Hypoxia-inducible factor 1A inhibition overcomes castration resistance of prostate tumors.

Androgen deprivation therapy (ADT) is a cornerstone of prostate cancer (PCa) management. Although tumors initially regress, many progress to a hormone-independent state termed castration-resistant PCa (CRPC), for which treatment options are limited. We here report that the major luminal cell population in tumors of Pten(i)pe-/- mice, generated by luminal epithelial cell-specific deletion of the tumor suppressor PTEN after puberty, is castration-resistant and that the expression of inflammation and stemness markers is enhanced in persistent luminal cells. In addition, hypoxia-inducible factor 1 (HIF1) signaling, which we have previously demonstrated to be induced in luminal cells of Pten(i)pe-/- mice and to promote malignant progression, is further activated. Importantly, we show that genetic and pharmacological inhibition of HIF1A sensitizes Pten-deficient prostatic tumors to castration and provides durable therapeutic responses. Furthermore, HIF1A inhibition induces apoptotic signaling in human CRPC cell lines. Therefore, our data demonstrate that HIF1A in prostatic tumor cells is a critical factor that enables their survival after ADT, and identify it as a target for CRPC management.

Hypoxia-mediated stabilization of HIF1A in prostatic intraepithelial neoplasia promotes cell plasticity and malignant progression.

Prostate cancer (PCa) is a leading cause of cancer-related deaths. The slow evolution of precancerous lesions to malignant tumors provides a broad time frame for preventing PCa. To characterize prostatic intraepithelial neoplasia (PIN) progression, we conducted longitudinal studies on Pten(i)pe-/- mice that recapitulate prostate carcinogenesis in humans. We found that early PINs are hypoxic and that hypoxia-inducible factor 1 alpha (HIF1A) signaling is activated in luminal cells, thus enhancing malignant progression. Luminal HIF1A dampens immune surveillance and drives luminal plasticity, leading to the emergence of cells that overexpress Transglutaminase 2 (TGM2) and have impaired androgen signaling. Elevated TGM2 levels in patients with PCa are associated with shortened progression-free survival after prostatectomy. Last, we show that pharmacologically inhibiting HIF1A impairs cell proliferation and induces apoptosis in PINs. Therefore, our study demonstrates that HIF1A is a target for PCa prevention and that TGM2 is a promising prognostic biomarker of early relapse after prostatectomy.

Single-cell analyses unravel cell type-specific responses to a vitamin D analog in prostatic precancerous lesions.

Epidemiological data have linked vitamin D deficiency to the onset and severity of various cancers, including prostate cancer, and although in vitro studies have demonstrated anticancer activities for vitamin D, clinical trials provided conflicting results. To determine the impact of vitamin D signaling on prostatic precancerous lesions, we treated genetically engineered Pten(i)pe-/- mice harboring prostatic intraepithelial neoplasia (PIN) with Gemini-72, a vitamin D analog with reported anticancer activities. We show that this analog induces apoptosis in senescent PINs, normalizes extracellular matrix remodeling by stromal fibroblasts, and reduces the prostatic infiltration of immunosuppressive myeloid-derived suppressor cells. Moreover, single-cell RNA-sequencing analysis demonstrates that while a subset of luminal cells expressing Krt8, Krt4, and Tacstd2 (termed luminal-C cells) is lost by such a treatment, antiapoptotic pathways are induced in persistent luminal-C cells. Therefore, our findings delineate the distinct responses of PINs and the microenvironment to Gemini-72, and shed light on mechanisms that limit treatment's efficacy.

Design, Synthesis, Evaluation and Structure of Allenic 1α,25-Dihydroxyvitamin D3 Analogs with Locked Mobility at C-17.

Vitamin D receptor ligands have potential for the treatment of hyperproliferative diseases and disorders related to the immune system. However, hypercalcemic effects limit their therapeutical uses and call for the development of tissue-selective new analogs. We have designed and synthesized the first examples of 1α,25-dihydroxyvitamin D3 analogs bearing an allenic unit attached to the D ring to restrict the side-chain conformational mobility. The triene system was constructed by a Pd0 -mediated cyclization/Suzuki-Miyaura cross-coupling process in the presence of an allenic side chain. The allenic moiety was built through an orthoester-Claisen rearrangement of a propargylic alcohol. The biological activity and structure of (22S)-1α,25-dihydroxy-17,20-dien-24-homo-21-nor-vitamin D3 bound to binding domain of the vitamin D receptor, provide information concerning side-chain conformational requirements for biological activity.

TRIM24 mediates the interaction of the retinoic acid receptor alpha with the proteasome.

The nuclear retinoic acid (RA) receptors (RARα, ß and γ) are ligand-dependent regulators of transcription. Upon activation by RA, they are recruited at the promoters of target genes together with several coregulators. Then, they are degraded by the ubiquitin proteasome system. Here, we report that the degradation of the RARα subtype involves ubiquitination and the tripartite motif protein TRIM24, which was originally identified as a ligand-dependent corepressor of RARα. We show that in response to RA, TRIM24 serves as an adapter linking RARα to the proteasome for its degradation. In addition, TRIM24 and the proteasome are recruited with RARα to the promoters of target genes and thus are inherently linked to RARα transcriptional activity.

PFN2a, a new partner of RARα in the cytoplasm.

Retinoic acid receptors (RARs) are classically considered as nuclear ligand-dependent regulators of transcription. Here we highlighted a novel face of the RARα subtype: RARα is present in low amounts in the cytoplasm of mouse embryonic fibroblasts (MEFs) where it interacts with profilin2a (PFN2A), a small actin-binding protein involved in filaments polymerization. The interaction involves the N-terminal proline-rich motif (PRM) of RARα and the SH3-like domain of PFN2a. When increased in the cytoplasm, RARα competes with other PFN2a-binding proteins bearing PRMs and involved in actin filaments elongation. Consequently, the actin filament network is altered and MEFs adhesion is decreased. This novel role opens novel avenues for the understanding of pathologies characterized by increased levels of cytoplasmic RARα.

Allosteric Regulation in the Ligand Binding Domain of Retinoic Acid Receptorγ.

Retinoic acid (RA) plays key roles in cell differentiation and growth arrest through nuclear retinoic acid receptors (RARs), which are ligand-dependent transcription factors. While the main trigger of RAR activation is the binding of RA, phosphorylation of the receptors has also emerged as an important regulatory signal. Phosphorylation of the RARγ N-terminal domain (NTD) is known to play a functional role in neuronal differentiation. In this work, we investigated the phosphorylation of RARγ ligand binding domain (LBD), and present evidence that the phosphorylation status of the LBD affects the phosphorylation of the NTD region. We solved the X-ray structure of a phospho-mimetic mutant of the LBD (RARγ S371E), which we used in molecular dynamics simulations to characterize the consequences of the S371E mutation on the RARγ structural dynamics. Combined with simulations of the wild-type LBD, we show that the conformational equilibria of LBD salt bridges (notably R387-D340) are affected by the S371E mutation, which likely affects the recruitment of the kinase complex that phosphorylates the NTD. The molecular dynamics simulations also showed that a conservative mutation in this salt bridge (R387K) affects the dynamics of the LBD without inducing large conformational changes. Finally, cellular assays showed that the phosphorylation of the NTD of RARγ is differentially regulated by retinoic acid in RARγWT and in the S371N, S371E and R387K mutants. This multidisciplinary work highlights an allosteric coupling between phosphorylations of the LBD and the NTD of RARγ and supports the importance of structural dynamics involving electrostatic interactions in the regulation of RARs activity.

Phosphoproteome and Transcriptome of RA-Responsive and RA-Resistant Breast Cancer Cell Lines.

Retinoic acid (RA), the main active vitamin A metabolite, controls multiple biological processes such as cell proliferation and differentiation through genomic programs and kinase cascades activation. Due to these properties, RA has proven anti-cancer capacity. Several breast cancer cells respond to the antiproliferative effects of RA, while others are RA-resistant. However, the overall signaling and transcriptional pathways that are altered in such cells have not been elucidated. Here, in a large-scale analysis of the phosphoproteins and in a genome-wide analysis of the RA-regulated genes, we compared two human breast cancer cell lines, a RA-responsive one, the MCF7 cell line, and a RA-resistant one, the BT474 cell line, which depicts several alterations of the "kinome". Using high-resolution nano-LC-LTQ-Orbitrap mass spectrometry associated to phosphopeptide enrichment, we found that several proteins involved in signaling and in transcription, are differentially phosphorylated before and after RA addition. The paradigm of these proteins is the RA receptor α (RARα), which was phosphorylated in MCF7 cells but not in BT474 cells after RA addition. The panel of the RA-regulated genes was also different. Overall our results indicate that RA resistance might correlate with the deregulation of the phosphoproteome with consequences on gene expression.

Genes involved in cell adhesion and signaling: a new repertoire of retinoic acid receptor target genes in mouse embryonic fibroblasts.

Nuclear retinoic acid (RA) receptors (RARα, ß and γ) are ligand-dependent transcription factors that regulate the expression of a battery of genes involved in cell differentiation and proliferation. They are also phosphoproteins and we previously showed the importance of their phosphorylation in their transcriptional activity. In the study reported here, we conducted a genome-wide analysis of the genes that are regulated by RARs in mouse embryonic fibroblasts (MEFs) by comparing wild-type MEFs to MEFs lacking the three RARs. We found that in the absence of RA, RARs control the expression of several gene transcripts associated with cell adhesion. Consequently the knockout MEFs are unable to adhere and to spread on substrates and they display a disrupted network of actin filaments, compared with the WT cells. In contrast, in the presence of the ligand, RARs control the expression of other genes involved in signaling and in RA metabolism. Taking advantage of rescue cell lines expressing the RARα or RARγ subtypes (either wild-type or mutated at the N-terminal phosphorylation sites) in the null background, we found that the expression of RA-target genes can be controlled either by a specific single RAR or by a combination of RAR isotypes, depending on the gene. We also selected genes that require the phosphorylation of the receptors for their regulation by RA. Our results increase the repertoire of genes that are regulated by RARs and highlight the complexity and diversity of the transcriptional programs regulated by RARs, depending on the gene.

Production and characterization of a retinoic acid receptor RARγ construction encompassing the DNA binding domain and the disordered N-terminal proline rich domain.

Gene activation by retinoic acid nuclear receptors (RAR) is regulated by a number of molecular events such as ligand binding, interaction with cognate DNA sequences and co-regulatory proteins, and phosphorylation. Among the several phosphorylation sites that are involved in the non-genomic regulatory pathways of the RAR, two are located in a proline rich domain (PRD) within the N-terminal domain (NTD) of the receptor. This region is predicted to be intrinsically disordered, complicating its production and purification. We present here an approach enabling the high yield production of RAR fragments encompassing the PRD and the DNA binding domain (DBD). We found that expression levels were dependent on where the position of the N-terminal boundary of the fragment was placed within the RAR sequence. The purification protocol involves the use of maltose binding protein as a solubilising tag and extensive centrifugation steps at critical points of the purification process. This protocol is suitable to express (15)N, (13)C labeled proteins enabling nuclear magnetic resonance studies. The resulting proteins were characterized by biophysical methods including Small Angle X-ray Scattering and NMR. These studies showed that PRD extension of RARγ is disordered in solution, a state that is compatible with modifications such as phosphorylation.