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Pituitary Adenylate Cyclase-Activating Polypeptide Precursor Is Processed Solely by Prohormone Convertase 4 in the Gonads¹

Department of Medicine, Tulane University School of Medicine (M.L., A.A.), New Orleans, Louisiana 70112; U.S.-Japan Biomedical Research Laboratories, Tulane University Hebert Center (M.L., A.A.), Belle Chasse, Louisiana 70037; and Protein Chemistry Center, Loeb Health Research Institute, Ottawa Hospital Medical School (M.M.), Ottawa, Ontario, Canada K1Y 4K9

Address all correspondence and requests for reprints to: Dr. Min Li, U.S.-Japan Biomedical Research Laboratories, Tulane University Hebert Center, 3705 Main Street, Belle Chasse, Louisiana 70037-3001. E-mail: minlee{at}mailhost.tcs.tulane.edu

Pituitary adenylate cyclase-activating polypeptide (PACAP) is abundant not only in the brain, but also in the testis. Immunohistochemical studies have shown that PACAP-LI in rat testis is expressed stage specifically in spermatids. This suggests that testicular PACAP participates in the regulatory mechanism of spermatogenesis. Additionally, the ovary contains a relatively small amount of PACAP, conceivably involved in the regulation of folliculogenesis. PACAP is synthesized as a preprohormone and is processed by prohormone convertases, such as PC1, PC2, and PC4. PC4 is expressed only in the testis and ovary, where neither PC1 nor PC2 is expressed. However, whether PC4 is the sole endoprotease for the PACAP precursor in the gonads remains unknown. Recent studies using PC4-transgenic mice revealed that male PC4-null mice exhibited severely impaired fertility, although spermatogenesis appeared to be normal. The female PC4-null mice exhibited delayed folliculogenesis in the ovaries. To examine whether PC4 is the sole processing enzyme for the PACAP precursor in the gonads, we analyzed testicular and ovarian extracts from the PC4-null and wild-type mice for PACAP (PACAP38 and PACAP27) and its messenger RNA using reverse phase HPLC combined with specific RIAs and ribonuclease protection assay, respectively. For RIAs, three different polyclonal antisera with different recognition sites were used to identify PACAP38, PACAP27, and its precursor. Neither the testis nor the ovary from the PC4-null mice expressed PACAP38 or PACAP27, but the levels of PACAP transcripts in the testis and ovary of homozygous PC4-deficient mice were considerably elevated compared with those of the wild-type and heterozygous animals. The findings indicate that PC4 is the sole processing enzyme for the precursor of PACAP in the testis and ovary of mice. The possibility that the absence of bioactive PACAP in the testis and ovary of PC4-null mice caused severely impaired fertility in the males and delayed folliculogenesis in females warrants investigation.

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