Hormonal regulation of nuclear cyclic AMP-dependent protein kinase subunit levels in rat ovaries

Mathematical model of FSH-induced cAMP production in ovarian follicles

During the terminal part of their development, ovarian follicles become totally dependent on gonadotropin supply to pursue their growth and maturation. Both gonadotropins, follicle-stimulating hormone (FSH) and luteining hormone (LH), operate mainly through stimulatory G protein-coupled receptors, their signal being transduced by the activation of the enzyme adenylyl cyclase and the production of second-messenger cAMP. In this paper, we develop a mathematical model of the dynamics of the coupling between FSH receptor stimulation and cAMP synthesis. This model takes the form of a set of nonlinear, ordinary differential equations that describe the changes in the different states of FSH receptors (free, bound, phosphorylated, and internalized), coupling efficiency (activated adenylyl cyclase), and cAMP response. Classical analysis shows that, in the case of constant FSH signal input, the system converges to a unique, stable equilibrium state, whose properties are here investigated. The system also appears to be robust to nonconstant input. Particular attention is given to the influence of biologically relevant parameters on cAMP dynamics.

Mediation of gonadotrophin-stimulated growth and differentiation of human granulosa cells by adenosine-3',5'-monophosphate: one molecule, two messages

OBJECTIVE

To determine how the second messenger adenosine-3',5'-monophosphate (cyclic AMP) is able to mediate divergent actions of FSH and LH on granulosa cell growth and differentiation in human ovaries.

DESIGN

Human granulosa cells were cultured for 96 hours in serum-free medium 199 containing increasing doses of either FSH, LH or dibutyryl cyclic AMP. Extra and intra-cellular cyclic AMP levels were determined by radioimmunoassay. Tritiated thymidine uptake and cell number were measured as indices of cell growth, and spent medium was assayed for steroids (oestradiol and progesterone) to reflect differentiation.

PATIENTS

'Mature' granulosa cells were aspirated from preovulatory follicles in the ovaries of clomiphene-stimulated patients undergoing laparoscopic sterilization; 'luteinized' granulosa cells were aspirated from periovulatory follicles in the ovaries of gonadotrophin-stimulated in-vitro fertilization patients.

RESULTS

LH consistently inhibited, whereas FSH maintained or stimulated, basal granulosa cell numbers. Steroidogenesis was dose-dependently increased by both gonadotrophins, with LH having the significantly greater effect over the entire dose-response range (1-100 micrograms/l). LH also induced significantly more cyclic AMP production than FSH, both intra and extra-cellularly, providing a basis for differential post-receptor signalling via a common second messenger. Addition of dibutyryl cyclic AMP, at low concentrations (10-250 mumol/l) to the cultured cells in the absence of gonadotrophins mimicked FSH effects with stimulation/maintenance of cell numbers and moderate steroidogenesis. High concentrations of dibutyryl cyclic AMP (500-1000 mumol/l) caused a significant inhibition of cell numbers together with maximal steroidogenesis, simulating LH action.

CONCLUSIONS

These results suggest that granulosa cell maturation in the follicular phase of the menstrual cycle (controlled by FSH) is associated with a low cyclic AMP tone that favours cell growth and expression of aromatase activity in the developing preovulatory follicle. During the early luteal phase (dominated by LH), the intracellular cycle AMP tone increases to allow maximal progesterone production and inhibition of cell growth in the corpus luteum. Thereby one second messenger can mediate divergent gonadotrophic effects on granulosa cell growth and differentiation in the human ovary.

Changes in cAMP-dependent phosphorylation of specific cytosol protein in the peri- and postmenopausal ovary

Changes in cAMP-dependent phosphorylation of 53 kDa protein in a human ovary with respect to the aging process were studied. The phosphorylation of endogenous proteins in ovarian cytosol decreased with aging. However, ovarian aging was accompanied by an increase in the cAMP-dependent phosphorylation of 53 kDa specific protein while the amount of this protein decreased with aging. The plasma gonadotropin levels of women with regular menstrual periods were significantly different from those of women whose menstrual periods had in the recent past become irregular (FSH: p less than 0.01; LH: p less than 0.05); however, there was no significant difference in the plasma estradiol levels between these two groups. Our data show the possible correlations between the non-steroidal ovarian factor (53 kDa protein) and/or its phosphorylation by cAMP-dependent protein kinase and the ovarian aging process.

Protein kinases associated with proliferation and differentiation in murine erythroleukaemic cells

1. The changes in electrophoretic distribution of cytosolic protein kinases have been studied in relation to proliferation, differentiation and transformation in murine erythroleukaemic cells, using a non-denaturing polyacrylamide gel electrophoresis system. 2. Native molecular masses of the major forms were determined by Ferguson plots. 3. A two dimensional electrophoresis method was developed for determination of the subunit molecular masses. 4. These studies suggest that the major bands of activity contain components which may correspond to cGMP dependent protein kinase, cAMP dependent protein kinase and protein kinase C. 5. On hexamethylene bisacetamide induced differentiation of the cells, changes in proportions of the different forms were observed.