractions / Q000502:physiology; D013737:Testis / Q000166:cytology / Q000502:physiology*; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology
C495402:Adcyap1 protein, mouse; C495403:Adcyap1 protein, rat; C495504:Adcyap1r1 protein, mouse; C495505:Adcyap1r1 protein, rat; D009479:Neuropeptides; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D051236:Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide; D051237:Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide, Type I; D011979:Receptors, Pituitary Hormone; D051239:Receptors, Vasoactive Intestinal Peptide, Type II; C495510:Vipr2 protein, mouse; C495511:Vipr2 protein, rat; D014660:Vasoactive Intestinal Peptide; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D020928:Mitogen-Activated Protein Kinases; D000262:Adenylyl Cyclases