Demonstration of relaxin precursors in pregnant rat ovaries with antisera against bacterially expressed rat prorelaxin

Relative expression of proprotein convertases in rat ovaries during pregnancy

Background

Proprotein convertases are a family of serine proteinases that are related to bacterial subtilisin and yeast kexin. They are involved in posttranslational processing of the precursors of a vast number of cellular proteins. With the exception of PC1/3, the relative expression levels of the proprotein convertases in the ovary during pregnancy have not been reported. The purpose of this study is to determine by real-time PCR the relative expression levels of all nine proprotein convertases in rat ovaries during pregnancy and at 3 days postpartum.

Methods

RNA was extracted from ovaries at Day 0, 4, 9, 11, 13, 15, 18, and 20 of pregnancy as well as 3 days postpartum. Relative expression levels of Pcsk1, Pcsk2, Furin, Pcsk4, Pcsk5, Pcsk6, Pcsk7, Mbtps1 and Pcsk9 were determined with real-time PCR. Results were reported as fold-change over the level at Day 0 of pregnancy.

Results

Results showed that Pcsk1 and Pcsk6 were upregulated as gestation advanced, in parallel with an observed increase in relaxin transcript. Pcsk2 showed downregulation as gestation advanced, while Pcsk5 showed relatively higher levels in early pregnancy and postpartum, but lower level in mid-pregnancy. On the other hand, Furin, Pcsk4, Pcsk7, Mbtps1 and Pcsk9 showed little change of expression throughout gestation.

Conclusion

PC1/3 (PCSK1) and PACE4 (PCSK6) may play an important role in proprotein processing in the ovary during late pregnancy.

Purification and partial characterization of relaxin and relaxin precursors from the hamster placenta

Previous immunological studies have indicated that the molecular structure of hamster relaxin is quite different from that of porcine relaxin. In the present study, hamster relaxin was purified from placentas and characterized in order to investigate its biochemical properties. Placentas from Days 14 and 15 of gestation were homogenized in 0.26 N HCl-62.5% acetone containing protease inhibitors. After centrifugation, soluble proteins were acetone precipitated. Soluble proteins were applied to a carboxymethyl cellulose ion-exchange column and bound proteins were eluted with 0.1 and 0.3 M NaCl. Western blot analysis detected 16.5-, 18.7-, and 36.0-kDa relaxin-immunoreactive (IR) proteins within the 0.1 M NaCl eluant and detected a 5.6-kDa relaxin-IR protein within the 0.3 M NaCl eluant. The 5.6-kDa protein was purified to homogeneity by gel filtration (Sephadex G-50), ion-exchange HPLC, and C18-HPLC. Reduction of the 5.6-kDa protein prior to electrophoresis resulted in a single band of lower molecular mass, suggesting that hamster relaxin consists of two chains of approximately equal molecular mass. Isoelectric point of the 5.6-kDa protein was 7.78. The 16.5- and 18.7-kDa IR proteins were copurified by gel filtration and ion-exchange HPLC. At least five isoelectric point variants were observed for the 16.5- and 18.7-kDa proteins. The N-terminal amino acid for the 5.6 and 18.7 relaxin-IR proteins was arginine, and subsequent cycles indicated an identical partial sequence that was consistent with that for relaxins from other species.