Small molecule inhibition of the steroid receptor coactivators, SRC-3 and SRC-1

Structural basis for the asymmetric binding of coactivator SRC1 to FXR-RXRα and allosteric communication within the complex

Farnesoid X receptor (FXR) is a promising target for treatment of metabolic associated fatty liver disease (MAFLD). In this study, we employed an integrative approach to investigate the interaction between FXR-RXRα-DNA complex and the entire coactivator SRC1-NRID (nuclear receptor interaction domain). We constructed a multi-domain model of FXR-RXRα-DNA, highlighting the interface between FXR-DBD and LBD. Using HDX-MS, XL-MS, and biochemical assays, we revealed the allosteric communications in FXR-RXRα-DNA upon agonist and DNA binding. We then demonstrated that SRC1 binds only to the coactivator binding surface of FXR within the FXR-RXRα heterodimer, with the NR-box2 and NR-box3 of SRC1 as the key binding motifs. Our findings, which provide the first model of SRC1-NRID in complex with FXR-RXRα-DNA, shed light on the molecular mechanism through which the coactivator asymmetrically interacts with nuclear receptors and provide structural basis for further understanding the function of FXR and its implications in diseases.

Lead Compound Development of SRC-3 Inhibitors with Improved Pharmacokinetic Properties and Anticancer Efficacy

Steroid receptor coactivator 3 (SRC-3) is a critical mediator of many intracellular signaling pathways that are crucial for cancer proliferation and metastasis. In this study, we performed structure-activity relationship exploration and drug-like optimization of the hit compound SI-2, guided by in vitro/in vivo metabolism studies and cytotoxicity assays. Our efforts led to the discovery of two lead compounds, SI-10 and SI-12. Both compounds exhibit potent cytotoxicity against a panel of human cancer cell lines and demonstrate acceptable pharmacokinetic properties. A biotinylated estrogen response element pull-down assay demonstrated that SI-12 could disrupt the recruitment of SRC-3 and p300 in the estrogen receptor complex. Importantly, SI-10 and SI-12 significantly inhibited tumor growth and metastasis in vivo without appreciable acute toxicity. These results demonstrate the potential of SI-10 and SI-12 as drug candidates for cancer therapy, given their potent SRC-3 inhibition and promising pharmacokinetic and toxicity profiles.

Androgen receptor cofactors: A potential role in understanding prostate cancer

Prostate cancer (PCa) is witnessing a concerning rise in incidence annually, with the androgen receptor (AR) emerging as a pivotal contributor to its growth and progression. Mounting evidence underscores the AR's ability to recruit cofactors, influencing downstream gene transcription and thereby fueling the proliferation and metastasis of PCa cells. Although, clinical strategies involving AR antagonists provide some relief, managing castration resistant prostate cancer (CRPC) remains a formidable challenge. Thus, the need of the hour lies in unearthing new drugs or therapeutic targets to effectively combat PCa. This review encapsulates the pivotal roles played by coactivators and corepressors of AR, notably androgen receptor-associated protein (ARA) and steroid receptor Coactivators (SRC) in PCa. Our data unveils how these cofactors intricately modulate histone modifications, cell cycling, SUMOylation, and apoptosis through their interactions with AR. Among the array of cofactors scrutinised, such as ARA70β, ARA24, ARA160, ARA55, ARA54, PIAS1, PIAS3, SRC1, SRC2, SRC3, PCAF, p300/CBP, MED1, and CARM1, several exhibit upregulation in PCa. Conversely, other cofactors like ARA70α, PIASy, and NCoR/SMRT demonstrate downregulation. This duality underscores the complexity of AR cofactor dynamics in PCa. Based on our findings, we propose that manipulating cofactor regulation to modulate AR function holds promise as a novel therapeutic avenue against advanced PCa. This paradigm shift offers renewed hope in the quest for effective treatments in the face of CRPC's formidable challenges.

Androgen Receptor-Interacting Proteins in Prostate Cancer Development and Therapy Resistance

Endocrine therapy for prostate cancer is based on the use of drugs that diminish androgen concentration and androgen receptor (AR) signaling inhibitors and is limited by the functional consequences of AR point mutations and increased expression of constitutively active receptors. Many coactivators (>280) interact with different AR regions. Most studies have determined the expression of coactivators and their effects in the presence of increasing concentrations of androgen or the antiandrogen enzalutamide. The p160 group of coactivators (SRC-1, SRC-2, and SRC-3) is highly expressed in prostate cancer and contributes to ligand-dependent activation of the receptor in models that represent therapy-sensitive and therapy-resistant cell lines. The transcriptional coactivators p300 and CREB-binding protein (CBP) are implicated in the regulation of a large number of cellular events, such as proliferation, apoptosis, migration, and invasion. AR coactivators also may predict biochemical and clinical recurrence. The AR coactivator expression, which is enhanced in enzalutamide resistance, includes growth regulating estrogen receptor binding 1 (GREB1) and GATA-binding protein 2 (GATA2). Several coactivators also activate AR-unrelated signaling pathways, such as those of insulin-like growth factors, which inhibit apoptosis in cancer cells. They are expressed in multiple models of resistance to therapy and can be targeted by various inhibitors in vitro and in vivo. The role of the glucocorticoid receptor in endocrine therapy-resistant prostate cancer has been documented previously. Specific coactivators may interact with the glucocorticoid receptor, thus contributing to therapy failure.

Function of Steroid Receptor Coactivators in T Cells and Cancers: Implications for Cancer Immunotherapy

Steroid receptor coactivator (SRC) family members (SRC1, SRC2 and SRC3) are transcriptional co-regulators. SRCs orchestrate gene transcription by inducing transactivation of nuclear receptors and other transcription factors. Overexpression of SRCs is widely implicated in a range of cancers, especially hormone-related cancers. As coactivators, SRCs regulate multiple metabolic pathways involved in tumor growth, invasion, metastasis, and chemo-resistance. Emerging evidence in recent years suggest that SRCs also regulate maturation, differentiation, and cytotoxicity of T cells by controlling metabolic activities. In this review, we summarize the current understanding of the function of SRCs in T cells as well as cancer cells. Importantly, the controversies of targeting SRCs for cancer immunotherapy as well as possible reconciliation strategies are also discussed.

Critical Roles of SRC-3 in the Development and Progression of Breast Cancer, Rendering It a Prospective Clinical Target

Breast cancer (BCa) is the most frequently diagnosed malignant tumor in women and is also one of the leading causes of cancer-related death. Most breast tumors are hormone-dependent and estrogen signaling plays a critical role in promoting the survival and malignant behaviors of these cells. Estrogen signaling involves ligand-activated cytoplasmic estrogen receptors that translocate to the nucleus with various co-regulators, such as steroid receptor co-activator (SRC) family members, and bind to the promoters of target genes and regulate their expression. SRC-3 is a member of this family that interacts with, and enhances, the transcriptional activity of the ligand activated estrogen receptor. Although SRC-3 has important roles in normal homeostasis and developmental processes, it has been shown to be amplified and overexpressed in breast cancer and to promote malignancy. The malignancy-promoting potential of SRC-3 is diverse and involves both promoting malignant behavior of tumor cells and creating a tumor microenvironment that has an immunosuppressive phenotype. SRC-3 also inhibits the recruitment of tumor-infiltrating lymphocytes with effector function and promotes stemness. Furthermore, SRC-3 is also involved in the development of resistance to hormone therapy and immunotherapy during breast cancer treatment. The versatility of SRC-3 in promoting breast cancer malignancy in this way makes it a good target, and methodical targeting of SRC-3 probably will be important for the success of breast cancer treatment.

Ncoa2 Promotes CD8+ T cell-Mediated Antitumor Immunity by Stimulating T-cell Activation via Upregulation of PGC-1α Critical for Mitochondrial Function

Nuclear receptor coactivator 2 (Ncoa2) is a member of the Ncoa family of coactivators, and we previously showed that Ncoa2 regulates the differentiation of induced regulatory T cells. However, it remains unknown if Ncoa2 plays a role in CD8+ T-cell function. Here, we show that Ncoa2 promotes CD8+ T cell-mediated immune responses against tumors by stimulating T-cell activation via upregulating PGC-1α expression to enhance mitochondrial function. Mice deficient in Ncoa2 in T cells (Ncoa2fl/fl/CD4Cre) displayed defective immune responses against implanted MC38 tumors, which associated with significantly reduced tumor-infiltrating CD8+ T cells and decreased IFNγ production. Consistently, CD8+ T cells from Ncoa2fl/fl/CD4Cre mice failed to reject tumors after adoptive transfer into Rag1-/- mice. Further, in response to TCR stimulation, Ncoa2fl/fl/CD4Cre CD8+ T cells failed to increase mitochondrial mass, showed impaired oxidative phosphorylation, and had lower expression of PGC-1α, a master regulator of mitochondrial biogenesis and function. Mechanically, T-cell activation-induced phosphorylation of CREB triggered the recruitment of Ncoa2 to bind to enhancers, thus, stimulating PGC-1α expression. Forced expression of PGC-1α in Ncoa2fl/fl/CD4Cre CD8+ T cells restored mitochondrial function, T-cell activation, IFNγ production, and antitumor immunity. This work informs the development of Ncoa2-based therapies that modulate CD8+ T cell-mediated antitumor immune responses.

Bioenergetic alteration in gastrointestinal cancers: The good, the bad and the ugly

Cancer cells exhibit metabolic reprogramming and bioenergetic alteration, utilizing glucose fermentation for energy production, known as the Warburg effect. However, there are a lack of comprehensive reviews summarizing the metabolic reprogramming, bioenergetic alteration, and their oncogenetic links in gastrointestinal (GI) cancers. Furthermore, the efficacy and treatment potential of emerging anticancer drugs targeting these alterations in GI cancers require further evaluation. This review highlights the interplay between aerobic glycolysis, the tricarboxylic acid (TCA) cycle, and oxidative phosphorylation (OXPHOS) in cancer cells, as well as hypotheses on the molecular mechanisms that trigger this alteration. The role of hypoxia-inducible transcription factors, tumor suppressors, and the oncogenetic link between hypoxia-related enzymes, bioenergetic changes, and GI cancer are also discussed. This review emphasizes the potential of targeting bioenergetic regulators for anti-cancer therapy, particularly for GI cancers. Emphasizing the potential of targeting bioenergetic regulators for GI cancer therapy, the review categorizes these regulators into aerobic glycolysis/ lactate biosynthesis/transportation and TCA cycle/coupled OXPHOS. We also detail various anti-cancer drugs and strategies that have produced pre-clinical and/or clinical evidence in treating GI cancers, as well as the challenges posed by these drugs. Here we highlight that understanding dysregulated cancer cell bioenergetics is critical for effective treatments, although the diverse metabolic patterns present challenges for targeted therapies. Further research is needed to comprehend the specific mechanisms of inhibiting bioenergetic enzymes, address side effects, and leverage high-throughput multi-omics and spatial omics to gain insights into cancer cell heterogeneity for targeted bioenergetic therapies.

SRC2 controls CD4+ T cell activation via stimulating c-Myc-mediated upregulation of amino acid transporter Slc7a5

T cell activation stimulates substantially increased protein synthesis activity to accumulate sufficient biomass for cell proliferation. The protein synthesis is fueled by the amino acids transported from the environment. Steroid nuclear receptor coactivator 2 (SRC2) is a member of a family of transcription coactivators. Here, we show that SRC2 recruited by c-Myc enhances CD4+ T cell activation to stimulate immune responses via upregulation of amino acid transporter Slc7a5. Mice deficient of SRC2 in T cells (SRC2fl/fl/CD4Cre) are resistant to the induction of experimental autoimmune encephalomyelitis (EAE) and susceptible to Citrobacter rodentium (C. rodentium) infection. Adoptive transfer of naive CD4+ T cells from SRC2fl/fl/CD4Cre mice fails to elicit EAE and colitis in Rag1/ recipients. Further, CD4+ T cells from SRC2fl/fl/CD4Cre mice display defective T cell proliferation, cytokine production, and differentiation both in vitro and in vivo. Mechanically, SRC2 functions as a coactivator to work together with c-Myc to stimulate the expression of amino acid transporter Slc7a5 required for T cell activation. Slc7a5 fails to be up-regulated in CD4+ T cells from SRC2fl/fl/CD4Cre mice, and forced expression of Slc7a5 rescues proliferation, cytokine production, and the ability of SRC2fl/fl/CD4Cre CD4+ T cells to induce EAE. Therefore, SRC2 is essential for CD4+ T cell activation and, thus, a potential drug target for controlling CD4+ T cell-mediated autoimmunity.

Estrogen-dependent activation of NCOA3 couples with p300 and NF-κB to mediate antiapoptotic genes in ER-positive breast cancer cells

Circumvention of apoptosis by the elevation of antiapoptotic proteins is an important cause of carcinogenesis. The induction of antiapoptotic genes, including B-cell CLL/lymphoma 2 (BCL2), BCL2 related protein A1 (BCL2A1), BCL2 like 1 (BCL2L1), BCL2L2, and myeloid cell leukemia 1 (MCL1), has been observed in multiple cancers, including breast cancer. However, the underlying mechanisms of their overexpression are still being investigated. Here, we revealed that BCL2, BCL2A1, BCL2L2, and MCL1 but not BCL2L1 were overexpressed in estrogen receptor (ER)-positive breast cancer cells and clinical biopsies. Stimulation with estrogen in ER-positive cell lines resulted in a dose-dependent increase in BCL2, BCL2A1, BCL2L2, and MCL1 mRNA levels. Molecular investigation revealed that nuclear factor kappa B (NF-κB) recruited histone acetyltransferase p300 and nuclear receptor coactivator 3 (NCOA3) to form a transcriptional complex. This complex docked the promoters of BCL2, BCL2A1, BCL2L2, and MCL1 and activated their expression. Interestingly, estrogen exposure dose-dependently activated NCOA3. Depletion of the NCOA3-p300-NF-κB components or blockage of NCOA3 function with inhibitors (gossypol and bufalin) in ER-positive cells suppressed BCL2, BCL2A1, BCL2L2, and MCL1 expression, while also decreasing cell viability, colony formation, cell invasion, and tumor growth. Collectively, our results demonstrate an upstream signaling that activates four antiapoptotic genes in ER-positive breast cancer cells. Importantly, our results also imply that targeting NCOA3 or blocking the assembly of the NCOA3-p300-NF-κB complex may be promising therapeutic strategies for treating ER-positive breast cancer.

Transcription networks rewire gene repertoire to coordinate cellular reprograming in prostate cancer

Transcription factors (TFs) represent the most commonly deregulated DNA-binding class of proteins associated with multiple human cancers. They can act as transcriptional activators or repressors that rewire the cistrome, resulting in cellular reprogramming during cancer progression. Deregulation of TFs is associated with the onset and maintenance of various cancer types including prostate cancer. An emerging subset of TFs has been implicated in the regulation of multiple cancer hallmarks during tumorigenesis. Here, we discuss the role of key TFs which modulate transcriptional cicuitries involved in the development and progression of prostate cancer. We further highlight the role of TFs associated with key cancer hallmarks, including, chromatin remodeling, genome instability, DNA repair, invasion, and metastasis. We also discuss the pluripotent function of TFs in conferring lineage plasticity, that aids in disease progression to neuroendocrine prostate cancer. At the end, we summarize the current understanding and approaches employed for the therapeutic targeting of TFs and their cofactors in the clinical setups to prevent disease progression.

Steroid receptor coactivators - their role in immunity

Steroid Receptor Coactivators (SRCs) are essential regulators of transcription with a wide range of impact on human physiology and pathology. In immunology, SRCs play multiple roles; they are involved in the regulation of nuclear factor-κB (NF-κB), macrophage (MΦ) activity, lymphoid cells proliferation, development and function, to name just a few. The three SRC family members, SRC-1, SRC-2 and SRC-3, can exert their immunological function either in an independent manner or act in synergy with each other. In certain biological contexts, one SRC family member can compensate for lack of activity of another member, while in other cases one SRC can exert a biological function that competes against the function of another family counterpart. In this review we illustrate the diverse biological functionality of the SRCs with regard to their role in immunity. In the light of recent development of SRC small molecule inhibitors and stimulators, we discuss their potential relevance as modulators of the immunological activity of the SRCs for therapeutic purposes.

AIB1 is a novel target of the high-risk HPV E6 protein and a biomarker of cervical cancer progression

The high-risk human papillomaviruses (HPV-16, -18) are critical etiologic agents in human malignancy, most importantly in cervical cancer. These oncogenic viruses encode the E6 and E7 proteins that are uniformly retained and expressed in cervical cancers and required for maintenance of the tumorigenic phenotype. The E6 and E7 proteins were first identified as targeting the p53 and pRB tumor suppressor pathways, respectively, in host cells, thereby leading to disruption of cell cycle controls. In addition to p53 degradation, a number of other functions and critical targets for E6 have been described, including telomerase, Myc, PDZ-containing proteins, Akt, Wnt, mTORC1, as well as others. In this study, we identified Amplified in Breast Cancer 1 (AIB1) as a new E6 target. We first found that E6 and hTERT altered similar profiling of gene expression in human foreskin keratinocytes (HFK), independent of telomerase activity. Importantly, AIB1 was a common transcriptional target of both E6 and hTERT. We then verified that high-risk E6 but not low-risk E6 expression led to increases in AIB1 transcript levels by real-time RT-PCR, suggesting that AIB1 upregulation may play an important role in cancer development. Western blots demonstrated that AIB1 expression increased in HPV-16 E6 and E7 expressing (E6E7) immortalized foreskin and cervical keratinocytes, and in three of four common cervical cancer cell lines as well. Then, we evaluated the expression of AIB1 in human cervical lesions and invasive carcinoma using immunohistochemical staining. Strikingly, AIB1 showed positivity in the nucleus of cells in the immediate suprabasal epithelium, while nuclei of the basal epithelium were negative, as evident in the Cervical Intraepithelial Neoplasia 1 (CIN1) samples. As the pathological grading of cervical lesions increased from CIN1, CIN2, CIN3 carcinoma in situ and invasive carcinoma, AIB1 staining increased progressively, suggesting that AIB1 may serve as a novel histological biomarker for cervical cancer development. For cases of invasive cervical carcinoma, AIB1 staining was specific to cancerous lesions. Increased expression of AIB1 was also observed in transgenic mouse cervical neoplasia and cancer models induced by E6E7 and estrogen. Knockdown of AIB1 expression in E6E7 immortalized human cervical cells significantly abolished cell proliferation. Taken together, these data support AIB1 as a novel target of HPV E6 and a biomarker of cervical cancer progression.

Steroid nuclear receptor coactivator 2 controls immune tolerance by promoting induced Treg differentiation via up-regulating Nr4a2

Steroid nuclear receptor coactivator 2 (SRC2) is a member of a family of transcription coactivators. While SRC1 inhibits the differentiation of regulatory T cells (Tregs) critical for establishing immune tolerance, we show here that SRC2 stimulates Treg differentiation. SRC2 is dispensable for the development of thymic Tregs, whereas naive CD4+ T cells from mice deficient of SRC2 specific in Tregs (SRC2fl/fl/Foxp3YFP-Cre) display defective Treg differentiation. Furthermore, the aged SRC2fl/fl/Foxp3YFP-Cre mice spontaneously develop autoimmune phenotypes including enlarged spleen and lung inflammation infiltrated with IFNγ-producing CD4+ T cells. SRC2fl/fl/Foxp3YFP-Cre mice also develop severer experimental autoimmune encephalomyelitis (EAE) due to reduced Tregs. Mechanically, SRC2 recruited by NFAT1 binds to the promoter and activates the expression of Nr4a2, which then stimulates Foxp3 expression to promote Treg differentiation. Members of SRC family coactivators thus play distinct roles in Treg differentiation and are potential drug targets for controlling immune tolerance.

2',3',4'-Trihydroxychalcone changes estrogen receptor α regulation of genes and breast cancer cell proliferation by a reprogramming mechanism

BACKGROUND

Menopausal hormone therapy (MHT) is recommended for only five years to treat vasomotor symptoms and vulvovaginal atrophy because of safety concerns with long-term treatment. We investigated the ability of 2',3',4'-trihydroxychalcone (2',3',4'-THC) to modulate estrogen receptor (ER)-mediated responses in order to find drug candidates that could potentially prevent the adverse effects of long-term MHT treatment.

METHODS

Transfection assays, real time-polymerase chain reaction, and microarrays were used to evaluate the effects of 2',3',4'-THC on gene regulation. Radioligand binding studies were used to determine if 2',3',4'-THC binds to ERα. Cell proliferation was examined in MCF-7 breast cancer cells by using growth curves and flow cytometry. Western blots were used to determine if 2',3',4'-THC alters the E2 activation of the MAPK pathway and degradation of ERα. Chromatin immunoprecipitation was used to measure ERα binding to genes.

RESULTS

The 2',3',4'-THC/E2 combination produced a synergistic activation with ERα on reporter and endogenous genes in human U2OS osteosarcoma cells. Microarrays identified 824 genes that we termed reprogrammed genes because they were not regulated in U2OS-ERα cells unless they were treated with 2',3',4'-THC and E2 at the same time. 2',3',4'-THC blocked the proliferation of MCF-7 cells by preventing the E2-induced activation of MAPK and c-MYC transcription. The antiproliferative mechanism of 2',3',4'-THC differs from selective estrogen receptor modulators (SERMs) because 2',3',4'-THC did not bind to the E2 binding site in ERα like SERMs.

CONCLUSION

Our study suggests that 2',3',4'-THC may represent a new class of ERα modulators that do not act as a direct agonists or antagonists. We consider 2',3',4'-THC to be a reprogramming compound, since it alters the activity of ERα on gene regulation and cell proliferation without competing with E2 for binding to ERα. The addition of a reprogramming drug to estrogens in MHT may offer a new strategy to overcome the adverse proliferative effects of estrogen in MHT by reprogramming ERα as opposed to an antagonist mechanism that involves blocking the binding of estrogen to ERα.

Nuclear receptor coactivator SRC-1 promotes colorectal cancer progression through enhancing GLI2-mediated Hedgehog signaling

Overexpression of nuclear coactivator steroid receptor coactivator 1 (SRC-1) and aberrant activation of the Hedgehog (Hh) signaling pathway are associated with various tumorigenesis; however, the significance of SRC-1 in colorectal cancer (CRC) and its contribution to the activation of Hh signaling are unclear. Here, we identified a conserved Hh signaling signature positively correlated with SRC-1 expression in CRC based on TCGA database; SRC-1 deficiency significantly inhibited the proliferation, survival, migration, invasion, and tumorigenesis of both human and mouse CRC cells, and SRC-1 knockout significantly suppressed azoxymethane/dextran sodium sulfate (AOM/DSS)-induced CRC in mice. Mechanistically, SRC-1 promoted the expression of GLI family zinc finger 2 (GLI2), a major downstream transcription factor of Hh pathway, and cooperated with GLI2 to enhance multiple Hh-regulated oncogene expression, including Cyclin D1, Bcl-2, and Slug. Pharmacological blockages of SRC-1 and Hh signaling retarded CRC progression in human CRC cell xenograft mouse model. Together, our studies uncover an SRC-1/GLI2-regulated Hh signaling looping axis that promotes CRC tumorigenesis, offering an attractive strategy for CRC treatment.

Drugging the Undruggable: Targeting the N-Terminal Domain of Nuclear Hormone Receptors

This chapter focuses on the development of drugs targeting the N-terminal domain of nuclear hormone receptors, using progress with the androgen receptor as an example. Historically, development of therapies targeting nuclear hormone receptors has focused on the folded C-terminal ligand-binding domain. Therapies were traditionally not developed to target the intrinsically disordered N-terminal domain as it was considered "undruggable". Recent developments have now shown it is possible to direct therapies to the N-terminal domain. This chapter will provide an introduction of the structure and function of the domains of nuclear hormone receptors, followed by a discussion of the rationale supporting the development of N-terminal domain inhibitors. Chemistry and mechanisms of action of small molecule inhibitors will be described with emphasis on N-terminal domain inhibitors developed to the androgen receptor including those in clinical trials.

Regulation of PXR Function by Coactivator and Corepressor Proteins: Ligand Binding Is Just the Beginning

The pregnane X receptor (PXR, NR1I2) is a nuclear receptor which exerts its regulatory function by heterodimerization with the retinoid-X-receptor α (RXRα, NR2B1) and binding to the promoter and enhancer regions of diverse target genes. PXR is involved in the regulation of drug metabolism and excretion, metabolic and immunological functions and cancer pathogenesis. PXR activity is strongly regulated by the association with coactivator and corepressor proteins. Coactivator proteins exhibit histone acetyltransferase or histone methyltransferase activity or associate with proteins having one of these activities, thus promoting chromatin decondensation and activation of the gene expression. On the contrary, corepressor proteins promote histone deacetylation and therefore favor chromatin condensation and repression of the gene expression. Several studies pointed to clear cell- and ligand-specific differences in the activation of PXR. In this article, we will review the critical role of coactivator and corepressor proteins as molecular determinants of the specificity of PXR-mediated effects. As already known for other nuclear receptors, understanding the complex mechanism of PXR activation in each cell type and under particular physiological and pathophysiological conditions may lead to the development of selective modulators with therapeutic potential.

Development of improved SRC-3 inhibitors as breast cancer therapeutic agents

Steroid receptor coactivators (SRCs) possess specific and distinct oncogenic roles in the initiation of cancer and in its progression to a more aggressive disease. These coactivators interact with nuclear receptors and other transcription factors to boost transcription of multiple genes, which potentiate cancer cell proliferation, migration, invasion, tumor angiogenesis and epithelial-mesenchymal transition (EMT). Targeting SRCs using small molecule inhibitors (SMIs) is a promising approach to control cancer progression and metastasis. By high-throughput screening analysis, we recently identified SI-2 as a potent SRC SMI. To develop therapeutic agents, SI-10 and SI-12, the SI-2 analogs are synthesized that incorporate the addition of F atoms to the SI-2 chemical structure. As a result, these analogs exhibit a significantly prolonged plasma half-life, minimal toxicity and improved hERG activity. Biological functional analysis showed that SI-10 and SI-12 treatment (5-50 nM) can significantly inhibit viability, migration and invasion of breast cancer cells in vitro and repress the growth of breast cancer PDX organoids. Treatment of mice with 10 mg/kg/day of either SI-10 or SI-12 was sufficient to repress the growth of xenograft tumors derived from MDA-MB-231 and LM2 cells. Furthermore, in spontaneous and experimental metastasis mouse models developed from MDA-MB-231 and LM2 cells, respectively, SI-10 and SI-12 effectively inhibited the progression of breast cancer lung metastasis. These results demonstrate that SI-10 and SI-12 are promising therapeutic agents and are specifically effective in blocking tumor metastasis, a key point in tumor progression to a more lethal state that results in patient mortality in the majority of cases.

Role of conformational dynamics and flexibilities in the steroid receptor-coregulator protein complex formation

Understanding of the mechanisms of actions of the steroid hormone receptor (SHR)-coregulator (CoR) protein complexes in the gene regulations has revolutionized the field of molecular endocrinology and endocrine-related oncology. The discovery and characterization of steroid receptor coactivators (SRCs) and their ability to bind various transcription factors including SHRs to coordinate the regulation of multiple target genes highlights their importance as key coregulators in various cellular signaling crosstalks as well as therapeutic target for various endocrine-related disorders specifically endocrine cancers. The dynamic nature of the SHR-CoR multi-protein complexes indicate the critical role of conformational flexibilities within specific protein(s). In recent years, the importance of conformational dynamics of the SHRs in the intramolecular and intermolecular allosteric regulations mediated via their intrinsically disordered (ID) surfaces has been highlighted. In this review article, we have discussed the importance of ID conformations within the SRCs that may also be playing an important role in the formation/deformation of multi protein complexes involving SHRs and CoRs and subsequent target gene regulation.

Src-1 and SP2 promote the proliferation and epithelial-mesenchymal transition of nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is characterized by high morbidity and morality, especially in Southern China. Transcription factors intensively participate in the initiation and development of NPC. This study aimed to investigate the roles of Src-1 in NPC. mRNA level was determined by qRT-PCR. Western blot was carried out for the protein level. CCK-8 assay was performed to determine cell viability, colony formation for NPC cell proliferation, and transwell for cell migration and invasion ability. The results showed Steroid receptor coactivator 1 (Src-1) was overexpressed in SNE-2 and 6-10B. The expression of Src-1 and SP2 was in positive correlation. Overexpression of Src-1 promoted the cell viability, colony formation, and epithelial-mesenchymal transition (EMT), manifested by the increase of migration and invasion ability, while knockdown of Src-1 exerted opposite effects. Additionally, knockdown or overexpression of SP2 reversed the effects of overexpressed or downregulated Src-1, which was reversed by the depletion of SP2. Moreover, Src-1 interacted with SP2 to regulate EMT-related genes such as E-cad, N-cad, Vimentin, and ZEB1, and proliferation- and apoptosis-related genes, such as bax, cytochrome c, and cleaved caspase3 and bcl-2. Thus, blocking the interaction between Src-1 and SP2 may be a therapeutic target for inhibiting the metastasis of NPC.

Steroid receptor coactivator-1: The central intermediator linking multiple signals and functions in the brain and spinal cord

The effects of steroid hormones are believed to be mediated by their nuclear receptors (NRs). The p160 coactivator family, including steroid receptor coactivator-1 (SRC-1), 2 and 3, has been shown to physically interact with NRs to enhance their transactivational activities. Among which SRC-1 has been predominantly localized in the central nervous system including brain and spinal cord. It is not only localized in neurons but also detectable in neuroglial cells (mainly localized in the nuclei but also detectable in the extra-nuclear components). Although the expression of SRC-1 is regulated by many steroids, it is also regulated by some non-steroidal factors such as injury, sound and light. Functionally, SRC-1 has been implied in normal function such as development and ageing, learning and memory, central regulation on reproductive behaviors, motor and food intake. Pathologically, SRC-1 may play a role in the regulation of neuropsychiatric disorders (including stress, depression, anxiety, and autism spectrum disorder), metabolite homeostasis and obesity as well as tumorigenesis. Under most conditions, the related mechanisms are far from elucidation; although it may regulate spatial memory through Rictor/mTORC2-actin polymerization related synaptic plasticity. Several inhibitors and stimulator of SRC-1 have shown anti-cancer potentials, but whether these small molecules could be used to modulate ageing and central disorder related neuropathology remain unclear. Therefore, to elucidate when and how SRC-1 is turned on and off under different stimuli is very interesting and great challenge for neuroscientists.

SRC-3, a Steroid Receptor Coactivator: Implication in Cancer

Steroid receptor coactivator-3 (SRC-3), also known as amplified in breast cancer 1 (AIB1), is a member of the SRC family. SRC-3 regulates not only the transcriptional activity of nuclear receptors but also many other transcription factors. Besides the essential role of SRC-3 in physiological functions, it also acts as an oncogene to promote multiple aspects of cancer. This review updates the important progress of SRC-3 in carcinogenesis and summarizes its mode of action, which provides clues for cancer therapy.

Targeted Degradation of Transcription Coactivator SRC-1 through the N-Degron Pathway

Aberrantly elevated steroid receptor coactivator-1 (SRC-1) expression and activity are strongly correlated with cancer progression and metastasis. Here we report, for the first time, the development of a proteolysis targeting chimera (PROTAC) that is composed of a selective SRC-1 binder linked to a specific ligand for UBR box, a unique class of E3 ligases recognizing N-degrons. We showed that the bifunctional molecule efficiently and selectively induced the degradation of SRC-1 in cells through the N-degron pathway. Importantly, given the ubiquitous expression of the UBR protein in most cells, PROTACs targeting the UBR box could degrade a protein of interest regardless of cell types. We also showed that the SRC-1 degrader significantly suppressed cancer cell invasion and migration in vitro and in vivo. Together, these results demonstrate that the SRC-1 degrader can be an invaluable chemical tool in the studies of SRC-1 functions. Moreover, our findings suggest PROTACs based on the N-degron pathway as a widely useful strategy to degrade disease-relevant proteins.

Discovery of drugs that directly target the intrinsically disordered region of the androgen receptor

Introduction: Intrinsically disordered proteins (IDPs) and regions (IDRs) lack stable three-dimensional structure making drug discovery challenging. A validated therapeutic target for diseases such as prostate cancer is the androgen receptor (AR) which has a disordered amino-terminal domain (NTD) that contains all of its transcriptional activity. Drug discovery against the AR-NTD is of intense interest as a potential treatment for disease such as advanced prostate cancer that is driven by truncated constitutively active splice variants of AR that lack the C-terminal ligand-binding domain (LBD).Areas covered: This article presents an overview of the relevance of AR and its intrinsically disordered NTD as a drug target. AR structure and approaches to blocking AR transcriptional activity are discussed. The discovery of small molecules, including the libraries used, proven binders to the AR-NTD, and site of interaction of these small molecules in the AR-NTD are presented along with discussion of the Phase I clinical trial.Expert opinion: The lack of drugs in the clinic that directly bind IDPs/IDRs reflects the difficulty of targeting these proteins and obtaining specificity. However, it may also point to an inappropriateness of too closely borrowing concepts and resources from drug discovery to folded proteins.

A potential target for liver cancer management, lysophosphatidic acid receptor 6 (LPAR6), is transcriptionally up-regulated by the NCOA3 coactivator

Lysophosphatidic acid receptor 6 (LPAR6) is a G protein-coupled receptor that plays critical roles in cellular morphology and hair growth. Although LPAR6 overexpression is also critical for cancer cell proliferation, its role in liver cancer tumorigenesis and the underlying mechanism are poorly understood. Here, using liver cancer and matched paracancerous tissues, as well as functional assays including cell proliferation, quantitative real-time PCR, RNA-Seq, and ChIP assays, we report that LPAR6 expression is controlled by a mechanism whereby hepatocyte growth factor (HGF) suppresses liver cancer growth. We show that high LPAR6 expression promotes cell proliferation in liver cancer. More importantly, we find that LPAR6 is transcriptionally down-regulated by HGF treatment and that its transcriptional suppression depends on nuclear receptor coactivator 3 (NCOA3). We note that enrichment of NCOA3, which has histone acetyltransferase activity, is associated with histone 3 Lys-27 acetylation (H3K27ac) at the LPAR6 locus in response to HGF treatment, indicating that NCOA3 transcriptionally regulates LPAR6 through the HGF signaling cascade. Moreover, depletion of either LPAR6 or NCOA3 significantly inhibited tumor cell growth in vitro and in vivo (in mouse tumor xenograft assays), similar to the effect of the HGF treatment. Collectively, our findings indicate an epigenetic link between LPAR6 and HGF signaling in liver cancer cells, and suggest that LPAR6 can serve as a biomarker and new strategy for therapeutic interventions for managing liver cancer.

Steroid receptor/coactivator binding inhibitors: An update

The purpose of this review is to highlight recent developments in small molecules and peptides that block the binding of coactivators to steroid receptors. These coactivator binding inhibitors bind at the coregulator binding groove, also known as Activation Function-2, rather than at the ligand-binding site of steroid receptors. Steroid receptors that have been targeted with coactivator binding inhibitors include the androgen receptor, estrogen receptor and progesterone receptor. Coactivator binding inhibitors may be useful in some cases of resistance to currently prescribed therapeutics. The scope of the review includes small-molecule and peptide coactivator binding inhibitors for steroid receptors, with a particular focus on recent compounds that have been assayed in cell-based models.

Metabolic Dysregulation Controls Endocrine Therapy-Resistant Cancer Recurrence and Metastasis

Cancer recurrence and metastasis involves many biological interactions, such as genetic, transcription, environmental, endocrine signaling, and metabolism. These interactions add a complex understanding of cancer recurrence and metastatic progression, delaying the advancement in therapeutic opportunities. We highlight the recent advances on the molecular complexities of endocrine-related cancers, focusing on breast and prostate cancer, and briefly review how endocrine signaling and metabolic programs can influence transcriptional complexes for metastasis competence. Nuclear receptors and transcriptional coregulators function as molecular nodes for the crosstalk between endocrine signaling and metabolism that alter downstream gene expression important for tumor progression and metastasis. This exciting regulatory axis may provide insights to the development of cancer therapeutics important for these desensitized endocrine-dependent cancers.

SRC-3/AIB-1 may Enhance Hepatic NFATC1 Transcription and Mediate Inflammation in a Tissue-Specific Manner in Morbid Obesity

BACKGROUND

Obesity is a global epidemic which is associated with several cardiometabolic comorbidities and is characterized by chronic, low grade systemic inflammation. Numerous biomarkers have been implicated in the pathophysiology of the disease, including transcription factors and coregulators. Steroid Receptor Coactivator (SRC)-family represent the master regulators of metabolic pathways and their dysregulation is strongly associated with numerous metabolic disorders.

METHODS

50 morbidly obese patients participated in the present study. Biopsies were collected from visceral adipose tissue, subcutaneous adipose tissue, skeletal muscle, extra-myocellular adipose tissue and liver. We evaluated the differential protein expression of NFATc1, SRC-2/TIF-2, SRC-3/AIB-1 and inflammatory biomarkers CD68 and CD3 by immunohistochemistry. The current study was designed to determine any correlations between the transcription factor NFATc1 and the SRC coregulators, as well as any associations with the inflammatory biomarkers.

RESULTS

We identified SRC-3 as a hepatic NFATc1 coactivator and we demonstrated its possible role in energy homeostasis and lipid metabolism. Moreover, we revealed a complex and extensive intraand inter-tissue network among the three main investigated proteins and the inflammatory biomarkers, suggesting their potential participation in the obesity-induced inflammatory cascade.

CONCLUSION

Steroid receptor coactivators are critical regulators of human metabolism with pleiotropic and tissue-specific actions. We believe that our study will contribute to the better understanding of the complex multi-tissue interactions that are disrupted in obesity and can therefore lead to numerous cardiometabolic diseases. Further on, our present findings suggest that SRC-3/AIB-1 could constitute possible future drug targets.

MicroRNA-449a Inhibits Tumor Metastasis through AKT/ERK1/2 Inactivation by Targeting Steroid Receptor Coactivator (SRC) in Endometrial Cancer

Endometrial cancer represents the leading frequency in gynecological malignancy in developed countries. Even with early detection, metastasis and recurrence remain the main reasons for a high death rate. MicroRNA-449a (miR-449a) has been reported to function as a tumor suppressor, yet the role of miR-449a in endometrial cancer metastasis has not been investigated. The present study identified that miR-449a was downregulated in advanced endometrial cancer. Overexpression of miR-449a decreased the migration and invasion of KLE and AN3CA endometrial cancer cells. Using luciferase reporter assays, we identified that miR-449a directly targeted the steroid receptor coactivator (SRC) by binding to sites in the 3' untranslated regions. Elevated expressions of SRC have been witnessed in advanced endometrial cancer tissues and have promoted tumor metastasis. We also identified that the suppressive effect of miR-449a on metastasis could be mediated by downregulating SRC and that miR-449a could suppress AKT and ERK1/2 pathway activation in endometrial cancer cells. These findings contribute to the current understanding of the function of miR-449a in endometrial cancer.

Steroid receptor coactivator-1 regulates glioma angiogenesis through polyomavirus enhancer activator 3 signaling

Steroid receptor coactivator 1 (SRC-1) is a transcriptional coactivator for steroid receptors and other transcription factors. SRC-1 has been shown to play an important role in the progression of breast cancer and prostate cancer. However, its role in glioma progression remains unknown. Here, in this study, we report that SRC-1 is upregulated in the vessels of human glioma and exerts important regulatory functions. Specifically, SRC-1 expression significantly enhanced basic fibroblast growth factor (bFGF)-mediated angiogenesis in vivo. Downregulating of SRC-1 expression suppressed endothelial cell migration and tube formation in vitro and upregulated the expression of pro-angiogenic factors, including vascular endothelial growth factor (VEGF) and matrix metallopeptidase (MMP)-9 in glioma cells. These SRC-1-mediated effects were dependent on the activation of polyomavirus enhancer activator 3 (PEA3) transcriptional activity. VEGF and VEGF inducer GS4012 induced the direct binding of SRC-1 and PEA3 in glioma cells, and PEA3 could directly bind with VEGF and MMP-9 promoter under GS4012 treatment in glioma cell. The expression of pro-angiogenic factors induced by SRC-1 was abrogated by sh-PEA3 knockdown. Taken together, these novel outcomes indicated that SRC-1 modulated endothelial cell (EC) function and facilitated a pro-angiogenic microenvironment through PEA3 signaling. Moreover, a combination of targeting SRC-1 and PEA3 signaling in glioma could be a promising strategy for suppressing tumor angiogenesis.

Steroid Receptor Coactivator-2 Controls the Pentose Phosphate Pathway through RPIA in Human Endometrial Cancer Cells

Steroid receptor coactivator-2 (SRC-2) is a transcriptional coregulator that modulates the activity of many transcription factors. Levels of SRC-2 are elevated in endometrial biopsies from polycystic ovary syndrome patients, a population predisposed to endometrial cancer (EC). Increased expression of SRC-2 is also detected in neoplastic endometrium suggesting a causal link between elevated SRC-2 expression and the emergence of endometrial disorders that can lead to cancer. Here, we reveal that SRC-2 knockdown reduces EC cell proliferation and anchorage-independence. Additionally, SRC-2 is required to maintain cellular glycolytic capacity and oxidative phosphorylation, processes essential for EC cell proliferation. Importantly, SRC-2 is critical for the normal performance of the pentose phosphate pathway (PPP). Perturbation of the PPP due to loss of SRC-2 expression may result from the depletion of ribose-5-P isomerase (RPIA), a key enzyme of the PPP. As with SRC-2, RPIA knockdown reduces EC cell proliferation, which is accompanied by a decrease in glycolytic capacity and oxidative phosphorylation. Glucose metabolite tracking experiments confirmed that knockdown of SRC-2 and RPIA downregulates the metabolic rate of both glycolysis and the PPP, highlighting a novel regulatory cross-talk between glycolysis and the PPP modulated by SRC-2.

Estrogen receptor-1 is a key regulator of HIV-1 latency that imparts gender-specific restrictions on the latent reservoir

The molecular mechanisms leading to the creation and maintenance of the latent HIV reservoir remain incompletely understood. Unbiased shRNA screens showed that the estrogen receptor acts as a potent repressor of proviral reactivation in T cells. Antagonists of ESR-1 activate latent HIV-1 proviruses while agonists, including β-estradiol, potently block HIV reactivation. Using a well-matched set of male and female donors, we found that ESR-1 plays an important role in regulating HIV transcription in both sexes. However, women are much more responsive to estrogen and appear to harbor smaller inducible RNA reservoirs. Accounting for the impact of estrogen on HIV viral reservoirs will therefore be critical for devising curative therapies for women, a group representing 51% of global HIV infections.

Unbiased shRNA library screens revealed that the estrogen receptor-1 (ESR-1) is a key factor regulating HIV-1 latency. In both Jurkat T cells and a Th17 primary cell model for HIV-1 latency, selective estrogen receptor modulators (SERMs, i.e., fulvestrant, raloxifene, and tamoxifen) are weak proviral activators and sensitize cells to latency-reversing agents (LRAs) including low doses of TNF-α (an NF-κB inducer), the histone deacetylase inhibitor vorinostat (soruberoylanilide hydroxamic acid, SAHA), and IL-15. To probe the physiologic relevance of these observations, leukapheresis samples from a cohort of 12 well-matched reproductive-age women and men on fully suppressive antiretroviral therapy were evaluated by an assay measuring the production of spliced envelope (env) mRNA (the EDITS assay) by next-generation sequencing. The cells were activated by T cell receptor (TCR) stimulation, IL-15, or SAHA in the presence of either β-estradiol or an SERM. β-Estradiol potently inhibited TCR activation of HIV-1 transcription, while SERMs enhanced the activity of most LRAs. Although both sexes responded to SERMs and β-estradiol, females showed much higher levels of inhibition in response to the hormone and higher reactivity in response to ESR-1 modulators than males. Importantly, the total inducible RNA reservoir, as measured by the EDITS assay, was significantly smaller in the women than in the men. We conclude that concurrent exposure to estrogen is likely to limit the efficacy of viral emergence from latency and that ESR-1 is a pharmacologically attractive target that can be exploited in the design of therapeutic strategies for latency reversal.

Bufalin suppresses endometriosis progression by inducing pyroptosis and apoptosis

The steroid receptor coactivator (SRC)-1 isoform/estrogen receptor (ER)-β axis has an essential role in endometriosis progression. In this context, therefore, bufalin was employed as a 'tool compound' to evaluate inhibitors of SRC in alternative endometriosis treatment. Bufalin effectively suppressed the growth of primary human endometrial stroma cells isolated from endometriosis patients compared to women without endometriosis and immortalized human endometrial epithelial and stromal cells expressing the SRC-1 isoform compared to their parental cells in vitroIn vivo, compared to the vehicle, bufalin treatment significantly suppressed the growth of endometriotic lesions in mice with surgically induced endometriosis because bufalin disrupted the functional axis of SRC-1 isoform/ERβ by increasing SRC-1 isoform protein stability, hyperactivating the transcriptional activity of the SRC-1 isoform and degrading the ERβ protein by proteasome 26S subunit, non-ATPase 2 in endometriotic lesions. Bufalin treatment elevated the apoptosis signaling in epithelial cells of endometriotic lesions. In stromal cells of endometriotic lesions, bufalin treatment increased the levels of pyroptosis markers (caspase 1 and the active form of interleukin 1β) and reduced proliferation. In addition, bufalin treatment increased the expression levels of endoplasmic reticulum-stress (ERS) markers (PKR-like ER kinase, protein disulfide isomerase and binding immunoglobulin) in endometriotic lesions. Collectively, the bufalin-induced disruption of the SRC-1 isoform/ERβ axis might induce apoptosis, pyroptosis and ERS signaling in endometriotic lesions, causing the suppression of endometriosis. Therefore, future generations of SRC-modulators could be employed as an alternative medical approach for endometriosis treatment.

Current and potential targets for drug design in the androgen receptor pathway for prostate cancer

INTRODUCTION

Modulating the androgen axis by different agents has been one of the most successful therapeutic interventions in the field of prostate cancer therapy. Newer agents such as abiraterone and enzalutamide have been widely adapted and have contributed to an increase in the overall survival of prostate cancer patients. However, most of these patients will develop resistance to these agents and will need chemotherapy. Areas covered: In this review, this author discusses current agents which modulate the androgen axis, the mechanisms of resistance to these agents and investigative agents which are designed to bypass these mechanisms of resistance. Potential targets in the androgen axis and related biochemical pathways are, furthermore, identified. Expert opinion: Understanding the mechanism of resistance to these agents is crucial in developing third generation anti-androgen agents which can potentially contribute to the longevity of prostate cancer patients to a greater extent. Besides developing more potent agents, it is also important to formulate new strategies to resensitize patients to current anti-androgen agents by carefully sequencing chemotherapy regimens and abrogating genetic changes which are known to cause resistance to anti-androgens. Combinatorial approach with immunotherapy offers prospects which may yield better results and need to be thoroughly explored.

Coregulator profiling of the glucocorticoid receptor in lymphoid malignancies

Coregulators cooperate with nuclear receptors, such as the glucocorticoid receptor (GR), to enhance or repress transcription. These regulatory proteins are implicated in cancer, yet, their role in lymphoid malignancies, including multiple myeloma (MM) and acute lymphoblastic leukemia (ALL), is largely unknown. Here, we report the use and extension of the microarray assay for real-time nuclear receptor coregulator interactions (MARCoNI) technology to detect coregulator associations with endogenous GR in cell lysates. We use MARCoNI to determine the GR coregulator profile of glucocorticoid-sensitive (MM and ALL) and glucocorticoid-resistant (ALL) cells, and identify common and unique coregulators for different cell line comparisons. Overall, we identify SRC-1/2/3, PGC-1α, RIP140 and DAX-1 as the strongest interacting coregulators of GR in MM and ALL cells and show that the interaction strength does not correlate with GR protein levels. Lastly, as a step towards patient samples, we determine the GR coregulator profile of peripheral blood mononuclear cells. We profile the interactions between GR and coregulators in MM and ALL cells and suggest to further explore the GR coregulator profile in hematological patient samples.

Androgen Signaling in Prostate Cancer

The androgen-signaling axis plays a pivotal role in the pathogenesis of prostate cancer. Since the landmark discovery by Huggins and Hodges, gonadal depletion of androgens has remained a mainstay of therapy for advanced disease. However, progression to castration-resistant prostate cancer (CRPC) typically follows and is largely the result of restored androgen signaling. Efforts to understand the mechanisms behind CRPC have revealed new insights into dysregulated androgen signaling and intratumoral androgen synthesis, which has ultimately led to the development of several novel androgen receptor (AR)-directed therapies for CRPC. However, emergence of resistance to these newer agents has also galvanized new directions in investigations of prereceptor and postreceptor AR regulation. Here, we review our current understanding of AR signaling as it pertains to the biology and natural history of prostate cancer.

A comprehensive analysis of coregulator recruitment, androgen receptor function and gene expression in prostate cancer

Standard treatment for metastatic prostate cancer (CaP) prevents ligand-activation of androgen receptor (AR). Despite initial remission, CaP progresses while relying on AR. AR transcriptional output controls CaP behavior and is an alternative therapeutic target, but its molecular regulation is poorly understood. Here, we show that action of activated AR partitions into fractions that are controlled preferentially by different coregulators. In a 452-AR-target gene panel, each of 18 clinically relevant coregulators mediates androgen-responsiveness of 0-57% genes and acts as a coactivator or corepressor in a gene-specific manner. Selectivity in coregulator-dependent AR action is reflected in differential AR binding site composition and involvement with CaP biology and progression. Isolation of a novel transcriptional mechanism in which WDR77 unites the actions of AR and p53, the major genomic drivers of lethal CaP, to control cell cycle progression provides proof-of-principle for treatment via selective interference with AR action by exploiting AR dependence on coregulators.

Prognostic and predictive importance of the estrogen receptor coactivator AIB1 in a randomized trial comparing adjuvant letrozole and tamoxifen therapy in postmenopausal breast cancer: the Danish cohort of BIG 1-98

PURPOSE

To evaluate the estrogen receptor coactivator amplified in breast cancer 1 (AIB1) as a prognostic marker, as well as a predictive marker for response to adjuvant tamoxifen and/or aromatase inhibitors, in early estrogen receptor-positive breast cancer.

METHOD

AIB1 was analyzed with immunohistochemistry in tissue microarrays of the Danish subcohort (N = 1396) of the International Breast Cancer Study Group's trial BIG 1-98 (randomization between adjuvant tamoxifen versus letrozole versus the sequence of the two drugs).

RESULTS

Forty-six percent of the tumors had a high AIB1 expression. In line with previous studies, AIB1 correlated to a more aggressive tumor-phenotype (HER2 amplification and a high malignancy grade). High AIB1 also correlated to higher estrogen receptor expression (80-100 vs. 1-79%), and ductal histological type. High AIB1 expression was associated with a poor disease-free survival (univariable: hazard ratio 1.35, 95% confidence interval 1.12-1.63. Multivariable: hazard ratio 1.29, 95% confidence interval 1.06-1.58) and overall survival (univariable: hazard ratio 1.34, 95% confidence interval 1.07-1.68. Multivariable: hazard ratio 1.25, 95% confidence interval 0.99-1.60). HER2 did not seem to modify the prognostic effect of AIB1. No difference in treatment effect between tamoxifen and letrozole in relation to AIB1 was found.

CONCLUSIONS

In a subset of the large international randomized trial BIG 1-98, we confirm AIB1 to be a strong prognostic factor in early breast cancer. Hence, although tumor AIB1 expression does not seem to be useful for the choice of tamoxifen versus an aromatase inhibitor in postmenopausal endocrine-responsive breast cancer, AIB1 is an interesting target for new anti-cancer therapies and further investigations of this biomarker is warranted.

Rationale for the development of alternative forms of androgen deprivation therapy

With few exceptions, the almost 30,000 prostate cancer deaths annually in the United States are due to failure of androgen deprivation therapy. Androgen deprivation therapy prevents ligand-activation of the androgen receptor. Despite initial remission after androgen deprivation therapy, prostate cancer almost invariably progresses while continuing to rely on androgen receptor action. Androgen receptor's transcriptional output, which ultimately controls prostate cancer behavior, is an alternative therapeutic target, but its molecular regulation is poorly understood. Recent insights in the molecular mechanisms by which the androgen receptor controls transcription of its target genes are uncovering gene specificity as well as context-dependency. Heterogeneity in the androgen receptor's transcriptional output is reflected both in its recruitment to diverse cognate DNA binding motifs and in its preferential interaction with associated pioneering factors, other secondary transcription factors and coregulators at those sites. This variability suggests that multiple, distinct modes of androgen receptor action that regulate diverse aspects of prostate cancer biology and contribute differentially to prostate cancer's clinical progression are active simultaneously in prostate cancer cells. Recent progress in the development of peptidomimetics and small molecules, and application of Chem-Seq approaches indicate the feasibility for selective disruption of critical protein-protein and protein-DNA interactions in transcriptional complexes. Here, we review the recent literature on the different molecular mechanisms by which the androgen receptor transcriptionally controls prostate cancer progression, and we explore the potential to translate these insights into novel, more selective forms of therapies that may bypass prostate cancer's resistance to conventional androgen deprivation therapy.

Honokiol inhibits bladder cancer cell invasion through repressing SRC-3 expression and epithelial-mesenchymal transition

Urinary bladder cancer (UBC) is one of the most common urological cancer types. Muscle invasive bladder cancer possesses high propensity for metastasis with poor prognosis. Honokiol is a lignan isolated from Magnolia officinalis with high bioavailability and potent anticancer effects. The results of the present study demonstrated that honokiol significantly inhibited UBC cell migration and invasion in a dose-dependent manner compared with the vehicle-treated control group. In addition, honokiol treatment suppressed epithelial-mesenchymal transition by induction of E-cadherin and repression of N-cadherin. Honokiol was capable of significantly downregulating the expression of cell invasion-associated genes, steroid receptor coactivator-3 (SRC-3), matrix metalloproteinase (MMP)-2 and Twist1. Notably, the inhibition of UBC cell invasion by honokiol was reversed by reintroduction of oncoprotein SRC-3 expression, with the restoration of MMP-2 and Twist1, and reduction of E-cadherin expression. Furthermore, the results of the luciferase assay confirmed that SRC-3 could regulate Twist1 promoter activity. Taken together, the results of the present study suggest that honokiol is a promising agent against UBC cell invasion via downregulation of SRC-3 and its target genes.

Small molecules as activators in medicinal chemistry (2000-2016)

INTRODUCTION

From therapeutic point of view, it is often beneficial to enhance the expression of certain enzymes whose low expression is responsible for the observed ailment. Small molecules as activators of several enzymes have great biological potential as anti-microbial and anti-cancer agents, for the treatment of diabetes, obesity, metabolic disorders, and for the treatment of neurological disorders including Alzheimer's disease. This review covers patents describing small molecules as activators, and provides structural leads for the design of even more potent activators. Area covered: This review is focused on small molecules that have been explored as activators of enzymes in the last and current decade (2000-2016). Expert opinion: The ability to modulate activity of enzymes has long been a quest of medicinal chemistry. This has been the impetus behind the development of a plethora of drugs as enzyme inhibitors. However only a few enzyme activators as drugs have made it to the market. Disorders characterized by supressed enzyme activity can be treated by enhancing the activity of a specific enzyme.

MRTF potentiates TEAD-YAP transcriptional activity causing metastasis

Yes-associated protein (YAP) and myocardin-related transcription factor (MRTF) play similar roles and exhibit significant crosstalk in directing transcriptional responses to chemical and physical extracellular cues. The mechanism underlying this crosstalk, however, remains unclear. Here, we show MRTF family proteins bind YAP via a conserved PPXY motif that interacts with the YAP WW domain. This interaction allows MRTF to recruit NcoA3 to the TEAD-YAP transcriptional complex and potentiate its transcriptional activity. We show this interaction of MRTF and YAP is critical for LPA-induced cancer cell invasion in vitro and breast cancer metastasis to the lung in vivo We also demonstrate the significance of MRTF-YAP binding in regulation of YAP activity upon acute actin cytoskeletal damage. Acute actin disruption induces nucleo-cytoplasmic shuttling of MRTF, and this process underlies the LATS-independent regulation of YAP activity. Our results provide clear evidence of crosstalk between MRTF and YAP independent of the LATS kinases that normally act upstream of YAP signaling. Our results also suggest a mechanism by which extracellular stimuli can coordinate physiological events downstream of YAP.

Epigenomic and transcriptional control of insulin resistance

Insulin resistance is one of the defining features of type 2 diabetes and the metabolic syndrome and accompanies many other clinical conditions, ranging from obesity to lipodystrophy to glucocorticoid excess. Extraordinary efforts have gone into defining the mechanisms that underlie insulin resistance, with most attention focused on altered signalling as well as mitochondrial and endoplasmic reticulum stress. Here, nuclear mechanisms of insulin resistance, including transcriptional and epigenomic effects, will be discussed. Three levels of control involving transcription factors, transcriptional cofactors, and chromatin-modifying enzymes will be considered. Well-studied examples of the first include PPAR-γ in adipose tissue and the glucocorticoid receptor and FoxO1 in a variety of insulin-sensitive tissues. These proteins work in concert with cofactors such as PGC-1α and CRTC2, and chromatin-modifying enzymes including DNA methyltransferases and histone acetyltransferases, to regulate key genes that promote insulin-stimulated glucose uptake, gluconeogenesis or other pathways that affect systemic insulin action. Furthermore, genetic variation associated with increased risk of type 2 diabetes is often related to altered transcription factor binding, either by affecting the transcription factor itself, or more commonly by changing the binding affinity of a noncoding regulatory region. Finally, several avenues for therapeutic exploitation in the battle against metabolic disease will be discussed, including small-molecule inhibitors and activators of these factors and their related pathways.

Nuclear and extranuclear-initiated estrogen receptor signaling crosstalk and endocrine resistance in breast cancer

Estrogens regulate function of reproductive and non-reproductive tissues in healthy and diseased states including breast cancer. They mainly work through estrogen receptor alpha (ERα) and/or estrogen receptor beta (ERβ). There are various ERα targeting agents that have been used for treatment of ER (+) breast tumors. The impact of direct nuclear activity of ER is very well characterized in ER (+) breast cancers and development and progression of endocrine resistance. Recent studies also suggested important roles for extranuclear-initiated ERα pathways, which would decrease the potency and efficiency of ERα targeting agents. In this mini-review, we will discuss the role of nuclear and extra-nuclear ER signaling and how they relate to therapy resistance in breast cancer.

Molecular Pathways: Targeting Steroid Receptor Coactivators in Cancer

Coactivators represent a large class of proteins that partner with nuclear receptors and other transcription factors to regulate gene expression. Given their pleiotropic roles in the control of transcription, coactivators have been implicated in a broad range of human disease states, including cancer. This is best typified by the three members of the steroid receptor coactivator (SRC) family, each of which integrates steroid hormone signaling and growth factor pathways to drive oncogenic gene expression programs in breast, endometrial, ovarian, prostate, and other cancers. Because of this, coactivators represent emerging targets for cancer therapeutics, and efforts are now being made to develop SRC-targeting agents, such as the SI-2 inhibitor and the novel SRC stimulator, MCB-613, that are able to block cancer growth in cell culture and animal model systems. Here, we will discuss the mechanisms through which coactivators drive cancer progression and how targeting coactivators represent a novel conceptual approach to combat tumor growth that is distinct from the use of other targeted therapeutic agents. We also will describe efforts to develop next-generation SRC inhibitors and stimulators that can be taken into the clinic for the treatment of recurrent, drug-resistant cancers. Clin Cancer Res; 22(22); 5403-7. ©2016 AACR.

Targeting hepatic glucose metabolism in the treatment of type 2 diabetes

Type 2 diabetes mellitus is characterized by the dysregulation of glucose homeostasis, resulting in hyperglycaemia. Although current diabetes treatments have exhibited some success in lowering blood glucose levels, their effect is not always sustained and their use may be associated with undesirable side effects, such as hypoglycaemia. Novel antidiabetic drugs, which may be used in combination with existing therapies, are therefore needed. The potential of specifically targeting the liver to normalize blood glucose levels has not been fully exploited. Here, we review the molecular mechanisms controlling hepatic gluconeogenesis and glycogen storage, and assess the prospect of therapeutically targeting associated pathways to treat type 2 diabetes.

NCOA1 promotes angiogenesis in breast tumors by simultaneously enhancing both HIF1α- and AP-1-mediated VEGFa transcription

Nuclear receptor coactivator 1 (NCOA1) is overexpressed in a subset of breast cancer and its increased expression positively correlates with disease recurrence and metastasis. Although NCOA1 is known to promote breast cancer metastasis through working with multiple transcription factors to upregulate the expression of Twist1, ITGA5, CSF-1, SDF1 and CXCR4, the role of NCOA1 in breast tumor angiogenesis has not been investigated. In this study, we found that the microvascular density (MVD) was significantly decreased and increased in Ncoa1-knockout and NCOA1-overexpressing mammary tumors, respectively, in several breast cancer mouse models. Knockout or knockdown of NCOA1 in breast cancer cell lines also markedly compromised their capability to induce angiogenesis in Matrigel plugs embedded subcutaneously in mice, while this compromised capability could be rescued by VEGFa treatment. At the molecular level, NCOA1 upregulates VEGFa expression in both mouse mammary tumors and cultured breast cancer cells, and it does so by associating with both c-Fos, which is recruited to the AP-1 site at bp −938 of the VEGFa promoter, and HIF1α, which is recruited to the HIF1α-binding element at bp −979 of the VEGFa promoter, to enhance VEGFa transcription. In 140 human breast tumors, high NCOA1 protein correlates with high MVD and patients with both high NCOA1 and high MVD showed significantly shorter survival time. In summary, this study revealed a novel mechanism that NCOA1 potentiates breast cancer angiogenesis through upregulating HIF1α and AP-1-mediated VEGFa expression, which reinforces the rational of targeting NCOA1 in controlling breast cancer progression and metastasis.