Expression of brx proto-oncogene in normal ovary and in epithelial ovarian neoplasms

AKAP13 Enhances CREB1 Activation by FSH in Granulosa Cells

Granulosa cells (GCs) must respond appropriately to follicle-stimulating hormone (FSH) for proper follicle maturation. FSH activates protein kinase A (PKA) leading to phosphorylation of the cyclic AMP response element binding protein-1 (CREB1). We identified a unique A-kinase anchoring protein (AKAP13) containing a Rho guanine nucleotide exchange factor (RhoGEF) region that was induced in GCs during folliculogenesis. AKAPs are known to coordinate signaling cascades, and we sought to evaluate the role of AKAP13 in GCs in response to FSH. Aromatase reporter activity was increased in COV434 human GCs overexpressing AKAP13. Addition of FSH, or the PKA activator forskolin, significantly enhanced this activity by 1.5- to 2.5-fold, respectively (p < 0.001). Treatment with the PKA inhibitor H89 significantly reduced AKAP13-dependent activation of an aromatase reporter (p = 0.0067). AKAP13 physically interacted with CREB1 in co-immunoprecipitation experiments and increased the phosphorylation of CREB1. CREB1 phosphorylation increased after FSH treatment in a time-specific manner, and this effect was reduced by siRNA directed against AKAP13 (p = 0.05). CREB1 activation increased by 18.5-fold with co-expression of AKAP13 in the presence of FSH (p < 0.001). Aromatase reporter activity was reduced by inhibitors of the RhoGEF region, C3 transferase and A13, and greatly enhanced by the RhoGEF activator, A02. In primary murine and COV43 GCs, siRNA knockdown of Akap13/AKAP13 decreased aromatase and luteinizing hormone receptor transcripts in cells treated with FSH, compared with controls. Collectively, these findings suggest that AKAP13 may function as a scaffolding protein in FSH signal transduction via an interaction with CREB, resulting in phosphorylation of CREB.

The role of Hippo pathway signaling and A-kinase anchoring protein 13 in primordial follicle activation and inhibition

OBJECTIVE

To determine whether the mechanotransduction and pharmacomanipulation of A-kinase anchoring protein 13 (AKAP13) altered Hippo signaling pathway transcription and growth factors in granulosa cells. Primary ovarian insufficiency is the depletion or dysfunction of primordial ovarian follicles. In vitro activation of ovarian tissue in patients with primary ovarian insufficiency alters the Hippo and phosphatase and tensin homolog/phosphatidylinositol 3-kinase/protein kinase B/forkhead box O3 pathways. A-kinase anchoring protein 13 is found in granulosa cells and may regulate the Hippo pathway via F-actin polymerization resulting in altered nuclear yes-associated protein (YAP)/transcriptional coactivator with PDZ-binding motif coactivators and Tea domain family (TEAD) transcription factors.

DESIGN

Laboratory studies.

SETTING

Translational science laboratory.

PATIENT(S)

None.

INTERVENTION(S)

COV434 cells, derived from a primary human granulosa tumor cell line, were studied under different cell density and well stiffness conditions. Cells were transfected with a TEAD-luciferase (TEAD-luc) reporter as well as expression constructs for AKAP13 or AKAP13 mutants and then treated with AKAP13 activators, inhibitors, and follicle-stimulating hormone.

MAIN OUTCOME MEASURE(S)

TEAD gene activation or inhibition was measured by TEAD-luciferase assays. The messenger ribonucleic acid levels of Hippo pathway signaling molecules, including connective tissue growth factor (CTGF), baculoviral inhibitors of apoptosis repeat-containing 5, Ankyrin repeat domain-containing protein 1, YAP1, and TEAD1, were measured by quantitative real-time polymerase chain reaction. Protein expressions for AKAP13, CTGF, YAP1, and TEAD1 were measured using Western blot.

RESULT(S)

Increased TEAD-luciferase activity and expression of markers for cellular growth were associated with decreased cell density, increased well stiffness, and AKAP13 activator (A02) treatment. Additionally, decreased TEAD-luc activity and expression of markers for cellular growth were associated with AKAP13 inhibitor (A13) treatment, including a reduced expression of the BIRC5 and ANKRD1 (YAP-responsive genes) transcript levels and CTGF protein levels. There were no changes in TEAD-luc with follicle-stimulating hormone treatment, supporting Hippo pathway involvement in the gonadotropin-independent portion of folliculogenesis.

CONCLUSION(S)

These findings suggest that AKAP13 mediates Hippo-regulated changes in granulosa cell growth via mechanotransduction and pharmacomanipulation. The AKAP13 regulation of the Hippo pathway may represent a potential target for regulation of follicle activation.

A deletion mutation within the goat AKAP13 gene is significantly associated with litter size

A-kinase anchoring protein 13 (AKAP13) is one of the AKAP protein family members, which is correlated with estrogen receptors (ERs) and progesterone receptor (PR) activity. Consequently, the AKAP13 gene is considered to be one of the candidate genes for regulating female fertility. Hence, the objectives of this study were to discover the potential insertion/deletion (indel) variants within the AKAP13 gene and evaluate their associations with litter size of Shaanbei white cashmere goats (SBWC) to screen candidate genes for the molecular marker-assisted selection (MAS). Ultimately, we found the 16-bp deletion of AKAP13 gene which displayed three genotypes (II, ID and DD). However, it was not confirmed to Hardy-Weinberg equilibrium (HWE) in the tested population. Statistical analysis demonstrated that this 16-bp indel locus was significantly associated with litter size in goats (p < 0.05), in which the ID genotype was a key genotype for increasing litter size in goats. Besides, independent χ² tests between different genotypes and litter size showed that high-prolific groups had higher frequency of the 'D' allele (p < 0.05). Briefly, AKAP13 gene is a candidate gene for improving fertility, and its 16-bp indel locus can be used as a valid DNA molecular marker for the MAS in goat breeding.

A-Kinase Anchoring Protein 13 (AKAP13) Augments Progesterone Signaling in Uterine Fibroid Cells

CONTEXT

Uterine leiomyomata (fibroids) are prevalent sex hormone‒dependent tumors with an altered response to mechanical stress. Ulipristal acetate, a selective progesterone receptor (PR) modulator, significantly reduces fibroid size in patients. However, PR signaling in fibroids and its relationship to mechanical signaling are incompletely understood.

OBJECTIVE

Our prior studies revealed that A-kinase anchoring protein 13 (AKAP13) was overexpressed in fibroids and contributed to altered mechanotransduction in fibroids. Because AKAP13 augmented nuclear receptor signaling in other tissues, we sought to determine whether AKAP13 might influence PR signaling in fibroids.

METHODS AND RESULTS

Fibroid samples from patients treated with ulipristal acetate or placebo were examined for AKAP13 expression by using immunohistochemistry. In immortalized uterine fibroid cell lines and COS-7 cells, we observed that AKAP13 increased ligand-dependent PR activation of luciferase reporters and endogenous progesterone-responsive genes for PR-B but not PR-A. Inhibition of ERK reduced activation of PR-dependent signaling by AKAP13, but inhibition of p38 MAPK had no effect. In addition, glutathione S-transferase‒binding assays revealed that AKAP13 was bound to PR-B through its carboxyl terminus.

CONCLUSION

These data suggest an intersection of mechanical signaling and PR signaling involving AKAP13 through ERK. Further elucidation of the integration of mechanical and hormonal signaling pathways in fibroids may provide insight into fibroid development and suggest new therapeutic strategies for treatment.

Mice deficient in AKAP13 (BRX) develop compulsive-like behavior and increased body weight

OBJECTIVE

Hormonal contributions to the sex-dependent development of both obsessive-compulsive disorder (OCD) and obesity have been described, but the underlying mechanisms are incompletely understood. A-kinase anchoring protein 13 (AKAP13) significantly augments ligand-dependent activation of estrogen receptors alpha and beta. The hypothalamus and pituitary gland are implicated in the development and exacerbation of OCD and obesity and have strong AKAP13 expression. The AKAP13 localization pattern observed in these key brain regions together with its effects on sex steroid action suggest a potential role for AKAP13 in compulsive-like behaviors. Here we tested the role of AKAP13 in compulsive-like behavior and body weight using an Akap13 haploinsufficient murine model.

MATERIALS AND METHODS

Targeted deletion of the Akap13 gene generated haploinsufficient (Akap13+/-) mice in a C57BL6/J genetic background. Established behavioral assays were conducted, video recorded, and scored blindly to assess compulsive-like behavior based on genotype and gender. Tests included: marble-burying, grooming, open- field and elevated plus-maze. Brain and body weights were also obtained. Mean levels of test outcomes were compared using multi-way ANOVA to test for genotype, sex, genotype*sex, and genotype*sex*age interaction effects with Bonferroni adjustment for multiple comparisons, to further explain any significant interactions.

RESULTS

The marble-burying and grooming assays revealed significant sex-dependent increases in perseverative, compulsive-like behaviors in female Akap13 haploinsufficient mice compared to female wild type (WT) mice by demonstrating increased marble-burying activity (p = .0025) and a trend towards increased grooming behavior (p = .06). Male Akap13 haploinsufficient mice exhibited no behavioral changes (p > 0.05). Elevated plus-maze and open-field test results showed no overt anxiety-like behavior in Akap13 haploinsufficient mice irrespective of sex (p > 0.05, both). No differences in brain weight were found in Akap13 haploinsufficient mice compared to WT mice (p > 0.05). However, female Akap13 haploinsufficient mice weighed more than female WT mice in the 4 to <7 months age range (p = .0051). Male Akap13 haploinsufficient mice showed no differences in weight compared to male WT mice (p = >0.05) at any age range examined.

CONCLUSION

Akap13 haploinsufficiency led to sex-dependent, compulsive-like behavioral changes in a murine model. Interestingly, Akap13 haploinsufficiency also led to a sex-dependent increase in body weight. These results revealed a requirement for AKAP13 in murine behavior, particularly in female mice, and is the first report of AKAP13 involvement in murine behavior. Future studies may examine the involvement of AKAP13 in the pathophysiology of OCD in female humans and may contribute to a better understanding of the role of AKAP13 and sex hormones in the development and exacerbation of OCD.

Gene Set-Based Functionome Analysis of Pathogenesis in Epithelial Ovarian Serous Carcinoma and the Molecular Features in Different FIGO Stages

Serous carcinoma (SC) is the most common subtype of epithelial ovarian carcinoma and is divided into four stages by the Federation of Gynecologists and Obstetrics (FIGO) staging system. Currently, the molecular functions and biological processes of SC at different FIGO stages have not been quantified. Here, we conducted a whole-genome integrative analysis to investigate the functions of SC at different stages. The function, as defined by the GO term or canonical pathway gene set, was quantified by measuring the changes in the gene expressional order between cancerous and normal control states. The quantified function, i.e., the gene set regularity (GSR) index, was utilized to investigate the pathogenesis and functional regulation of SC at different FIGO stages. We showed that the informativeness of the GSR indices was sufficient for accurate pattern recognition and classification for machine learning. The function regularity presented by the GSR indices showed stepwise deterioration during SC progression from FIGO stage I to stage IV. The pathogenesis of SC was centered on cell cycle deregulation and accompanied with multiple functional aberrations as well as their interactions.

A regulatory SNP in AKAP13 is associated with blood pressure in Koreans

High blood pressure contributes to more than 10 million deaths per year worldwide through stroke and ischemic heart disease. Yet, genome-wide association studies (GWASs) have identified a small fraction of its underlying genetic factors. To identify biologically important single-nucleotide polymorphisms (SNPs) that regulate variations in blood pressure, we analyzed SNPs in a genome-wide association study. Genome-wide genotype data (original study n = 7551, SNP = 352,228; replication study n = 3703, SNP = 20) were obtained from the Korea National Institute of Health, wherein 29,921 of 352,228 SNPs lay within 5 kbp upstream of genes. Linear regression analysis was performed for systolic and diastolic blood pressure (DBP) by controlling for cohort, age, sex and body mass index. For the 20 SNPs that were associated with both blood pressure values, a replication study was performed in an independent population. A total of 20 SNPs were significantly associated with both blood pressure values in the original study, 13 of which lay in a conserved transcription factor-binding site. One SNP (rs11638762), in the GATA-3 binding site upstream of the AKAP13 gene, was significantly replicated in another cohort (P-value of the meta-analysis = 1.4 × 10(-5) for systolic blood pressure and 6.3 × 10(-4) for DBP). A functional GWAS was performed using upstream SNPs, and a novel genetic factor (AKAP13), which is essential for cardiac myocyte development in mice, was identified as a regulator of blood pressure.

The Rho guanine nucleotide exchange factor AKAP13 (BRX) is essential for cardiac development in mice

A fundamental biologic principle is that diverse biologic signals are channeled through shared signaling cascades to regulate development. Large scaffold proteins that bind multiple proteins are capable of coordinating shared signaling pathways to provide specificity to activation of key developmental genes. Although much is known about transcription factors and target genes that regulate cardiomyocyte differentiation, less is known about scaffold proteins that couple signals at the cell surface to differentiation factors in developing heart cells. Here we show that AKAP13 (also known as Brx-1, AKAP-Lbc, and proto-Lbc), a unique protein kinase A-anchoring protein (AKAP) guanine nucleotide exchange region belonging to the Dbl family of oncogenes, is essential for cardiac development. Cardiomyocytes of Akap13-null mice had deficient sarcomere formation, and developing hearts were thin-walled and mice died at embryonic day 10.5-11.0. Disruption of Akap13 was accompanied by reduced expression of Mef2C. Consistent with a role of AKAP13 upstream of MEF2C, Akap13 siRNA led to a reduction in Mef2C mRNA, and overexpression of AKAP13 augmented MEF2C-dependent reporter activity. The results suggest that AKAP13 coordinates Galpha(12) and Rho signaling to an essential transcription program in developing cardiomyocytes.

Mechanical homeostasis is altered in uterine leiomyoma

OBJECTIVE

Uterine leiomyoma produce an extracellular matrix (ECM) that is abnormal in its volume, content, and structure. Alterations in ECM can modify mechanical stress on cells and lead to activation of Rho-dependent signaling and cell growth. Here we sought to determine whether the altered ECM that is produced by leiomyoma was accompanied by an altered state of mechanical homeostasis.

STUDY DESIGN

We measured the mechanical response of paired leiomyoma and myometrial samples and performed immunogold, confocal microscopy, and immunohistochemical analyses.

RESULTS

Leiomyoma were significantly stiffer than matched myometrium. The increased stiffness was accompanied by alteration of the ECM, cell shape, and cytoskeleton in leiomyoma, compared with myometrial samples from the same uterus. Levels of AKAP13, a protein that is known to activate Rho, were increased in leiomyoma compared to myometrium. AKAP13 was associated with cytoskeletal filaments of immortalized leiomyoma cells.

CONCLUSION

Leiomyoma cells are exposed to increased mechanical loading and show structural and biochemical features that are consistent with the activation of solid-state signaling.

Estrogen effects on the expression of Brx in the brain and pituitary of the mouse

A member of the Dbl family of oncoproteins was discovered in breast cancer tissue extracts. This novel protein, designated Brx, contains an estrogen-receptor binding motif and is highly expressed in hormone-responsive breast tissue. Due to its ability to augment ligand-dependent activation of estrogen receptors, we analyzed the expression of Brx in the adult mouse brain and pituitary. Results indicated that Brx was expressed in specific regions of the brain and pituitary. Furthermore, the results indicate that differences exist in both brain and pituitary tissue of male and female mice with greater expression in the female. However, estrogen did not influence Brx expression in ovariectomized mice. The anatomical studies support a role for Brx in its association with the estrogen receptor and that Brx may be involved in neuronal and pituitary function in a sexually dimorphic manner.

Expression of the proto-oncoprotein breast cancer nuclear receptor auxiliary factor (Brx) is altered in eutopic endometrium of women with endometriosis

OBJECTIVE

To evaluate the expression of estrogen receptor alpha (ERalpha), estrogen receptor beta (ERbeta), and breast cancer nuclear receptor auxiliary factor (Brx) in eutopic endometrium of normal women and women with endometriosis.

DESIGN

Prospective observational study.

SETTING

Tertiary care and research center.

PATIENT(S)

Twenty-nine women with endometriosis and 35 healthy ovulatory volunteers of similar ages.

INTERVENTION(S)

Endometrial biopsy.

MAIN OUTCOME MEASURE(S)

Expression of immunohistochemical staining intensity and localization of ERalpha, ERbeta, and Brx proteins in eutopic endometrium during the menstrual cycle.

RESULT(S)

Expression of ERalpha and ERbeta was highest in the proliferative phase and was similar in both groups. Brx expression differed between healthy volunteers and those with endometriosis. During the proliferative phase, immunostaining intensity of Brx was greater in both the glandular and the stromal compartments of biopsies from patients with endometriosis compared to healthy volunteers; nuclear stromal Brx staining was more common in patients with endometriosis.

CONCLUSION(S)

The spatiotemporal expression of Brx was altered in eutopic endometrium of women with endometriosis. These findings suggest a fundamental alteration in the endometrium of women who have endometriosis. The role of Brx in ectopic implantation of endometrium deserves further study.

Association of genetic variants in the Rho guanine nucleotide exchange factor AKAP13 with familial breast cancer

The A-kinase anchor protein 13 (AKAP13, alias BRX and lbc) tethers cAMP-dependent protein kinase to its subcellular environment and catalyses Rho GTPases activity as a guanine nucleotide exchange factor. The crucial role of members of the Rho family of GTPases in carcinogenesis is well established and targeting Rho proteins with antineoplastic compounds has become a major effort in the fight against cancer. Thus, genetic alterations within the candidate cancer susceptibility gene AKAP13 would be expected to provoke a constitutive Rho signalling, thereby facilitating the development of cancer. Here, we analysed the potential impact of four polymorphic non-conservative amino acid exchanges (Arg494Trp, Lys526Gln, Asn1086Asp and Gly2461Ser) in AKAP13 on familial breast cancer. We performed a case-control study using genomic DNA of BRCA1/2 mutation-negative German female index patients from 601 unrelated families, among a subset of 356 high-risk families, and 1053 German female unrelated controls. The newfound Lys526Gln polymorphism revealed a significant association with familial breast cancer (OR = 1.58, 95% CI = 1.07-2.35) and an even stronger association with high-risk familial breast cancer (OR = 1.85, 95% CI = 1.19-2.88). Haplotype analyses were in line with genotype results displaying a similar significance as analyses of individual polymorphisms. Due to the pivotal role of AKAP13 in the Rho GTPases signalling network, this variant might affect the susceptibility to other cancers as well.

Oncogenic pathways implicated in ovarian epithelial cancer

Characterization of intracellular signaling pathways should lead to a better understanding of ovarian epithelial carcinogenesis and provide an opportunity to interfere with signal transduction targets involved in ovarian tumor cell growth, survival, and progression. Challenges toward such an effort are significant because many of these signals are part of cascades within an intricate and likely redundant intracellular signaling network (Fig.1). For instance, a given signal may activate a dual intracellular pathway (ie, MEK1-MAPK and PI3K/Akt required for fibronectin-dependent activation of matrix metalloproteinase 9). A single pathway also may transduce more than one biologic or oncogenic signal (ie, PI3K signaling in epithelial and endothelial cell growth and sprouting of neovessels). Despite these challenges, evidence for therapeutic targeting of signal transduction pathways is accumulating in human cancer. For instance, the EGF-specific tyrosine kinase inhibitor ZD 1839 (Iressa) may have a beneficial therapeutic effect on ovarian epithelial cancer. Therapy of this cancer may include inhibitors of PI kinase (quercetin), ezrin and PIP kinase (genistein). The G protein-coupled family of receptors, including LPA, also is an attractive target to drugs, although their frequent pleiotropic functions may be at times toxic and lack specificity. Because of the lack of notable toxicity, PI3K/Akt pathway inhibitors such as FTIs are a promising targeted therapy of ovarian epithelial cancer. Increasing insight into the oncogenic pathways involved in ovarian epithelial cancer also is helping clinicians to understand better the phenomenon of chemoresistance in this malignancy. Oncogenic activation of gamma-synuclein promotes cell survival and provides resistance to paclitaxel, but such a resistance is partially overcome by an MEK inhibitor that suppresses ERK activity. Ovarian epithelial cancer is a complex group of neoplasms with an overall poor prognosis. Comprehension of this cancer pathobiology suffers because of an incomplete understanding of precursor lesions and the absence of an orthotopic animal model until very recently. It can be predicted with confidence, however, that the discovery of potent inhibitors of signal transduction and the development of discovery tools, such as proteomics and metabolomics, may change the way by which clinicians may now address basic biomedical questions in this insidious and lethal disease.

The proto-oncoprotein Brx activates estrogen receptor beta by a p38 mitogen-activated protein kinase pathway

The estrogen receptors (ERs) are ligand-inducible transcription factors that play key roles in the control of growth and differentiation in reproductive tissues. We showed that the novel Dbl family proto-oncoprotein Brx enhances ligand-dependent activity of ERalpha via a Cdc42-dependent pathway. Brx also significantly enhances ligand-dependent activity of ERbeta. This enhancement is not affected by inhibition of p44/42 mitogen-activated protein kinase (MAPK) activation by PD98059. However, addition of the p38 MAPK inhibitor SB202190 abrogates the enhancement of ERbeta activity by Brx, showing that p38 MAPK activity is required for the enhancement of ERbeta function by Brx. In COS-7 cells, transfection of Brx leads to activation of endogenous p38 MAPK activity. Co-expression of the beta2 isoform of human p38 MAPK and a constitutively active form of the p38 MAPK kinase MKK6 (MKK6-EE) synergistically augments ligand-dependent activity of ERbeta. Our findings suggest that p38 MAPKs may be important regulators of ERbeta activity.

Ht31: the first protein kinase A anchoring protein to integrate protein kinase A and Rho signaling

In an attempt to isolate protein kinase A anchoring proteins (AKAPs) involved in vasopressin-mediated water reabsorbtion, the complete sequence of the human AKAP Ht31 was determined and a partial cDNA of its rat orthologue (Rt31) was cloned. The Ht31 cDNA includes the estrogen receptor cofactor Brx and the RhoA GDP/GTP exchange factor proto-lymphoid blast crisis (Lbc) sequences. The Ht31 gene was assigned to chromosome 15 (region q24-q25). It encodes Ht31 and the smaller splice variants Brx and proto-Lbc. A protein of the predicted size of Ht31 (309 kDa) was detected in human mammary carcinoma and HeLa cells. Anti-Ht31/Rt31 antibodies immunoprecipitated RhoA from primary cultured rat renal inner medullary collecting duct cells, indicating an interaction between the AKAP and RhoA in vivo. These results suggest that Ht31/Rt31 represent a new type of AKAP, containing both an anchoring and a catalytic domain, which appears to be capable of modulating the activity of an interacting partner. Ht31/Rt31 have the potential to integrate Rho and protein kinase A signaling pathways, and thus, are prime candidates to regulate vasopressin-mediated water reabsorbtion.