The FOXN3-NEAT1-SIN3A repressor complex promotes progression of hormonally responsive breast cancer

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Abstract

The pathophysiological function of the forkhead transcription factor FOXN3 remains to be explored. Here we report that FOXN3 is a transcriptional repressor that is physically associated with the SIN3A repressor complex in estrogen receptor–positive (ER+) cells. RNA immunoprecipitation–coupled high-throughput sequencing identified that NEAT1, an estrogen-inducible long noncoding RNA, is required for FOXN3 interactions with the SIN3A complex. ChIP-Seq and deep sequencing of RNA genomic targets revealed that the FOXN3-NEAT1-SIN3A complex represses genes including GATA3 that are critically involved in epithelial-to-mesenchymal transition (EMT). We demonstrated that the FOXN3-NEAT1-SIN3A complex promotes EMT and invasion of breast cancer cells in vitro as well as dissemination and metastasis of breast cancer in vivo. Interestingly, the FOXN3-NEAT1-SIN3A complex transrepresses ER itself, forming a negative-feedback loop in transcription regulation. Elevation of both FOXN3 and NEAT1 expression during breast cancer progression corresponded to diminished GATA3 expression, and high levels of FOXN3 and NEAT1 strongly correlated with higher histological grades and poor prognosis. Our experiments uncovered that NEAT1 is a facultative component of the SIN3A complex, shedding light on the mechanistic actions of NEAT1 and the SIN3A complex. Further, our study identified the ERα-NEAT1-FOXN3/NEAT1/SIN3A-GATA3 axis that is implicated in breast cancer metastasis, providing a mechanistic insight into the pathophysiological function of FOXN3.

Authors

Wanjin Li, Zihan Zhang, Xinhua Liu, Xiao Cheng, Yi Zhang, Xiao Han, Yu Zhang, Shumeng Liu, Jianguo Yang, Bosen Xu, Lin He, Luyang Sun, Jing Liang, Yongfeng Shang

Ubiquitin ligase RNF146 coordinates bone dynamics and energy metabolism

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Abstract

Cleidocranial dysplasia (CCD) is an autosomal dominant human disorder characterized by abnormal bone development that is mainly due to defective intramembranous bone formation by osteoblasts. Here, we describe a mouse strain lacking the E3 ubiquitin ligase RNF146 that shows phenotypic similarities to CCD. Loss of RNF146 stabilized its substrate AXIN1, leading to impairment of WNT3a-induced β-catenin activation and reduced Fgf18 expression in osteoblasts. We show that FGF18 induces transcriptional coactivator with PDZ-binding motif (TAZ) expression, which is required for osteoblast proliferation and differentiation through transcriptional enhancer associate domain (TEAD) and runt-related transcription factor 2 (RUNX2) transcription factors, respectively. Finally, we demonstrate that adipogenesis is enhanced in Rnf146^–/– mouse embryonic fibroblasts. Moreover, mice with loss of RNF146 within the osteoblast lineage had increased fat stores and were glucose intolerant with severe osteopenia because of defective osteoblastogenesis and subsequent impaired osteocalcin production. These findings indicate that RNF146 is required to coordinate β-catenin signaling within the osteoblast lineage during embryonic and postnatal bone development.

Authors

Yoshinori Matsumoto, Jose La Rose, Melissa Lim, Hibret A. Adissu, Napoleon Law, Xiaohong Mao, Feng Cong, Paula Mera, Gerard Karsenty, David Goltzman, Adele Changoor, Lucia Zhang, Megan Stajkowski, Marc D. Grynpas, Carsten Bergmann, Robert Rottapel

Cell-penetrating peptides selectively targeting SMAD3 inhibit profibrotic TGF-β signaling

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Abstract

TGF-β is considered a master switch in the pathogenesis of organ fibrosis. The primary mediators of this activity are the SMAD proteins, particularly SMAD3. In the current study, we have developed a cell-penetrating peptide (CPP) conjugate of the HIV TAT protein that is fused to an aminoterminal sequence of sorting nexin 9 (SNX9), which was previously shown to bind phosphorylated SMAD3 (pSMAD3). We determined that specifically preventing the nuclear import of pSMAD3 using the TAT-SNX9 peptide inhibited profibrotic TGF-β activity in murine cells and human lung fibroblasts as well as in vivo with no demonstrable toxicity. TGF-β signaling mediated by pSMAD2, bone morphogenetic protein 4 (BMP4), EGF, or PDGF was unaffected by the TAT-SNX9 peptide. Furthermore, while the TAT-SNX9 peptide prevented TGF-β’s profibrotic activity in vitro as well as in 2 murine treatment models of pulmonary fibrosis, a 3–amino acid point mutant that was unable to bind pSMAD3 proved ineffective. These findings indicate that specifically targeting pSMAD3 can ameliorate both the direct and indirect fibroproliferative actions of TGF-β.

Authors

Jeong-Han Kang, Mi-Yeon Jung, Xueqian Yin, Mahefatiana Andrianifahanana, Danielle M. Hernandez, Edward B. Leof

Ca²⁺ channel clustering with insulin-containing granules is disturbed in type 2 diabetes

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Abstract

Loss of first-phase insulin secretion is an early sign of developing type 2 diabetes (T2D). Ca²⁺ entry through voltage-gated L-type Ca²⁺ channels triggers exocytosis of insulin-containing granules in pancreatic β cells and is required for the postprandial spike in insulin secretion. Using high-resolution microscopy, we have identified a subset of docked insulin granules in human β cells and rat-derived clonal insulin 1 (INS1) cells for which localized Ca²⁺ influx triggers exocytosis with high probability and minimal latency. This immediately releasable pool (IRP) of granules, identified both structurally and functionally, was absent in β cells from human T2D donors and in INS1 cells cultured in fatty acids that mimic the diabetic state. Upon arrival at the plasma membrane, IRP granules slowly associated with 15 to 20 L-type channels. We determined that recruitment depended on a direct interaction with the synaptic protein Munc13, because expression of the II–III loop of the channel, the C2 domain of Munc13-1, or of Munc13-1 with a mutated C2 domain all disrupted L-type channel clustering at granules and ablated fast exocytosis. Thus, rapid insulin secretion requires Munc13-mediated recruitment of L-type Ca²⁺ channels in close proximity to insulin granules. Loss of this organization underlies disturbed insulin secretion kinetics in T2D.

Authors

Nikhil R. Gandasi, Peng Yin, Michela Riz, Margarita V. Chibalina, Giuliana Cortese, Per-Eric Lund, Victor Matveev, Patrik Rorsman, Arthur Sherman, Morten G. Pedersen, Sebastian Barg

Geminin facilitates FoxO3 deacetylation to promote breast cancer cell metastasis

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Abstract

Geminin expression is essential for embryonic development and the maintenance of chromosomal integrity. In spite of this protective role, geminin is also frequently overexpressed in human cancers and the molecular mechanisms underlying its role in tumor progression remain unclear. The histone deacetylase HDAC3 modulates transcription factors to activate or suppress transcription. Little is known about how HDAC3 specifies substrates for modulation among highly homologous transcription factor family members. Here, we have demonstrated that geminin selectively couples the transcription factor forkhead box O3 (FoxO3) to HDAC3, thereby specifically facilitating FoxO3 deacetylation. We determined that geminin–associated HDAC3 deacetylates FoxO3 to block its transcriptional activity, leading to downregulation of the downstream FoxO3 target Dicer, an RNase that suppresses metastasis. Breast cancer cells depleted of geminin or HDAC3 exhibited poor metastatic potential that was attributed to reduced suppression of the FoxO3-Dicer axis. Moreover, elevated levels of geminin, HDAC3, or both together with decreased FoxO3 acetylation and reduced Dicer expression were detected in aggressive human breast cancer specimens. These results underscore a prominent role for geminin in promoting breast cancer metastasis via the enzyme-substrate–coupling mechanism in HDAC3-FoxO3 complex formation.

Authors

Lei Zhang, Meizhen Cai, Zhicheng Gong, Bingchang Zhang, Yuanpei Li, Li Guan, Xiaonan Hou, Qing Li, Gang Liu, Zengfu Xue, Muh-hua Yang, Jing Ye, Y. Eugene Chin, Han You

Mutant p53 establishes targetable tumor dependency by promoting unscheduled replication

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Abstract

Gain-of-function (GOF) p53 mutations are observed frequently in most intractable human cancers and establish dependency for tumor maintenance and progression. While some of the genes induced by GOF p53 have been implicated in more rapid cell proliferation compared with p53-null cancer cells, the mechanism for dependency of tumor growth on mutant p53 is unknown. This report reveals a therapeutically targetable mechanism for GOF p53 dependency. We have shown that GOF p53 increases DNA replication origin firing, stabilizes replication forks, and promotes micronuclei formation, thus facilitating the proliferation of cells with genomic abnormalities. In contrast, absence or depletion of GOF p53 leads to decreased origin firing and a higher frequency of fork collapse in isogenic cells, explaining their poorer proliferation rate. Following genome-wide analyses utilizing ChIP-Seq and RNA-Seq, GOF p53–induced origin firing, micronuclei formation, and fork protection were traced to the ability of GOF p53 to transactivate cyclin A and CHK1. Highlighting the therapeutic potential of CHK1’s role in GOF p53 dependency, experiments in cell culture and mouse xenografts demonstrated that inhibition of CHK1 selectively blocked proliferation of cells and tumors expressing GOF p53. Our data suggest the possibility that checkpoint inhibitors could efficiently and selectively target cancers expressing GOF p53 alleles.

Authors

Shilpa Singh, Catherine A. Vaughan, Rebecca A. Frum, Steven R. Grossman, Sumitra Deb, Swati Palit Deb

AKT-mediated stabilization of histone methyltransferase WHSC1 promotes prostate cancer metastasis

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Abstract

Loss of phosphatase and tensin homolog (PTEN) and activation of the PI3K/AKT signaling pathway are hallmarks of prostate cancer (PCa). However, these alterations alone are insufficient for cells to acquire metastatic traits. Here, we have shown that the histone dimethyl transferase WHSC1 critically drives indolent PTEN-null tumors to become metastatic PCa. In a PTEN-null murine PCa model, WHSC1 overexpression in prostate epithelium cooperated with Pten deletion to produce a metastasis-prone tumor. Conversely, genetic ablation of Whsc1 prevented tumor progression in PTEN-null mice. Molecular characterization revealed that increased AKT activity due to PTEN loss directly phosphorylates WHSC1 at S172, preventing WHSC1 degradation by CRL4^Cdt2 E3 ligase. Increased WHSC1 expression transcriptionally upregulates expression of RICTOR, a pivotal component of mTOR complex 2 (mTORC2), to further enhance AKT activity. Therefore, the AKT/WHSC1/mTORC2 signaling cascade represents a vicious feedback loop that elicits unrestrained AKT signaling. Furthermore, we determined that WHSC1 positively regulates Rac1 transcription to increase tumor cell motility. The biological importance of a WHSC1-mediated signaling cascade is substantiated by patient sample analysis in which WHSC1 signaling is tightly correlated with disease progression and recurrence. Taken together, our findings highlight a pivotal link between an epigenetic regulator, WHSC1, and key intracellular signaling molecules, AKT, RICTOR, and Rac1, to drive PCa metastasis.

Authors

Ni Li, Wei Xue, Huairui Yuan, Baijun Dong, Yufeng Ding, Yongfeng Liu, Min Jiang, Shan Kan, Tongyu Sun, Jiale Ren, Qiang Pan, Xiang Li, Peiyuan Zhang, Guohong Hu, Yan Wang, Xiaoming Wang, Qintong Li, Jun Qin

HDAC6-mediated acetylation of lipid droplet–binding protein CIDEC regulates fat-induced lipid storage

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Abstract

Obesity is characterized by aberrant fat accumulation. However, the intracellular signaling pathway that senses dietary fat and leads to fat storage remains elusive. Here, we have observed that the levels of histone deacetylase 6 (HDAC6) and the related family member HDAC10 are markedly reduced in adipose tissues of obese animals and humans. Mice with adipocyte-specific depletion of Hdac6 exhibited increased fat accumulation and reduced insulin sensitivity. In normal adipocytes, we found that reversal of P300/CBP-associated factor–induced (PCAF-induced) acetylation at K56 on cell death-inducing DFFA-like effector C (CIDEC, also known as FSP27) critically regulated lipid droplet fusion and lipid storage. Importantly, HDAC6 deacetylates CIDEC, leading to destabilization and reduced lipid droplet fusion. Accordingly, we observed elevated levels of CIDEC and its acetylated form in HDAC-deficient adipocytes as well as the adipose tissue of obese animals and humans. Fatty acids (FAs) prevented CIDEC deacetylation by promoting the dissociation of CIDEC from HDAC6, which resulted in increased association of CIDEC with PCAF on the endoplasmic reticulum. Control of CIDEC acetylation required the conversion of FAs to triacylglycerols. Thus, we have revealed a signaling axis that is involved in the coordination of nutrient availability, protein acetylation, and cellular lipid metabolic responses.

Authors

Hui Qian, Yuanying Chen, Zongqian Nian, Lu Su, Haoyong Yu, Feng-Jung Chen, Xiuqin Zhang, Wenyi Xu, Linkang Zhou, Jiaming Liu, Jinhai Yu, Luxin Yu, Yan Gao, Hongchao Zhang, Haihong Zhang, Shimin Zhao, Li Yu, Rui-Ping Xiao, Yuqian Bao, Shaocong Hou, Pingping Li, Jiada Li, Haiteng Deng, Weiping Jia, Peng Li

Sirtuin 2 regulates cellular iron homeostasis via deacetylation of transcription factor NRF2

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Abstract

SIRT2 is a cytoplasmic sirtuin that plays a role in various cellular processes, including tumorigenesis, metabolism, and inflammation. Since these processes require iron, we hypothesized that SIRT2 directly regulates cellular iron homeostasis. Here, we have demonstrated that SIRT2 depletion results in a decrease in cellular iron levels both in vitro and in vivo. Mechanistically, we determined that SIRT2 maintains cellular iron levels by binding to and deacetylating nuclear factor erythroid-derived 2–related factor 2 (NRF2) on lysines 506 and 508, leading to a reduction in total and nuclear NRF2 levels. The reduction in nuclear NRF2 leads to reduced ferroportin 1 (FPN1) expression, which in turn results in decreased cellular iron export. Finally, we observed that Sirt2 deletion reduced cell viability in response to iron deficiency. Moreover, livers from Sirt2^–/– mice had decreased iron levels, while this effect was reversed in Sirt2^–/– Nrf2^–/– double-KO mice. Taken together, our results uncover a link between sirtuin proteins and direct control over cellular iron homeostasis via regulation of NRF2 deacetylation and stability.

Authors

Xiaoyan Yang, Seong-Hoon Park, Hsiang-Chun Chang, Jason S. Shapiro, Athanassios Vassilopoulos, Konrad T. Sawicki, Chunlei Chen, Meng Shang, Paul W. Burridge, Conrad L. Epting, Lisa D. Wilsbacher, Supak Jenkitkasemwong, Mitchell Knutson, David Gius, Hossein Ardehali

RANKL coordinates multiple osteoclastogenic pathways by regulating expression of ubiquitin ligase RNF146

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Abstract

Bone undergoes continuous remodeling due to balanced bone formation and resorption mediated by osteoblasts and osteoclasts, respectively. Osteoclasts arise from the macrophage lineage, and their differentiation is dependent on RANKL, a member of the TNF family of cytokines. Here, we have provided evidence that RANKL controls the expression of 3BP2, an adapter protein that is required for activation of SRC tyrosine kinase and simultaneously coordinates the attenuation of β-catenin, both of which are required to execute the osteoclast developmental program. We found that RANKL represses the transcription of the E3 ubiquitin ligase RNF146 through an NF-κB–related inhibitory element in the RNF146 promoter. RANKL-mediated suppression of RNF146 results in the stabilization of its substrates, 3BP2 and AXIN1, which consequently triggers the activation of SRC and attenuates the expression of β-catenin, respectively. Depletion of RNF146 caused hypersensitivity to LPS-induced TNF-α production in vivo. RNF146 thus acts as an inhibitory switch to control osteoclastogenesis and cytokine production and may be a control point underlying the pathogenesis of chronic inflammatory diseases.

Authors

Yoshinori Matsumoto, Jose Larose, Oliver A. Kent, Melissa Lim, Adele Changoor, Lucia Zhang, Yaryna Storozhuk, Xiaohong Mao, Marc D. Grynpas, Feng Cong, Robert Rottapel