Role of cyclic nucleotide signaling in oocyte maturation

The development of the ovarian follicle, oocyte maturation, and ovulation require a complex set of endocrine, paracrine, and autocrine inputs that are translated into the regulation of cyclic nucleotide levels. Changes in intracellular cAMP mediate the gonadotropin regulation of granulosa and theca cell functions. Likewise, a decrease in cAMP concentration in the oocyte has been associated with the resumption of meiosis. Using pharmacological and molecular approaches, we determined that the expression of cyclic nucleotide phosphodiesterases (PDEs), the enzymes that degrade and inactivate cAMP, is compartmentalized in the ovarian follicle of all species studied, with PDE3 present in the oocytes and PDE4s in granulosa cells. The PDE3 expressed in the mouse oocyte was cloned, and the protein expressed in a heterologous system had properties similar to those of a PDE3A derived from somatic cells. Inhibition of the oocyte PDE3 completely blocked oocyte maturation in vitro and in vivo, demonstrating that the activity of this enzyme is essential for oocyte maturation. Heterologous expression of PDE3A in Xenopus oocyte causes morphological changes distinctive of resumption of meiosis (GVBD), as well as activation of mos translation and MAPK phosphorylation. Using mRNA and antibody microinjection in the Xenopus eggs, we have shown that PDE3 is downstream from the kinase PKB/Akt in the pathway that mediates IGF-1 but not progesterone-induced meiotic resumption. The presence of a similar regulatory module in mammalian oocytes is inferred by pharmacological studies with PDE3 inhibitors and measurement of PDE activity. Thus, PDE3 plays an essential role in the signaling pathway that controls resumption of meiosis in amphibians and mammals. Understanding the regulation of this enzyme may shed some light on the signals that trigger oocyte maturation.

Cyclic nucleotide phosphodiesterases and their role in endocrine cell signaling

The discovery that degradation and inactivation of the second messengers cAMP and cGMP are mediated by a complex enzymatic machinery has changed our perspective on cyclic nucleotide-mediated processes. In the cell, these second messengers are inactivated by no fewer than 11 distinct families of phosphodiesterases (PDEs). Much is known about the structure and function of these enzymes, their complex subcellular distribution and regulation. Yet, their potential as targets for therapeutic intervention in a broad range of endocrine abnormalities still needs to be investigated. This review explores the involvement of PDEs in the regulation of intracellular signaling and focuses on the known and potential roles that are of interest to endocrinologists.

Cellular mechanisms underlying prostaglandin-induced transient cAMP signals near the plasma membrane of HEK-293 cells

We have previously used cyclic nucleotide-gated (CNG) channels as sensors to measure cAMP signals in human embryonic kidney (HEK)-293 cells. We found that prostaglandin E(1) (PGE(1)) triggered transient increases in cAMP concentration near the plasma membrane, whereas total cAMP levels rose to a steady plateau over the same time course. In addition, we presented evidence that the decline in the near-membrane cAMP levels was due primarily to a PGE(1)-induced stimulation of phosphodiesterase (PDE) activity, and that the differences between near-membrane and total cAMP levels were largely due to diffusional barriers and differential PDE activity. Here, we examine the mechanisms regulating transient, near-membrane cAMP signals. We observed that 5-min stimulation of HEK-293 cells with prostaglandins triggered a two- to threefold increase in PDE4 activity. Extracellular application of H89 (a PKA inhibitor) inhibited stimulation of PDE4 activity. Similarly, when we used CNG channels to monitor cAMP signals we found that both extracellular and intracellular (via the whole-cell patch pipette) application of H89, or the highly selective PKA inhibitor, PKI, prevented the decline in prostaglandin-induced responses. Following pretreatment with rolipram (a PDE4 inhibitor), H89 had little or no effect on near-membrane or total cAMP levels. Furthermore, disrupting the subcellular localization of PKA with the A-kinase anchoring protein (AKAP) disruptor Ht31 prevented the decline in the transient response. Based on these data we developed a plausible kinetic model that describes prostaglandin-induced cAMP signals. This model has allowed us to quantitatively demonstrate the importance of PKA-mediated stimulation of PDE4 activity in shaping near-membrane cAMP signals.

Correlation Between the Clinical Parameters and Tissue Phenotype in Patients Affected by Deep-Infiltrating Endometriosis

The current study aimed to identify and validate an applicable immunohistochemistry panel including Ki-67, c-MYC, estrogen receptor-α (ER-α), and progesterone receptor isoforms A/B (PR-A/B) in correlation with clinicopathological parameters in patients affected by deep infiltrating endometriosis. Tissue microarrays were prepared from a cohort of 113 patients. Phenotypic profile of the panel molecules was evaluated in glands and stroma in parallel with microvessels and stroma density measurements. Principal component analysis was performed on 8 immunohistochemical variables, 2 histological variables, and 8 subgroups of clinical parameters. The immunohistochemical profiling showed consistent Ki-67 immunostaining in 17.9% of the samples and c-MYC in 83.1%, while intense ER-α immunoreactivity was detected in 84% of the samples and PR-A/B isoforms in 24.1% of them. The combination of clinical parameters and tissue phenotype allowed a stratification of endometriosis-affected patients. Such novel phenotypical and clinical correlation could be helpful in the future studies for a better stratification of the disease aiming at a personalized patient care.