Signal transduction pathways involved in FSH- and LH-induced granulosa cell differentiation: Role of PKA and AKAPs

The purpose of the studies described in this dissertation was to investigate the signal transduction pathways activated in response to FSH receptor activation in granulosa cells of preantral (PA) follicles and the pathways activated in response to LH receptor activation in granulosa cells of preovulatory (PO) follicles.; FSH receptor activation in granulosa cells from PA follicles leads to an increase in p42/44 extracellular regulated kinase (ERK) phosphorylation in a PKA-dependent manner. While FSH-stimulated ERK activation is blocked by the MAPK ERK kinase (MEK) inhibitor PD98059, FSH does not increase MEK phosphorylation, Raf-1 activity, or activation of Ras or Rap 1. ERK activation in response to FSH receptor activation appears to occur via the PKA-dependent phosphorylation of a 100 kDa protein tyrosine phosphatase (PTP) that allows for its dissociation from ERK, relieving the inhibition of ERK phosphorylation and allowing for an increase in ERK phosphorylation. Results also show that FSH stimulates the phosphorylation on Ser 10 and the acetylation on Lys 9 and 14 of histone H3 in granulosa cells from PA follicles. FSH-stimulated histone H3 phosphorylation is mediated by PKA, and, in coordination with acetylation, results in the association of histone H3 with promoters for FSH responsive genes such as serum glucocorticoid kinase, inhibin α and c-fos .; Activation of the LH receptor in granulosa cells from PO follicles also leads to the phosphorylation of ERK and histone H3 in a PKA-dependent and PKC-independent manner. However, in contrast to FSH receptor signaling, LH stimulates the phosphorylation of MEK. We find, therefore, that the PKA-mediated pathways activated in response to FSH and LH receptor activation are different.; We identified an 80 kDa A kinase anchoring protein (AKAP) induced by FSH as ovarian granulosa cells mature to a PO phenotype as microtubule associated protein (MAP) 2D. MAP 2D is expressed predominately in granulosa cells of PO follicles and expression is retained in luteal cells. MAP 2D was found to associate with PKA RI over PKA RII in granulosa cells from PO follicles. Experiments performed using antisense oligonucleotides to MAP 2D revealed a functional role for MAP 2D in LH receptor signaling events.