Differential expression of GRK isoforms in nonmalignant and malignant human granulosa cells

Transcriptome signatures of host tissue infected with African swine fever virus reveal differential expression of associated oncogenes

African swine fever (ASF) has emerged as a threat to swine production worldwide. Evasion of host immunity by ASF virus (ASFV) is well understood. However, the role of ASFV in triggering oncogenesis is still unclear. In the present study, ASFV-infected kidney tissue samples were subjected to Illumina-based transcriptome analysis. A total of 2463 upregulated and 825 downregulated genes were differentially expressed (p < 0.05). A literature review revealed that the majority of the differentially expressed host genes were key molecules in signaling pathways involved in oncogenesis. Bioinformatic analysis indicated the activation of certain oncogenic KEGG pathways, including basal cell carcinoma, breast cancer, transcriptional deregulation in cancer, and hepatocellular carcinoma. Analysis of host-virus interactions revealed that the upregulated oncogenic RELA (p65 transcription factor) protein of Sus scrofa can interact with the A238L (hypothetical protein of unknown function) of ASFV. Differential expression of oncogenes was confirmed by qRT-PCR, using the H3 histone family 3A gene (H3F3A) as an internal control to confirm the RNA-Seq data. The levels of gene expression indicated by qRT-PCR matched closely to those determined through RNA-Seq. These findings open up new possibilities for investigation of the mechanisms underlying ASFV infection and offer insights into the dynamic interaction between viral infection and oncogenic processes. However, as these investigations were conducted on pigs that died from natural ASFV infection, the role of ASFV in oncogenesis still needs to be investigated in controlled experimental studies.

Interactions between AT1R and GRKs: the determinants for activation of signaling pathways involved in blood pressure regulation

The success of Angiotensin II receptor blockers, specifically Angiotensin II type 1 receptor (AT1R) antagonists as antihypertensive drug emphasizes the involvement of AT1R in Essential hypertension. The structural insights and mutational studies of Ang II-AT1R have brought about the vision to design Ang II analogs that selectively activate the pathways with beneficial and cardioprotective effects such as cell survival and hinder the deleterious effects such as hypertrophy and cell death. AT1R belongs to G-protein coupled receptors and is regulated by G-protein coupled receptor kinases (GRKs) that either uncouples Gq protein for receptor desensitization or phosphorylate C-terminus to recruit β-arrestin for internalization of the receptor. The interaction of GRKs with ligand activated AT1R induces conformational changes and signal either Gq dependent or Gq independent pathways. These interactions might explain the complex regulatory mechanisms and offer promising ideas for hypertension therapeutics. This article reviews the functional role of AT1R, organization of GRK genes and regulation of AT1R by GRKs that play significant role in desensitization and internalization of the receptors.

Computational analysis of G-protein-coupled receptor kinase family members as potential targets for colorectal cancer therapy

Background

G-protein-coupled receptor (GPCR) kinases (GRKs) interact with ligand-activated GPCR, causing intracellular phosphorylation and interfering with the intracellular signal transduction associated with the development of cancer. Colorectal cancer (CRC) is a fast-growing disease, and its molecular mechanism involves various regulatory proteins, including kinases. However, the GRK mechanism in CRC has not been explored.

Methods

We used an integrated computational approach to investigate the potential of GRK family members as targeted proteins in CRC. The GRK expression levels in tumor and normal tissues, colon adenocarcinoma samples, and metastatic colon adenocarcinoma were analyzed using ONCOMINE, GEPIA, and UALCAN, as well as TNM plots. Genetic changes in the GRK family genes were investigated using cBioportal. The prognostic value related to the gene expression of the GRK family was examined using GEPIA and UALCAN. Co-expression analysis of the GRK family was conducted using COXPRESdb. Association analysis of the Gene Ontology, KEGG pathway enrichment, and drug-gene analyses were performed using the over-representation analysis (ORA) in WebGestalt.

Results

GRK2, GRK3, and GRK5 mRNA levels increased significantly in patients with CRC and metastatic CRC. Genetic changes were detected in patients with CRC, including GRK7 (1.1%), GRK2 (1.7%), GRK4 (2.3%), GRK5 (2.5%), GRK6 (2.5%), GRK3 (2.9%), and GRK1 (4%). CRC patients with low mRNA of GRK7 levels had better disease-free and overall survival than those with high GRK7 levels. Hierarchical clustering analysis revealed significant positive correlations between GRK5 and GRK2 and between GRK2 and GRK6. KEGG pathway enrichment analysis showed that the gene network (GN) regulated several cellular pathways, such as the morphine addiction signaling and chemokine signaling pathways in cancer. The drug-gene association analysis indicated that the GN was associated with several drugs, including reboxetine, pindolol, beta-blocking agents, and protein kinase inhibitors.

Conclusion

No research has been conducted on the relation of GRK1 and GRK7 to cancer, particularly CRC. In this work, genes GRK2, GRK3, GRK5, and GRK6 were found to be oncogenes in CRC. Although inhibitors against GRK2, GRK5, and GRK6 have previously been developed, further research, particularly preclinical and clinical studies, is needed before these agents may be used to treat CRC.

G Protein-Coupled Receptor Kinase 4 Is a Novel Prognostic Factor in Hepatocellular Carcinoma

Purpose

We previously reported that G protein-coupled receptor kinase (GRK) 4 halts cell cycle progression and induces cellular senescence in HEK293 cells. The present study was aimed at assessing the prognostic value of GRK4 in hepatocellular carcinoma (HCC).

Methods

GRK4 expression was detected by immunohistochemistry in paired tumoral and peritumoral tissues of 325 HCC patients. One hundred and twenty-six patients from Western China were utilized as a training cohort to develop a nomogram, while 86 patients from Eastern China were used as a validation cohort. The proliferation and migration of lentiviral-GRK4 expressing HepG2 cells were determined by MTT and wound healing assays.

Results

GRK4 was differentially expressed in HCC tissues. Tumoral GRK4 intensity, tumor type, and T stage were independent prognostic factors and used to form a nomogram for predicting overall survival (OS), which obtained a good concordance index of 0.82 and 0.77 in training and validation cohort, respectively. The positive and negative prediction values with nomogram were, respectively, 83% and 75% in training cohort and 100% and 52% in validation cohort. Patients with nomogram scores > 32 and 78 showed high risk for OS. Proliferation and motility capabilities were significantly restrained in GRK4-overexpressing HCC cells. Discussion. Low GRK4 expression in HCC tumor tissues indicates poor clinical outcomes. A prognostic nomogram including tumoral GRK4 expression would improve the predictive accuracy of OS in HCC patients. We also demonstrated that GRK4 overexpression inhibits proliferation and migration of HCC cells. The molecular mechanism underlying is worth further study.

The GRKs Reactome: Role in Cell Biology and Pathology

G protein-coupled receptor kinases (GRKs) are protein kinases that function in concert with arrestins in the regulation of a diverse class of G protein-coupled receptors (GPCRs) signaling. Although GRKs and arrestins are key participants in the regulation of GPCR cascades, the complex regulatory mechanisms of GRK expression, its alternation, and their function are not thoroughly understood. Several studies together with the work from our lab in recent years have revealed the critical role of these kinases in various physiological and pathophysiological processes, including cardiovascular biology, inflammation and immunity, neurodegeneration, thrombosis, and hemostasis. A comprehensive understanding of the mechanisms underlying functional interactions with multiple receptor proteins and how these interactions take part in the development of various pathobiological processes may give rise to novel diagnostic and therapeutic strategies. In this review, we summarize the current research linking the role of GRKs to various aspects of cell biology, pathology, and therapeutics, with a particular focus on thrombosis and hemostasis.

The role of G protein-coupled receptor kinases in the pathology of malignant tumors

G protein-coupled receptor kinases (GRKs) constitute seven subtypes of serine/threonine protein kinases that specifically recognize and phosphorylate agonist-activated G protein-coupled receptors (GPCRs), thereby terminating the GPCRs-mediated signal transduction pathway. Recent research shows that GRKs also interact with non-GPCRs and participate in signal transduction in non-phosphorylated manner. Besides, GRKs activity can be regulated by multiple factors. Changes in GRKs expression have featured prominently in various tumor pathologies, and they are associated with angiogenesis, proliferation, migration, and invasion of malignant tumors. As a result, GRKs have been intensively studied as potential therapeutic targets. Herein, we review evolving understanding of the function of GRKs, the regulation of GRKs activity and the role of GRKs in human malignant tumor pathophysiology.

The Role of G Protein-coupled Receptor Kinases in Cancer

G protein-coupled receptors (GPCRs) are the largest family of plasma membrane receptors. Emerging evidence demonstrates that signaling through GPCRs affects numerous aspects of cancer biology such as vascular remolding, invasion, and migration. Therefore, development of GPCR-targeted drugs could provide a new therapeutic strategy to treating a variety of cancers. G protein-coupled receptor kinases (GRKs) modulate GPCR signaling by interacting with the ligand-activated GPCR and phosphorylating its intracellular domain. This phosphorylation initiates receptor desensitization and internalization, which inhibits downstream signaling pathways related to cancer progression. GRKs can also regulate non-GPCR substrates, resulting in the modulation of a different set of pathophysiological pathways. In this review, we will discuss the role of GRKs in modulating cell signaling and cancer progression, as well as the therapeutic potential of targeting GRKs.

G Protein-Coupled Receptor Kinases in the Inflammatory Response and Signaling

G protein-coupled receptor kinases (GRKs) are serine/threonine kinases that regulate a large and diverse class of G protein-coupled receptors (GPCRs). Through GRK phosphorylation and β-arrestin recruitment, GPCRs are desensitized and their signal terminated. Recent work on these kinases has expanded their role from canonical GPCR regulation to include noncanonical regulation of non-GPCR and nonreceptor substrates through phosphorylation as well as via scaffolding functions. Owing to these and other regulatory roles, GRKs have been shown to play a critical role in the outcome of a variety of physiological and pathophysiological processes including chemotaxis, signaling, migration, inflammatory gene expression, etc. This diverse set of functions for these proteins makes them popular targets for therapeutics. Role for these kinases in inflammation and inflammatory disease is an evolving area of research currently pursued in many laboratories. In this review, we describe the current state of knowledge on various GRKs pertaining to their role in inflammation and inflammatory diseases.

Adrenergic signaling in heart failure and cardiovascular aging

Both cardiovascular disease and aging are associated with changes in the sympathetic nervous system. Indeed, mounting evidence indicates that adrenergic receptors are functionally involved in numerous processes underlying both aging and cardiovascular disorders, in particular heart failure. This article will review the pathophysiological role of the sympathetic nervous system in heart failure and cardiovascular aging.

G-protein-coupled receptor kinase 2 in pancreatic cancer: clinicopathologic and prognostic significance

G-protein-coupled receptor kinase 2 (GRK2) was found to regulate biological behaviors in some cancers, including pancreatic cancer (PC). However, its clinicopathologic and prognostic implications in cancer remain unclear. This study was designed to address the issues in PC. Expression of GRK2 was measured by Western blotting and tissue microarray-based immunohistochemical staining in 3 and 171 patients with PC, respectively. The H-score was used to evaluate the staining results. In addition, GRK2 expression was correlated with clinicopathologic variables and overall survival. Finally, the prognostic value of GRK2 was validated in a publically available PC dataset, GSE21501. It was suggested that GRK2 expression was highly up-regulated in 2 out of 3 tumor samples, in contrast to corresponding non-tumor ones. Furthermore, H-score of GRK2 staining was significantly higher in tumor than in non-tumor tissues. Tumoral expression of GRK2 was significantly associated with T stage. Univariate analysis showed that high GRK2 expression in tumor tissues was predictive for poor overall survival of PC. However, GRK2 expression was not identified as an independent prognostic marker in multivariate Cox regression test, although close to the statistical significance. In dataset GSE21501, GRK2 was also revealed to be prognostic. Our data establish that GRK2 is overexpressed in PC, and might serve as a potential indicator of unfavorable prognosis.

Chapter Three - Ubiquitination and Protein Turnover of G-Protein-Coupled Receptor Kinases in GPCR Signaling and Cellular Regulation

G-protein-coupled receptors (GPCRs) are responsible for regulating a wide variety of physiological processes, and distinct mechanisms for GPCR inactivation exist to guarantee correct receptor functionality. One of the widely used mechanisms is receptor phosphorylation by specific G-protein-coupled receptor kinases (GRKs), leading to uncoupling from G proteins (desensitization) and receptor internalization. GRKs and β-arrestins also participate in the assembly of receptor-associated multimolecular complexes, thus initiating alternative G-protein-independent signaling events. In addition, the abundant GRK2 kinase has diverse "effector" functions in cellular migration, proliferation, and metabolism homeostasis by means of the phosphorylation or interaction with non-GPCR partners. Altered expression of GRKs (particularly of GRK2 and GRK5) occurs during pathological conditions characterized by impaired GPCR signaling including inflammatory syndromes, cardiovascular disease, and tumor contexts. It is increasingly appreciated that different pathways governing GRK protein stability play a role in the modulation of kinase levels in normal and pathological conditions. Thus, enhanced GRK2 degradation by the proteasome pathway occurs upon GPCR stimulation, what allows cellular adaptation to chronic stimulation in a physiological setting. β-arrestins participate in this process by facilitating GRK2 phosphorylation by different kinases and by recruiting diverse E3 ubiquitin ligase to the receptor complex. Different proteolytic systems (ubiquitin-proteasome, calpains), chaperone activities and signaling pathways influence the stability of GRKs in different ways, thus endowing specificity to GPCR regulation as protein turnover of GRKs can be differentially affected. Therefore, modulation of protein stability of GRKs emerges as a versatile mechanism for feedback regulation of GPCR signaling and basic cellular processes.

G Protein Coupled Receptor Kinase 3 Regulates Breast Cancer Migration, Invasion, and Metastasis

Triple negative breast cancer (TNBC) is a heterogeneous disease that has a poor prognosis and limited treatment options. Chemokine receptor interactions are important modulators of breast cancer metastasis; however, it is now recognized that quantitative surface expression of one important chemokine receptor, CXCR4, may not directly correlate with metastasis and that its functional activity in breast cancer may better inform tumor pathogenicity. G protein coupled receptor kinase 3 (GRK3) is a negative regulator of CXCR4 activity, and we show that GRK expression correlates with tumorigenicity, molecular subtype, and metastatic potential in human tumor microarray analysis. Using established human breast cancer cell lines and an immunocompetent in vivo mouse model, we further demonstrate that alterations in GRK3 expression levels in tumor cells directly affect migration and invasion in vitro and the establishment of distant metastasis in vivo. The effects of GRK3 modulation appear to be specific to chemokine-mediated migration behaviors without influencing tumor cell proliferation or survival. These data demonstrate that GRK3 dysregulation may play an important part in TNBC metastasis.

G protein-coupled receptor kinase 2 (GRK2) is localized to centrosomes and mediates epidermal growth factor-promoted centrosomal separation

G protein-coupled receptor kinases (GRKs) play a central role in regulating receptor signaling, but recent studies suggest a broader role in modulating normal cellular functions. For example, GRK5 has been shown to localize to centrosomes and regulate microtubule nucleation and cell cycle progression. Here we demonstrate that GRK2 is also localized to centrosomes, although it has no role in centrosome duplication or microtubule nucleation. Of interest, knockdown of GRK2 inhibits epidermal growth factor receptor (EGFR)-mediated separation of duplicated centrosomes. This EGFR/GRK2-mediated process depends on the protein kinases mammalian STE20-like kinase 2 (Mst2) and Nek2A but does not involve polo-like kinase 1. In vitro analysis and dominant-negative approaches reveal that GRK2 directly phosphorylates and activates Mst2. Collectively these findings demonstrate that GRK2 is localized to centrosomes and plays a central role in mitogen-promoted centrosome separation most likely via its ability to phosphorylate Mst2.

G-protein coupled receptor kinase (GRK)-5 regulates proliferation of glioblastoma-derived stem cells

Glioblastoma multiforme (GBM) is a grade IV malignant brain tumor with high mortality and has been well known to involve many molecular pathways, including G-protein coupled receptor (GPCR)-mediated signaling (such as epithelial growth factor receptor [EGFR] and platelet derived growth factor receptor [PDGFR]). G protein-coupled receptor kinases (GRK) directly regulate GPCR activity by phosphorylating activated agonist-bound receptors to desensitize signaling and internalize receptors through beta-arrestins. Recent studies in various cancers, including prostate and breast cancer, have highlighted the role of change in GRK expression to oncogenesis and tumor proliferation. In this study, we evaluated the expression of GRK5 in grade II to grade IV glioma specimens using immunohistochemistry and found that GRK5 expression levels are highly correlated with aggressiveness of glioma. We used culture conditions to selectively promote the growth of either glioblastoma cells with stem cell markers (GSC) or differentiated glioblastoma cells (DGC) from fresh GBM specimens. GSC are known to be highly invasive and mobile, and have the capacity to self-renew and are more resistant to chemotherapy and radiation compared to differentiated populations of GBM. We examined the expression of GRK5 in these two sets of culturing conditions for GBM cells and found that GRK5 expression is upregulated in GSC compared to differentiated GBM cells. To better understand the role of GRK5 in GBM-derived stem cells, we created stable GRK5 knockdown and evaluated the proliferation rate. Using an ATP chemiluminescence assay, we show, for the first time, that knocking down the expression of GRK5 decreased the proliferation rate of GSC in contrast to control.

G-protein-coupled receptor kinase 2 and hypertension: molecular insights and pathophysiological mechanisms

Numerous factors partake in the fine-tuning of arterial blood pressure. The heptahelical G-protein-coupled receptors (GPCRs) represent one of the largest classes of cell-surface receptors. Further, ligands directed at GPCRs account for nearly 30 % of current clinical pharmaceutical agents available. Given the wide variety of GPCRs involved in blood pressure control, it is reasonable to speculate for a potential role of established intermediaries involved in the GPCR desensitization process, like the G-protein-coupled receptor kinases (GRKs), in the regulation of vascular tone. Of the seven mammalian GRKs, GRK2 seems to be the most relevant isoform at the cardiovascular level. This review attempts to assemble the currently available information concerning GRK2 and hypertension, opening new potential fields of translational investigation to treat this vexing disease.

G-protein coupled receptor kinase 5 regulates prostate tumor growth

PURPOSE

The limited success of cancer therapeutics is largely attributable to the ability of cancer to become resistant to conventional cytotoxic chemotherapy. Thus, further identification of signaling molecules and pathways that influence tumorigenesis is needed to increase the overall therapeutic options. GRKs, originally recognized for their conserved role in GPCR signal control, have now emerged as regulators of additional biological molecules and functions.

MATERIALS AND METHODS

We used Western blot analysis to determine GRK expression in prostate cancer and RNA interference to establish the role of GRK5 in prostate cancer growth and progression through the cell cycle.

RESULTS

GRK5 was expressed highly in the aggressive prostate cancer PC3 cell line and its silencing by RNA interference attenuated in vitro cell proliferation. PC3 cells that stably expressed lentiviral small hairpin RNA and targeted GRK5 evidence reduced xenograft tumor growth in mice. This was reversed by rescuing expression with wild-type but not with kinase inactive K215R GRK5, implying the need of GRK5 kinase activity for tumor growth. To investigate possible cellular mechanism(s) for GRK5 in cell growth regulation we tested whether kinase activity would impact cell cycle progression. Like forced over expression of kinase-inactive K215R GRK5, GRK5 knockdown led to G2/M arrest in the cell cycle. Also, evidence revealed that the loss of GRK5 activity resulted in decreased cyclin D1 expression, Rb protein phosphorylation and E2F target gene expression involved in cell cycle control.

CONCLUSIONS

Results provide direct evidence that GRK5 has an immediate role in the regulation of prostate tumor growth.

Anti-apoptotic activity of porcine cFLIP in ovarian granulosa cell lines

In mammalian ovaries, more than 99% of follicles undergo atresia during growth and development. Recently, we found that the expression of cellular FLICE-like inhibitory protein long form (cFLIP(L)) decreased during follicular atresia in granulosa cells of porcine ovaries. In humans and other species, both the short (cFLIP(S)) and long (cFLIP(L)) forms of cFLIP are considered to function as cell survival factors that inhibit death ligand receptor-mediated apoptosis. Since the anti-apoptotic activity of porcine cFLIP (pcFLIP) in granulosa cells had not been determined, we examined the effect of pcFLIP on survival using granulosa-derived cell lines. A human cervix adenocarcinoma cell line, HeLa, human ovarian granulosa tumor cell line, KGN, and porcine granulosa-derived cell line, JC-410, were used. By Western blotting, internal cFLIP(L) was detected in all cell lines, but only trace levels of cFLIP(S) were found in HeLa and KGN cells. To examine the anti-apoptotic activity, pcFLIP(S) or pcFLIP(L) was overexpressed in HeLa and KGN cells. Transfected cells in which pcFLIP(S) or pcFLIP(L) was overexpressed, survived the induction of Fas-mediated apoptosis, while almost all of the cells transfected with empty vector died. Then, we suppressed the expression of porcine cFLIP(S) and/or cFLIP(L) in JC-410 cells using small interfering RNA (siRNA). When both cFLIP(S) and cFLIP(L), or only cFLIP(L) was suppressed, cell viability declined significantly. From the results, we conclude that porcine cFLIP(S) and cFLIP(L) exhibit anti-apoptotic activity in granulosa-derived cells. It was strongly suggested that pcFLIP acts as a survival-promoting factor in granulosa cells and determines whether porcine ovarian follicles survive or undergo atresia.

Mdm2 is involved in the ubiquitination and degradation of G-protein-coupled receptor kinase 2

G-protein-coupled receptor kinase 2 (GRK2) is a central regulator of G-protein-coupled receptor signaling. We report that Mdm2, an E3-ubiquitin ligase involved in the control of cell growth and apoptosis, plays a key role in GRK2 degradation. Mdm2 and GRK2 association is enhanced by beta(2)-adrenergic receptor stimulation and beta-arrestin. Increased Mdm2 expression accelerates GRK2 proteolysis and promotes kinase ubiquitination at defined residues, whereas GRK2 turnover is markedly impaired in Mdm2-deficient cells. Moreover, we find that activation of the PI3K/Akt pathway by insulin-like growth factor-1 alters Mdm2-mediated GRK2 degradation, leading to enhanced GRK2 stability and increased kinase levels. These data put forward a novel mechanism for controlling GRK2 expression in physiological and pathological conditions.

GRK et arrestines : la piste thérapeutique ?

Phosphorylation of the agonist-activated form of G-protein-coupled receptors (GPCRs) by a protein kinase from the G-protein-coupled receptor kinase (GRK) family initiates, with arrestin proteins, a negative feedback process known as desensitization. Because these receptors are involved in so many vital functions, it seems likely that disorders affecting GRK- or arrestin-mediated regulation of GPCRs would contribute to, if not engender, disease. Traditionally, it is believed that the desensitization process protects the cell against an overstimulation; however, in certain situations, this process is maladjusted and participes in disease progression. For example, in Oguchi disease, excessive rhodopsin stimulation due to a functional loss of GRK1 or arrestin 1 leads to light sensitization and stationary night blindness. Also, transgenic mice with vascular smooth muscle-targeted overexpression of GRK2 showed an elevated resting blood pressure, suggesting that increase in GRK2 level in humans is involved in hypertension associated with a decreased effect of beta-adrenergic receptor-mediated vasorelaxation. The restoration of normal GPCR function in modulating the desensitization process has been successfully demonstrated in animal models of heart failure, which indicates that targeting GRKs or arrestins may open a novel therapeutic strategy in human diseases with GPCR dysregulation. However, the few effective pharmacological compounds in this domain currently preclude human clinical tests.

Pathophysiological roles of G-protein-coupled receptor kinases

G-protein-coupled receptor kinases (GRKs) interact with the agonist-activated form of G-protein-coupled receptors (GPCRs) to effect receptor phosphorylation and to initiate profound impairment of receptor signalling, or desensitization. GPCRs form the largest family of cell surface receptors known and defects in GRK function have the potential consequence to affect GPCR-stimulated biological responses in many pathological situations. This review focuses on the physiological role of GRKs revealed by genetically modified animals but also develops the involvement of GRKs in human diseases as, Oguchi disease, heart failure, hypertension or rhumatoid arthritis. Furthermore, the regulation of GRK levels in opiate addiction, cancers, psychiatric diseases, cystic fibrosis and cardiac diseases is discussed. Both transgenic mice and human pathologies have demonstrated the importance of GRKs in the signalling pathways of rhodopsin, beta-adrenergic and dopamine-1 receptors. The modulation of GRK activity in animal models of cardiac diseases can be effective to restore cardiac function in heart failure and opens a novel therapeutic strategy in diseases with GPCR dysregulation.

Ovarian granulosa cell lines

The ovary is a complex endocrine gland responsible for production of sex steroids and is the source of fertilizable ova for reproduction. It also produces various growth factors, transcription factors and cytokines that assist in the complex signaling pathways of folliculogenesis. The ovary possesses two primary steroidogenic cell types. The theca cells (and to a lesser extent, the stroma) are responsible for androgen synthesis, and the granulosa cells are responsible for conversion of androgens to estrogens, as well as progesterone synthesis. These cells undergo a transformation in the luteal phase of the menstrual cycle, converting them from estrogen producing, to predominantly progesterone producing cells. Understanding the molecular mechanisms regulating these cells is essential in understanding the regulation of steroidogenesis and reproduction. Creation of appropriate in vitro cell model systems can provide important tools for the study of ovarian function. This has led to the development of ovarian steroidogenic cell lines in several laboratories. Developing theca cell lines has met with limited success. Conversely, numerous human and animal granulosa cell lines have been developed. This review will discuss the existing granulosa cell lines and their characteristics.

Mechanisms regulating the constitutive activation of the extracellular signal-regulated kinase (ERK) signaling pathway in ovarian cancer and the effect of ribonucleic acid interference for ERK1/2 on cancer cell proliferation

The ERK1/2 MAPK pathway is a critical signaling system that mediates ligand-stimulated signals for the induction of cell proliferation, differentiation, and cell survival. Studies have shown that this pathway is constitutively active in several human malignancies and may be involved in the pathogenesis of these tumors. In the present study we examined the ERK1/2 pathway in cell lines derived from epithelial and granulosa cell tumors, two distinct forms of ovarian cancer. We show that ERK1 and ERK2 are constitutively active and that this activation results from both MAPK kinase-dependent and independent mechanisms and is correlated with elevated BRAF expression. MAPK phosphatase 1 (MKP-1) expression, which is involved in ERK1/2 deactivation, is down-regulated in the cancer cells, thus further contributing to ERK hyperactivity in these cells. Treatment of these cancer cell lines with the proteasome inhibitor ZLLF-CHO increased MKP-1 but not MKP-2 expression and decreased ERK1/2 phosphorylation. More importantly, silencing of ERK1/2 protein expression using RNA interference led to the complete suppression of tumor cell proliferation. These results provide evidence that the ERK pathway plays a major role in ovarian cancer pathogenesis and that down-regulation of this master signaling pathway is highly effective for the inhibition of ovarian tumor growth.