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Activation of RAR? induces autophagy in SKBR3 breast cancer cells and depletion of key autophagy genes enhances ATRA toxicity.
ABSTRACT: All-trans retinoic acid (ATRA), a pan-retinoic acid receptor (RAR) agonist, is, along with other retinoids, a promising therapeutic agent for the treatment of a variety of solid tumors. On the one hand, preclinical studies have shown promising anticancer effects of ATRA in breast cancer; on the other hand, resistances occurred. Autophagy is a cellular recycling process that allows the degradation of bulk cellular contents. Tumor cells may take advantage of autophagy to cope with stress caused by anticancer drugs. We therefore wondered if autophagy is activated by ATRA in mammary tumor cells and if modulation of autophagy might be a potential novel treatment strategy. Indeed, ATRA induces autophagic flux in ATRA-sensitive but not in ATRA-resistant human breast cancer cells. Moreover, using different RAR agonists as well as RAR?-knockdown breast cancer cells, we demonstrate that autophagy is dependent on RAR? activation. Interestingly, inhibition of autophagy in breast cancer cells by either genetic or pharmacological approaches resulted in significantly increased apoptosis under ATRA treatment and attenuated epithelial differentiation. In summary, our findings demonstrate that ATRA-induced autophagy is mediated by RAR? in breast cancer cells. Furthermore, inhibition of autophagy results in enhanced apoptosis. This points to a potential novel treatment strategy for a selected group of breast cancer patients where ATRA and autophagy inhibitors are applied simultaneously.
Project description:Retinoids are a family of signaling molecules derived from vitamin A with well established roles in cellular differentiation. Physiologically active retinoids mediate transcriptional effects on cells through interactions with retinoic acid (RARs) and retinoid-X (RXR) receptors. Chromosomal translocations involving the RAR? gene, which lead to impaired retinoid signaling, are implicated in acute promyelocytic leukemia (APL). All-trans-retinoic acid (ATRA), alone and in combination with arsenic trioxide (ATO), restores differentiation in APL cells and promotes degradation of the abnormal oncogenic fusion protein through several proteolytic mechanisms. RAR? fusion-protein elimination is emerging as critical to obtaining sustained remission and long-term cure in APL. Autophagy is a degradative cellular pathway involved in protein turnover. Both ATRA and ATO also induce autophagy in APL cells. Enhancing autophagy may therefore be of therapeutic benefit in resistant APL and could broaden the application of differentiation therapy to other cancers. Here we discuss retinoid signaling in hematopoiesis, leukemogenesis, and APL treatment. We highlight autophagy as a potential important regulator in anti-leukemic strategies.
Project description:Acute myeloid leukemia (AML) is a malignancy of myeloid progenitor cells that are blocked in differentiation. Acute promyelocytic leukemia (APL) is a rare form of AML, which generally presents with a t(15;17) translocation causing expression of the fusion protein PML-RARA. Pharmacological doses of all-trans retinoic acid (ATRA) induce granulocytic differentiation of APL cells leading to cure rates of >80% if combined with conventional chemotherapy. Autophagy is a lysosomal degradation pathway for the removal of cytoplasmic content and recycling of macromolecules. ATRA induces autophagy in ATRA-sensitive AML and APL cells and autophagy inhibition attenuates ATRA-triggered differentiation. In this study, we aimed at identifying if the autophagy-linked FYVE-domain containing protein (ALFY/WDFY3) is involved in autophagic degradation of protein aggregates contributes to ATRA therapy-induced autophagy. We found that ALFY mRNA levels increase significantly during the course of ATRA-induced differentiation of APL and AML cell lines. Importantly ALFY depletion impairs ATRA-triggered granulocytic differentiation of these cells. In agreement with its function in aggrephagy, knockdown of ALFY results in reduced ATRA-induced proteolysis. Our data further suggest that PML-RAR? is an autophagy substrate degraded with the help of ALFY. In summary, we present a crucial role for ALFY in retinoid triggered maturation of AML cells.
Project description:Forty-two cell lines recapitulating mammary carcinoma heterogeneity were profiled for all-trans retinoic acid (ATRA) sensitivity. Luminal and ER(+) (estrogen-receptor-positive) cell lines are generally sensitive to ATRA, while refractoriness/low sensitivity is associated with a Basal phenotype and HER2 positivity. Indeed, only 2 Basal cell lines (MDA-MB157 and HCC-1599) are highly sensitive to the retinoid. Sensitivity of HCC-1599 cells is confirmed in xenotransplanted mice. Short-term tissue-slice cultures of surgical samples validate the cell-line results and support the concept that a high proportion of Luminal/ER(+) carcinomas are ATRA sensitive, while triple-negative (Basal) and HER2-positive tumors tend to be retinoid resistant. Pathway-oriented analysis of the constitutive gene-expression profiles in the cell lines identifies RAR? as the member of the retinoid pathway directly associated with a Luminal phenotype, estrogen positivity and ATRA sensitivity. RAR?3 is the major transcript in ATRA-sensitive cells and tumors. Studies in selected cell lines with agonists/antagonists confirm that RAR? is the principal mediator of ATRA responsiveness. RAR? over-expression sensitizes retinoid-resistant MDA-MB453 cells to ATRA anti-proliferative action. Conversely, silencing of RAR? in retinoid-sensitive SKBR3 cells abrogates ATRA responsiveness. All this is paralleled by similar effects on ATRA-dependent inhibition of cell motility, indicating that RAR? may mediate also ATRA anti-metastatic effects. We define gene sets of predictive potential which are associated with ATRA sensitivity in breast cancer cell lines and validate them in short-term tissue cultures of Luminal/ER(+) and triple-negative tumors. In these last models, we determine the perturbations in the transcriptomic profiles afforded by ATRA. The study provides fundamental information for the development of retinoid-based therapeutic strategies aimed at the stratified treatment of breast cancer subtypes.
Project description:Retinoic acid (RA), is a promising therapeutic agent for the treatment of breast cancer. However, metabolic disorders and drug resistance reduce the efficacy of RA. In this study, we found that RA and ?-3 polyunsaturated fatty acids (?-3 PUFAs) synergistically induced cell death in vitro and in vivo and autophagy activation. Moreover, RA-induced hypercholesterolemia was completely corrected by ?-3 PUFA supplementation. In addition, we demonstrated that the effects of this combination on the autophagic flux were independent of the two major canonic regulatory complexes controlling autophagic vesicle formation. The treatment activated G?q-p38 MAPK signaling pathways, which resulted in autophagy of breast cancer cells. Knockdown of G?q or P38 expression prevented RA and ?-3 PUFAs from inducing autophagy. Data indicated that G?q-p38activation was mediated by the co-activation of GPR40 and RAR? in lipid rafts, rather than by the activation of GPR120, RAR?, or RAR?. The results of this study suggest that hyperlipidemic drug side effects may be ameliorated by the administration of ?-3 PUFAs. Thus, the therapeutic indexes of the corresponding drugs may be increased.
Project description:Many human cancer cells are sensitive to killing by the proapoptotic ligand TNF-related apoptosis-inducing ligand (TRAIL), which is under study for cancer treatment in clinical trials. The TRAIL receptor (TRAIL-R1; also known as death receptor 4) is a transmembrane receptor that mediates TRAIL-induced apoptosis in cancer cells. In this study, we show that retinoids sensitize cancer cells to TRAIL-induced apoptosis by upregulating expression of TRAIL-R1. All-trans retinoic acid (ATRA) upregulated TRAIL-R1 expression in human cancer cells at the transcriptional level. The ability of ATRA to activate TRAIL-R1 expression was inhibited by retinoic acid receptor (RAR) antagonists or siRNAs, but augmented by several RAR agonists. In analyzing how ATRA induces RAR-dependent transcriptional upregulation of TRAIL-R1, we identified 2 putative retinoic acid response elements termed Pal-17 (a palindrome separated by 17 bases) and DR-11 (a direct repeat separated by 11 bases) in the 5'-flanking region of TRAIL-R1 gene. Deletion of DR-11, but not Pal-17, abrogated the ability of ATRA to stimulate TRAIL-R1 promoter activity. Consistent with this observation, RAR binding to DR-11, but not to Pal-17, was detected by chromatin immunoprecipitation assay in ATRA-treated cells, arguing that DR-11 was responsible for ATRA-mediated activation of the TRAIL-R1 gene. ATRA augmented TRAIL-induced apoptosis of cancer cells, and this activity was attenuated by a blockade to upregulation of TRAIL-R1 expression. Taken together, our findings establish that ATRA accentuates TRAIL-induced apoptosis, reveal a novel mechanism by which retinoids modulate apoptosis, and suggest a novel strategy to augment the anti-cancer activity of TRAIL.
Project description:We recently demonstrated that retinoic acid receptor-? (RAR?) is overexpressed and acts as a tumor promoter in hepatocellular carcinoma (HCC). The oncogenic activity of RAR? is mainly attributed to its physiological interaction with p85? regulatory subunit of PI3K leading to constitutive activation of AKT. Here we report RAR? as a negative regulator of p53 signaling and thus extend the oncogenic potential of RAR? to a new role in controlling the balance between AKT and p53. A natural flavonoid acacetin is then identified to be capable of modulating RAR?-dependent AKT-p53 network. It specifically binds to RAR? and inhibits all-trans retinoic acid (atRA) stimulation of RAR? transactivation. However, the anticancer action of acacetin is independent on its modulation of RAR?-driven transcriptional activity. Acacetin induces cancer cell apoptosis through antagonizing the non-genomic effect of RAR? on AKT and p53. When bound to RAR?, acacetin prevents RAR? from its activation of AKT followed by recovery of the normal p53 signaling. Given the implication of AKT-p53 dysregulation in most HCC, targeting the non-genomic signaling of RAR? that switches AKT-p53 from a pro-survival to a pro-apoptotic program in cancer cells should be a promising strategy for developing novel anti-HCC drugs.
Project description:All-trans retinoic acid (ATRA) plays an important role in ocular development. Previous studies found that retinoic acid could influence the metabolism of scleral remodeling by promoting retinal pigment epithelium (RPE) cells to secrete secondary signaling factors. The purpose of this study was to investigate whether retinoic acid affected secretion of bone morphogenetic protein 2 (BMP-2) and matrix metalloproteinase 2 (MMP-2) and to explore the signaling pathway of retinoic acid in cultured acute retinal pigment epithelial 19 (ARPE-19) cells.The effects of ATRA (concentrations from 10-9 to 10-5 mol/l) on the expression of retinoic acid receptors (RARs) in ARPE-19 cells were examined at the mRNA and protein levels using reverse transcription-polymerase chain reaction (RT-PCR) and western blot assay, respectively. The effects of treating ARPE-19 cells with ATRA concentrations ranging from 10-9 to 10-5 mol/l for 24 h and 48 h or with 10-6mol/l ATRA at different times ranging from 6h to 72h were assessed using real-time quantitative PCR (qPCR) and enzyme-linked immunosorbent assay (ELISA). The contribution of RAR?-induced activation of ARPE-19 cells was confirmed using LE135, an antagonist of RAR?.RAR? mRNA levels significantly increased in the ARPE-19 cells treated with ATRA for 24h and 48h. These increases in RAR? mRNA levels were dose dependent (at concentrations of 10-9 to 10-5 mol/l) with a maximum effect observed at 10-6 mol/l. There were no significant changes in the mRNA levels of RAR? and RAR?. Western blot assay revealed that RAR? protein levels were increased significantly in a time-dependent manner in ARPE-19 cells treated with 10-6 mol/l ATRA from 12 h to 72 h, with a marked increase observed at 24 h and 48 h. The upregulation of RAR? and the ATRA-induced secretion in ARPE-19 cells could be inhibited by the RAR? antagonist LE135.ATRA induced upregulation of RAR? in ARPE-19 cells and stimulated these cells to secrete BMP-2 and MMP-2.
Project description:With the purpose of creating a multifunctional drug for gastric cancer treatment, a novel all-trans-retinoic acid (ATRA) conjugate with podophyllotoxin (PPT) was designed and synthesized, and its in vitro antiproliferative activity was evaluated against human gastric cancer cell lines using CCK-8 assay. The conjugate, P-A, exhibited significant anticancer activity against MKN-45 and BGC-823 cells with IC50 values of 0.419 ± 0.032 and 0.202 ± 0.055 ?M, respectively. Moreover, P-A efficiently triggered cell cycle arrest and induced apoptosis in MKN-45 and BGC-823 cells due to modulation of cell cycle arrest- (CDK1, CDK2, CyclinA and CyclinB1) and apoptosis- (cleaved caspase-3, -8 and -9) related proteins, respectively. Further mechanism studies revealed that P-A could increase the expression levels of RAR? and RAR?, and decrease the level of RAR? in MKN-45 and BGC-823 cells. Finally, P-A inhibited the ERK1/2 and AKT signaling in the above two cancer cell lines. More importantly, the underlying mechanisms of P-A were similar to those of precursor PPT but different with the other precursor ATRA. Together, the conjugate P-A was a promising candidate for the potential treatment of human gastric cancer.
Project description:The key molecular mechanism governing the cancer cell state (stem cell-like state vs differentiation state) to control the cancer stem cell (CSC) pool remains elusive. This study provides the first evidence showing that all-trans retinoic acid (ATRA) induces the interaction and chromatin recruitment of a novel RAR?-TET2 complex to epigenetically activate a specific cohort of gene targets, including MiR-200c. TET2-activated miR-200c further targets and suppresses PKC?, a cell polarity protein that has a pivotal role in directing asymmetric division of mammalian stem cells to sustain the stem cell pool. Our data reveal that pharmacological concentration of ATRA effectively downregulates PKC? through activation of miR-200c, leading to a decrease of the stem cell-like populations from non-tumorigenic mammary epithelial cells and non-aggressive breast cancer cells. However, aggressive breast cancer cells that manifest TET2-miR-200c dysregulation sustain a CSC pool highly resistant to ATRA, where inhibition of PKC? directs the resistant CSCs to the luminal cell-like state and sensitization to tamoxifen, resulting in abrogation of mammary tumor growth and progression. Together, these findings elucidate a novel RAR?-TET2-miR-200c-PKC? signaling pathway that directs cancer cell state changes and also provide previously unidentified therapeutic implications for PKC? inhibitors in diminishment of breast CSCs to eradicate breast cancer.