Stress-induced c-Jun-dependent Vitamin D receptor (VDR) activation dissects the non-classical VDR pathway from the classical VDR activity

Nuclear localization signal in nuclear receptor VDR facilitates the mitotic genome bookmarking by involving distinct amino acid residues

Mitotic genome-bookmarking preserves epigenetic information, re-establishing progenitor's gene expression profile through transcription factors, chromatin remodelers, and histone modifiers, thereby regulating cell fate and lineage commitment post-mitotically in progeny cells. Our recent study revealed that the constitutive association of VDR with mitotic chromatin involves its DNA-binding domain. However, amino acid residues in this domain, crucial for genome bookmarking, remain elusive. This study demonstrates that nuclear localization signal (NLS) residues between 49 and 55 amino acids in VDR are essential for receptor-chromatin interaction during mitosis. Furthermore, it is revealed that both bipartite nature of VDR-NLS region and N-terminally located positively charged arginine residues are critical for its 'genome-bookmarking' property. Since mitotic chromatin association of heterodimeric partner RXR depends on VDR-chromatin association, interventions in VDR binding also abort RXR-chromatin interaction. Overall, this study documents the mechanistic details underlying VDR-chromatin interactions in genome-bookmarking behavior, potentially aiding in comprehending VDR-mediated diseases attributed to certain SNPs.

Tracing vitamins on the long non-coding lane of the transcriptome: vitamin regulation of LncRNAs

A major revelation of genome-scale biological studies in the post-genomic era has been that two-thirds of human genes do not encode proteins. The majority of non-coding RNA transcripts in humans are long non-coding RNA (lncRNA) molecules, non-protein-coding regulatory transcripts with sizes greater than 500 nucleotides. LncRNAs are involved in nearly every aspect of cellular physiology, playing fundamental regulatory roles both in normal cells and in disease. As result, they are functionally linked to multiple human diseases, from cancer to autoimmune, inflammatory, and neurological disorders. Numerous human conditions and diseases stem from gene-environment interactions; in this regard, a wealth of reports demonstrate that the intake of specific and essential nutrients, including vitamins, shapes our transcriptome, with corresponding impacts on health. Vitamins command a vast array of biological activities, acting as coenzymes, antioxidants, hormones, and regulating cellular proliferation and coagulation. Emerging evidence suggests that vitamins and lncRNAs are interconnected through several regulatory axes. This type of interaction is expected, since lncRNA has been implicated in sensing the environment in eukaryotes, conceptually similar to riboswitches and other RNAs that act as molecular sensors in prokaryotes. In this review, we summarize the peer-reviewed literature to date that has reported specific functional linkages between vitamins and lncRNAs, with an emphasis on mammalian models and humans, while providing a brief overview of the source, metabolism, and function of the vitamins most frequently investigated within the context of lncRNA molecular mechanisms, and discussing the published research findings that document specific connections between vitamins and lncRNAs.

Microglia and Brain Disorders: The Role of Vitamin D and Its Receptor

Accounting for 5-20% of the total glial cells present in the adult brain, microglia are involved in several functions: maintenance of the neural environment, response to injury and repair, immunesurveillance, cytokine secretion, regulation of phagocytosis, synaptic pruning, and sculpting postnatal neural circuits. Microglia contribute to some neurodevelopmental disorders, such as Nasu-Hakola disease (NHD), Tourette syndrome (TS), autism spectrum disorder (ASD), and schizophrenia. Moreover, microglial involvement in neurodegenerative diseases, such as Alzheimer's (AD) and Parkinson's (PD) diseases, has also been well established. During the last two decades, epidemiological and research studies have demonstrated the involvement of vitamin D3 (VD3) in the brain's pathophysiology. VD3 is a fat-soluble metabolite that is required for the proper regulation of many of the body's systems, as well as for normal human growth and development, and shows neurotrophic and neuroprotective actions and influences on neurotransmission and synaptic plasticity, playing a role in various neurological diseases. In order to better understand the exact mechanisms behind the diverse actions of VD3 in the brain, a large number of studies have been performed on isolated cells or tissues of the central nervous system (CNS). Here, we discuss the involvement of VD3 and microglia on neurodegeneration- and aging-related diseases.

Hereditary Vitamin D-Resistant Rickets (HVDRR) associated SNP variants of vitamin D receptor exhibit malfunctioning at multiple levels

Vitamin D receptor (VDR) is a member of the nuclear receptor superfamily. It is a primary regulator of calcium and phosphate homeostasis required for skeleton and bone mineralization. Vitamin D in active form 1α,25 dihydroxyvitamin-D3 mediates its cellular functions by binding to VDR. Active VDR forms heterodimers with partner RXR (retinoid X receptor) to execute its physiological actions. HVDRR (Hereditary Vitamin D-Resistant Rickets) is a rare genetic disorder that occurs because of generalized resistance to the 1α,25(OH)₂D3. HVDRR is caused by the polymorphic variations in VDR gene leading to defective intestinal calcium absorption and mineralization of newly forming bones. Using point and deletion SNPs of VDR we have studied several HVDRR-associated SNP variants for their subcellular dynamics, transcriptional functions, 'genome bookmarking', heterodimeric interactions with RXR, and receptor stability. We previously reported that VDR is a 'mitotic bookmarking factor' that remains constitutively associated with the mitotic chromatin to inherit 'transcriptional memory', however the mechanistic details remained unclear. We document that 'genome bookmarking' property by VDR is critically impaired by naturally occurring HVDRR-associated point and deletion variants found in patients. Furthermore, these HVDRR-associated SNP variants of VDR were found to be compromised in transcriptional function, nuclear translocation, protein stability and intermolecular interactions with its heterodimeric partner RXR. Intriguingly, majority of these disease-allied functional defects failed to be rescued by RXR. Our findings suggest that the HVDRR-associated SNP variations influence the normal functioning of the receptor, and this derived understanding may help in the management of disease with precisely designed small molecule modulators.

Mitotic genome bookmarking by nuclear receptor VDR advocates transmission of cellular transcriptional memory to progeny cells

Mitosis is an essential process for the self-renewal of cells that is accompanied by dynamic changes in nuclear architecture and chromatin organization. Despite all the changes, the cell manages to re-establish all the parental epigenetic marks, post-mitotically. Recent reports suggest that some sequence-specific transcription factors remain attached to mitotic chromatin during cell division to ensure timely reactivation of a subset of transcription factors necessary to maintain cell identity. These mitotically associated factors are suggested to act as 'genome bookmarking factors' and the phenomenon is termed 'genome bookmarking'. Here, we studied this phenomenon with Vitamin D Receptor (VDR), a key regulator of calcium and phosphate homeostasis and a member of the nuclear receptor superfamily. This study, for the first time, has confirmed VDR as a mitotic bookmarking factor that may be playing a crucial role in the maintenance of cell identity and genome bookmarking. Full 'DNA binding domain (DBD)' present in VDR was identified as essential for enrichment of VDR on mitotic chromatin. Furthermore, the study also demonstrates that VDR evokes mitotic chromatin binding behaviour in its heterodimeric partner Retinoid X receptor (RXR). Interestingly, for promoting bookmarking behaviour in RXR, both DBD and/or ligand-binding domain (LBD) in conjunction with hinge region of VDR were required. Additionally, ChIP analysis showed that VDR remains associated with DR3 (direct repeat 3) region of its specific target gene promoter CYP24A1(Cytochrome P450 family 24 subfamily A member1), during mitosis. Altogether, our study illustrates a novel function of VDR in the epigenetic transmission and control of expression of target proteome for maintenance of cell identity and traits in progeny cells.

Non-genomic rewiring of vitamin D receptor to p53 as a key to Alzheimer's disease

Observational epidemiological studies have associated vitamin D deficiency with Alzheimer's disease (AD). However, whether vitamin D deficiency would result in some impacts on the vitamin D binding receptor (VDR) remains to be characterized in AD. Vitamin D helps maintain adult brain health genomically through binding with and activating a VDR/retinoid X receptor (RXR) transcriptional complex. Thus, we investigated the role of VDR in AD using postmortem human brains, APP/PS1 mice, and cell cultures. Intriguingly, although vitamin D was decreased in AD patients and mice, hippocampal VDR levels were inversely increased. The abnormally increased levels of VDR were found to be colocalized with Aβ plaques, gliosis and autophagosomes, implicating a non-genomic activation of VDR in AD pathogenesis. Mechanistic investigation revealed that Aβ upregulated VDR without its canonical ligand vitamin D and switched its heterodimer binding-partner from RXR to p53. The VDR/p53 complex localized mostly in the cytosol, increased neuronal autophagy and apoptosis. Chemically inhibiting p53 switched VDR back to RXR, reversing amyloidosis and cognitive impairment in AD mice. These results suggest a non-genomic rewiring of VDR to p53 is key for the progression of AD, and thus VDR/p53 pathway might be targeted to treat people with AD.

Targeting an oncogenic kinase/phosphatase signaling network for cancer therapy

Protein kinases and phosphatases signal by phosphorylation and dephosphorylation to precisely control the activities of their individual and common substrates for a coordinated cellular outcome. In many situations, a kinase/phosphatase complex signals dynamically in time and space through their reciprocal regulations and their cooperative actions on a substrate. This complex may be essential for malignant transformation and progression and can therefore be considered as a target for therapeutic intervention. p38γ is a unique MAPK family member that contains a PDZ motif at its C-terminus and interacts with a PDZ domain-containing protein tyrosine phosphatase PTPH1. This PDZ-coupled binding is required for both PTPH1 dephosphorylation and inactivation of p38γ and for p38γ phosphorylation and activation of PTPH1. Moreover, the p38γ/PTPH1 complex can further regulate their substrates phosphorylation and dephosphorylation, which impacts Ras transformation, malignant growth and progression, and therapeutic response. This review will use the p38γ/PTPH1 signaling network as an example to discuss the potential of targeting the kinase/phosphatase signaling complex for development of novel targeted cancer therapy.

Histological and Immunohistochemical Basis of the Effect of Aminoguanidine on Renal Changes Associated with Hemorrhagic Shock in a Rat Model

Acute kidney failure is the main cause of death among patients with severe trauma due to massive blood loss and hemorrhagic shock (HS). Renal cell injury is caused by tissue ischemia. Renal ischemia initiates a complex and interconnected chain of events resulting in cell injury and renal cell necrosis. Nitric oxide plays a crucial role in renal function and can be inhibited by aminoguanidine (AG). We studied whether AG can ameliorate pathological renal changes associated with HS syndrome in a rat model and explored the AG protection mechanism. Rats were intraperitoneally injected with heparin sodium and mean arterial blood pressure was monitored. Animals were divided into three groups: control (without hemorrhage), with or without intra-arterially injected AG; HS (blood continuously withdrawn or reinfused to maintain an MABP of 35-40 mmHg); and HS with AG. We found that AG decreased plasma concentrations of urea, creatinine, and nitrates; ameliorated histological changes of HS-induced rats; and decreased the expressions of inducible nitrogen oxide synthase (iNOS), proapoptotic protein (BAX), and vitamin D receptors (VDR). AG ameliorated kidney injury by inhibiting iNOS resulting in decreased BAX and VDR expressions. Therefore, a therapeutic strategy targeting AG may provide new insights into kidney injury during severe shock.

c-Jun NH2-teminal kinase 1 interacts with vitamin D receptor and affects vitamin D-mediated inhibition of cancer cell proliferation

BACKGROUND

Vitamin D is a chemopreventive agent that acts against colorectal carcinogenesis in vivo and in vitro through vitamin D receptor (VDR). Previous studies showed that stress-activated protein kinase JNKs (c-Jun NH2-terminal kinases) and p38 cooperated to activate VDR and increase vitamin D3-dependent growth inhibition in breast cancer cells. This study is to determine whether vitamin D-mediated inhibition of cell proliferation is associated with JNK1 in colorectal cancer cells.

METHODS AND RESULTS

Human colon cancer cells were treated with calcitriol, an active vitamin D3. The results showed that calcitriol significantly inhibited cell proliferation and caused cell cycle arrest in HT29 cells, which was associated with induction of phosphorylated JNK1 (p-JNK). The induction of VDR and p-JNK by calcitriol was also observed in Caco-2 cells. Furthermore, VDR expression was significantly downregulated in JNK1-/- mouse intestinal epithelial cells, and VDR reporter activity was reduced in JNK1-/- mouse embryonic fibroblasts (MEFs). However, increasing activated JNK1 upregulated VDR expression and transcriptional activity in vitro. Moreover, JNK1 co-localized with VDR in nuclei and cytoplasm and physically bound together. Reduced expression of JNK1 and VDR in HT29 and Caco-2 cells and JNK1 absence in JNK1-/- MEFs attenuated calcitriol-mediated inhibition of cell proliferation.

CONCLUSION

JNK1 physically and functionally interacted with VDR and positively regulated VDR expression at transcriptional and translational levels, which influenced calcitriol-mediated inhibition of cancer cell proliferation.

The Non-Genomic Actions of Vitamin D

Since its discovery in 1920, a great deal of effort has gone into investigating the physiological actions of vitamin D and the impact its deficiency has on human health. Despite this intense interest, there is still disagreement on what constitutes the lower boundary of adequacy and on the Recommended Dietary Allowance. There has also been a major push to elucidate the biochemistry of vitamin D, its metabolic pathways and the mechanisms that mediate its action. Originally thought to act by altering the expression of target genes, it was realized in the mid-1980s that some of the actions of vitamin D were too rapid to be accounted for by changes at the genomic level. These rapid non-genomic actions have attracted as much interest as the genomic actions and they have spawned additional questions in an already busy field. This mini-review attempts to summarise the in vitro and in vivo work that has been conducted to characterise the rapid non-genomic actions, the mechanisms that give rise to these properties and the roles that these play in the overall action of vitamin D at the cellular level. Understanding the effects of vitamin D at the cellular level should enable the design of elegant human studies to extract the full potential of vitamin D to benefit human health.

TNF-α increases the expression and activity of vitamin D receptor in keratinocytes: role of c-Jun N-terminal kinase

Several inflammatory mediators increase calcitriol production by epidermal keratinocytes. In turn calcitriol attenuates the keratinocyte inflammatory response. Since the effect of the in-situ generated calcitriol depends also on the sensitivity to the hormone we studied the effect of inflammatory cytokines on the response of HaCaT human keratinocytes to calcitriol by examining the expression and transcriptional activity of VDR. Treatment with TNF, but not with IL-1β or interferon γ, increased VDR protein level, while decreasing the level of its heterodimerization partner RXRα. This was associated with increased VDR mRNA levels. c-Jun N-terminal kinase, but not P38 MAPK or NFκB, was found to participate in the upregulation of VDR by TNF. The functional significance of the modulation of VDR and RXRα levels by TNF is manifested by increased induction of VDR target gene CYP24A1 by calcitriol. Calcitriol, in turn, inhibited the enhanced expression of VDR by TNF. In conclusion, the inflammatory cytokine TNF increases the response of keratinocytes to calcitriol through upregulation of its receptor VDR, which in turn is subject to negative feedback by the hormone accelerating the return of the keratinocyte vitamin D system to its basal activity. We surmise that the increased generation and sensitivity to calcitriol in keratinocytes play a role in the resolution of epidermal inflammation.

The new insight on the regulatory role of the vitamin D3 in metabolic pathways characteristic for cancerogenesis and neurodegenerative diseases

Apart from the classical function of regulating intestinal, bone and kidney calcium and phosphorus absorption as well as bone mineralization, there is growing evidence for the neuroprotective function of vitamin D3 through neuronal calcium regulation, the antioxidative pathway, immunomodulation and detoxification. Vitamin D3 and its derivates influence directly or indirectly almost all metabolic processes such as proliferation, differentiation, apoptosis, inflammatory processes and mutagenesis. Such multifactorial effects of vitamin D3 can be a profitable source of new therapeutic solutions for two radically divergent diseases, cancer and neurodegeneration. Interestingly, an unusual association seems to exist between the occurrence of these two pathological states, called "inverse comorbidity". Patients with cognitive dysfunctions or dementia have considerably lower risk of cancer, whereas survivors of cancer have lower prevalence of central nervous system (CNS) disorders. To our knowledge, there are few publications analyzing the role of vitamin D3 in biological pathways existing in carcinogenic and neuropathological disorders.

Non-classical mechanisms of transcriptional regulation by the vitamin D receptor: insights into calcium homeostasis, immune system regulation and cancer chemoprevention

Hormonal 1,25-dihydroxyvitamin D [1,25(OH)2D] signals through the nuclear vitamin D receptor (VDR), a ligand-regulated transcription factor. Gene expression profiling studies have revealed that 1,25(OH)2D signaling through the VDR can lead to activation or repression of target gene transcription in roughly equal proportions. Classically, transcriptional regulation by the VDR, similar to other nuclear receptors, has been characterized by its capacity to recognize high affinity cognate vitamin D response elements (VDREs), located in the regulatory regions of target genes. Several biochemical studies revealed that the VDRE-bound receptor recruits a series of coregulatory proteins, leading to transactivation of adjacent target genes. However, genome-wide and other analyses of VDR binding have revealed that a subset of VDR binding sites does not contain VDREs, and that VDREs are not associated with transcriptionally repressed VDR target genes. Work over the last ∼20 years and in particular recent findings have revealed a diverse array of mechanisms by which VDR can form complexes with several other classes of transcriptional activators, leading to repression of gene transcription. Moreover, these efforts have led to several insights into the molecular basis for the physiological regulation of calcium homeostasis, immune system function and cancer chemoprevention by 1,25(OH)2D/VDR signaling. This article is part of a Special Issue entitled '16th Vitamin D Workshop'.

Vitamin D deficiency may be a risk factor for recurrent pregnancy losses by increasing cellular immunity and autoimmunity

STUDY QUESTION

Do women with recurrent pregnancy losses (RPL) and low vitamin D have increased prevalence of auto- and cellular immune abnormalities when compared with women with RPL who have normal vitamin D, and does vitamin D have any effect on cellular immunity in vitro?

SUMMARY ANSWER

A high proportion of women with RPL have vitamin D deficiency and the risk of auto- and cellular immune abnormalities is increased in women with RPL and vitamin D deficiency.

WHAT IS KNOWN ALREADY

Vitamin D deficiency in pregnant women is associated with increased risk of obstetrical complications such as pre-eclampsia, bacterial vaginosis associated preterm delivery, gestational diabetes mellitus and small-for-gestational age births.

STUDY DESIGN, SIZE, DURATION

A retrospective cross-sectional study of 133 women with RPL who were enrolled in a 2-year period, together with laboratory experiments.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Women with three or more consecutive spontaneous abortions prior to 20 weeks of gestation who were enrolled at the University clinic. Serum vitamin D level, cellular activity and autoimmune parameters in vivo and in vitro were measured.

MAIN RESULTS AND THE ROLE OF CHANCE

Sixty-three out of 133 women (47.4%) had low vitamin D (<30 ng/ml). The prevalence of antiphospholipid antibody (APA) was significantly higher in low vitamin D group (VDlow) (39.7%) than in the normal vitamin D group (VDnl) (22.9%) (P< 0.05) and the adjusted odds ratio (OR) for APA in VDlow was 2.22 with the 95% confidence interval (CI) of 1.0-4.7. The prevalence of antinuclear antigen antibody (VDlow versus VDnl; 23.8% versus 10.0%, OR 2.81, 95% CI 1.1-7.4), anti-ssDNA (19.0% versus 5.7%, OR 3.76, 95% CI 1.1-12.4) and thyroperoxidase antibody (33.3% versus 15.7%, OR 2.68, 95% CI 1.2-6.1) was significantly higher in VDlow than those of VDnl (P < 0.05 each). Peripheral blood CD19(+) B and CD56(+) NK cell levels and NK cytotoxicity at effector to target cell (E:T) ratio of 25:1 were significantly higher in VDlow when compared with those of VDnl (P < 0.05 each). Reduction (%) of NK cytotoxicity (at E:T ratio of 50:1 and 25:1) by IgG (12.5 mg/dl) was significantly lower in VDlow than those of VDnl (P < 0.05, P < 0.01, respectively). There were no differences in Th1/Th2 ratios between VDlow and VDnl. When vitamin D3 was added in NK cytotoxicity assay in vitro, NK cytotoxicity at E:T ratio of 50:1 was significantly suppressed with 10 nMol/L (nM) (11.9 ± 3.3%) and 100 nM (10.9 ± 3.7%) of vitamin D3 when compared with controls (15.3 ± 4.7%) (P < 0.01 each). TNF-α/IL-10 expressing CD3(+)/4(+) cell ratios were significantly decreased with 100 nM of vitamin D3 (31.3 ± 9.4, P < 0.05) when compared with controls (40.4 ± 11.3) in vitro. Additionally, INF-γ/IL-10 expressing CD3(+)/4(+) cell ratio was significantly decreased with 100 nM of vitamin D3 (12.1 ± 4.0, P < 0.05) when compared with controls (14.8 ± 4.6). IFN-γ and TNF-α secretion from NK cells were significantly decreased (P < 0.01 each), and IL-10, IL-1β, vascular endothelial growth factor and granulocyte colony stimulating factor levels were significantly increased (P < 0.01 each) with vitamin D3 100 nM when compared with those of controls.

LIMITATIONS, REASONS FOR CAUTION

The prevalence of vitamin D deficiency in women with RPL in this study is open to a possible type I error since women with vitamin D supplementation were excluded from this study.

WIDER IMPLICATIONS OF THE FINDINGS

Assessment of vitamin D level is recommended in women with RPL. Vitamin D supplementation should be explored further as a possible therapeutic option for RPL.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the intramural funding from Department of Microbiology and Immunology, Chicago Medical School at Rosalind Franklin University of Medicine and Science. None of the authors has any conflict of interest to declare.

TRIAL REGISTRATION NUMBER

N/A.

PTPH1 cooperates with vitamin D receptor to stimulate breast cancer growth through their mutual stabilization

Tyrosine phosphorylation is tightly regulated by protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs), and plays a critical role in malignant transformation and progression. While PTKs have a well-established role in regulating breast cancer growth, contribution of PTPs remains mostly unknown. Here, we report that the tyrosine phosphatase PTPH1 stimulates breast cancer growth through regulating vitamin D receptor (VDR) expression. PTPH1 was shown to be over-expressed in 49% of primary breast cancer and levels of its protein expression positively correlate with the clinic metastasis, suggesting its oncogenic activity. Indeed, PTPH1 promotes breast cancer growth by a mechanism independent of its phosphatase activity but dependent of its stimulatory effect on the nuclear receptor VDR protein expression and depletion of induced VDR abolishes the PTPH1 oncogenic activity. Additional analyses showed that PTPH1 binds VDR and increases its cytoplasmic accumulation leading to their mutual stabilization and stable expression of a nuclear localization deficient VDR abolishes the growth-inhibitory activity of the receptor independent of 1, 25-dihydroxyvitamin D3 (vitamin D3). These results reveal a new paradigm in which a protein tyrosine phosphatase may stimulate breast cancer growth through increasing cytoplasmic translocation of a nuclear receptor leading to their mutual stabilization.

Vitamin D receptor negatively regulates bacterial-stimulated NF-kappaB activity in intestine

Vitamin D receptor (VDR) plays an essential role in gastrointestinal inflammation. Most investigations have focused on the immune response; however, how bacteria regulate VDR and how VDR modulates the nuclear factor (NF)-kappaB pathway in intestinal epithelial cells remain unexplored. This study investigated the effects of VDR ablation on NF-kappaB activation in intestinal epithelia and the role of enteric bacteria on VDR expression. We found that VDR(-/-) mice exhibited a pro-inflammatory bias. After Salmonella infection, VDR(-/-) mice had increased bacterial burden and mortality. Serum interleukin-6 in noninfected VDR(+/+) mice was undetectable, but was easily detectable in VDR(-/-) mice. NF-kappaB p65 formed a complex with VDR in noninfected wild-type mouse intestine. In contrast, deletion of VDR abolished VDR/P65 binding. P65 nuclear translocation occurred in colonic epithelial cells of untreated VDR(-/-) mice. VDR deletion also elevated NF-kappaB activity in intestinal epithelia. VDR was localized to the surface epithelia of germ-free mice, but to crypt epithelial cells in conventionalized mice. VDR expression, distribution, transcriptional activity, and target genes were regulated by Salmonella stimulation, independent of 1,25-dihydroxyvitamin D3. Our study demonstrates that commensal and pathogenic bacteria directly regulate colonic epithelial VDR expression and location in vivo. VDR negatively regulates bacterial-induced intestinal NF-kappaB activation and attenuates response to infection. Therefore, VDR is an important contributor to intestinal homeostasis and host protection from bacterial invasion and infection.

p38gamma MAPK cooperates with c-Jun in trans-activating matrix metalloproteinase 9

Mitogen-activated protein kinases (MAPKs) regulate gene expression through transcription factors. However, the precise mechanisms in this critical signal event are largely unknown. Here, we show that the transcription factor c-Jun is activated by p38gamma MAPK, and the activated c-Jun then recruits p38gamma as a cofactor into the matrix metalloproteinase 9 (MMP9) promoter to induce its trans-activation and cell invasion. This signaling event was initiated by hyperexpressed p38gamma that led to increased c-Jun synthesis, MMP9 transcription, and MMP9-dependent invasion through p38gamma interacting with c-Jun. p38gamma requires phosphorylation and its C terminus to bind c-Jun, whereas both c-Jun and p38gamma are required for the trans-activation of MMP9. The active p38gamma/c-Jun/MMP9 pathway also exists in human colon cancer, and there is a coupling of increased p38gamma and MMP9 expression in the primary tissues. These results reveal a new paradigm in which a MAPK acts both as an activator and a cofactor of a transcription factor to regulate gene expression leading to an invasive response.

Phosphorylation of Williams syndrome transcription factor by MAPK induces a switching between two distinct chromatin remodeling complexes

Changes in the environment of a cell precipitate extracellular signals and sequential cascades of protein modification and elicit nuclear transcriptional responses. However, the functional links between intracellular signaling-dependent gene regulation and epigenetic regulation by chromatin-modifying proteins within the nucleus are largely unknown. Here, we describe novel epigenetic regulation by MAPK cascades that modulate formation of an ATP-dependent chromatin remodeling complex, WINAC (WSTF Including Nucleosome Assembly Complex), an SWI/SNF-type complex containing Williams syndrome transcription factor (WSTF). WSTF, a specific component of two chromatin remodeling complexes (SWI/SNF-type WINAC and ISWI-type WICH), was phosphorylated by the stimulation of MAPK cascades in vitro and in vivo. Ser-158 residue in the WAC (WSTF/Acf1/cbpq46) domain, located close to the N terminus of WSTF, was identified as a major phosphorylation target. Using biochemical analysis of a WSTF mutant (WSTF-S158A) stably expressing cell line, the phosphorylation of this residue (Ser-158) was found to be essential for maintaining the association between WSTF and core BAF complex components, thereby maintaining the ATPase activity of WINAC. WINAC-dependent transcriptional regulation of vitamin D receptor was consequently impaired by this WSTF mutation, but the recovery from DNA damage mediated by WICH was not impaired. Our results suggest that WSTF serves as a nuclear sensor of the extracellular signals to fine-tune the chromatin remodeling activity of WINAC. WINAC mediates a previously unknown MAPK-dependent step in epigenetic regulation, and this MAPK-dependent switching mechanism between the two functionally distinct WSTF-containing complexes might underlie the diverse functions of WSTF in various nuclear events.

Vitamin D and differentiation in cancer

This paper reviews the current understanding of the vitamin D-induced differentiation of neoplastic cells, which results in the generation of cells that acquire near-normal, mature phenotype. Examples of the criteria by which differentiation is recognized in each cell type are provided, and only those effects of 1alpha,25-dihydroxyvitamin D(3) (1,25D) on cell proliferation and survival that are associated with the differentiation process are emphasized. The existing knowledge, often fragmentary, of the signaling pathways that lead to vitamin D-induced differentiation of colon, breast, prostate, squamous cell carcinoma, osteosarcoma, and myeloid leukemia cancer cells is outlined. The important distinctions between the different mechanisms of 1,25D-induced differentiation that are cell-type and cell-context specific are pointed out where known. There is a considerable body of evidence that the principal human cancer cells can be suitable candidates for chemoprevention or differentiation therapy with vitamin D. However, further studies are needed to fully understand the underlying mechanisms in order to improve the therapeutic approaches.

p38α Antagonizes p38γ Activity through c-Jun-dependent Ubiquitin-proteasome Pathways in Regulating Ras Transformation and Stress Response

p38 MAPK family consists of four isoform proteins (alpha, beta, gamma, and delta) that are activated by the same stimuli, but the information about how these proteins act together to yield a biological response is missing. Here we show a feed-forward mechanism by which p38alpha may regulate Ras transformation and stress response through depleting its family member p38gamma protein via c-Jun-dependent ubiquitin-proteasome pathways. Analyses of MAPK kinase 6 (MKK6)-p38 fusion proteins showed that constitutively active p38alpha (MKK6-p38alpha) and p38gamma (MKK6-p38gamma) stimulates and inhibits c-Jun phosphorylation respectively, leading to a distinct AP-1 regulation. Depending on cell type and/or stimuli, p38alpha phosphorylation results in either Ras-transformation inhibition or a cell-death escalation that invariably couples with a decrease in p38gamma protein expression. p38gamma, on the other hand, increases Ras-dependent growth or inhibits stress induced cell-death independent of phosphorylation. In cells expressing both proteins, p38alpha phosphorylation decreases p38gamma protein expression, whereas its inhibition increases cellular p38gamma concentrations, indicating an active role of p38alpha phosphorylation in negatively regulating p38gamma protein expression. Mechanistic analyses show that p38alpha requires c-Jun activation to deplete p38gamma proteins by ubiquitin-proteasome pathways. These results suggest that p38alpha may, upon phosphorylation, act as a gatekeeper of the p38 MAPK family to yield a coordinative biological response through disrupting its antagonistic p38gamma family protein.