Immunolocalization and expression of prohibitin, a mitochondrial associated protein within the rat ovaries

Prohibitin modulates periodontium differentiation in mice development

Introduction: Prohibitin (PHB) is an essential scaffold protein that modulates signaling pathways controlling cell survival, metabolism, inflammation, and bone formation. However, its specific role in periodontium development remains less understood. This study aims to elucidate the expression pattern and function of PHB in periodontium development and its involvement in alveolar bone formation. Methods: Immunolocalization of PHB in the periodontium of postnatal (PN) mice were examined. Phb morpholino was micro-injected into the right-side mandible at PN5, corresponding to the position where the alveolar bone process forms in relation to the lower first molar. The micro-injection with a scramble control (PF-127) and the left-side mandibles were used as control groups. Five days post-micro-injection, immunohistochemical analysis and micro-CT evaluation were conducted to assess bone mass and morphological changes. Additionally, expression patterns of signaling molecules were examined following Phb downregulation using 24-h in vitro cultivation of developing dental mesenchyme at E14.5. Results: The immunostaining of PHB showed its localization in the periodontium at PN5, PN8, and PN10. The in vitro cultivation of dental mesenchyme resulted in alterations in Bmps, Runx2, and Wnt signalings after Phb knock-down. At 5 days post-micro-injection, Phb knocking down showed weak immunolocalizations of runt-related transcription factor (RUNX2) and osteocalcin (OCN). However, knocking down Phb led to histological alterations characterized by decreased bone mass and stronger localizations of Ki67 and PERIOSTIN in the periodontium compared 1 to control groups. The micro-CT evaluation showed decreased bone volume and increased PDL space in the Phb knock-down specimens, suggesting its regulatory role in bone formation. Discussion: The region-specific localization of PHB in the margin where alveolar bone forms suggests its involvement in alveolar bone formation and the differentiation of the periodontal ligament. Overall, our findings suggest that Phb plays a modulatory role in alveolar bone formation by harmoniously regulating bone-forming-related signaling molecules during periodontium development.

Characterization of PHB in the gonadal development of the swimming crab Portunus trituberculatus

Prohibitin (PHB) is an evolutionarily conserved multifunctional protein with ubiquitous expression. In this study, we cloned the PHB gene from the testis of the swimming crab Portunus trituberculatus (PtPHB) and analyzed the deduced amino acid sequence. The expression level of phb mRNA in larvae was analyzed using qRT-PCR. The expression level of phb mRNA and PHB protein in different tissues were analyzed using qRT-PCR and Western blot respectively. Enzyme-linked immunosorbent assay analyses of the PHB protein were conducted with the testis and ovaries from P. trituberculatus specimens at different developmental stages. PHB was localized with mitochondria and ubiquitin in the testis and ovaries. The PtPHB gene was found to contain an open reading frame of 825 bp, encoding a predicted peptide with 275 amino acids, sharing between 65.9% and 96.7% similarity with that of other species. The qRT-PCR and Western blot results showed that the phb gene and PHB protein both expressed less in the testis and ovary than in other tissues, and the phb gene presented the lowest expression in the Z1 stage. Furthermore, the phb gene and PHB protein expression were different in the testis and ovaries at different developmental stages. PHB was mainly found to be co-localized with mitochondria and ubiquitin in cytoplasm and acrosome complex during spermatogenesis and in follicular cells during oogenesis. Interestingly, PHB-mitochondria signals and ubiquitin signal were also found in oocytes. These results indicated that PHB might play important roles during spermatogenesis and oogenesis by regulating mitochondrial activities.

Prohibitin confers cytoprotection against ISO-induced hypertrophy in H9c2 cells via attenuation of oxidative stress and modulation of Akt/Gsk-3β signaling

Numerous hypertrophic stimuli, including β-adrenergic agonists such as isoproterenol (ISO), result in generation of reactive oxygen species (ROS) and alteration in the mitochondrial membrane potential (Δψ) leading to oxidative stress. This process is well associated with phosphorylation of thymoma viral proto-oncogene Akt (Ser473) and glycogen synthase kinase-3β (Gsk-3β) (Ser9), with resultant inactivation of Gsk-3β. In the present study, we found that the protective defensive role of prohibitin (PHB) against ISO-induced hypertrophic response in rat H9c2 cells is via attenuation of oxidative stress-dependent signaling pathways. The intracellular levels of mitochondrial membrane potential along with cellular ROS levels and mitochondrial superoxide generation were determined. In order to understand the regulation of Akt/Gsk-3β signaling pathway, we carried out immmunoblotting for key proteins of the pathway such as PTEN, PI3K, phosphorylated, and unphosphorylated forms of Akt, Gsk-3β, and immunofluorescence experiments of p-Gsk-3β. Enforced expression of PHB in ISO-treated H9c2 cells suppressed cellular ROS production with mitochondrial superoxide generation and enhanced the mitochondrial membrane potential resulting in suppression of oxidative stress which likely offered potent cellular protection, led to the availability of more healthy cells, and also, significant constitutive activation of Gsk-3β via inactivation of Akt was observed. Knockdown of PHB expression using PHB siRNA in control H9c2 cells reversed these effects. Overall, our results demonstrate that PHB confers cytoprotection against oxidative stress in ISO-induced hypertrophy and this process is associated with modulation of Akt/Gsk-3β signaling mechanisms as evident from our PHB overexpression and knockdown experiments.

Prohibitin regulates the FSH signaling pathway in rat granulosa cell differentiation

Published results from our laboratory identified prohibitin (PHB), a gene product expressed in granulosa cells (GCs) that progressively increases during follicle maturation. Our current in vitro studies demonstrate that follicle-stimulating hormone (FSH) stimulates Phb expression in rat primary GCs. The FSH-dependent expression of PHB was primarily localized within mitochondria, and positively correlates with the morphological changes in GCs organelles, and synthesis and secretions of estradiol (E2) and progesterone (P4). In order to confirm that PHB plays a regulatory role in rat GC differentiation, endogenous PHB-knockdown studies were carried out in undifferentiated GCs using adenoviral (Ad)-mediated RNA interference methodology. Knockdown of PHB in GCs resulted in the suppression of the key steroidogenic enzymes including steroidogenic acute regulatory protein (StAR), p450 cholesterol side-chain cleavage enzyme (p450scc), 3β-hydroxysteroid dehydrogenase (3β-HSD), and aromatase (Cyp19a1); and decreased E2 and P4 synthesis and secretions in the presence of FSH stimulation. Furthermore, these experimental studies also provided direct evidence that PHB within the mitochondrial fraction in GCs is phosphorylated at residues Y249, T258, and Y259 in response to FSH stimulation. The observed levels of phosphorylation of PHB at Y249, T258, and Y259 were significantly low in GCs in the absence of FSH stimulation. In addition, during GC differentiation FSH-induced expression of phospho-PHB (pPHB) requires the activation of MEK1-ERK1/2 signaling pathway. Taken together, these studies provide new evidence supporting FSH-dependent PHB/pPHB upregulation in GCs is required to sustain the differentiated state of GCs.

Prohibitin( PHB) roles in granulosa cell physiology

Ovarian granulosa cells (GC) play an important role in the growth and development of the follicle in the process known as folliculogenesis. In the present review, we focus on recent developments in prohibitin (PHB) research in relation to GC physiological functions. PHB is a member of a highly conserved eukaryotic protein family containing the repressor of estrogen activity (REA)/stomatin/PHB/flotillin/HflK/C (SPFH) domain (also known as the PHB domain) found in diverse species from prokaryotes to eukaryotes. PHB is ubiquitously expressed in a circulating free form or is present in multiple cellular compartments including mitochondria, nucleus and plasma membrane. In mitochondria, PHB is anchored to the mitochondrial inner membrane and forms complexes with the ATPases associated with proteases having diverse cellular activities. PHB continuously shuttles between the mitochondria, cytosol and nucleus. In the nucleus, PHB interacts with various transcription factors and modulates transcriptional activity directly or through interactions with chromatin remodeling proteins. Many functions have been attributed to the mitochondrial and nuclear PHB complexes such as cellular differentiation, anti-proliferation, morphogenesis and maintenance of the functional integrity of the mitochondria. However, to date, the regulation of PHB expression patterns and GC physiological functions are not completely understood.

Mitochondrial prohibitin and its ubiquitination during crayfish Procambarus clarkii spermiogenesis

Prohibitin (PHB), an evolutionarily conserved mitochondrial membrane protein, is associated with spermatogenesis and sperm quality control in mammals. It is identified as a substrate of ubiquitin and thus may function via a mitochondrial ubiquitin-proteasome pathway. In this study, we examined the localization of PHB during spermiogenesis of the macrura crustacean Procambarus clarkii. We traced phb mRNA's temporal and spatial expression pattern in spermiogenesis, and found its localization highly coherent with acrosome formation and nuclear shaping, two key events during crustacean spermiogenesis. We further detected the associations of PHB with mitochondria and ubiquitin using immunofluorescent staining. PHB was co-localized with mitochondria through spermiogenesis. PHB as well as mitochondria were co-localized with ubiquitin from the late stage of spermiogenesis, and the co-signals reached their peak in the mature sperm. The results raise the hypothesis that PHB is likely to function in nuclear shaping and acrosome formation in the spermiogenesis of P. clarkii. In addition, it might possess a more profound role in mediating mitochondrial ubiquitination. For the first time this study uncovers the role of PHB in the spermiogenesis of macrura crustacean species.

Prohibitins role in cellular survival through Ras-Raf-MEK-ERK pathway

Prohibitins are members of a highly conserved protein family containing the stomatin/prohibitin/flotillin/HflK/C (SPFH) domain (also known as the prohibitin [PHB] domain) found in unicellular eukaryotes, fungi, plants, animals, and humans. Two highly homologous members of prohibitins expressed in eukaryotes are prohibitin (PHB; B-cell receptor associated protein-32, BAP-32) and prohibitin 2/repressor of estrogen receptor activity (PHB2, REA, BAP-37). Both PHB and REA/PHB2 are ubiquitously expressed and are present in multiple cellular compartments including the mitochondria, nucleus, and the plasma membrane. Multiple functions have been attributed to the mitochondrial and nuclear PHB and PHB2/REA including cellular differentiation, anti-proliferation, and morphogenesis. One of the major functions of the prohibitins are in maintaining the functional integrity of the mitochondria and protecting cells from various stresses. In the present review, we focus on the recent research developments indicating that PHB and PHB2/REA are involved in maintaining cellular survival through the Ras-Raf-MEK-Erk pathway. Understanding the molecular mechanisms by which the intracellular signaling pathways utilize prohibitins in governing cellular survival is likely to result in development of therapeutic strategies to overcome various human pathological disorders such as diabetes, obesity, neurological diseases, inflammatory bowel disease, and cancer.

Prohibitin (PHB) inhibits apoptosis in rat granulosa cells (GCs) through the extracellular signal-regulated kinase 1/2 (ERK1/2) and the Bcl family of proteins

Mammalian ovarian follicular development is tightly regulated by crosstalk between cell death and survival signals, which include both endocrine and intra-ovarian regulators. Whether the follicle ultimately ovulates or undergoes atresia is dependent on the expression and actions of factors promoting follicular cell proliferation, differentiation or apoptosis. Prohibitin (PHB) is a highly conserved, ubiquitous protein that is abundantly expressed in granulosa cells (GCs) and associated with GC differentiation and apoptosis. The current study was designed to characterize the regulation of anti-apoptotic and pro-apoptotic factors in undifferentiated rat GCs (gonadotropin independent phase) governed by PHB. Microarray technology was initially employed to identify potential apoptosis-related genes, whose expression levels within GCs were altered by either staurosporine (STS) alone or STS in presence of ectopically over-expressed PHB. Next, immunoblot studies were performed to examine the expression patterns of selective Bcl-2 family members identified by the microarray analysis, which are commonly regulated in the intrinsic-apoptotic pathway. These studies were designed to measure protein levels of Bcl2 family in relation to expression of the acidic isoform (phosphorylated) PHB and the components of MEK-Erk1/2 pathway. These studies indicated that over-expression of PHB in undifferentiated GCs inhibit apoptosis which concomitantly results in an increased level of the anti-apoptotic proteins Bcl2 and Bclxl, reduced release of cytochrome c from mitochondria and inhibition of caspase-3 activity. In contrast, silencing of PHB expression resulted in change of mitochondrial morphology from the regular reticular network to a fragmented form, which enhanced sensitization of these GCs to the induction of apoptosis. Collectively, these studies have provided new insights on the PHB-mediated anti-apoptotic mechanism, which occurs in undifferentiated GCs through a PHB → Mek-Erk1/2 → Bcl/Bcl-xL pathway and may have important clinical implications.

Follicular stage-dependent regulation of apoptosis and steroidogenesis by prohibitin in rat granulosa cells

BACKGROUND

Follicular growth and atresia are tightly regulated processes, which involve the participation of endocrine, autocrine and paracrine factors at the cellular level. Prohibitin (PHB) is a multifunctional intracellular protein playing an important role in the regulation of proliferation, apoptosis and differentiation. Here we examined the expression of PHB and its regulation by FSH in vitro and studied the role of PHB in the regulation of apoptosis and steroidogenesis in response to the apoptosis inducer staurosporine (STS) and to FSH, respectively.

METHODS

Undifferentiated and differentiated granulosa cells were collected from diethylstilbestrol (DES)- and equine chronic gonadotropin (eCG)-primed immature rats, respectively and then cultured with various treatments (FSH, adenovirus infection, STS) according to experimental design. The apoptosis rate, the production of estradiol and progesterone, and the expression of distinct proteins (PHB, caspase-3, phospho- and total Akt) were assessed.

RESULTS

PHB is anti-apoptotic and its action is dependent on the differentiated state of the granulosa cells. Data from gain- and loss-of-function experiments demonstrate that PHB inhibited STS-induced caspase-3 cleavage and apoptosis in undifferentiated granulosa cells, but was ineffective in differentiated cells. In contrast, PHB suppresses FSH-induced steroidogenesis and this response is evident irrespective of the differentiated state of granulosa cells.

CONCLUSION

These findings suggest that PHB regulates granulosa cell apoptosis and steroidogenesis in a follicular stage-dependent manner and that the dysregulation of PHB expression and action may be relevant to ovarian dysfunction.

Characterization of Cherax quadricarinatus prohibitin and its potential role in spermatogenesis

Prohibitin (PHB) proteins have diverse functions, such as cellular signaling, transcriptional control and mitochondrial biogenesis. In this study, we characterized PHB gene and its protein expression in Cherax quadricarinatus. PHB cDNA comprises 1472 nucleotides with an open reading frame of 828bp, which encodes 275 amino acid residues. The highest transcript levels were found during the spermatogonial developmental phase, with the lowest levels detected during the resting phase in the reproductive cycle. Western blot analysis revealed that PHB is an approximately 30kDa protein, and occurs in a number of unexpected isoforms, ranging from 30kDa to greater than 180kDa in the testes of different developmental phases, which may be the ubiquitinated substrates. The strongest immunolabeling signal was found in spermatogonia, with lower levels of staining in secondary spermatocytes, and weak or absent expression in mature sperm. Immunogold electron microscopy results confirmed the localization of PHB in the inner mitochondrial membranes. The results showed that PHB is a substrate protein for spermatogenesis, with a potential reproductive function involving sperm ubiquitination in invertebrates.

Inhibitory roles of prohibitin and chemerin in FSH-induced rat granulosa cell steroidogenesis

Follicular differentiation is a tightly regulated process involving various endocrine, autocrine, and paracrine factors. The biosynthesis of progesterone and estradiol in response to FSH involves the regulation of multiple steroidogenic enzymes, such as p450 cholesterol side-chain cleavage enzyme and aromatase. Here we demonstrated that prohibitin (PHB), a multifunctional protein, inhibits FSH-induced progesterone and estradiol secretion in rat granulosa cells. The mRNA abundances of cyp11a (coding p450 cholesterol side-chain cleavage enzyme) and cyp19 (coding aromatase) were also suppressed by PHB in a time-dependent manner. It is known that a novel adipokine chemerin suppresses FSH-induced steroidogenesis in granulosa cells. Chemerin up-regulates the content of PHB, and PHB knockdown attenuates the suppressive role of chemerin on steroidogenesis. In addition, inhibition of phosphatidylinositol 3-kinase/Akt pathway enhances the suppressive action of PHB, whereas expression of constitutively active Akt attenuates this response. These findings suggest that PHB is a novel negative regulator of FSH-induced steroidogenesis, and its action with chemerin may contribute to the dysregulation of steroidogenesis in the pathogenesis of polycystic ovarian syndrome.

The emerging roles of prohibitins in folliculogenesis

Prohibitins are members of a highly conserved eukaryotic protein family containing the stomatin/prohibitin/flotillin/HflK/C (SPFH) domain (also known as the prohibitin (PHB) domain) found in divergent species from prokaryotes to eukaryotes. Prohibitins are found in unicellular eukaryotes, fungi, plants, animals and humans. Prohibitins are ubiquitously expressed and present in multiple cellular compartments including the mitochondria, nucleus, and the plasma membrane, and shuttles between the mitochondria, cytosol and nucleus. Multiple functions have been attributed to the mitochondrial and nuclear prohibitins, including cellular differentiation, anti-proliferation, and morphogenesis. In the present review, we focus on the recent developments in prohibitins research related to folliculogenesis. Based on current research findings, the data suggest that these molecules play important roles in modulating specific responses of granulose cells to follicle stimulating hormone (FSH) by acting at multiple levels of the FSH signal transduction pathway. Understanding the molecular mechanisms by which the intracellular signaling pathways utilize prohibitins in governing folliculogenesis is likely to result in development of strategies to overcome fertility disorders and suppress ovarian cancer growth.

Prohibitin (PHB) acts as a potent survival factor against ceramide induced apoptosis in rat granulosa cells

AIM

Ceramide is a key factor in inducing germ cell apoptosis by translocating from cumulus cells into the adjacent oocyte and lipid rafts through gap junctions. Therefore studies designed to elucidate the mechanistic pathways in ceramide induced granulosa cell (GC) apoptosis and follicular atresia may potentially lead to the development of novel lipid-based therapeutic strategies that will prevent infertility and premature menopause associated with chemo and/or radiation therapy in female cancer patients. Our previous studies have shown that Prohibitin (PHB) is intimately involved in GCs differentiation, atresia, and luteolysis.

MAIN METHODS

In the present study, we have examined the functional effects of loss-/gain-of-function of PHB using adenoviral technology in delaying apoptosis induced by the physiological ligand ceramide in rat GCs.

KEY FINDINGS

Under these experimental conditions, exogenous ceramide C-8 (50 μM) augmented the expression of mitochondrial PHB and subsequently cause the physical destruction of GC by the release of mitochondrial cytochrome c and activation of caspase-3. In further studies, silencing of PHB expression by adenoviral small interfering RNA (shRNA) sensitized GCs to ceramide C8-induce apoptosis. In contrast, adenovirus (Ad) directed overexpression of PHB in GCs resulted in increased PHB content in mitochondria and delayed the onset of ceramide induced apoptosis in the infected GCs.

SIGNIFICANCE

Taken together, these results provide novel evidences that a critical level of PHB expression within the mitochondria plays a key intra-molecular role in GC fate by mediating the inhibition of apoptosis and may therefore, contribute significantly to ceramide induced follicular atresia.

Rescue of paclitaxel sensitivity by repression of Prohibitin1 in drug-resistant cancer cells

Paclitaxel has emerged as a front line treatment for aggressive malignancies of the breast, lung, and ovary. Successful therapy of cancer is frequently undermined by the development of paclitaxel resistance. There is a growing need to find other therapeutic targets to facilitate treatment of drug-resistant cancers. Using a proteomics approach, elevated levels of Prohibitin1 (PHB1) and GSTpi were found associated with paclitaxel resistance in discrete subcellular fractions of two drug-resistant sublines relative to their sensitive sublines. Immunofluorescence staining and fractionation studies revealed increased levels of PHB1 on the surface of resistant cell lines. Transiently silencing either PHB1 or GSTpi gene expression using siRNA in the paclitaxel-resistant cancer cell sublines partially sensitized these cells toward paclitaxel. Intriguingly, silencing PHB1 but not GSTpi resulted in activation of the intrinsic apoptosis pathway in response to paclitaxel. Similarly, stably silencing either PHB1 or GSTpi significantly improved paclitaxel sensitivity in A549TR cells both in vitro and in vivo. Our results indicate that PHB1 is a mediator of paclitaxel resistance and that this resistance may depend on the cellular localization of the protein. We suggest PHB1 as a potential target for therapeutic strategies for the treatment of drug-resistant tumors.

Prohibitin protects against oxidative stress-induced cell injury in cultured neonatal cardiomyocyte

Oxidative stress is one of the main causes of myocardial injury, which is associated with cardiomyocyte death. Mitochondria play a key role in triggering the necrosis and apoptosis pathway of cardiomyocytes under oxidative stress. Although prohibitin (PHB) has been acknowledged as a mitochondrial chaperone, its functions in cardiomyocytes are poorly characterized. The present research was designed to investigate the cardioprotective role of PHB in mitochondria. Oxidative stress can increase the PHB content in mitochondria in a time-dependent manner. Overexpression of PHB in cultured cardiomyocytes by transfection of recombinant adenovirus vector containing PHB sense cDNA resulted in an increase of PHB in mitochondria. Compared with the non-transfection cardiomyocytes, PHB overexpression could protect the mitochondria from oxidative stress-induced injury. The mitochondria-mediated apoptosis pathway was consistently suppressed in PHB-overexpressed cardiomyocytes after hydrogen peroxide (H(2)O(2)) treatment, including a reduced change in mitochondrial membrane permeability transition and an inhibited release of cytochrome c from mitochondria to cytoplasma. As a result, the oxidative stress-induced cardiomyocyte apoptosis was suppressed. These data indicated that PHB protected the cardiomyocytes from oxidative stress-induced damage, and that increasing PHB content in mitochondria constituted a new therapeutic target for myocardium injury.

Prohibitin silencing reverses stabilization of mitochondrial integrity and chemoresistance in ovarian cancer cells by increasing their sensitivity to apoptosis

Current approaches to the treatment of ovarian cancer are limited because of the development of resistance to chemotherapy. Prohibitin (Phb1) is a possible candidate protein that contributes to development of drug resistance, which could be targeted in neoplastic cells. Phb1 is a highly conserved protein that is associated with a block in the G0/G1 phase of the cell cycle and also with cell survival. Our study was designed to determine the role of Phb1 in regulating cellular growth and apoptosis in ovarian cancer cells. Our results showed that Phb1 content is differentially overexpressed in papillary serous ovarian carcinoma and endometrioid ovarian adenocarcinoma when compared to normal ovarian epithelium and was inversely related to Ki67 expression. Immunofluorescence microscopy and Western analyses revealed that Phb1 is primarily associated with the mitochondria in ovarian cancer cells. Over-expression of Phb1 by adenoviral Phb1 infection resulted in an increase in the percentage of ovarian cancer cells accumulating at G0/G1 phase of the cell cycle. Treatment of ovarian cancer cells with staurosporine (STS) induced apoptosis in a time-dependent manner. Phb1 over-expression induced cellular resistance to STS via the intrinsic apoptotic pathway. In contrast, silencing of Phb1 expression by adenoviral small interfering RNA (siRNA) sensitized ovarian cancer cells to STS-induce apoptosis. Taken together, these results suggest that Phb1 induces block at G0/G1 phase of the cell cycle and promotes survival of cancer cells. Furthermore, silencing of the Phb1 gene expression may prove to be a valuable therapeutic approach for chemoresistant ovarian cancer by increasing sensitivity of cancer cells to apoptosis.

Plasmodium yoelii 17XL infection up-regulates RANTES, CCR1, CCR3 and CCR5 expression, and induces ultrastructural changes in the cerebellum

BACKGROUND

Malaria afflicts 300-500 million people causing over 1 million deaths globally per year. The immunopathogenesis of malaria is mediated partly by co mplex cellular and immunomodulator interactions involving co-regulators such as cytokines and adhesion molecules. However, the role of chemokines and their receptors in malaria immunopathology remains unclear. RANTES (Regulated on Activation Normal T-Cell Expressed and Secreted) is a chemokine involved in the generation of inflammatory infiltrates. Recent studies indicate that the degradation of cell-cell junctions, blood-brain barrier dysfunction, recruitment of leukocytes and Plasmodium-infected erythrocytes into and occlusion of microvessels relevant to malaria pathogenesis are associated with RANTES expression. Additionally, activated lymphocytes, platelets and endothelial cells release large quantities of RANTES, thus suggesting a unique role for RANTES in the generation and maintenance of the malaria-induced inflammatory response. The hypothesis of this study is that RANTES and its corresponding receptors (CCR1, CCR3 and CCR5) modulate malaria immunopathogenesis. A murine malaria model was utilized to evaluate the role of this chemokine and its receptors in malaria.

METHODS

The alterations in immunomodulator gene expression in brains of Plasmodium yoelii 17XL-infected mice was analysed using cDNA microarray screening, followed by a temporal comparison of mRNA and protein expression of RANTES and its corresponding receptors by qRT-PCR and Western blot analysis, respectively. Plasma RANTES levels was determined by ELISA and ultrastructural studies of brain sections from infected and uninfected mice was conducted.

RESULTS

RANTES (p < 0.002), CCR1 (p < 0.036), CCR3 (p < 0.033), and CCR5 (p < 0.026) mRNA were significantly upregulated at peak parasitaemia and remained high thereafter in the experimental mouse model. RANTES protein in the brain of infected mice was upregulated (p < 0.034) compared with controls. RANTES plasma levels were significantly upregulated; two to three fold in infected mice compared with controls (p < 0.026). Some distal microvascular endothelium in infected cerebellum appeared degraded, but remained intact in controls.

CONCLUSION

The upregulation of RANTES, CCR1, CCR3, and CCR5 mRNA, and RANTES protein mediate inflammation and cellular degradation in the cerebellum during P. yoelii 17XL malaria.

Apoptosis in the ovary: molecular mechanisms

Cell death was first described in rabbit ovaries (Graaffian follicles), the phenomenon being called 'chromatolysis' rather than apoptosis. In humans, the ovarian endowment of primordial follicles is established during fetal life. Apoptotic cell death depletes this endowment by at least two-thirds before birth, executed with the help of several players and pathways conserved from worms to humans. To date, apoptosis has been reported to be involved in oogenesis, folliculogenesis, oocyte loss/selection and atresia. Several pro-survival and pro-apoptotic molecules are involved in ovarian apoptosis with the delicate balance between them being the determinant for the final destiny of the follicular cells. This review critically analyses the current knowledge about the biological roles of these molecules and their relevance to the dynamics of follicle development. It also presents the existing literature and assesses the gaps in our knowledge.

Identification of genes expressed in primate primordial oocytes

BACKGROUND

The factors involved in oocyte survival and transition from quiescence to the growing phenotype remain unknown. Herein we report genes that are differentially expressed in the primordial oocyte revealed by DNA arrays.

METHODS

Primordial oocytes were captured selectively in rhesus monkey ovary sections using laser capture microdissection. The RNA was extracted and amplified in two rounds by T7-based linear RNA amplification, fluorescence labelled and then hybridized to human cDNA arrays containing 7680 elements. RNA from human placenta served as a reference sample.

RESULTS

Ninety-five genes were found to be consistently expressed at a higher level in primordial oocytes. Expression of several of these genes in the oocyte has been reported before, e.g. deleted in azoospermia (DAZ), prohibitin and transglutaminase 2. Oocyte expression of several novel transcripts revealed on array hybridization, such as gene 33, ubiquitin-conjugating enzyme E2A, G1 to S phase transition 1, growth arrest and DNA damage-inducible (GADD), and dendritic cell-derived ubiquitin-like protein (DC-UbP) was confirmed by in situ hybridization. Some array-identified gene products [integrin beta3, alpha-tubulin, regulatory telomere elongation protein (RAP1) and cellular repressor of EIA-stimulated genes (CREG protein)] were detected in human oocytes by immunofluorescence. Bioinformatic analysis of the oocyte-enriched transcripts reveals a functional profile summarized as follows: cell cycle (14%); transporter (13%); signal transduction (10%); cytoskeletal (7%); transcription factor (5%); immune response (5%); apoptosis-related (5%); RNA processing (5%); and the remainder of miscellaneous categories.

CONCLUSIONS

These observations may contribute to the elucidation of molecular pathways involved in oocyte survival and maturation.

Proteasomal Interference Prevents Zona Pellucida Penetration and Fertilization in Mammals1

The ubiquitin-proteasome pathway has been implicated in the penetration of ascidian vitelline envelope by the fertilizing spermatozoon (Sawada et al., Proc Natl Acad Sci U S A 2002; 99:1223-1228). The present study provides experimental evidence demonstrating proteasome involvement in the penetration of mammalian zona pellucida (ZP). Using porcine in vitro fertilization as a model, penetration of ZP was completely inhibited by specific proteasomal inhibitors MG-132 and lactacystin. Three commercial rabbit sera recognizing 20S proteasomal core subunits beta-1i, beta-2i, alpha-6, and beta-5 completely blocked fertilization at a very low concentration (i.e., diluted 1/2000 to 1/8000 in fertilization medium). Neither proteasome inhibitors nor antibodies had any effects on sperm-ZP binding and acrosome exocytosis in zona-enclosed oocytes or on fertilization rates in zona-free oocytes, which were highly polyspermic. Consistent with a possible role of ubiquitin-proteasome pathway in ZP penetration, ubiquitin and various alpha and beta type proteasomal subunits were detected in boar sperm acrosome by specific antibodies, immunoprecipitated and microsequenced by MALDI-TOF from boar sperm extracts. Antiubiquitin-immunoreactive substrates were detected on the outer face of ZP by epifluorescence microscopy. This study therefore provides strong evidence implicating the ubiquitin-proteasome pathway in mammalian fertilization and zona penetration. This finding opens a new line of acrosome/ZP research because further studies of the sperm acrosomal proteasome can provide new tools for the management of polyspermia during in vitro fertilization and identify new targets for contraceptive development.

Androgens target prohibitin to regulate proliferation of prostate cancer cells

Proteins involved in the growth response of prostate cancer cells to androgen were investigated by comparing the proteomes of LNCaP cells treated with vehicle or androgen. Whole-cell lysates were separated by two-dimensional PAGE, and HPLC-MS/MS was used to identify androgen-regulated proteins. Prohibitin, a protein with cell-cycle regulatory activity, was shown to be downregulated by 50% following androgen stimulation. Western blot and reverse transcription-PCR experiments confirmed the result and showed that regulation occurs at the level of transcription. To determine the importance of prohibitin in androgen-stimulated growth, we used transient transfection to overexpress the protein and RNA interference to knock down the protein. Subsequent FACS analysis showed that cells with reduced levels of prohibitin showed a slight but reproducible increase in the percentage of population in cell cycle, while cells with increased prohibitin levels showed a clear reduction in the percentage entering cell cycle, following dihydrotestosterone stimulation, when compared to untransfected controls. Confocal microscopy showed localization of prohibitin in the nucleus as well as the mitochondria of LNCaP cells. It therefore seems that the regulation of prohibitin is a vital part of the cellular growth response to androgen stimulation in LNCaPs and prohibitin may have a nuclear regulatory role in cell-cycle progression.

Regulation of Prohibitin Expression During Follicular Development and Atresia in the Mammalian Ovary1

Prohibitin is a ubiquitous and highly conserved protein implicated as an important regulator in cell survival. Prohibitin content is inversely associated with cell proliferation, but it increases during granulosa cell differentiation as well as in earlier events of apoptosis in a temperature-sensitive granulosa cell line. In the present study, we have characterized the spatial expression patterns for prohibitin using established in vivo models for the induction of follicular development and atresia in the mammalian ovary. Comparative Western blot analyses of granulosa cell lysates from control ovaries and from ovaries primed with eCG or treated with eCG plus anti-eCG (gonadotropin withdrawal) were conducted. Prohibitin was immunolocalized in rat ovarian sections probed with antibodies against either proliferating cell nuclear antigen (PCNA) or cholesterol side-chain cleavage cytochrome P450 (P450(scc)) or in terminal deoxynucleotidyl transferase-mediated dUTP nick end labeled sections. Additionally, porcine oocytes, zygotes, and blastocyts were also immunolocalized with prohibitin antibody. Immunolocalization revealed the presence of prohibitin in granulosa cells, theca-interstitial cells, and the oocyte. The results indicate that prohibitin protein expression in the gonadotropin-treated cells was upregulated. Immunoreactivity of prohibitin was inversely related to PCNA expression during follicular maturation and colocalized with P450(scc). Prohibitin appeared to be translocated from the cytoplasm to the nucleus in atretic follicles, germinal vesicle-stage oocytes, zygotes, and blastocysts. These results suggest that prohibitin has several functional regulatory roles in granulosa and theca-interstitial cells and in the ovum during follicular maturation and atresia. It is likely that prohibitin may play an important role in determining the fate of these cells and eventual follicular destiny.

Trypanosome apoptotic factor mediates apoptosis in human brain vascular endothelial cells

Human African trypanosomiasis (HAT, sleeping sickness) is a devastating disease caused by infection with Trypanosoma brucei ssp. These hemoflagellates invade the central nervous system (CNS) and induce meningo-encephalitis, neuronal demyelination, blood-brain-barrier (BBB) dysfunction, peri-vascular infiltration, astrocytosis and apoptosis. The molecular basis of these manifestations is unclear. We previously reported T. brucei-induced apoptosis in cerebella and brain-stem nuclei in mice at peak parasitemia. Here, we identify and characterize a trypanosome apoptotic factor (TAF) expressed by T. brucei that mediates apoptosis in mouse-brain and human-brain vascular endothelial cells (HBVEC). Molecular, biochemical and apoptotic assays, coupled with surface enhanced laser desorption ionization (SELDI), and protein database analyses were utilized to show that TAF is a soluble, non-serum, parasite-derived, heat-labile protein that causes DNA laddering and apoptosis in HBVEC. Protein-chip assay analysis of the SELDI spectrum of infected mouse serum and procyclic culture supernatants revealed a single major peak at 8652.7 Da. Further database analysis indicated that the TAF may be a procyclin or procyclin derivative. A synthetic 27 mer peptide (ProEP2-1), corresponding to a region common to EP procyclins (EP2-1), induced apoptosis in HBVEC and in cerebella of mice similar to that induced in T. brucei-infected mice. Western blot analysis utilizing an anti-procyclin monoclonal antibody (mAb) revealed that TAF is present in infected but not uninfected brain tissue lysates. Furthermore, this mAb blocked T. brucei- and ProEP2-1-induced apoptosis in HBVEC in vitro. We conclude that T. brucei TAF or its derivative(s) play a major role in the apoptosis associated with HAT pathology.

Chemoresistance in human ovarian cancer: the role of apoptotic regulators

Ovarian cancer is among the most lethal of all malignancies in women. While chemotherapy is the preferred treatment modality, chemoresistance severely limits treatment success. Recent evidence suggests that deregulation of key pro- and anti-apoptotic pathways is a key factor in the onset and maintenance of chemoresistance. Furthermore, the discovery of novel interactions between these pathways suggests that chemoresistance may be multi-factorial. Ultimately, the decision of the cancer cell to live or die in response to a chemotherapeutic agent is a consequence of the overall apoptotic capacity of that cell. In this review, we discuss the biochemical pathways believed to promote cell survival and how they modulate chemosensitivity. We then conclude with some new research directions by which the fundamental mechanisms of chemoresistance can be elucidated.

Ubiquitination of prohibitin in mammalian sperm mitochondria: possible roles in the regulation of mitochondrial inheritance and sperm quality control

Ubiquitination of the sperm mitochondria during spermatogenesis has been implicated in the targeted degradation of paternal mitochondria after fertilization, a mechanism proposed to promote the predominantly maternal inheritance of mitochondrial DNA in humans and animals. The identity of ubiquitinated substrates in the sperm mitochondria is not known. In the present study, we show that prohibitin, a highly conserved, 30- to 32-kDa mitochondrial membrane protein, occurs in a number of unexpected isoforms, ranging from 64 to greater than 185 kDa in the mammalian sperm mitochondria, which are the ubiquitinated substrates. These bands bind antiubiquitin antibodies, displaying a pattern consistent with polyubiquitinated "ladders." Immunoprecipitation of sperm extracts with antiprohibitin antibodies followed by probing of the resultant immunocomplexes with antiubiquitin yields a banding pattern identical to that observed by antiprohibitin Western blot analysis. In fact, the presumably nonubiquitinated 30-kDa prohibitin band shows no antiubiquitin immunoreactivity. We demonstrate that ubiquitination of prohibitin occurs in testicular spermatids and spermatozoa. Ubiquitinated prohibitin molecules also accumulate in the defective fractions of ejaculated spermatozoa, which are thought to undergo surface ubiquitination during epididymal passage. In such sperm fractions, ubiquitin also coprecipitates with tubulin and microtubule-associated proteins, presumably contributed by the axonemes of defective, ubiquitinated spermatozoa. The results of the present study suggest that prohibitin is one of the ubiquitinated substrates that makes the sperm mitochondria recognizable by the egg's ubiquitin-proteasome dependent proteolytic machinery after fertilization and most likely facilitates the marking of defective spermatozoa in the epididymis for degradation.

Gonadotropin-releasing hormone-agonist inhibits synthesis of nitric oxide and steroidogenesis by luteal cells in the pregnant rat

We have demonstrated that continuous administration of a gonadotropin-releasing hormone agonist (GnRH-Ag) in vivo suppressed progesterone production and induced apoptosis in the corpus luteum (CL) of the pregnant rat. To investigate the mechanism(s) by which progesterone secretion is suppressed and apoptosis is induced in the luteal cells, we studied nitric oxide (NO) as a messenger molecule for GnRH action. Rats were treated individually on Day 8 of pregnancy with 5 microg/day of GnRH-Ag for 4, 8, and 24 h. GnRH-Ag decreased the production of progesterone and pregnenolone 8 and 24 h after the administration. Corresponding with the reduction in these steroid hormones, luteal NO concentrations decreased at 8 and 24 h. Western blotting and immunohistochemical studies of endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS), and neuronal nitric oxide synthase (nNOS) in the CL demonstrated that administration of GnRH-Ag was associated with a marked decrease in eNOS and iNOS compared with sham controls at 4 and 8 h, but nNOS did not change throughout the experimental period. We demonstrated, for the first time, the presence of nNOS protein in the CL of the pregnant rat. To determine if this suppressive action of GnRH-Ag is directly on the CL, luteal cells were treated with GnRH-Ag for 4, 8, 12, and 24 h in vitro. Progesterone and NO concentrations in the media decreased at 8 and 12 h after the treatment and recovered at 24 h. Western blots revealed that eNOS and iNOS decreased in luteal cells treated with GnRH-Ag compared with controls at 4 and 8 h. These results demonstrate that suppression of luteal NO synthesis by GnRH-Ag is direct and leads to a decrease in the luteal production and release of progesterone and pregnenolone and thus suggest that GnRH could induce luteolysis in pregnant rats via NO.

Gonadotropin-releasing hormone attenuates pregnancy-associated thymic involution and modulates the expression of antiproliferative gene product prohibitin

Thymic involution during pregnancy is believed to be a critical adaptive mechanism for regulation and control of the maternal immune system. These regulatory feedback mechanisms are important for the survival of the semiallogeneic fetus. In the present study, we examined the effects of GnRH on pregnancy-induced thymic involution by characterizing the expression patterns of prohibitin (PHB), an antiproliferative gene product, GnRH, and GnRH receptor (GnRH-R) proteins in the rat thymus and in mature splenic lymphocytes. GnRH agonist infusions in pregnant rats markedly attenuated pregnancy-induced thymic involution resulting in significant increases in thymic weight and thymocyte numbers. In addition, histological examination of the thymus revealed increase in cortical cellularity. Western blot analyses revealed a significant increase of total PHB protein content in thymi during pregnancy. Furthermore, distinct changes in PHB isoform expression were observed in the pregnant involuting thymi with greater expression of the basic PHB isoform. Basic isoform expression decreased in pregnant rats and was comparable with nonpregnant rat thymi upon GnRH agonist treatment. PHB is mainly expressed in mature cells of the thymic medulla, where it strongly colocalized with GnRH. We have observed GnRH-R immunoreactivity mainly in thymic medulla. Furthermore, as assessed by immunofluorescence double labeling with proliferating cell nuclear antigen, PHB was preferentially expressed in nonproliferating thymocytes. In this study, we demonstrated that GnRH, GnRH-R, and PHB show characteristic polarized expression in thymocytes. In addition, GnRH and PHB were coexpressed in mature splenic T cells. Our results suggest that PHB and GnRH are involved in thymic growth and may be important for maturation of T lymphocytes.

Prohibitin co-localizes with Rb in the nucleus and recruits N-CoR and HDAC1 for transcriptional repression

The potential tumor suppressor protein prohibitin can prevent cell proliferation and this required its binding to the Rb protein. Prohibitin could repress the transcriptional activity of E2F family members and this required a part of the marked box region of E2F. The sub-cellular localization of prohibitin has been variously attributed to the mitochondria as well as the inner cell membrane. Here we show that a subset of prohibitin molecules are present in the nucleus where it co-localizes with the Rb protein. Deletion of a putative amino-terminal membrane-docking domain of prohibitin had no effect on its ability to suppress cell proliferation or inhibit E2F activity. Our experiments show that a 53 amino-acid stretch of E2F1 is sufficient for being targeted by prohibitin; fusion of this region to GAL4-VP16 construct could make it susceptible to prohibitin-mediated, but not Rb-mediated repression. Prohibitin, like Rb, could repress transcription from SV40 and major late promoters when recruited directly to DNA. Prohibitin mediated transcriptional repression required histone-deacetylase activity, but unlike Rb, additional co-repressors like N-CoR are also involved. Repression by prohibitin correlates with histone deacetylation on promoters and this was reversed by IgM stimulation of cells; IgM did not affect Rb-mediated repression or deacetylation of the promoters. Prohibitin thus appears to repress E2F-mediated transcription utilizing different molecular mediators and facilitate channeling of specific signaling pathways to the cell cycle machinery.

Characterization of prohibitin in a newly established rat ovarian granulosa cell line

Prohibitin is an evolutionary conserved protein that is associated with cellular differentiation, atresia, and luteolysis in the rat ovary. However, the specific cellular location and function of prohibitin in ovarian cells has not been clearly elucidated. To characterize the expression of prohibitin during cell proliferation, differentiation, and cell death, we have successfully established a temperature-sensitive granulosa cell line, designated RGA-1. At a permissive temperature of 33 C, RGA-1 cells proliferate, but revert to a differentiated phenotype at a nonpermissive temperature of 39 C. Significant inductions of prohibitin mRNA and protein expression were observed in the differentiated phenotype when compared with proliferating cells. Differentiated RGA-1 cells were found to express inhibin alpha- and beta-transcripts, as well as steroidogenic acute regulatory protein and peripheral-type benzodiazepine receptor proteins in a manner reminiscent of steroidogenic functional responses observed in primary differentiated granulosa cells. Prohibitin expression correlated well with the expression of these steroidogenic proteins. At 39 C, RGA-1 cells also displayed increases in p53 protein levels, indicative of growth arrest in the nonproliferating cells. Confocal and electron microscopic examinations revealed increased prohibitin localization to the mitochondria at 39 C, along with changes in mitochondrial size and shape. These changes were accompanied by marked reductions in cytochrome c oxidase subunit II levels and in unit mitochondrial transmembrane potential. In addition, cell fractionation studies demonstrated that the prohibitin protein was mainly localized to the mitochondrial membrane. Collectively, these findings suggest a role for prohibitin in mitochondrial structure and function during growth and differentiation in ovarian granulosa cells. Prohibitin expression may also be indicative of mitochondrial destabilization during apoptosis-related events.