Glucocorticoid Receptor Regulates and Interacts with LEDGF/p75 to Promote Docetaxel Resistance in Prostate Cancer Cells

Patients with advanced prostate cancer (PCa) invariably develop resistance to anti-androgen therapy and taxane-based chemotherapy. Glucocorticoid receptor (GR) has been implicated in PCa therapy resistance; however, the mechanisms underlying GR-mediated chemoresistance remain unclear. Lens epithelium-derived growth factor p75 (LEDGF/p75, also known as PSIP1 and DFS70) is a glucocorticoid-induced transcription co-activator implicated in cancer chemoresistance. We investigated the contribution of the GR-LEDGF/p75 axis to docetaxel (DTX)-resistance in PCa cells. GR silencing in DTX-sensitive and -resistant PCa cells decreased LEDGF/p75 expression, and GR upregulation in enzalutamide-resistant cells correlated with increased LEDGF/p75 expression. ChIP-sequencing revealed GR binding sites in the LEDGF/p75 promoter. STRING protein-protein interaction analysis indicated that GR and LEDGF/p75 belong to the same transcriptional network, and immunochemical studies demonstrated their co-immunoprecipitation and co-localization in DTX-resistant cells. The GR modulators exicorilant and relacorilant increased the sensitivity of chemoresistant PCa cells to DTX-induced cell death, and this effect was more pronounced upon LEDGF/p75 silencing. RNA-sequencing of DTX-resistant cells with GR or LEDGF/p75 knockdown revealed a transcriptomic overlap targeting signaling pathways associated with cell survival and proliferation, cancer, and therapy resistance. These studies implicate the GR-LEDGF/p75 axis in PCa therapy resistance and provide a pre-clinical rationale for developing novel therapeutic strategies for advanced PCa.

Glucocorticoid Receptor and β-Catenin Interact in Prostate Cancer Cells and Their Co-Inhibition Attenuates Tumorsphere Formation, Stemness, and Docetaxel Resistance

Therapy resistance hinders the efficacy of anti-androgen therapies and taxane-based chemotherapy for advanced prostate cancer (PCa). Glucocorticoid receptor (GR) signaling mediates resistance to androgen receptor signaling inhibitors (ARSI) and has also been recently implicated in PCa resistance to docetaxel (DTX), suggesting a role in therapy cross-resistance. Like GR, β-catenin is upregulated in metastatic and therapy-resistant tumors and is a crucial regulator of cancer stemness and ARSI resistance. β-catenin interacts with AR to promote PCa progression. Given the structural and functional similarities between AR and GR, we hypothesized that β-catenin also interacts with GR to influence PCa stemness and chemoresistance. As expected, we observed that treatment with the glucocorticoid dexamethasone promotednuclear accumulation of GR and active β-catenin in PCa cells. Co-immunoprecipitation studies showed that GR and β-catenin interact in DTX-resistant and DTX-sensitive PCa cells. Pharmacological co-inhibition of GR and β-catenin, using the GR modulator CORT-108297 and the selective β-catenin inhibitor MSAB, enhanced cytotoxicity in DTX-resistant PCa cells grown in adherent and spheroid cultures and decreased CD44+/CD24- cell populations in tumorspheres. These results indicate that GR and β-catenin influence cell survival, stemness, and tumorsphere formation in DTX-resistant cells. Their co-inhibition could be a promising therapeutic strategy to overcome PCa therapy cross-resistance.

Abstract 1455: The glucocorticoid receptor-LEDGFp75 interaction in prostate cancer therapy cross-resistance

Prostate cancer (PCa) is the second leading cause of cancer deaths in the U.S., disproportionally affecting African American (AA) men. PCa patients with recurrent disease develop therapy resistance and fail to respond to both anti-androgen receptor signaling (ARSI) therapy and taxane-based chemotherapy. Glucocorticoid receptor, a transcription factor, has been implicated in resistance to ARSI (via the GR bypass), and docetaxel (DTX) therapies. However, the mechanisms underlying this GR-mediated therapy cross-resistance are poorly understood. Previously, we demonstrated that glucocorticoids, which are co-administered with current PCa therapies and activate GR signaling, upregulate the chemoresistance-associated transcription coactivator LEDGFp75 in PCa cells. We also identified consensus GR binding sites in the promoter region of the gene encoding LEDGFp75, suggesting it is a GR target gene. We hypothesized that GR transcriptionally upregulates LEDGFp75 and then interacts with this protein in the nucleus to promote DTX resistance in PCa cells. Genetic silencing of GR in a panel of DTX-sensitive and -resistant PCa cell lines decreased the expression of LEDGFp75 at both the protein and transcript levels, confirming its status as a candidate GR target gene. However, genetic silencing of LEDGFp75 had no effects on GR protein expression. Pharmacological inhibition of GR also decreased LEDGFp75 in DTX-sensitive cells. The effects of Exicorilant and Relacorilant (Corcept Therapeutics) were evaluated on LEDGFp75 protein expression levels. Immunoprecipitation and confocal microscopy studies revealed that GR and LEDGFp75 interact in the nucleus of PCa cells. Interestingly, upregulation of GR in enzalutamide resistant LNCaP cells correlated with LEDGFp75 upregulation, and GR silencing in these cells decreased this upregulation. These results suggested a possible role for GR and LEDGFp75 in PCa therapy cross-resistance. Further studies are underway to determine if co-targeting these two proteins genetically and pharmacologically attenuates both enzalutamide resistance and DTX resistance and other aggressive properties of PCa cells. In addition, RNAseq studies have been initiated to determine the degree of transcriptional overlap between GR and LEDGFp75 in chemoresistant PCa cells. Our goal is to link mechanistically the GR-LEDGFp75 transcriptional network to ARSI/taxane cross-resistance in PCa and target this network to attenuate therapy resistance.

Citation Format: Evelyn S. Sanchez-Hernandez, Pedro T. Ochoa, Greisha L. Ortiz-Hernandez, Shannalee Martinez, Carlos Casiano. The glucocorticoid receptor-LEDGFp75 interaction in prostate cancer therapy cross-resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1455.

The Nuclear Dense Fine Speckled (DFS) Immunofluorescence Pattern: Not All Roads Lead to DFS70/LEDGFp75

The monospecific dense fine speckled (DFS) immunofluorescence assay (IFA) pattern is considered a potential marker to aid in exclusion of antinuclear antibody (ANA)-associated rheumatic diseases (AARD). This pattern is typically produced by autoantibodies against transcription co-activator DFS70/LEDGFp75, which are frequently found in healthy individuals and patients with miscellaneous inflammatory conditions. In AARD patients, these antibodies usually co-exist with disease-associated ANAs. Previous studies reported the occurrence of monospecific autoantibodies that generate a DFS-like or pseudo-DFS IFA pattern but do not react with DFS70/LEDGFp75. We characterized this pattern using confocal microscopy and immunoblotting. The target antigen associated with this pattern partially co-localized with DFS70/LEDGFp75 and its interacting partners H3K36me2, an active chromatin marker, and MLL, a transcription factor, in HEp-2 cells, suggesting a role in transcription. Immunoblotting did not reveal a common protein band immunoreactive with antibodies producing the pseudo-DFS pattern, suggesting they may recognize diverse proteins or conformational epitopes. Given the subjectivity of the HEp-2 IFA test, the awareness of pseudo-DFS autoantibodies reinforces recommendations for confirmatory testing when reporting patient antibodies producing a putative DFS pattern in a clinical setting. Future studies should focus on defining the potential diagnostic utility of the pseudo-DFS pattern and its associated antigen(s).

Abstract 2348: Contribution of the GR/LEDGFp75 axis to prostate cancer chemoresistance

Prostate cancer (PCa) is the second leading cause of cancer deaths in the U.S., disproportionally affecting African American (AA) men. Glucocorticoids (GCs) are administered to PCa patients and have been implicated in therapy resistance. This may be critical to AA men with PCa since they have elevated endogenous GCs levels compared to Caucasian American (CA) men. GCs bind to the glucocorticoid receptor (GR) to exert their actions. The mechanisms of GR-mediated chemoresistance, and its possible contribution to PCa mortality disparities are unknown. We demonstrated that GCs upregulate the chemoresistance-associated protein and transcription co-activator LEDGF/p75 in PCa cells and identified consensus GR binding sites in the promoter region of this protein. Given that both GR and LEDGF/p75 are components of the RNA polymerase II transcription complex, we hypothesized that GR transcriptionally upregulates LEDGF/p75 and then interacts with it to enhance taxane resistance in PCa cells. Pharmacological and genetic inhibition of GR in a panel of docetaxel (DTX)-sensitive and -resistant PCa cells decreased the expression of LEDGF/p75, confirming its status as a candidate GR target gene. However, silencing of LEDGF/p75 had no effects on GR expression. Immunoprecipitation studies revealed that GR and LEDGF/p75 interact in DTX-resistant PCa cells. This interaction was confirmed by confocal microscopy. Immunohistochemical analysis of GR and LEDGF/p75 expression in normal and tumor prostate tissues was performed, and the results are currently being analyzed. Our studies use a mechanistic approach to evaluate the potential contribution of the GR-LEDGF/p75 axis to PCa chemoresistance. Evaluating the co-expression of these proteins in racially diverse PCa tissues may also reveal race-related differential expression, providing insights into the potential contribution of this axis to PCa chemoresistance and mortality disparities.

Citation Format: Evelyn S. Sanchez Hernandez, Greisha L. Ortiz Hernandez, Pedro T. Ochoa, Christian R. Gomez, Carlos A. Casiano. Contribution of the GR/LEDGFp75 axis to prostate cancer chemoresistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2348.

Abstract 399: The glucocorticoid receptor and β-catenin interact in prostate cancer cells and their co-inhibition attenuates stemness and docetaxel resistance

The efficacy of anti-androgen receptor (AR) therapies and taxane-based chemotherapy for the treatment of advanced prostate cancer (PCa) is hindered by the development of therapy resistance. Our previous studies demonstrated that docetaxel (DTX)-resistant PCa cells activates a transcriptomic program associated with stemness and display cancer stem cell (CSC) properties, consistent with the notion that CSCs within prostate tumors contribute to chemoresistance. Glucocorticoid receptor (GR) signaling is a critical mediator of resistance to AR-targeted therapy, and has been recently implicated in the development of PCa cell tumorsphere formation and chemoresistance. Like GR, β-catenin is overexpressed in metastatic and therapy-resistant tumors, and is considered a key regulator of cancer stemness and androgen-targeted therapy resistance. Given the structural and functional overlap between GR and AR, a known interacting partner of β-catenin, we hypothesized that GR also interacts with β-catenin to support stemness and chemoresistance in PCa cells. We observed that treatment with the glucocorticoid dexamethasone induces enhanced nuclear accumulation of both GR and β-catenin in DTX-resistant PCa cells compared to their DTX-sensitive counterparts. Knockdown studies revealed that GR and β-catenin do no regulate each other at the protein level. However, using whole cell and nuclear co-immunoprecipitation, we demonstrated the interaction between GR and β-catenin in both DTX-resistant and DTX-sensitive PC3, DU145, and 22RV1 cells. Pharmacological inhibition and RNA interference-mediated silencing of GR with concomitant inhibition of β-catenin enhanced DTX cytotoxicity in resistant PCa cells grown in both adherent and spheroid cultures, and decreased CD44+/CD24- cell populations in tumorspheres. These results indicate that both GR and β-catenin interact and influence stemness, and may be promising therapeutic targets to overcome PCa chemoresistance.

Citation Format: Shannalee R. Martinez, Catherine C. Elix, Pedro T. Ochoa, Evelyn S. Sanchez-Hernandez, Hossam R. Alkashgari, Greisha L. Ortiz-Hernandez, Lubo Zhang, Carlos A. Casiano. The glucocorticoid receptor and β-catenin interact in prostate cancer cells and their co-inhibition attenuates stemness and docetaxel resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 399.

Abstract PO-145: Contribution of the GR-LEDGF/p75 axis to prostate cancer chemoresistance

Prostate cancer (PCa) is the second leading cause of cancer deaths in the U.S., disproportionally affecting African American (AA) men. Glucocorticoids (GCs) are administered to PCa patients and have been implicated in therapy resistance. This may be critical to AA men with PCa since they have elevated endogenous GCs levels compared to Caucasian American (CA) men. GCs bind to the glucocorticoid receptor (GR) to exert their actions. The mechanisms of GR-mediated chemoresistance, and its possible contribution to PCa mortality disparities are unknown. We demonstrated that GCs upregulate the chemoresistance-associated protein and transcription co-activator LEDGF/p75 in PCa cells and identified consensus GR binding sites in the promoter region of this protein. Given that both GR and LEDGF/p75 are components of the RNA polymerase II transcription complex, we hypothesized that GR transcriptionally upregulates LEDGF/p75 and then interacts with it to enhance taxane resistance in PCa cells. Pharmacological and genetic inhibition of GR in a panel of docetaxel (DTX)-sensitive and -resistant PCa cells decreased the expression of LEDGF/p75, confirming its status as a candidate GR target gene. However, silencing of LEDGF/p75 had no effects on GR expression. Immunoprecipitation studies revealed that GR and LEDGF/p75 interact in DTX-sensitive and -resistant PCa cells. This interaction was confirmed by confocal microscopy. Immunohistochemical analysis of GR and LEDGF/p75 expression in normal and tumor prostate tissues was performed and the results are currently being analyzed. Our studies use a mechanistic approach to evaluate the potential contribution of the GR-LEDGF/p75 axis to PCa chemoresistance. Evaluating the co-expression of these proteins in racially diverse PCa tissues may also reveal race-related differential expression, providing insights into the potential contribution of this axis to PCa chemoresistance and mortality disparities.

Citation Format: Evelyn S Sanchez-Hernandez, Greisha L. Ortiz-Hernandez, Pedro T. Ochoa, Christian R Gomez, Carlos A Casiano. Contribution of the GR-LEDGF/p75 axis to prostate cancer chemoresistance [abstract]. In: Proceedings of the AACR Virtual Conference: 14th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2021 Oct 6-8. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2022;31(1 Suppl):Abstract nr PO-145.