Action of transcription factors in the control of transferrin receptor expression in human brain endothelium

Muscle mTOR controls iron homeostasis and ferritinophagy via NRF2, HIFs and AKT/PKB signaling pathways

Balanced mTOR activity and iron levels are crucial for muscle integrity, with evidence suggesting mTOR regulates cellular iron homeostasis. In this study, we investigated iron metabolism in muscle-specific mTOR knockout mice (mTORmKO) and its relation to their myopathy. The mTORmKO mice exhibited distinct iron content patterns across muscle types and ages. Slow-twitch soleus muscles initially showed reduced iron levels in young mice, which increased with the dystrophy progression but remained within control ranges. In contrast, the less affected fast-twitch muscles maintained near-normal iron levels from a young age. Interestingly, both mTORmKO muscle types exhibited iron metabolism markers indicative of iron excess, including decreased transferrin receptor 1 (TFR1) and increased levels of ferritin (FTL) and ferroportin (FPN) proteins. Paradoxically, these changes were accompanied by downregulated Ftl and Fpn mRNA levels, indicating post-transcriptional regulation. This discordant regulation resulted from disruption of key iron metabolism pathways, including NRF2/NFE2L2, HIFs, and AKT/PKB signaling. Mechanistically, mTOR deficiency impaired transcriptional regulation of iron-related genes mediated by NRF2 and HIFs. Furthermore, it triggered ferritin accumulation through two NRF2 mechanisms: (1) derepression of ferritin translation via suppression of the FBXL5-IRP axis, and (2) autophagosomal sequestration driven by NCOA4-dependent ferritin targeting to autophagosomes, coupled with age-related impairments of autophagy linked to chronic AKT/PKB activation. Three-week spermidine supplementation in older mTORmKO mice was associated with normalized AKT/PKB-FOXO signaling, increased endolysosomal FTL and reduced total FTL levels in the dystrophic soleus muscle. These findings underscore mTOR's crucial role in skeletal muscle iron metabolism and suggest spermidine as a potential strategy to address impaired ferritinophagy due to autophagy blockade in dystrophic muscle.

Ying Yang 1 engagement in brain pathology

Herein, we discuss data concerning the involvement of transcription factor Yin Yang 1 (YY1) in the development of brain diseases, highlighting mechanisms of its pathological actions. YY1 plays an important role in the developmental and adult pathology of the nervous system. YY1 is essential for neurulation as well as maintenance and differentiation of neuronal progenitor cells and oligodendrocytes regulating both neural and glial tissues of the brain. Lack of a YY1 gene causes many developmental abnormalities and anatomical malformations of the central nervous system (CNS). Once dysregulated, YY1 exerts multiple neuropathological actions being involved in the induction of many brain disorders like stroke, epilepsy, Alzheimer's and Parkinson's diseases, autism spectrum disorder, dystonia, and brain tumors. Better understanding of YY1's dysfunction in the nervous system may lead to the development of novel therapeutic strategies related to YY1's actions.

Expression of transferrin receptor-1 (TFR-1) in canine osteosarcomas

Due to high rates of proliferation and DNA synthesis, neoplastic cells have higher requirements of iron than normal cells. For that reason, neoplastic cells have remodelled iron metabolism pathways, over‐expressing genes encoding for iron uptake proteins, among which Transferrin Receptor‐1 (TFR‐1). Accumulating evidence has proven that overexpression of TFR‐1 and high Iron concentration, are both widespread condition of cancer cells, both essential to tumour onset and progression. We studied TFR‐1 and PCNA immunohistochemical expression in fifteen (15) Canine osteoblastic osteosarcomas (COS). After immunohistochemical staining, counting of TFR‐1 positive cells by two independent observers showed that 85%–95% of neoplastic cells were strongly labelled at cytoplasmic level by anti‐TFR‐1 antibody in all examined COS. Furthermore, 70%–80% of neoplastic cells were positively labelled at the nuclear level by PCNA. Surprisingly, about 100% of intratumour vascular endothelial cells were also positive, whereas extratumour vascular endothelial cells were negative. The latter is an interesting finding, as TFR‐1 is usually not expressed in normal vasculature, with the exception of normal brain vascular endothelium, where it allows transport of transferrin, and thus iron, into tissues, suggesting a similar function here to support cancer growth. The early results presented highlight the relevance of TFR‐1 expression in canine OS, suggesting therapies involving both TFR‐1 and Iron metabolisms in dogs with osteosarcoma should be developed.

Targeting the Overexpressed YY1 in Cancer Inhibits EMT and Metastasis

There have been recent developments in the treatment of various cancers, in particular non-metastatic cancers. However, many of the responding patients often relapse initially through the development of spread micro and macro-metastases. Unfortunately, there are very few therapeutic modalities for the treatment of metastatic cancers. The development of cancer metastasis has been proposed to involve the epithelial-mesenchymal transition (EMT), in which the tumor cells with the EMT phenotype exhibit various phenotypic markers and molecular modifications that are manifested to resist most conventional therapies. YY1 is a target of the hyperactivated nuclear factor-kappa beta pathway in cancer and it was reported that YY1 also regulates cell survival and cell proliferation in addition to its role in EMT and resistance. The overexpression of YY1 in the majority of cancers has been correlated with poor prognosis. It is hypothesized that targeting YY1 may result in several anti-tumor activities, including inhibition of cell survival and cell proliferation, inhibition of EMT, and reversal of resistance. This review discusses the potential therapeutic targeting of an overexpressed transcription factor, Yin Yang 1 (YY1), which has been implicated in the development of EMT and drug resistance. Several examples targeting YY1 in experimental models are presented.

Transcriptional control of the multi-drug transporter ABCB1 by transcription factor Sp3 in different human tissues

The ATP-binding cassette (ABC) transporter ABCB1, encoded by the multidrug resistance gene MDR1, is expressed on brain microvascular endothelium and several types of epithelium, but not on endothelia outside the CNS. It is an essential component of the blood-brain barrier. The aim of this study was to identify cell-specific controls on the transcription of MDR1 in human brain endothelium. Reporter assays identified a region of 500 bp around the transcription start site that was optimally active in brain endothelium. Chromatin immunoprecipitation identified Sp3 and TFIID associated with this region and EMSA (electrophoretic mobility shift assays) confirmed that Sp3 binds preferentially to an Sp-target site (GC-box) on the MDR1 promoter in brain endothelium. This result contrasts with findings in other cell types and with the colon carcinoma line Caco-2, in which Sp1 preferentially associates with the MDR1 promoter. Differences in MDR1 transcriptional control between brain endothelium and Caco-2 could not be explained by the relative abundance of Sp1:Sp3 nor by the ratio of Sp3 variants, because activating variants of Sp3 were present in both cell types. However differential binding of other transcription factors was also detected in two additional upstream regions of the MDR1 promoter. Identification of cell-specific controls on the transcription of MDR1 indicates that it may be possible to modulate multi-drug resistance on tumours, while leaving the blood brain barrier intact.

The oncogenic role of Yin Yang 1

Yin Yang 1 (YY1) is a transcription factor with diverse and complex biological functions. YY1 either activates or represses gene transcription, depending on the stimuli received by the cells and its association with other cellular factors. Since its discovery, a biological role for YY1 in tumor development and progression has been suggested because of its regulatory activities toward multiple cancer-related proteins and signaling pathways and its overexpression in most cancers. In this review, we primarily focus on YY1 studies in cancer research, including the regulation of YY1 as a transcription factor, its activities independent of its DNA binding ability, the functions of its associated proteins, and mechanisms regulating YY1 expression and activities. We also discuss the correlation of YY1 expression with clinical outcomes of cancer patients and its target potential in cancer therapy. Although there is not a complete consensus about the role of YY1 in cancers based on its activities of regulating oncogene and tumor suppressor expression, most of the currently available evidence supports a proliferative or oncogenic role of YY1 in tumorigenesis.

Interplay between heme oxygenase-1 and the multifunctional transcription factor yin yang 1 in the inhibition of intimal hyperplasia

RATIONALE

induction of heme oxygenase (HO)-1 protects against experimental atherosclerotic diseases, and certain pharmacological HO-1 inducers, like probucol, inhibit the proliferation of vascular smooth muscle cells and, at the same time, promote the growth of endothelial cells in vivo and in vitro.

OBJECTIVE

because such cell-specific effects are reminiscent of the action of the transcription factor Yin Yang (YY)1, we tested the hypothesis that there is a functional relationship between HO-1 and YY1.

METHODS AND RESULTS

we report that probucol increases the number of YY1(+) cells in rat carotid artery following balloon injury at a time coinciding with increased HO-1 expression. The drug also induces the expression of YY1 mRNA and protein in rat aortic smooth muscle cells (RASMCs) in vitro, as do other known HO-1 inducers (tert-butylhydroquinone and hemin) and overexpression of HO-1 using a human HMOX1 cDNA plasmid. Conversely, overexpression of YY1 induces expression of HO-1 in RASMCs. Induction of YY1 expression is dependent on HO-1 enzyme activity and its reaction product CO, because pharmacological inhibition of heme oxygenase activity or CO scavenging block, whereas exposure of RASMCs to a CO-releasing molecule increases, YY1 expression. Furthermore, RNA interference knockdown of YY1 prevents probucol or adeno-HO-1 from inhibiting RASMC proliferation in vitro and neointimal formation in vivo.

CONCLUSIONS

our findings show, for the first time, that HO-1 functionally interplays with the multifunctional transcription factor YY1 and that this interplay explains some of the protective activities of HO-1.

Circadian rhythm of transferrin receptor 1 gene expression controlled by c-Myc in colon cancer-bearing mice

The abundance of cell surface levels of transferrin receptor 1 (TfR1), which regulates the uptake of iron-bound transferring, correlates with the rate of cell proliferation. Because TfR1 expression is higher in cancer cells than in normal cells, it offers a target for cancer therapy. In this study, we found that the expression of TfR1 in mouse colon cancer cells was affected by the circadian organization of the molecular clock. The core circadian oscillator is composed of an autoregulatory transcription-translation feedback loop, in which CLOCK and BMAL1 are positive regulators and the Period (Per), Cryptochrome (Cry), and Dec genes act as negative regulators. TfR1 in colon cancer-bearing mice exhibited a 24-hour rhythm in mRNA and protein levels. Luciferase reporter analysis and chromatin immunoprecipitation experiments suggested that the clock-controlled gene c-MYC rhythmically activated the transcription of the TfR1 gene. Platinum incorporation into tumor DNA and the antitumor efficacy of transferrin-conjugated liposome-delivered oxaliplatin could be enhanced by drug administration at times when TfR1 expression increased. Our findings suggest that the 24-hour rhythm of TfR1 expression may form an important aspect of strategies for TfR1-targeted cancer therapy.

Expression and induction of p-glycoprotein-1 on cultured human brain endothelium

The ABC-transporter, p-glycoprotein-1 (pgp-1), is expressed on brain endothelium and is reported to be induced by several cytotoxic drugs, which are themselves substrates of pgp-1. Pgp-1 was increased on a human brain endothelial cell line (hCMEC/D3) after treatment with puromycin or verapamil. However, flow cytometry showed that the apparent upregulation caused by puromycin was not because of a global increase in expression levels, but selective cell death of a subpopulation of endothelium expressing the lowest levels of pgp-1. If a cytotoxic substrate of pgp-1 increases pgp-1 expression in vitro, it can easily be misinterpreted as a transcriptional activator of pgp-1.

Delivery of CD44 shRNA/nanoparticles within cancer cells: perturbation of hyaluronan/CD44v6 interactions and reduction in adenoma growth in Apc Min/+ MICE

Our studies have shown that constitutive interactions between hyaluronan and CD44 on tumor cells induces various anti-apoptotic cell survival pathways through the formation of a multimeric signaling complex that contains activated receptor tyrosine kinases. Inhibition of the hyaluronan-CD44 interactions on tumor cells by hyaluronan-CD44 interaction antagonists suppresses these activities by disassembling the complex. Although the anti-tumor activity of hyaluronan-oligosaccharides, a hyaluronan-CD44 interaction antagonist, is effective in sensitizing tumor cells to chemotherapeutic agents and reducing tumor growth in xenografts, hyaluronan-oligosaccharide alone was not effective in reducing tumor progression in Apc Min/+ mice. We now show in vitro and in vivo that targeted inhibition of the expression of CD44v6 depletes the ability of the colon tumor cells to signal through hyaluronan-CD44v6 interactions. First, we cloned oligonucleotides coding CD44v6 shRNA into a conditionally silenced pSico vector. Second, using pSico-CD44v6 shRNA and a colon-specific Fabpl promoter-driven Cre recombinase expression vector packaged into transferrin-coated nanoparticles, we successfully delivered the CD44v6 shRNA within pre-neoplastic and neoplastic colon malignant cells. Third, using the Apc Min/+ mice model, we demonstrated that inhibition of the CD44v6 expression reduces the signaling through a hyaluronan/CD44v6-pErbB2-Cox-2 interaction pathway and reduced adenoma number and growth. Together, these data provide insight into the novel therapeutic strategies of short hairpin RNA/nanoparticle technology and its potential for silencing genes associated with colon tumor cells.

Transferrin receptor 2 is frequently expressed in human cancer cell lines

Different proteins ensure the fine control of iron metabolism at the level of various tissues. Among these proteins, it was discovered a second transferrin receptor (TfR2), that seems to play a key role in the regulation of iron homeostasis. Its mutations are responsible for type 3 hemochromatosis (Type 3 HH). Although TfR2 expression in normal tissues was restricted at the level of liver and intestine, we observed that TfR2 was frequently expressed in tumor cell lines. Particularly frequent was its expression in ovarian cancer, colon cancer and glioblastoma cell lines; less frequent was its expression in leukemic and melanoma cell lines. Interestingly, in these tumor cell lines, TfR2 expression was inversely related to that of receptor 1 for transferrin (TfR1). Experiments of in vitro iron loading or iron deprivation provided evidence that TfR2 is modulated in cancer cell lines according to cellular iron levels following two different mechanisms: (i) in some cells, iron loading caused a downmodulation of total TfR2 levels; (ii) in other cell types, iron loading caused a downmodulation of membrane-bound TfR2, without affecting the levels of total cellular TfR2 content. Iron deprivation caused in both conditions an opposite effect compared to iron loading. These observations suggest that TfR2 expression may be altered in human cancers and warrant further studies in primary tumors. Furthermore, our studies indicate that, at least in tumor cells, TfR2 expression is modulated by iron through different biochemical mechanisms, whose molecular basis remains to be determined.