14-3-3 sigma increases the transcriptional activity of the androgen receptor in the absence of androgens

14-3-3ζ regulates adipogenesis by modulating chromatin accessibility during the early stages of adipocyte differentiation

We previously established the scaffold protein 14-3-3ζ as a critical regulator of adipogenesis and adiposity, but the temporal specificity of its action during adipocyte differentiation remains unclear. To decipher if 14-3-3ζ exerts its regulatory functions on mature adipocytes or on adipose precursor cells (APCs), we generated Adipoq14-3-3ζKO and Pdgfra14-3-3ζKO mouse models. Our findings revealed a pivotal role for 14-3-3ζ in APC differentiation in a sex-dependent manner, whereby male and female Pdgfra14-3-3ζKO mice display impaired or potentiated weight gain, respectively, as well as fat mass. To better understand how 14-3-3ζ regulates the adipogenic transcriptional program in APCs, CRISPR-Cas9 was used to generate TAP-tagged 14-3-3ζ-expressing 3T3-L1 preadipocytes. Using these cells, we examined if the 14-3-3ζ nuclear interactome is enriched with adipogenic regulators during differentiation. Regulators of chromatin remodeling, such as DNMT1 and HDAC1, were enriched in the nuclear interactome of 14-3-3ζ, and their activities were impacted upon 14-3-3ζ depletion. The interactions between 14-3-3ζ and chromatin-modifying enzymes suggested that 14-3-3ζ may control chromatin remodeling during adipogenesis, and this was confirmed by ATAC-seq, which revealed that 14-3-3ζ depletion impacted the accessibility of up to 1,244 chromatin regions corresponding in part to adipogenic genes, promoters, and enhancers during the initial stages of adipogenesis. Moreover, 14-3-3ζ-dependent chromatin accessibility was found to directly correlate with the expression of key adipogenic genes. Altogether, our study establishes 14-3-3ζ as a crucial epigenetic regulator of adipogenesis and highlights the usefulness of deciphering the nuclear 14-3-3ζ interactome to identify novel pro-adipogenic factors and pathways.

Molecular basis and dual ligand regulation of tetrameric Estrogen Receptor α/14-3-3ζ protein complex

Therapeutic strategies targeting Nuclear Receptors (NRs) beyond their endogenous ligand binding pocket have gained significant scientific interest, driven by a need to circumvent problems associated with drug resistance and pharmacological profile. The hub protein 14-3-3 is an endogenous regulator of various NRs, providing a novel entry point for small molecule modulation of NR activity. Exemplified, 14-3-3 binding to the C-terminal F-domain of the Estrogen Receptor alpha (ERα), and small molecule stabilization of the ERα/14-3-3ζ protein complex by the natural product Fusicoccin A (FC-A), was demonstrated to downregulate ERα-mediated breast cancer proliferation. This presents a novel drug discovery approach to target ERα, however, structural and mechanistic insights into ERα/14-3-3 complex formation are lacking. Here, we provide an in-depth molecular understanding of the ERα/14-3-3ζ complex by isolating 14-3-3ζ in complex with an ERα protein construct comprising its Ligand Binding Domain (LBD) and phosphorylated F-domain. Bacterial co-expression and co-purification of the ERα/14-3-3ζ complex, followed by extensive biophysical and structural characterization, revealed a tetrameric complex between the ERα homodimer and the 14-3-3ζ homodimer. 14-3-3ζ binding to ERα, and ERα/14-3-3ζ complex stabilization by FC-A, appeared to be orthogonal to ERα endogenous agonist (E2) binding, E2-induced conformational changes, and cofactor recruitment. Similarly, the ERα antagonist 4-hydroxytamoxifen inhibited cofactor recruitment to the ERα LBD while ERα was bound to 14-3-3ζ. Furthermore, stabilization of the ERα/14-3-3ζ protein complex by FC-A was not influenced by the disease-associated and 4-hydroxytamoxifen resistant ERα-Y537S mutant. Together, these molecular and mechanistic insights provide direction for targeting ERα via the ERα/14-3-3 complex as an alternative drug discovery approach.

In Silico Studies on GCP-Lys-OMe as a Potential 14-3-3σ Homodimer Stabilizer

14-3-3 sigma is a vital negative cell cycle regulator. Its expression is consistently downregulated in many types of cancer through gene promoter hypermethylation or proteasomal degradation. 14-3-3 sigma needs to form a homodimer to be functional, while dimers are less prone to degradation than monomers. This suggests that a homodimer stabilizer may increase the tumor suppressive activities of 14-3-3 sigma. However, no known homodimer stabilizer of 14-3-3 sigma has been reported to date. Therefore, this study attempts to test the potential capability of GCP-Lys-OMe (previously reported to bind at the dimer interface of 14-3-3 zeta isoform), to bind and stabilize the 14-3-3 sigma homodimer. In silico docking of GCP-Lys-OMe on 14-3-3 sigma showed more favorable interaction energy (−9.63 kcal/mole) to the dimer interface than 14-3-3 zeta (−7.73 kcal/mole). Subsequent 100 ns molecular dynamics simulation of the GCP-Lys-OMe/14-3-3 sigma complex revealed a highly stable interaction with an average root-mean-square deviation of 0.39 nm (protein backbone) and 0.77 nm (ligand atoms). More contacts between residues at the homodimer interface and a smaller coverage of conformational space of protein atoms were detected for the bound form than for the apo form. These results suggest that GCP-Lys-OMe is a potential homodimer stabilizer of 14-3-3 sigma.

Quantitative proteomic analysis of chicken serum reveals key proteins affecting follicle development during reproductive phase transitions

Avian reproductive behavior is regulated through the neuroendocrine system. The transition from laying to brooding is strictly controlled by the hypothalamus-pituitary-gonadal (HPG) axis. Cross talk on the HPG axis relies on the circulatory system, where the dynamics of serum proteins can be observed during different reproductive phases. Some canonical hormones, such as prolactin and luteinizing hormone, play important roles in the transition through reproductive phases. However, little is known at the whole-proteome level. To discover novel serum proteins, we employed isobaric tags for relative and absolute quantification to assay the serum proteome during different reproductive phases in chicken. We identified a total of 1,235 proteins from chicken serum; 239 of these proteins showed differential expression between the laying and brooding stages, including a low concentration of steroid metabolism-related proteins and a high concentration of calcium signaling-related proteins (fold change ≥1.5 or ≤0.66; P < 0.05). Pathway analysis and protein–protein interaction networks predicated the difference in follicle development between the brooding stage and laying stages and were related to the 14-3-3 protein family, which is associated with oocyte meiosis and maturation. Together, these results provided a proteomics foundation for investigating the dynamic changes taking place in the circulatory system during reproductive phase transition, and also uncovered new insights regarding follicle development that underlie the avian reproductive cycle.

miR-31-5p Regulates 14-3-3 ɛ to Inhibit Prostate Cancer 22RV1 Cell Survival and Proliferation via PI3K/AKT/Bcl-2 Signaling Pathway

Introduction

Prostate cancer (PCa) is one of the most common malignancies, and almost all patients with advanced PCa will develop castration-resistant prostate cancer (CRPC) after receiving endocrine therapy. Effective treatment for patients with CRPC has not been established. Novel approaches are needed to identify therapeutic targets for CRPC.

Purpose

Recent research studies have found that members of the 14-3-3 family play an important role in the development and progression of PCa. Previous results have shown that 14-3-3 ɛ is significantly upregulated in several cancers. This study aimed to identify novel miRNAs that regulate 14-3-3 ɛ expression and therapeutic targets for CRPC.

Methods

In this study, we used computation and experimental approaches for the prediction and verification of the miRNAs targeting 14-3-3 ɛ, and investigated the potential roles of 14-3-3 ɛ in the survival and proliferation of 22RV1 cells.

Results

We confirm that mir-31-5p is downregulated in 22RV1 cells and acts as a tumor suppressor by regulating 14-3-3 ɛ. Ectopic expression of miR-31-5p or 14-3-3 ɛ interference significantly inhibits cell proliferation, invasion, and migration in 22RV1 cells, as well as promotes cell apoptosis via the PI3K/AKT/Bcl-2 signaling pathway. Moreover, 14-3-3 ɛ is required for the miR-31-5p-mediated upregulation of the PI3K/AKT/Bcl-2 signaling pathway.

Conclusion

Our findings provide information on the underlying mechanisms of miR-31-5p/14-3-3 ɛ in 22RV1 cell proliferation and apoptosis through the PI3K/AKT/Bcl-2 signaling pathway. These results suggest that miR-31-5p and 14-3-3 ɛ may potentially be utilized as novel prognostic markers and therapeutic targets for PCa treatment.

An androgen-independent mechanism underlying the androgenic effects of 3-methylcholanthrene, a potent aryl hydrocarbon receptor agonist

Aryl hydrocarbon receptor (AhR) and androgen receptor (AR) are ligand-activated transcription factors with profound cross-talk between their signal transduction pathways. Previous studies have shown that AhR agonists activate the transcription of AR-regulated genes in an androgen-independent manner; however, the underlying mechanism remains unclear. To decipher this mechanism, we evaluated the effects of 3-methylcholanthrene (3MC), a potent AhR agonist, on the transcription of AR-regulated genes in three AR-expressing cell lines. 3MC induced the expression of not only three representative AR-regulated chromosomal genes but also the exogenous AR-responsive luciferase reporter gene. No significant difference in the 3MC-induced luciferase activity was detected in the presence of SKF-525A, a non-specific inhibitor of CYP enzymes. The androgenic effects of 3MC were diminished by AhR and AR knockdown. Following 3MC treatment, the amount of nuclear AhR and AR increased synchronously. Co-immunoprecipitation revealed that AhR and AR formed a complex in the nucleus of cells treated with 3MC. AR was recruited to the proximal promoter and distal enhancer regions of the PSA gene upon the addition of 3MC. We propose that AhR activated by 3MC forms a complex with unliganded AR which translocates from the cytoplasm to the nucleus. Nuclear AR now binds the transcriptional regulatory region of AR-regulated genes and activates the transcription.

Drosha-independent miR-6778-5p strengthens gastric cancer stem cell stemness via regulation of cytosolic one-carbon folate metabolism

Drosha-dependent canonical microRNAs (miRNAs) play a crucial role in the biological functions and development of cancer. However, the effects of Drosha-independent non-canonical miRNAs remain poorly understood. In our previous work, we found a set of aberrant miRNAs, including some upregulated miRNAs, called Drosha-independent noncanonical miRNAs, in Drosha-knockdown gastric cancer (GC) cells. Surprisingly, Drosha-silenced GC cells still retained strong malignant properties (e.g., proliferation ability and cancer stem cell (CSC) characteristics), indicating that aberrantly upregulated non-canonical miRNAs may play an important role in the maintenance of the malignant properties in GC cells that express low Drosha levels. Here, we report that miR-6778-5p, a noncanonical miRNA, acts as a crucial regulator for maintenance of CSC stemness in Drosha-silenced GC cells. MiR-6778-5p belongs to the 5'-tail mirtron type of non-canonical miRNAs and is transcript splice-derived from intron 5 of SHMT1 (coding cytoplasmic serine hydroxymethyltransferase). It positively regulates expression of its host gene, SHMT1, via targeting YWHAE in Drosha-knockdown GC cells. Similar to its family member SHMT2, SHMT1 plays a crucial role in folate-dependent serine/glycine inter-conversion in one-carbon metabolism. In Drosha wild type GC cells, SHMT2 mediates a mitochondrial-carbon metabolic pathway, which is a major pathway of one-carbon metabolism in normal cells and most cancer cells. However, in Drosha-silenced or Drosha low-expressing GC cells, miR-6778-5p positively regulates SHMT1, instead of SHMT2, thus mediating a compensatory activation of cytoplasmic carbon metabolism that plays an essential role in the maintenance of CSCs in gastric cancer (GCSCs). Drosha wild type GCSCs with SHMT2 are sensitive to 5-fluorouracil; however, Drosha low-expressing GCSCs with SHMT1 are 5-FU-resistant. The loss of miR-6778-5p or SHMT1 notably mitigates GCSC sphere formation and increases sensitivity to 5-fluorouracil in Drosha-knockdown gastric cancer cells. Thus, our study reveals a novel function of Drosha-independent noncanonical miRNAs in maintaining the stemness of GCSCs.

Akt regulates progesterone receptor B-dependent transcription and angiogenesis in endometrial cancer cells

Progestins have long been used clinically for the treatment of endometrial cancers, however, the response rates to progestin therapy vary and the molecular mechanisms behind progestin insensitivity are poorly understood. We hypothesized that in PTEN mutated endometrial cancers, hyperactive Akt signaling downregulates Progesterone Receptor B (PRB) transcriptional activity, leading to overall impaired progestin responses. We report that inhibition of Akt with the Akt inhibitor, MK-2206 (MK), in conjunction with progestin (R5020) treatment, is sufficient to upregulate a subset of PRB target genes in Ishikawa cells stably expressing PRB (PRB-Ishikawa). Through gene ontology analysis of Akt-regulated PRB target genes, angiogenesis was found to be the principle process regulated by Akt-PRB. To further interrogate the mechanism by which Akt modulates PRB transcriptional activity, ChIP-Mass Spectrometry was performed to identify potential cofactors that differentially interact with PRB in the presence of the R5020 and MK+R5020. 14-3-3σ was identified as a protein enriched in the MK+R5020 dataset, and it was demonstrated that 14-3-3σ is required for the upregulation in PRB target gene expression following inhibition of Akt. In order to determine the ramifications of MK+R5020 treatment on angiogenesis, in vitro assays were performed and combinatorial MK+R5020 treatment significantly decreased endothelial cell invasion and tube formation more than MK or R5020 treatment alone. Furthermore, we found that combinatorial MK-2206+Progesterone treatments decreased angiogenesis and proliferation in the Pten^d/d conditional mouse model of endometrial cancer. Taken together, these findings suggest that a combinatorial therapeutic approach utilizing Akt inhibitors with progestins may improve the efficacy of progestin therapy for the treatment of endometrial cancer.

14-3-3ζ interacts with hepatocyte nuclear factor 1α and enhances its DNA binding and transcriptional activation

14-3-3 proteins regulate numerous cellular processes through interaction with a variety of proteins, and have been identified as HNF1α binding partner by mass spectrometry analysis in our previous study. In the present study, the interaction between 14-3-3ζ and HNF1α has been further validated by in vivo and in vitro assays. Moreover, we have found that overexpression of 14-3-3ζ potentiated the transcriptional activity of HNF1α in cultured cells, and silencing of 14-3-3ζ by RNA interference in HepG2 cells specifically affected the HNF1α-dependent gene expression. Furthermore, we have demonstrated that 14-3-3ζ is recruited to endogenous HNF1α responsive promoters and enhances HNF1α binding to its cognate DNA sequences. In addition, we have also provided evidence that the association between HNF1α and 14-3-3ζ is phosphorylation-dependent. Taken together, these results suggest that 14-3-3ζ may be an endogenous physiologic regulator of HNF1α.

The progesterone-responsive gene 14-3-3τ enhances the transcriptional activity of progesterone receptor in uterine cells

Members of the 14-3-3 family are intracellular dimeric phosphoserine-binding proteins that can associate with and modulate the activities of many proteins. In our efforts to isolate the genes regulated by progesterone (P(4)) using suppressive subtractive hybridization, we previously found that 14-3-3τ is one of the genes upregulated by P(4). In this study, we demonstrated by quantitative RT-PCR (qRT-PCR), western blot analyses, and immunohistochemistry that 14-3-3τ mRNA and protein levels were increased in the rat uterus after P(4) treatment. Furthermore, qRT-PCR indicated that P(4) increased 14-3-3τ mRNA levels in human endometrial epithelial cells and endometrial stromal cells (ESCs). Western blot and qRT-PCR analyses revealed that in vitro decidualization using cAMP and medroxyprogesterone 17-acetate increased levels of 14-3-3τ mRNA and protein in ESCs. We have shown by qRT-PCR and western blot analyses that P(4) increased the mRNA and protein levels of 14-3-3τ in Ishikawa cells that stably express P(4) receptor-B (PR-B). Immunocytochemistry revealed that 14-3-3τ colocalizes with PR and translocates from the cytoplasm to the nucleus in response to P(4). Moreover, by luciferase reporter assay, we demonstrated that 14-3-3τ enhances the transcriptional activity of PR-B. Taken together, we propose that 14-3-3τ is a P(4)-responsive gene in uterine cells that modulates P(4) signaling.

14-3-3ζ, a novel androgen-responsive gene, is upregulated in prostate cancer and promotes prostate cancer cell proliferation and survival

PURPOSE

Androgen receptor is an essential transcriptional factor that contributes to the development and progression of prostate cancer. In this study, we investigated the androgen regulation and functional analysis of 14-3-3ζ in prostate cancer.

EXPERIMENTAL DESIGN

Using chromatin immunoprecipitation (ChIP) combined with DNA microarray (ChIP-chip) analysis in LNCaP cells, we identified a functional androgen receptor-binding site in the downstream region of the 14-3-3ζ gene. Androgen regulation was examined by quantitative reverse transcription PCR and Western blot analysis. Prostate cancer cells stably expressing 14-3-3ζ and siRNA knockdown were used for functional analyses. We further examined 14-3-3ζ expression in clinical samples of prostate cancer by immunohistochemistry and quantitative reverse transcription PCR.

RESULTS

Androgen-dependent upregulation of 14-3-3ζ was validated at the mRNA and protein levels. The 14-3-3ζ gene is favorable for cancer-cell survival, as its ectopic expression in LNCaP cells contributes to cell proliferation and the acquired resistance to etoposide-induced apoptosis. 14-3-3ζ expression was associated with androgen receptor transcriptional activity and prostate-specific antigen (PSA) mRNA expression. Immunoprecipitation indicated that 14-3-3ζ was associated with androgen receptor in the nucleus. Clinicopathologic studies further support the relevance of 14-3-3ζ in prostate cancers, as its higher expression is associated with malignancy and lymph node metastasis.

CONCLUSIONS

14-3-3ζ is a novel androgen-responsive gene that activates proliferation, cell survival, and androgen receptor transcriptional activity. 14-3-3ζ may facilitate the progression of prostate cancer.

14-3-3 σ expression effects G2/M response to oxygen and correlates with ovarian cancer metastasis

BACKGROUND

In vitro cell culture experiments with primary cells have reported that cell proliferation is retarded in the presence of ambient compared to physiological O₂ levels. Cancer is primarily a disease of aberrant cell proliferation, therefore, studying cancer cells grown under ambient O₂ may be undesirable. To understand better the impact of O₂ on the propagation of cancer cells in vitro, we compared the growth potential of a panel of ovarian cancer cell lines under ambient (21%) or physiological (3%) O₂.

PRINCIPAL FINDINGS

Our observations demonstrate that similar to primary cells, many cancer cells maintain an inherent sensitivity to O₂, but some display insensitivity to changes in O₂ concentration. Further analysis revealed an association between defective G2/M cell cycle transition regulation and O₂ insensitivity resultant from overexpression of 14-3-3 σ. Targeting 14-3-3 σ overexpression with RNAi restored O₂ sensitivity in these cell lines. Additionally, we found that metastatic ovarian tumors frequently overexpress 14-3-3 σ, which in conjunction with phosphorylated RB, results in poor prognosis.

CONCLUSIONS

Cancer cells show differential proliferative sensitivity to changes in O₂ concentration. Although a direct link between O₂ insensitivity and metastasis was not determined, this investigation showed that an O₂ insensitive phenotype in cancer cells to correlate with metastatic tumor progression.

Involvement of Stat3 in mouse brain development and sexual dimorphism: a proteomics approach

Although the role of STAT3 in cell physiology and tissue development has been largely investigated, its involvement in the development and maintenance of nervous tissue and in the mechanisms of neuroprotection is not yet known. The potentially wide range of STAT3 activities raises the question of tissue- and gender-specificity as putative mechanisms of regulation. To explore the function of STAT3 in the brain and the hypothesis of a gender-linked modulation of STAT3, we analyzed a neuron-specific STAT3 knockout mouse model investigating the influence of STAT3 activity in brain protein expression pattern in both males and females in the absence of neurological insult. We performed a proteomic study aimed to reveal the molecular pathways directly or indirectly controlled by STAT3 underscoring its role in brain development and maintenance. We identified several proteins, belonging to different neuronal pathways such as energy metabolism or synaptic transmission, controlled by STAT3 that confirm its crucial role in brain development and maintenance. Moreover, we investigated the different processes that could contribute to the sexual dimorphic behavior observed in the incidence of neurological and mental disease. Interestingly both STAT3 KO and gender factors influence the expression of several mitochondrial proteins conferring to mitochondrial activity high importance in the regulation of brain physiology and conceivable relevance as therapeutic target.

14-3-3{eta} Amplifies Androgen Receptor Actions in Prostate Cancer

PURPOSE: Androgen receptor abundance and androgen receptor-regulated gene expression in castration-recurrent prostate cancer are indicative of androgen receptor activation in the absence of testicular androgen. Androgen receptor transactivation of target genes in castration-recurrent prostate cancer occurs in part through mitogen signaling that amplifies the actions of androgen receptor and its coregulators. Herein we report on the role of 14-3-3eta in androgen receptor action. Experimental Design and RESULTS: Androgen receptor and 14-3-3eta colocalized in COS cell nuclei with and without androgen, and 14-3-3eta promoted androgen receptor nuclear localization in the absence of androgen. 14-3-3eta interacted with androgen receptor in cell-free binding and coimmunoprecipitation assays. In the recurrent human prostate cancer cell line, CWR-R1, native endogenous androgen receptor transcriptional activation was stimulated by 14-3-3eta at low dihydrotestosterone concentrations and was increased by epidermal growth factor. Moreover, the dihydrotestosterone- and epidermal growth factor-dependent increase in androgen receptor transactivation was inhibited by a dominant negative 14-3-3eta. In the CWR22 prostate cancer xenograft model, 14-3-3eta expression was increased by androgen, suggesting a feed-forward mechanism that potentiates both 14-3-3eta and androgen receptor actions. 14-3-3eta mRNA and protein decreased following castration of tumor-bearing mice and increased in tumors of castrate mice after treatment with testosterone. CWR22 tumors that recurred 5 months after castration contained 14-3-3eta levels similar to the androgen-stimulated tumors removed before castration. In a human prostate tissue microarray of clinical specimens, 14-3-3eta localized with androgen receptor in nuclei, and the similar amounts expressed in castration-recurrent prostate cancer, androgen-stimulated prostate cancer, and benign prostatic hyperplasia were consistent with androgen receptor activation in recurrent prostate cancer. CONCLUSION: 14-3-3eta enhances androgen- and mitogen-induced androgen receptor transcriptional activity in castration-recurrent prostate cancer. (Clin Cancer Res 2009;15(24):7571-81).

Cyclin D3/CDK11p58 complex is involved in the repression of androgen receptor

Androgen receptor (AR) is essential for the maintenance of the male reproductive systems and is critical for the carcinogenesis of human prostate cancers (PCas). D-type cyclins are closely related to the repression of AR function. It has been well documented that cyclin D1 inhibits AR function through multiple mechanisms, but the mechanism of how cyclin D3 exerts its repressive role in the AR signaling pathway remains to be identified. In the present investigation, we demonstrate that cyclin D3 and the 58-kDa isoform of cyclin-dependent kinase 11 (CDK11p58) repressed AR transcriptional activity as measured by reporter assays of transformed cells and prostate-specific antigen expression in PCa cells. AR, cyclin D3, and CDK11p58 formed a ternary complex in cells and were colocalized in the luminal epithelial layer of the prostate. AR activity is controlled by phosphorylation at specific sites. We found that AR was phosphorylated at Ser-308 by cyclin D3/CDK11p58 in vitro and in vivo, leading to the repressed activity of AR transcriptional activation unit 1 (TAU1). Furthermore, androgen-dependent proliferation of PCa cells was inhibited by cyclin D3/CDK11p58 through AR repression. These data suggest that cyclin D3/CDK11p58 signaling is involved in the negative regulation of AR function.