did not ovulate and showed low secretion of progesterone and oestradiol. Addition of LH + 3-isobutyl-1-methylxanthine resulted in a marked stimulation of steroid release, and ovulations occurred in all ovaries (9.0 \ m=+-\ 0.9; mean \ m=+-\ sem). The protein tyrosine kinase inhibitors, genistein and tyrphostin A25, significantly inhibited ovulation at the higher concentrations tested (3.0 \m=+-\0.3at 100 \g=m\molgenistein l \m=-\1; 5.8 \ m=+-\ 1.0 at 500 \g=m\mol tyrphostin A25 l \ m=-\ 1) but no effect was seen at lower concentrations. The presence of genistein and tyrphostin A25 at any concentration used did not significantly decrease the LH + 3-isobutyl-1-methylxanthine-induced progesterone or oestradiol concentrations. The intraovarian concentrations of plasminogen activator activity, and prostaglandin E2 and F2\ g=a\ were not altered by the presence genistein (100 \g=m\moll \ m=-\ 1) . In conclusion, the results of the present study indicate that protein tyrosine kinase signalling pathways are integral parts of the mammalian ovulatory process but do not involve actions on the synthesis of steroids, plasminogen activator or prostaglandins.
Glucose-6-phosphatase (G6Pase) is a key regulator of gluconeogenesis. We previously found that administration of glycerol, a substrate for gluconeogenesis, transactivates G6Pase in the mouse liver. To clarify its cell-autonomous transcriptional activation in hepatocytes, we examined the mechanism of expression of the gene G6pc, which encodes G6Pase, in rat hepatoma cell line FAO cells. Endogenous G6pc expression in FAO cells was increased by glycerol administration as well as by the fatty acid oleate. Luciferase reporter assay revealed that the ~2.0 kb mouse G6pc promoter contains the element(s) responsible for glycerol-stimulated G6pc transactivation. Using several deletion-or chimeric-constructs of G6pc promoter, we found that the DNA response element for hepatocyte nuclear factor 4α (HNF4α) (−77/−65) in the G6pc promoter is essential for transactivation by glycerol. Similarly to glycerol, oleate also increased G6pc expression through its action on the HNF4α element (−77/−65). Furthermore, the reporter activities were higher in the cells co-treated with glycerol plus oleate than in those singly treated with glycerol or oleate. In addition, the temporal profiles of G6pc expression differed between glycerol and oleate administration. Our present results suggest that glycerol and oleate induce G6pc expression both via the HNF4α element (−77/−65) and also through other regulatory mechanisms.
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