Enhancing the effectiveness of androgen deprivation in prostate cancer by inducing Filamin A nuclear localization

Role of actin-binding proteins in prostate cancer

The molecular mechanisms driving the onset and metastasis of prostate cancer remain poorly understood. Actin, under the control of actin-binding proteins (ABPs), plays a crucial role in shaping the cellular cytoskeleton, which in turn supports the morphological alterations in normal cells, as well as the invasive spread of tumor cells. Previous research indicates that ABPs of various types serve distinct functions, and any disruptions in their activities could predispose individuals to prostate cancer. These ABPs are intricately implicated in the initiation and advancement of prostate cancer through a complex array of intracellular processes, such as severing, linking, nucleating, inducing branching, assembling, facilitating actin filament elongation, terminating elongation, and promoting actin molecule aggregation. As such, this review synthesizes existing literature on several ABPs linked to prostate cancer, including cofilin, filamin A, and fascin, with the aim of shedding light on the molecular mechanisms through which ABPs influence prostate cancer development and identifying potential therapeutic targets. Ultimately, this comprehensive examination seeks to contribute to the understanding and management of prostate diseases.

Pan-cancer and single-cell analysis of actin cytoskeleton genes related to disulfidptosis

Disulfidptosis was recently reported to be caused by abnormal disulfide accumulation in cells with high SLC7A11 levels subjected to glucose starvation, suggesting that targeting disulfidptosis was a potential strategy for cancer treatment. We analyzed the relationships between gene expression and mutations and prognoses of patients. In addition, the correlation between gene expression and immune cell infiltration was explored. The potential regulatory mechanisms of these genes were assessed by investigating their related signaling pathways involved in cancer, their expression patterns, and their cellular localization. Most cancer types showed a negative correlation between the gene-set variation analysis (GSVA) scores and infiltration of B cells and neutrophils, and a positive correlation between GSVA scores and infiltration of natural killer T and induced regulatory T cells. Single-cell analysis revealed that ACTB, DSTN, and MYL6 were highly expressed in different bladder urothelial carcinoma subtypes, but MYH10 showed a low expression. Immunofluorescence staining showed that actin cytoskeleton proteins were mainly localized in the actin filaments and plasma membrane. Notably, IQGAP1 was localized in the cell junctions. In conclusion, this study provided an overview of disulfidptosis-related actin cytoskeleton genes in pan-cancer. These genes were associated with the survival of patients and might be involved in cancer-related pathways.

The Potential of Extracellular Matrix- and Integrin Adhesion Complex-Related Molecules for Prostate Cancer Biomarker Discovery

Prostate cancer is among the top five cancer types according to incidence and mortality. One of the main obstacles in prostate cancer management is the inability to foresee its course, which ranges from slow growth throughout years that requires minimum or no intervention to highly aggressive disease that spreads quickly and resists treatment. Therefore, it is not surprising that numerous studies have attempted to find biomarkers of prostate cancer occurrence, risk stratification, therapy response, and patient outcome. However, only a few prostate cancer biomarkers are used in clinics, which shows how difficult it is to find a novel biomarker. Cell adhesion to the extracellular matrix (ECM) through integrins is among the essential processes that govern its fate. Upon activation and ligation, integrins form multi-protein intracellular structures called integrin adhesion complexes (IACs). In this review article, the focus is put on the biomarker potential of the ECM- and IAC-related molecules stemming from both body fluids and prostate cancer tissue. The processes that they are involved in, such as tumor stiffening, bone turnover, and communication via exosomes, and their biomarker potential are also reviewed.

Androgen receptor transcriptional activity is required for heregulin-1β-mediated nuclear localization of the HER3/ErbB3 receptor tyrosine kinase

Prostate cancer is initially regulated by the androgen receptor (AR), a ligand-activated, transcription factor, and is in a hormone-dependent state (hormone-sensitive prostate cancer (HSPC)), but eventually becomes androgen-refractory (castration-resistant prostate cancer (CRPC)) because of mechanisms that bypass the AR, including by activation of ErbB3, a member of the epidermal growth factor receptor family. ErbB3 is synthesized in the cytoplasm and transported to the plasma membrane for ligand binding and dimerization, where it regulates downstream signaling, but nuclear forms are reported. Here, we demonstrate in prostatectomy samples that ErbB3 nuclear localization is observed in malignant, but not benign prostate, and that cytoplasmic (but not nuclear) ErbB3 correlated positively with AR expression but negatively with AR transcriptional activity. In support of the latter, androgen depletion upregulated cytoplasmic, but not nuclear ErbB3, while in vivo studies showed that castration suppressed ErbB3 nuclear localization in HSPC, but not CRPC tumors. In vitro treatment with the ErbB3 ligand heregulin-1β (HRG) induced ErbB3 nuclear localization, which was androgen-regulated in HSPC but not in CRPC. In turn, HRG upregulated AR transcriptional activity in CRPC but not in HSPC cells. Positive correlation between ErbB3 and AR expression was demonstrated in AR-null PC-3 cells where stable transfection of AR restored HRG-induced ErbB3 nuclear transport, while AR knockdown in LNCaP reduced cytoplasmic ErbB3. Mutations of ErbB3's kinase domain did not affect its localization but was responsible for cell viability in CRPC cells. Taken together, we conclude that AR expression regulated ErbB3 expression, its transcriptional activity suppressed ErbB3 nuclear translocation, and HRG binding to ErbB3 promoted it.

Integrins in cancer: Emerging mechanisms and therapeutic opportunities

Integrins are vital surface adhesion receptors that mediate the interactions between the extracellular matrix (ECM) and cells and are essential for cell migration and the maintenance of tissue homeostasis. Aberrant integrin activation promotes initial tumor formation, growth, and metastasis. Recently, many lines of evidence have indicated that integrins are highly expressed in numerous cancer types and have documented many functions of integrins in tumorigenesis. Thus, integrins have emerged as attractive targets for the development of cancer therapeutics. In this review, we discuss the underlying molecular mechanisms by which integrins contribute to most of the hallmarks of cancer. We focus on recent progress on integrin regulators, binding proteins, and downstream effectors. We highlight the role of integrins in the regulation of tumor metastasis, immune evasion, metabolic reprogramming, and other hallmarks of cancer. In addition, integrin-targeted immunotherapy and other integrin inhibitors that have been used in preclinical and clinical studies are summarized.

Interaction of LARP4 to filamin A mechanosensing domain regulates cell migrations

Filamin A (FLNA) is an actin cross-linking protein that mediates mechanotransduction. Force-dependent conformational changes of FLNA molecule expose cryptic binding site of FLNA, allowing interaction with partners such as integrin, smoothelin, and fimbacin. Here, we identified La-related protein 4 (LARP4) as a new FLNA mechanobinding partner. LARP4 specifically interacts with the cleft formed by C and D strands of immunoglobulin-like repeat 21 (R21) which is blocked by A strand of R20 without force. We validated the interaction between LARP4 and FLNA R21 both in vivo and in vitro. We also determined the critical amino acid that is responsible for the interaction and generated the non-FLNA-binding mutant LARP4 (F277A in human: F273A in mouse Larp4) that disrupts the interaction. Fluorescence recovery after photobleaching (FRAP) of GFP-labeled LARP4 in living cells demonstrated that mutant LARP4 diffuses faster than WT LARP4. Proximity ligation assay (PLA) also confirmed their interaction and disruption of actin polymerization diminishes the interaction. Data mining of RNAseq analysis of LARP4 knockdown (KD) HEK293T cells suggested that LARP4 is involved in morphogenesis and cell motility. Consistent with this prediction, we found that KD of LARP4 increases cell migration speed and expression of the F277A mutant LARP4 in LARP4-KD cells also leads to a higher cell migration speed compared to WT LARP4. These results demonstrated that the LARP4 interaction with FLNA regulates cell migration.

Filamin A Is a Potential Driver of Breast Cancer Metastasis via Regulation of MMP-1

Recurrent metastasis is a major fatal cause of breast cancer. Regretfully, the driving force and the molecular beneath have not been fully illustrated yet. In this study, a cohort of breast cancer patients with locoregional metastasis was recruited. For them, we collected the matched samples of the primary tumor and metastatic tumor, and then we determined the mutation profiles with whole-exome sequencing (WES). On basis of the profiles, we identified a list of deleterious variants in eight susceptible genes. Of them, filamin A (FLNA) was considered a potential driver gene of metastasis, and its low expression could enhance 5 years’ relapse survival rate by 15%. To prove the finding, we constructed a stable FLNA knockout tumor cell line, which manifested that the cell abilities of proliferation, migration, and invasion were significantly weakened in response to the gene knockout. Subsequently, xenograft mouse experiments further proved that FLNA knockout could inhibit local or distal metastasis. Putting all the results together, we consolidated that FLNA could be a potential driver gene to metastasis of breast cancer, in particular triple-negative breast cancer. Additional experiments also suggested that FLNA might intervene in metastasis via the regulation of MMP-1 expression. In summary, this study demonstrates that FLNA may play as a positive regulator in cancer proliferation and recurrence. It provides new insight into breast cancer metastasis and suggests a potential new therapeutic target for breast cancer therapy.

Filamin-A expression in laryngeal squamous cell carcinoma and its clinical significance

BACKGROUND

Laryngeal squamous cell carcinomas (LSCCs) are tumours with a high incidence of treatment failure and recurrence. Recent strategies to improve the five-year survival rate and to decrease the rates of recurrence and metastases did not improve outcomes significantly. Research efforts in recent years have started focusing on discovering biomarkers of prognosis and management in LSCCs. Filamin-A reportedly has been associated with metastatic disease in a recent study. Analysis of this protein's expression in LSCCs is lacking in the literature.

MATERIALS AND METHODS

This study analysed the expression of filamin-A, using immunohistochemistry, in a tissue microarray of 80 cases of laryngeal squamous cell cancers. Clinical-pathological parameters were analysed according to filamin-A expression in the tissue microarray. Furthermore, a review of possible mechanisms of this protein in cancer, in general, was presented, along with a review of the protein's expression in other head and neck tumours.

RESULTS

A significant majority of laryngeal squamous cell cancers exhibited positive expression of filamin-A protein. All the filamin-A positive tumours expressed it in their cytoplasm. Significant correlation between filamin-A expression and grade, stage, lymph node status and metastases were found.

CONCLUSION

The above may suggest an important role for filamin-A in LSCCs. Overall, filamin-A expression in laryngeal cancer is in line with evidence seen in other head and neck cancers. Further studies are in order to pinpoint the exact role of this protein in LSCCs, and its possible utilization in the management of these difficult-to-treat tumours.

Androgen Receptor-Mediated Nuclear Transport of NRDP1 in Prostate Cancer Cells Is Associated with Worse Patient Outcomes

Simple Summary

NRDP1 is an E3 ubiquitin ligase that has been shown by our group and others to target ErbB3 for proteasomal degradation in prostate and breast cancer cells and thereby decrease the likelihood cancer progression. Our group has found that NRDP1 can be located in the nucleus as well as the cytoplasm of prostate cancer (CaP) cells, which is unexpected as NRDP1 lacks a nuclear localization signal. Here we elucidate the mechanism by which nuclear translocation of NRDP1 can occur and demonstrate that nuclear NRDP1 retains its ubiquitin ligase activity. Our patient data and cell line studies indicate that increased levels of nuclear NRDP1 contributes CaP progression, thereby underscoring the clinical relevance of our findings and supporting continued investigation and elucidation of the specific role(s) played by NRDP1 in the nucleus of CaP cells.

Abstract

To our knowledge, our group is the first to demonstrate that NRDP1 is located in the nucleus as well as the cytoplasm of CaP cells. Subcellular fractionation, immunohistochemistry, and immunofluorescence analysis combined with confocal microscopy were used to validate this finding. Subcellular fractionation followed by western blot analysis revealed a strong association between AR and NRDP1 localization when AR expression and/or cellular localization was manipulated via treatment with R1881, AR-specific siRNA, or enzalutamide. Transfection of LNCaP with various NRDP1 and AR constructs followed by immunoprecipitation confirmed binding of NRDP1 to AR is possible and determined that binding requires the hinge region of AR. Co-transfection with NRDP1 constructs and HA-ubiquitin followed by subcellular fractionation confirmed that nuclear NRDP1 retains its ubiquitin ligase activity. We also show that increased nuclear NRDP1 is associated with PSA recurrence in CaP patients (n = 162, odds ratio; 1.238, p = 0.007) and that higher levels of nuclear NRDP1 are found in castration resistant cell lines (CWR22Rv1 and PC3) compared to androgen sensitive cell lines (LNCaP and MDA-PCa-3B). The combined data indicate that NRDP1 plays a role in mediating CaP progression and supports further investigation of both the mechanism by which nuclear transport occurs and the identification of specific nuclear targets.

Clinical utility of a serum biomarker panel in distinguishing prostate cancer from benign prostate hyperplasia

Prostate-specific antigen (PSA) screening for prostate cancer (PCa) is limited by the lack of specificity but is further complicated in the benign prostatic hyperplasia (BPH) population which also exhibit elevated PSA, representing a clear unmet need to distinguish BPH from PCa. Herein, we evaluated the utility of FLNA IP-MRM, age, and prostate volume to stratify men with BPH from those with PCa. Diagnostic performance of the biomarker panel was better than PSA alone in discriminating patients with negative biopsy from those with PCa, as well as those who have had multiple prior biopsies (AUC 0.75 and 0.87 compared to AUC of PSA alone 0.55 and 0.57 for patients who have had single compared to multiple negative biopsies, respectively). Of interest, in patients with PCa, the panel demonstrated improved performance than PSA alone in those with Gleason scores of 5–7 (AUC 0.76 vs. 0.56) and Gleason scores of 8–10 (AUC 0.74 vs. 0.47). With Gleason scores (8–10), the negative predictive value of the panel is 0.97, indicating potential to limit false negatives in aggressive cancers. Together, these data demonstrate the ability of the biomarker panel to perform better than PSA alone in men with BPH, thus preventing unnecessary biopsies.

The function and pathogenic mechanism of filamin A

Filamin A(FLNa) is an actin-binding protein, which participates in the formation of the cytoskeleton, anchors a variety of proteins in the cytoskeleton and regulates cell adhesion and migration. It is involved in signal transduction, cell proliferation and differentiation, pseudopodia formation, vesicle transport, tumor resistance and genetic diseases by binding with interacting proteins. In order to fully elucidate the structure, function and pathogenesis of FLNa, we summarized all substances which directly or indirectly act on FLNa so far, upstream and downstream targets which having effect on it, signaling pathways and their functions. It also recorded the expression and effect of FLNa in different diseases, including hereditary disease and tumors.

Artificial Intelligence (AI) to the Rescue: Deploying Machine Learning to Bridge the Biorelevance Gap in Antioxidant Assays

Oxidative stress induced by excessive levels of reactive oxygen species (ROS) underlies several diseases. Therapeutic strategies to combat oxidative damage are, therefore, a subject of intense scientific investigation to prevent and treat such diseases, with the use of phytochemical antioxidants, especially polyphenols, being a major part. Polyphenols, however, exhibit structural diversity that determines different mechanisms of antioxidant action, such as hydrogen atom transfer (HAT) and single-electron transfer (SET). They also suffer from inadequate in vivo bioavailability, with their antioxidant bioactivity governed by permeability, gut-wall and first-pass metabolism, and HAT-based ROS trapping. Unfortunately, no current antioxidant assay captures these multiple dimensions to be sufficiently "biorelevant," because the assays tend to be unidimensional, whereas biorelevance requires integration of several inputs. Finding a method to reliably evaluate the antioxidant capacity of these phytochemicals, therefore, remains an unmet need. To address this deficiency, we propose using artificial intelligence (AI)-based machine learning (ML) to relate a polyphenol's antioxidant action as the output variable to molecular descriptors (factors governing in vivo antioxidant activity) as input variables, in the context of a biomarker selectively produced by lipid peroxidation (a consequence of oxidative stress), for example F2-isoprostanes. Support vector machines, artificial neural networks, and Bayesian probabilistic learning are some key algorithms that could be deployed. Such a model will represent a robust predictive tool in assessing biorelevant antioxidant capacity of polyphenols, and thus facilitate the identification or design of antioxidant molecules. The approach will also help to fulfill the principles of the 3Rs (replacement, reduction, and refinement) in using animals in biomedical research.

The Androgen Receptor in Prostate Cancer: Effect of Structure, Ligands and Spliced Variants on Therapy

The androgen receptor (AR) plays a predominant role in prostate cancer (PCa) pathology. It consists of an N-terminal domain (NTD), a DNA-binding domain (DBD), a hinge region (HR), and a ligand-binding domain (LBD) that binds androgens, including testosterone (T) and dihydrotestosterone (DHT). Ligand binding at the LBD promotes AR dimerization and translocation to the nucleus where the DBD binds target DNA. In PCa, AR signaling is perturbed by excessive androgen synthesis, AR amplification, mutation, or the formation of AR alternatively spliced variants (AR-V) that lack the LBD. Current therapies for advanced PCa include androgen synthesis inhibitors that suppress T and/or DHT synthesis, and AR inhibitors that prevent ligand binding at the LBD. However, AR mutations and AR-Vs render LBD-specific therapeutics ineffective. The DBD and NTD are novel targets for inhibition as both perform necessary roles in AR transcriptional activity and are less susceptible to AR alternative splicing compared to the LBD. DBD and NTD inhibition can potentially extend patient survival, improve quality of life, and overcome predominant mechanisms of resistance to current therapies. This review discusses various small molecule and other inhibitors developed against the DBD and NTD—and the current state of the available compounds in clinical development.

Genistein Combined Polysaccharide (GCP) Can Inhibit Intracrine Androgen Synthesis in Prostate Cancer Cells

Our group and others have previously shown that genistein combined polysaccharide (GCP), an aglycone isoflavone-rich extract with high bioavailability and low toxicity, can inhibit prostate cancer (CaP) cell growth and survival as well as androgen receptor (AR) activity. We now elucidate the mechanism by which this may occur using LNCaP and PC-346C CaP cell lines; GCP can inhibit intracrine androgen synthesis in CaP cells. UPLC-MS/MS and qPCR analyses demonstrated that GCP can mediate a ~3-fold decrease in testosterone levels (p < 0.001) and cause decreased expression of intracrine androgen synthesis pathway enzymes (~2.5-fold decrease of 3βHSD (p < 0.001), 17βHSD (p < 0.001), CYP17A (p < 0.01), SRB1 (p < 0.0001), and StAR (p < 0.01)), respectively. Reverse-phase HPLC fractionation and bioassay identified three active GCP fractions. Subsequent NMR and LC-MS analysis of the fraction with the highest level of activity, fraction 40, identified genistein as the primary active component of GCP responsible for its anti-proliferative, pro-apoptotic, and anti-AR activity. GCP, fraction 40, and genistein all mediated at least a ~2-fold change in these biological activities relative to vehicle control (p < 0.001). Genistein caused similar decreases in the expression of 17βHSD and CYP17A (2.5-fold (p < 0.001) and 1.5-fold decrease (p < 0.01), respectively) compared to GCP, however it did not cause altered expression of the other intracrine androgen synthesis pathway enzymes; 3βHSD, SRB1, and StAR. Our combined data indicate that GCP and/or genistein may have clinical utility and that further pre-clinical studies are warranted.

Methylation Profile of X-Chromosome-Related Genes in Male Breast Cancer

Background: Androgen receptor (AR) has been described to play a prominent role in male breast cancer (MBC). It maps on chromosome X, and recent reports indicate that X-chromosome polysomy is frequent in MBC. Since the response to anti-androgen therapy may depend on AR polysomy and on its overexpression similarly to prostate cancer, the aim of the present study was to investigate the DNA methylation level of AR and its coregulators, especially those mapped on the X-chromosome, that may influence the activity of AR in MBC.

Methods: The DNA methylation level of AR, MAGEA2, MAGEA11, MAGEC1, MAGEC2, FLNA, HDAC6, and UXT, mapped on the X-chromosome, was evaluated by quantitative bisulfite-NGS. Bioinformatic analysis was performed in a Galaxy Project environment using BWA-METH, MethylDackel, and Methylation Plotter tools. The study population consisted of MBC (41 cases) compared with gynecomastia (17 cases).

Results:MAGEA family members, especially MAGEA2, MAGEA11, MAGEC, and UXT and HDAC6 showed hypomethylation of several CpGs, reaching statistical significance by the Kruskal–Wallis test (p < 0.01) in MBC when compared to gynecomastia. AR showed almost no methylation at all.

Conclusions: Our study demonstrated for the first time that MAGEA family members mapped on the X-chromosome and coregulators of AR are hypomethylated in MBC. This may lead to their overexpression, enhancing AR activity.

The p14ARF tumor suppressor restrains androgen receptor activity and prevents apoptosis in prostate cancer cells

Prostate cancer (PCa) is characterized by a unique dependence on optimal androgen receptor (AR) activity where physiological androgen concentrations induce proliferation but castrate and supraphysiological levels suppress growth. This feature has been exploited in bipolar androgen therapy (BAT) for castrate resistant malignancies. Here, we investigated the role of the tumor suppressor protein p14ARF in maintaining optimal AR activity and the function of the AR itself in regulating p14ARF levels. We used a tumor tissue array of differing stages and grades to define the relationships between these components and identified a strong positive correlation between p14ARF and AR expression. Mechanistic studies utilizing CWR22 xenograft and cell culture models revealed that a decrease in AR reduced p14ARF expression and deregulated E2F factors, which are linked to p14ARF and AR regulation. Chromatin immunoprecipitation studies identified AR binding sites upstream of p14ARF. p14ARF depletion enhanced AR-dependent PSA and TMPRSS2 transcription, hence p14ARF constrains AR activity. However, p14ARF depletion ultimately results in apoptosis. In PCa cells, AR co-ops p14ARF as part of a feedback mechanism to ensure optimal AR activity for maximal prostate cancer cell survival and proliferation.

Calpain suppresses cell growth and invasion of glioblastoma multiforme by producing the cleavage of filamin A

BACKGROUND

Filamin A is the most widely expressed isoform of filamin in mammalian tissues. It can be hydrolyzed by Calpain, producing a 90-kDa carboxyl-terminal fragment (ABP90). Calpeptin is a chemical inhibitor of Calpain, which can inhibit this effect. It has been shown that ABP90 acts as a transcription factor which is involved in mediating cell signaling. However, the significance of ABP90 and its clinical signature with underlying mechanisms have not been well studied in glioblastoma multiforme (GBM).

METHODS

ABP90 protein was measured in 36 glioma patients by Western blot. Human GBM cell lines U87 and A172 were used to clarify the precise role of ABP90. CCK-8 assay was used to analyze the cell viability. Transwell invasion assay and wound healing assay were used to analyze the migration and invasion. Expression of matrix metalloproteinase 2/tissue inhibitors of metalloproteinase 2 (MMP2/TIMP2) protein was analyzed by Western blot.

RESULTS

ABP90 protein expression was lower in GBM tissues. The patients with low ABP90 protein expression had a shorter OS time (p = 0.046). After being treated with Calpain, the expression of ABP90 was upregulated, which led to a decline of cell viability, enhanced the efficacy of temozolomide and restrained the cell invasion. Calpeptin could inhibit the effect. The mechanism might be involved in the balance of MMP2/TIMP2.

CONCLUSIONS

Our present data suggest that ABP90 expression is a significant prognostic factor and may play an important role in cell viability, chemotherapeutic sensitivity and invasion of GBM.

Biological roles of filamin a in prostate cancer cells

OBJECTIVE

This study aims to investigate the association of filamin A with the function and morphology of prostate cancer (PCa) cells, and explore the role of filamin A in the development of PCa, in order to analyze its significance in the evolvement of PCa.

MATERIALS AND METHODS

A stably transfected cell line, in which filamin A expression was suppressed by RNA interference, was first established. Then, the effects of the suppression of filamin A gene expression on the biological characteristics of human PCa LNCaP cells were observed through cell morphology, in vitro cell growth curve, soft agar cloning assay, and scratch test.

RESULTS

A cell line model with a low expression of filamin A was successfully constructed on the basis of LNCaP cells. The morphology of cells transfected with plasmid pSilencer-filamin A was the following: Cells were loosely arranged, had less connection with each other, had fewer tentacles, and presented a fibrous look. The growth rate of LNCap cells was faster than cells transfected with plasmid pSilencer-filamin A (P<0.05). The clones of LNCap cells in the soft agar cloning assay was significantly fewer than that of cells stably transfected with plasmid pSilencer-filamin A (P<0.05). Cells stably transfected with plasmid pSilencer-filamin A presented with a stronger healing and migration ability compared to LNCap cells (healing rate was 32.2% and 12.1%, respectively; P<0.05).

CONCLUSION

The expression of the filamin A gene inhibited the malignant development of LNCap cells. Therefore, the filamin A gene may be a tumor suppressor gene.

Dacomitinib, but not lapatinib, suppressed progression in castration-resistant prostate cancer models by preventing HER2 increase

BACKGROUND

Despite overexpression of the ErbB (EGFR/HER2/ErbB3/ErbB4) family in castration-resistant prostate cancer (CRPC), some inhibitors of this family, including the dual EGFR/HER2 inhibitor lapatinib, failed in Phase II clinical trials. Hence, we investigated mechanisms of lapatinib resistance to determine whether alternate ErbB inhibitors can succeed.

METHODS

The CWR22 human tumour xenograft and its CRPC subline 22Rv1 and sera from lapatinib-treated CRPC patients from a previously reported Phase II trial were used to study lapatinib resistance. Mechanistic studies were conducted in LNCaP, C4-2 and 22Rv1 cell lines.

RESULTS

Lapatinib increased intratumoral HER2 protein, which encouraged resistance to this treatment in mouse models. Sera from CRPC patients following lapatinib treatment demonstrated increased HER2 levels. Investigation of the mechanism of lapatinib-induced HER2 increase revealed that lapatinib promotes HER2 protein stability, leading to membrane localisation, EGFR/HER2 heterodimerisation and signalling, elevating cell viability. Knockdown of HER2 and ErbB3, but not EGFR, sensitised CRPC cells to lapatinib. At equimolar concentrations, the recently FDA-approved pan-ErbB inhibitor dacomitinib decreased HER2 protein stability, prevented ErbB membrane localisation (despite continued membrane integrity) and EGFR/HER2 heterodimerisation, thereby decreasing downstream signalling and increasing apoptosis.

CONCLUSIONS

Targeting the EGFR axis using the irreversible pan-ErbB inhibitor dacomitinib is a viable therapeutic option for CRPC.

ATPR-induced G0 /G1 phase arrest in gastric cancer cells by regulating the binding of 14-3-3ε and filamin A

4‐amino‐2‐trifluoromethyl‐phenyl retinate (ATPR) was able to induce the G₀/G₁ phase arrest in gastric cancer SGC‐7901 cells by downregulating 14‐3‐3ε. However, the mechanisms underlying this effect have not been fully elucidated. Because 14‐3‐3ε functions as a molecular chaperone on cell cycle regulation, the interaction between 14‐3‐3ε and the target proteins is worth an in‐depth study. In this study, the use of targeting proteomics identified 352 14‐3‐3ε‐binding proteins in SGC‐7901 cells. Analysis of gene ontology (GO) was performed using PANTHER to annotate the biological processes, protein classes, and pathways of these proteins. In 25 cell cycle‐related proteins, filamin A was reduced following ATPR treatment, and this change was validated by immunoprecipitation. The cell cycle was arrested at the G₀/G₁ phase following ATPR treatment or filamin A silencing in SGC‐7901 cells. Furthermore, subcellular expression analysis showed that 14‐3‐3ε and filamin A were transferred from the cytoplasm to the nucleus after ATPR treatment. On the other hand, overexpression of 14‐3‐3ε, in SGC‐7901 cells, resulted in an increase in the total cellular level of filamin A and an increase in the subcellular localization of filamin A in the cytoplasm. ATPR treatment of the 14‐3‐3ε overexpression cells decreased the total level of filamin A and redistributed filamin A protein from the cytoplasm to the nucleus. Immunohistochemical analysis showed that the expression levels of 14‐3‐3ε and filamin A in gastric cancer tissues were significantly higher, with a predominant localization in the cytoplasm, compared to the levels in matched tissues. Taken together, our results suggest that ATPR can induce nuclear localization of filamin A by reducing the binding of 14‐3‐3ε and filamin A, which may be the mechanism of ATPR‐induced G₀/G₁ phase arrest.

Signaling regulation and role of filamin A cleavage in Ca2+-stimulated migration of androgen receptor-deficient prostate cancer cells

Ca²⁺, a ubiquitous cellular signal, and filamin A, an actin-binding protein, play an important role in the regulation of cell adhesion, shape and motility. Using transwell filters to analyze cell migration, we found that extracellular Ca²⁺ (Ca_o²⁺) promotes the migration of androgen receptor (AR)-deficient and highly metastatic prostate cancer cell lines (DU145 and PC-3) compared to AR-positive and relatively less metastatic prostate cancer cells (LNCaP). Furthermore, we found that expression of filamin A is up-regulated in DU145 and PC-3 cells, and that Ca_o²⁺ significantly induces the cleavage of filamin A. Silencing expression of Ca²⁺-sensing receptor (CaR) and p115RhoGEF, and treating with leupeptin, a protease inhibitor, and ALLM, a calpain specific inhibitor, we further demonstrate that Ca_o²⁺-induced filamin A cleavage occurs via a CaR- p115RhoGEF-calpain dependent pathway. Our data show that Ca_o²⁺ via CaR- mediated signaling induces filamin A cleavage and promotes the migration in AR-deficient and highly metastatic prostate cancer cells.

The androgen receptor is a negative regulator of eIF4E phosphorylation at S209: implications for the use of mTOR inhibitors in advanced prostate cancer

The anti-androgen bicalutamide is widely used in the treatment of advanced prostate cancer (PCa) in many countries, but its effect on castration resistant PCa (CRPC) is limited. We previously showed that resistance to bicalutamide results from activation of mechanistic target of rapamycin (mTOR). Interestingly, clinical trials testing combinations of the mTOR inhibitor RAD001 with bicalutamide were effective in bicalutamide-naïve CRPC patients, but not in bicalutamide-pre-treated ones. Here we investigate causes for their difference in response. Evaluation of CRPC cell lines identified resistant vs sensitive in-vitro models, and revealed that increased eIF4E(S209) phosphorylation is associated with resistance to the combination. We confirmed using a human-derived tumor-xenograft mouse model that bicalutamide pre-treatment is associated with an increase in eIF4E(S209) phosphorylation. Thus, AR suppressed eIF4E phosphorylation, while the use of anti-androgens relieved this suppression, thereby triggering its increase. Additional investigation in human prostatectomy samples showed that increased eIF4E phosphorylation strongly correlated with the cell proliferation marker Ki67. SiRNA-mediated knock-down of eIF4E sensitized CRPC cells to RAD001+bicalutamide, while eIF4E overexpression induced resistance. Inhibition of eIF4E phosphorylation by treatment with CGP57380 (an inhibitor of MAPK interacting serine-threonine kinases Mnk1/2, the eIF4E upstream kinase) or inhibitors of ERK1/2, the upstream kinase regulating Mnk1/2, also sensitized CRPC cells to RAD001+bicalutamide. Examination of downstream targets of eIF4E-mediated translation, including survivin, demonstrated that eIF4E(S209) phosphorylation increased cap-independent translation whereas its inhibition restored cap-dependent translation which could be inhibited by mTOR inhibitors. Thus, our results demonstrate that while combinations of AR and mTOR inhibitors were effective in suppressing tumor growth by inhibiting both AR-induced transcription and mTOR-induced cap-dependent translation, pre-treatment with AR antagonists including bicalutamide increased eIF4E phosphorylation that induced resistance to combinations of AR and mTOR inhibitors by inducing cap-independent translation. We conclude that this resistance can be overcome by inhibiting eIF4E phosphorylation with Mnk1/2 or ERK1/2 inhibitors.

RNase L Suppresses Androgen Receptor Signaling, Cell Migration and Matrix Metalloproteinase Activity in Prostate Cancer Cells

The interferon antiviral pathways and prostate cancer genetics converge on a regulated endoribonuclease, RNase L. Positional cloning and linkage studies mapped Hereditary Prostate Cancer 1 (HPC1) to RNASEL. To date, there is no correlation of viral infections with prostate cancer, suggesting that RNase L may play additional roles in tumor suppression. Here, we demonstrate a role of RNase L as a suppressor of androgen receptor (AR) signaling, cell migration and matrix metalloproteinase activity. Using RNase L mutants, we show that its nucleolytic activity is dispensable for both AR signaling and migration. The most prevalent HPC1-associated mutations in RNase L, R462Q and E265X, enhance AR signaling and cell migration. RNase L negatively regulates cell migration and attachment on various extracellular matrices. We demonstrate that RNase L knockdown cells promote increased cell surface expression of integrin β1 which activates Focal Adhesion Kinase-Sarcoma (FAK-Src) pathway and Ras-related C3 botulinum toxin substrate 1-guanosine triphosphatase (Rac1-GTPase) activity to increase cell migration. Activity of matrix metalloproteinase (MMP)-2 and -9 is significantly increased in cells where RNase L levels are ablated. We show that mutations in RNase L found in HPC patients may promote prostate cancer by increasing expression of AR-responsive genes and cell motility and identify novel roles of RNase L as a prostate cancer susceptibility gene.

Lentiviral vector-mediated insertional mutagenesis screen identifies genes that influence androgen independent prostate cancer progression and predict clinical outcome

Prostate cancer (PC) is the second leading cause of cancer related deaths in US men. Androgen deprivation therapy (ADT) improves clinical outcome, but tumors often recur and progress to androgen independent prostate cancer (AIPC) which no longer responds to ADT. The progression to AIPC is due to genetic alterations that allow PC cancer cells to grow in the absence of androgen. Here we performed an insertional mutagenesis screen using a replication-incompetent lentiviral vector (LV) to identify the genes that promote AIPC in an orthotopic mouse model. Androgen sensitive PC cells, LNCaP, were mutagenized with LV and injected into the prostate of male mice. After tumor development, mice were castrated to select for cells that proliferate in the absence of androgen. Proviral integration sites and nearby dysregulated genes were identified in tumors developed in an androgen deficient environment. Using publically available datasets, the expression of these candidate androgen independence genes in human PC tissues were analyzed. A total of 11 promising candidate AIPC genes were identified: GLYATL1, FLNA, OBSCN, STRA13, WHSC1, ARFGAP3, KDM2A, FAM83H, CLDN7, CNOT6, and B3GNT9. Seven out the 11 candidate genes; GLYATL1, OBSCN, STRA13, KDM2A, FAM83H, CNOT6, and B3GNT6, have not been previously implicated in PC. An in vitro clonogenic assay showed that knockdown of KDM2A, FAM83H, and GLYATL1 genes significantly inhibited the colony forming ability of LNCaP cells. Additionally, we showed that a combination of four genes, OBSCN, FAM83H, CLDN7, and ARFGAP3 could significantly predicted the recurrence risk in PC patients after prostatectomy (P = 5.3 × 10-5 ). © 2015 Wiley Periodicals, Inc.

Cytoskeletal Filamin A Differentially Modulates RNA Polymerase III Gene Transcription in Transformed Cell Lines

Cytoskeletal filamin A (FLNA) is an important protein involved in multiple cellular processes. Previous studies have shown that FLNA can promote or inhibit cancer growth and development; however, the mechanisms underlying these events are not fully understood. Here we show that, in both 293T and SaOS2 cells, knockdown of FLNA significantly enhanced transcription of RNA polymerase (pol) III-transcribed genes except for a subset of tRNA genes. In contrast, re-expression of FLNA in an FLNA-deficient melanoma cell line (A7) repressed transcription of all pol III-transcribed genes, suggesting that FLNA inhibits pol III transcription in a cell type-specific manner. Chromatin immunoprecipitation assays revealed that the repression of pol III gene transcription by FLNA correlates with the decreased occupancy of the RNA pol III transcription machinery at promoters. Immunofluorescence microscopy and coimmunoprecipitation assays revealed that FLNA can associate with the RNA pol III transcription machinery through its actin-binding domain within nuclei. Mechanistic analysis revealed that FLNA suppresses pol III gene transcription by confining the recruitment of the RNA pol III transcription machinery at the promoters of the genes that are sensitive to the alteration of FLNA expression. These findings not only extend the understanding of FLNA function in cells but also provide novel insights into the mechanism by which FLNA represses cell proliferation.

The Androgen Receptor Antagonizes Wnt/β-Catenin Signaling in Epidermal Stem Cells

Activation of Wnt/β-catenin signaling in adult mouse epidermis leads to expansion of the stem cell compartment and redirects keratinocytes in the interfollicular epidermis and sebaceous glands (SGs) to differentiate along the hair follicle (HF) lineages. Here we demonstrate that during epidermal development and homeostasis there is reciprocal activation of the androgen receptor (AR) and β-catenin in cells of the HF bulb. AR activation reduced β-catenin-dependent transcription, blocked β-catenin-induced induction of HF growth, and prevented β-catenin-mediated conversion of SGs into HFs. Conversely, AR inhibition enhanced the effects of β-catenin activation, promoting HF proliferation and differentiation, culminating in the formation of benign HF tumors and a complete loss of SG identity. We conclude that AR signaling has a key role in epidermal stem cell fate selection by modulating responses to β-catenin in adult mouse skin.

Cross-talk between androgen receptor/filamin A and TrkA regulates neurite outgrowth in PC12 cells

Steroids and growth factors control neuronal development through their receptors under physiological and pathological conditions. We show that PC12 cells harbor endogenous androgen receptor (AR), whose inhibition or silencing strongly interferes with neuritogenesis stimulated by the nonaromatizable synthetic androgen R1881 or NGF. This implies a role for AR not only in androgen signaling, but also in NGF signaling. In turn, a pharmacological TrkA inhibitor interferes with NGF- or androgen-induced neuritogenesis. In addition, androgen or NGF triggers AR association with TrkA, TrkA interaction with PI3-K δ, and downstream activation of PI3-K δ and Rac in PC12 cells. Once associated with AR, filamin A (FlnA) contributes to androgen or NGF neuritogenesis, likely through its interaction with signaling effectors, such as Rac. This study thus identifies a previously unrecognized reciprocal cross-talk between AR and TrkA, which is controlled by β1 integrin. The contribution of FlnA/AR complex and PI3-K δ to neuronal differentiation by androgens and NGF is also novel. This is the first description of AR function in PC12 cells.

Transcription of Nrdp1 by the androgen receptor is regulated by nuclear filamin A in prostate cancer

Prostate cancer (PCa) progression is regulated by the androgen receptor (AR); however, patients undergoing androgen-deprivation therapy (ADT) for disseminated PCa eventually develop castration-resistant PCa (CRPC). Results of previous studies indicated that AR, a transcription factor, occupies distinct genomic loci in CRPC compared with hormone-naïve PCa; however, the cause of this distinction was unknown. The E3 ubiquitin ligase Nrdp1 is a model AR target modulated by androgens in hormone-naïve PCa but not in CRPC. Using Nrdp1, we investigated how AR switches transcription programs during CRPC progression. The proximal Nrdp1 promoter contains an androgen response element (ARE); we demonstrated AR binding to this ARE in androgen-sensitive PCa. Analysis of hormone-naive human prostatectomy specimens revealed correlation between Nrdp1 and AR expression, supporting AR regulation of NRDP1 levels in androgen-sensitive tissue. However, despite sustained AR levels, AR binding to the Nrdp1 promoter and Nrdp1 expression were suppressed in CRPC. Elucidation of the suppression mechanism demonstrated correlation of NRDP1 levels with nuclear localization of the scaffolding protein filamin A (FLNA) which, as we previously showed, is itself repressed following ADT in many CRPC tumors. Restoration of nuclear FLNA in CRPC stimulated AR binding to Nrdp1 ARE, increased its transcription, and augmented NRDP1 protein expression and responsiveness to ADT, indicating that nuclear FLNA controls AR-mediated androgen-sensitive Nrdp1 transcription. Expression of other AR-regulated genes lost in CRPC was also re-established by nuclear FLNA. Thus, our results indicate that nuclear FLNA promotes androgen-dependent AR-regulated transcription in PCa, while loss of nuclear FLNA in CRPC alters the AR-regulated transcription program.

The dual role of filamin A in cancer: can't live with (too much of) it, can't live without it

Filamin A (FlnA) has been associated with actin as cytoskeleton regulator. Recently its role in the cell has come under scrutiny for FlnA's involvement in cancer development. FlnA was originally revealed as a cancer-promoting protein, involved in invasion and metastasis. However, recent studies have also found that under certain conditions, it prevented tumor formation or progression, confusing the precise function of FlnA in cancer development. Here, we try to decipher the role of FlnA in cancer and the implications for its dual role. We propose that differences in subcellular localization of FlnA dictate its role in cancer development. In the cytoplasm, FlnA functions in various growth signaling pathways, such as vascular endothelial growth factor, in addition to being involved in cell migration and adhesion pathways, such as R-Ras and integrin signaling. Involvement in these pathways and various others has shown a correlation between high cytoplasmic FlnA levels and invasive cancers. However, an active cleaved form of FlnA can localize to the nucleus rather than the cytoplasm and its interaction with transcription factors has been linked to a decrease in invasiveness of cancers. Therefore, overexpression of FlnA has a tumor-promoting effect, only when it is localized to the cytoplasm, whereas if FlnA undergoes proteolysis and the resulting C-terminal fragment localizes to the nucleus, it acts to suppress tumor growth and inhibit metastasis. Development of drugs to target FlnA and cause cleavage and subsequent localization to the nucleus could be a new and potent field of research in treating cancer.

Regulation of the transcriptional coactivator FHL2 licenses activation of the androgen receptor in castrate-resistant prostate cancer

It is now clear that progression from localized prostate cancer to incurable castrate-resistant prostate cancer (CRPC) is driven by continued androgen receptor (AR), signaling independently of androgen. Thus, there remains a strong rationale to suppress AR activity as the single most important therapeutic goal in CRPC treatment. Although the expression of ligand-independent AR splice variants confers resistance to AR-targeted therapy and progression to lethal castrate-resistant cancer, the molecular regulators of AR activity in CRPC remain unclear, in particular those pathways that potentiate the function of mutant AR in CRPC. Here, we identify FHL2 as a novel coactivator of ligand-independent AR variants that are important in CRPC. We show that the nuclear localization of FHL2 and coactivation of the AR is driven by calpain cleavage of the cytoskeletal protein filamin, a pathway that shows differential activation in prostate epithelial versus prostate cancer cell lines. We further identify a novel FHL2-AR-filamin transcription complex, revealing how deregulation of this axis promotes the constitutive, ligand-independent activation of AR variants, which are present in CRPC. Critically, the calpain-cleaved filamin fragment and FHL2 are present in the nucleus only in CRPC and not benign prostate tissue or localized prostate cancer. Thus, our work provides mechanistic insight into the enhanced AR activation, most notably of the recently identified AR variants, including AR-V7 that drives CRPC progression. Furthermore, our results identify the first disease-specific mechanism for deregulation of FHL2 nuclear localization during cancer progression. These results offer general import beyond prostate cancer, given that nuclear FHL2 is characteristic of other human cancers where oncogenic transcription factors that drive disease are activated like the AR in prostate cancer.