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Heterogeneous nuclear ribonucleoprotein R enhances transcription from the naturally configured c-fos promoter in vitro.

ABSTRACT: Transcription of a proto-oncogene c-fos is induced rapidly to high levels by various extracellular stimuli. To explore the molecular mechanism of c-fos gene induction, we established a defined in vitro transcription system for the c-fos promoter that consists of purified activators (SRF, Elk-1, cAMP-responsive element-binding protein, and ATF1), general transcription factors, and RNA polymerase II. In this reconstituted transcription system, activation of c-fos transcription was highly dependent upon coactivators such as PC4 and Mediator, indicating a very weak activation potential of the activators in the context of an unaltered promoter structure. This heightened coactivator dependence, however, allowed us to identify from HeLa nuclear extract a coactivator-like activity termed transcriptional regulator of c-fos (TREF) that enhanced c-fos transcription but not GAL4-VP16-dependent transcription. TREF cooperated with Mediator to enhance c-fos transcription by approximately 60-fold over its basal level and, like Mediator, stimulated activator-independent (basal) transcription as well. Further purification of TREF revealed that it consists of at least three distinct components, one of which was purified to near homogeneity and identified as heterogeneous nuclear ribonucleoprotein R. Recombinant heterogeneous nuclear ribonucleoprotein R enhanced transcription from the c-fos promoter and displayed cooperativity with PC4 and Mediator, thus demonstrating its direct transcriptional activity.

SUBMITTER: Fukuda A

PROVIDER: S-EPMC2749121 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Heterogeneous nuclear ribonucleoprotein R cooperates with mediator to facilitate transcription reinitiation on the c-Fos gene.

Project description:The c-fos gene responds to extracellular stimuli and undergoes robust but transient transcriptional activation. Here we show that heterogeneous nuclear ribonucleoprotein R (hnRNP R) facilitates transcription reinitiation of the c-fos promoter in vitro in cooperation with Mediator. Consistently, hnRNP R interacts with the Scaffold components (Mediator, TBP, and TFIIH) as well as TFIIB, which recruits RNA polymerase II (Pol II) and TFIIF to Scaffold. The cooperative action of hnRNP R and Mediator is diminished by the cyclin-dependent kinase 8 (CDK8) module, which is comprised of CDK8, Cyclin C, MED12 and MED13 of the Mediator subunits. Interestingly, we find that the length of the G-free cassettes, and thereby their transcripts, influences the hnRNP R-mediated facilitation of reinitiation. Indeed, indicative of a possible role of the transcript in facilitating transcription reinitiation, the RNA transcript produced from the G-free cassette interacts with hnRNP R through its RNA recognition motifs (RRMs) and arginine-glycine-glycine (RGG) domain. Mutational analyses of hnRNP R indicate that facilitation of initiation and reinitiation requires distinct domains of hnRNP R. Knockdown of hnRNP R in mouse cells compromised rapid induction of the c-fos gene but did not affect transcription of constitutive genes. Together, these results suggest an important role for hnRNP R in regulating robust response of the c-fos gene.

| S-EPMC3742609 | biostudies-literature

Heterogeneous nuclear ribonucleoprotein K represses transcription from a cytosine/thymidine-rich element in the osteocalcin promoter.

Project description:HnRNP K (heterogeneous nuclear ribonucleoprotein K) was biochemically purified from a screen of proteins co-purifying with binding activity to the osteocalcin promoter. We identify hnRNP K as a novel repressor of osteocalcin gene transcription. Overexpression of hnRNP K lowers the expression of osteocalcin mRNA by 5-fold. Furthermore, luciferase reporter assays demonstrate that overexpression of hnRNP K represses osteocalcin transcription from a CT (cytosine/thymidine)-rich element in the proximal promoter. Electrophoretic mobility-shift analysis reveals that recombinant hnRNP K binds to the CT-rich element, but binds ss (single-stranded), rather than ds (double-stranded) oligonucleotide probes. Accordingly, hnRNP K antibody can supershift a binding activity present in nuclear extracts using ss sense, but not antisense or ds oligonucleotides corresponding to the CT-rich -95 to -47 osteocalcin promoter. Importantly, addition of recombinant hnRNP K to ROS 17/2.8 nuclear extract disrupts formation of a DNA-protein complex on ds CT element oligonucleotides. This action is mutually exclusive with hnRNP K's ability to bind ss DNA. These results demonstrate that hnRNPK, although co-purified with a dsDNA-binding activity, does not itself bind dsDNA. Rather, hnRNP K represses osteocalcin gene transcription by inhibiting the formation of a transcriptional complex on the CT element of the osteocalcin promoter.

| S-EPMC1134736 | biostudies-other

Heterogeneous Nuclear Ribonucleoprotein M Facilitates Enterovirus Infection.

Project description:Picornavirus infection involves a dynamic interplay of host and viral protein interactions that modulates cellular processes to facilitate virus infection and evade host antiviral defenses. Here, using a proteomics-based approach known as TAILS to identify protease-generated neo-N-terminal peptides, we identify a novel target of the poliovirus 3C proteinase, the heterogeneous nuclear ribonucleoproteinM(hnRNP M), a nucleocytoplasmic shuttling RNA-binding protein that is primarily known for its role in pre-mRNA splicing. hnRNPMis cleaved in vitro by poliovirus and coxsackievirus B3 (CVB3) 3C proteinases and is targeted in poliovirus- and CVB3-infected HeLa cells and in the hearts of CVB3-infected mice. hnRNPMrelocalizes from the nucleus to the cytoplasm during poliovirus infection. Finally, depletion of hnRNPMusing small interfering RNA knockdown approaches decreases poliovirus and CVB3 infections in HeLa cells and does not affect poliovirus internal ribosome entry site translation and viral RNA stability. We propose that cleavage of and subverting the function of hnRNPMis a general strategy utilized by picornaviruses to facilitate viral infection.Enteroviruses, a member of the picornavirus family, are RNA viruses that cause a range of diseases, including respiratory ailments, dilated cardiomyopathy, and paralysis. Although enteroviruses have been studied for several decades, the molecular basis of infection and the pathogenic mechanisms leading to disease are still poorly understood. Here, we identify hnRNPMas a novel target of a viral proteinase. We demonstrate that the virus subverts the function of hnRNPMand redirects it to a step in the viral life cycle. We propose that cleavage of hnRNPMis a general strategy that picornaviruses use to facilitate infection.

| S-EPMC4473559 | biostudies-literature

Heterogeneous nuclear ribonucleoprotein A2 is a common transcriptional coactivator in the nuclear transcription response to mitochondrial respiratory stress.

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| S-EPMC2743628 | biostudies-literature

Heterogeneous nuclear ribonucleoprotein A/B and G inhibits the transcription of gonadotropin-releasing-hormone 1.

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| S-EPMC2262047 | biostudies-literature

Heterogeneous nuclear ribonucleoprotein H blocks MST2-mediated apoptosis in cancer cells by regulating A-Raf transcription.

Project description:A-Raf belongs to the family of oncogenic Raf kinases that are involved in mitogenic signaling by activating the mitogen-activated protein (MAP)/extracellular signal-regulated kinase (ERK) kinase (MEK)-ERK pathway. Low kinase activity of A-Raf toward MEK suggested that A-Raf might have alternative functions. Here, we show that A-Raf prevents cancer cell apoptosis contingent on the expression of the heterogeneous nuclear ribonucleoprotein H (hnRNP H) splice factor, which is required for the correct transcription and expression of a-raf. Apoptosis was prevented by A-Raf through sequestration and inactivation of the proapoptotic MST2 kinase. Small interfering RNA-mediated knockdown of hnRNP H or A-Raf resulted in MST2-dependent apoptosis. In contrast, enforced expression of either hnRNP H or A-Raf partially counteracted apoptosis induced by etoposide. In vivo expression studies of colon specimens corroborated the overexpression of hnRNP H in malignant tissues and its correlation with A-Raf levels. Our findings define a novel mechanism that is usurped in tumor cells to escape naturally imposed apoptotic signals.

| S-EPMC2880479 | biostudies-literature

Transcriptional regulation of heterogeneous nuclear ribonucleoprotein K gene expression.

Project description:Heterogeneous nuclear ribonucleoprotein K (hnRNP K) is importantly involved in the regulation of development, DNA damage response, and several human diseases. The molecular mechanisms that control the expression of hnRNP K are largely unknown. In the present study, we investigated the detailed mechanism of the transcriptional regulation of human hnRNP K gene. Two activating and one repressive elements located in the proximal segment of the transcriptional initiation site were identified in hnRNP K gene. A 19 bp-region was responsible for the inhibitory activities of the repressor element. Twenty proteins were identified by DNA-affinity purification and mass spectrometry analyses as binding partners of the primary activating element in the hnRNP K promoter. Chromatin immunoprecipitation and EMSA analysis confirmed the binding of Sp1 with hnRNP K promoter. Sp1 enhanced the promoter activity, increased the expression of hnRNP K, and reduced the mRNA level of angiotensinogen, a gene known to be negatively regulated by hnRNP K. In summary, the current study characterized the promoter elements that regulate the transcription of human hnRNP K gene, identified 20 proteins that bind to the primary activating element of hnRNP K promoter, and demonstrated a functional effect of Sp1 on hnRNP K transcription.

| S-EPMC4414404 | biostudies-literature

Higher expression of the heterogeneous nuclear ribonucleoprotein k in melanoma.

Project description:BackgroundThe heterogeneous nuclear ribonucleoprotein (hnRNP) K is an essential RNA and DNA binding protein involved in gene expression and signal transduction. The role of hnRNP K in cancer is relatively understudied. However, several cellular functions strongly indicate that hnRNP K is involved in tumorigenesis. Oncogenes c-Src, c-myc, and eIF4E are regulated by hnRNP K. We have shown an increased cytoplasmic hnRNP K in pancreatic cancer. In the present study, we investigated the altered expression of hnRNP K protein and its correlation with p-ERK in melanoma using human melanoma cell lines and tissue microarray.Materials and methodsThe protein levels of hnRNP K and p-ERK in 8 human melanoma cell lines and a melanoma progression tissue microarray containing 80 melanoma, 23 dysplastic nevi, and 14 benign nevi specimens were analyzed using Western blot and immunohistochemistry analysis. hnRNP K was knocked down by siRNA, and its effect on melanoma cells was assessed.ResultsWe showed a higher hnRNP K protein level in both melanoma cell lines and melanoma tissue specimens, which correlated with a higher c-myc expression. An increase in the cytoplasmic hnRNP K and eIF4E protein levels in melanoma cells is also seen. p-ERK level was also higher in dysplastic nevi and melanoma tissues, but did not correlate with hnRNP K protein level. We then demonstrated that knocking down of hnRNP K by siRNA inhibited melanoma cell growth and colony formation, as well as c-myc expression.ConclusionshnRNP K expression correlated with melanoma and may play a role in melanoma tumorigenesis.

| S-EPMC2943057 | biostudies-literature

Muscle developmental defects in heterogeneous nuclear Ribonucleoprotein A1 knockout mice.

Project description:Heterogeneous ribonucleoprotein A1 (hnRNP A1) is crucial for regulating alternative splicing. Its integrated function within an organism has not, however, been identified. We generated hnRNP A1 knockout mice to study the role of hnRNP A1 in vivo The knockout mice, hnRNP A1-/-, showed embryonic lethality because of muscle developmental defects. The blood pressure and heart rate of the heterozygous mice were higher than those of the wild-type mice, indicating heart function defects. We performed mouse exon arrays to study the muscle development mechanism. The processes regulated by hnRNP A1 included cell adhesion and muscle contraction. The expression levels of muscle development-related genes in hnRNP A1+/- mice were significantly different from those in wild-type mice, as detected using qRT-PCR. We further confirmed the alternative splicing patterns of muscle development-related genes including mef2c, lrrfip1, usp28 and abcc9 Alternative mRNA isoforms of these genes were increased in hnRNP A1+/- mice compared with wild-type mice. Furthermore, we revealed that the functionally similar hnRNP A2/B1 did not compensate for the expression of hnRNP A1 in organisms. In summary, our study demonstrated that hnRNP A1 plays a critical and irreplaceable role in embryonic muscle development by regulating the expression and alternative splicing of muscle-related genes.

| S-EPMC5303281 | biostudies-literature

Heterogeneous nuclear ribonucleoprotein M associates with mTORC2 and regulates muscle differentiation.

Project description:Mammalian target of rapamycin (mTOR) plays a range of crucial roles in cell survival, growth, proliferation, metabolism, and morphology. However, mTOR forms two distinct complexes, mTOR complex 1 and mTOR complex 2 (mTORC1 and mTORC2), via association with a series of different components; this allows the complexes to execute their wide range of functions. This study explores further the composition of the mTORC2 complex. Utilizing Rictor knock-out cells, immunoprecipitation and mass spectrometry, a novel Rictor associated protein, heterogeneous nuclear ribonucleoprotein M (hnRNP M), was identified. The association between hnRNP M and Rictor was verified using recombinant and endogenous protein and the binding site was found to be within aa 1~532 of hnRNP M. The presence of hnRNP M significantly affects phosphorylation of SGK1 S422, but not of Akt S473, PKC? S657 and PKC? T560. Furthermore, hnRNP M also plays a critical role in muscle differentiation because knock-down of either hnRNP M or Rictor in C2C12 myoblasts reduced differentiation. This decrease is able to be rescued by overexpression SGK S422D in hnRNP M knockdown C2C12 myoblasts. Taken together, we have identified a novel Rictor/mTOR binding molecule, hnRNP M, that allows mTORC2 signaling to phosphorylate SGK1 thus regulating muscle differentiation.

| S-EPMC5247691 | biostudies-literature

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