Biomedical subjects

Myriam Gorospe

Publications and source records attributed to Myriam Gorospe.

At least 19 recordsLinked to original sources

PubMed2026

Macrophage regulation of extracellular matrix remodeling in aging skeletal muscle.

The extracellular matrix (ECM) is a dynamic structural network that supports tissue architecture and regulates cell function. It is primarily composed of collagens, elastin, proteoglycans, and glycoproteins, which are synthesized by canonical and non-canonical ECM-producing cells. During aging, the ECM undergoes progressive changes in structure and composition, a process recently recognized as the 13th hallmark of aging. In skeletal muscle (SKM), age-associated ECM remodeling, largely regulated by immune system-ECM crosstalk, contributes to sarcopenia and impaired regeneration. Macrophages (MΦs), as key innate immune cells, regulate ECM dynamics both indirectly by activating canonical ECM-producing cells and directly by synthesizing ECM components. Notably, a distinct subset of ECM-producing MΦs that express collagen (COL+ MΦs) has been identified across multiple tissues, although their function in SKM homeostasis and aging remains poorly understood. Here, we review current knowledge of ECM production and remodeling, with special emphasis on MΦ involvement, including COL+ MΦs, as critical regulators of fibrogenesis, especially during SKM aging and regeneration.

Extracellular Matrix↗

PubMed2026

Long noncoding RNA GAS5 disrupts intestinal epithelial barrier function by increasing small vault RNA levels.

Disruptions in the integrity of the intestinal epithelium occur commonly in inflammatory bowel disease (IBD) and critical surgical disorders, but the underlying mechanisms remain largely unknown. Here we identified long noncoding RNA GAS5 as a repressor of intestinal mucosal growth and the function of the gut epithelial barrier. The levels of tissue GAS5/Gas5 increased in mouse intestinal mucosa after colitis and septic stress, as well as in human intestinal mucosa from patients with IBD. Transient and tissue-specific knockdown of Gas5 in mice using CRISPR/Cas9 enhanced the renewal of the mucosa of the small intestine, increased the levels of tight junction (TJ) proteins ZO-1, ZO-2, claudin-1, and claudin-2, and improved gut barrier function. Conversely, ectopic overexpression of GAS5 in intestinal organoids and in cultured intestinal epithelium cells decreased the levels of these TJ proteins and caused epithelial barrier dysfunction. Mechanistic studies revealed that GAS5 acted as a transcriptional enhancer of the gene (2. AUTHOR: Do you mean "genes"?) encoding small noncoding vault RNAs (vtRNAs) and that GAS5 repressed TJ expression by increasing the levels of vtRNAs. Together, our results indicate that GAS5 disrupts the integrity of the intestinal epithelium by impairing mucosal growth and epithelial barrier function and that it represses TJ expression, at least in part, via vtRNAs.

Animals↗

PubMed2024

SUMOylation controls Hu antigen R posttranscriptional activity in liver cancer.

The posttranslational modification of proteins critically influences many biological processes and is a key mechanism that regulates the function of the RNA-binding protein Hu antigen R (HuR), a hub in liver cancer. Here, we show that HuR is SUMOylated in the tumor sections of patients with hepatocellular carcinoma in contrast to the surrounding tissue, as well as in human cell line and mouse models of the disease. SUMOylation of HuR promotes major cancer hallmarks, namely proliferation and invasion, whereas the absence of HuR SUMOylation results in a senescent phenotype with dysfunctional mitochondria and endoplasmic reticulum. Mechanistically, SUMOylation induces a structural rearrangement of the RNA recognition motifs that modulates HuR binding affinity to its target RNAs, further modifying the transcriptomic profile toward hepatic tumor progression. Overall, SUMOylation constitutes a mechanism of HuR regulation that could be potentially exploited as a therapeutic strategy for liver cancer.

Animals↗

PubMed2006

Eukaryotic initiation factor 2alpha-independent pathway of stress granule induction by the natural product pateamine A.

Stress granules are aggregates of small ribosomal subunits, mRNA, and numerous associated RNA-binding proteins that include several translation initiation factors. Stress granule assembly occurs in the cytoplasm of higher eukaryotic cells under a wide variety of stress conditions, including heat shock, UV irradiation, hypoxia, and exposure to arsenite. Thus far, a unifying principle of eukaryotic initiation factor 2alpha phosphorylation prior to stress granule formation has been observed from the majority of experimental evidence. Pateamine A, a natural product isolated from marine sponge, was recently reported to inhibit eukaryotic translation initiation and induce the formation of stress granules. In this report, the protein composition and fundamental progression of stress granule formation and disassembly induced by pateamine A was found to be similar to that for arsenite. However, pateamine A-induced stress granules were more stable and less prone to disassembly than those formed in the presence of arsenite. Most significantly, pateamine A induced stress granules independent of eukaryotic initiation factor 2alpha phosphorylation, suggesting an alternative mechanism of formation from that previously described for other cellular stresses. Taking into account the known inhibitory effect of pateamine A on eukaryotic translation initiation, a model is proposed to account for the induction of stress granules by pateamine A as well as other stress conditions through perturbation of any steps prior to the rejoining of the 60S ribosomal subunit during the entire translation initiation process.

Animals↗

PubMed2006

Egad, more forms of gene regulation: the gadd45a story.

Despite the historical hegemony of transcription, mounting evidence supports the importance of posttranscriptional gene regulation via processes such as mRNA splicing, localization, turnover, and translation. However, each of these steps is still largely viewed as an exclusive proposition, whereby a particular gene under given circumstances is controlled by a single specific regulatory mechanism. Our recent investigation of gadd45a expression in response to genotoxic stress illustrates a more complex scenario, wherein transcriptional changes operate in concert with mRNA turnover and translational regulation. gadd45a thus joins a handful of reported genes whose levels are potently altered in response to cellular damage or mitogenic cues through the coordinated action of DNA- and RNA-binding proteins. Eliciting cellular responses that are strong, swift, and versatile, gene regulation by multiple factors acting on different levels is emerging as the norm, rather than the exception, for a growing collection of gene products which critically influence cellular homeostasis.

Animals↗

PubMed2006

Differential stability of thymidylate synthase 3'-untranslated region polymorphic variants regulated by AUF1.

A 6-nucleotide insertion (I)/deletion (D) polymorphism in the 3'-untranslated region of the thymidylate synthase gene was shown to influence mRNA stability, but the molecular basis of this effect has not been elucidated. Here, studies of both endogenous and ectopically expressed thymidylate synthase alleles revealed that the mRNA-binding, decay-promoting protein AUF1 has higher affinity for allele D mRNA. AUF1 overexpression preferentially suppressed D allele mRNA levels, whereas AUF1 silencing selectively elevated D allele mRNA levels. Our results illustrate the functional consequences of ribonucleoprotein associations involving a polymorphic RNA sequence and uncover a novel mechanism of action for non-coding RNA polymorphisms.

3' Untranslated Regions↗

PubMed2006

Targeted deletion of MKK4 in cancer cells: a detrimental phenotype manifests as decreased experimental metastasis and suggests a counterweight to the evolution of tumor-suppressor loss.

Tumor-suppressors have commanded attention due to the selection for their inactivating mutations in human tumors. However, relatively little is understood about the inverse, namely, that tumors do not select for a large proportion of seemingly favorable mutations in tumor-suppressor genes. This could be explained by a detrimental phenotype accruing in a cell type-specific manner to most cells experiencing a biallelic loss. For example, MKK4, a tumor suppressor gene distinguished by a remarkably consistent mutational rate across diverse tumor types and an unusually high rate of loss of heterozygosity, has the surprisingly low rate of genetic inactivation of only approximately 5%. To explore this incongruity, we engineered a somatic gene knockout of MKK4 in human cancer cells. Although the null cells resembled the wild-type cells regarding in vitro viability and proliferation in plastic dishes, there was a marked difference in a more relevant in vivo model of experimental metastasis and tumorigenesis. MKK4(-/-) clones injected i.v. produced fewer lung metastases than syngeneic MKK4-competent cells (P = 0.0034). These findings show how cell type-specific detrimental phenotypes can offer a paradoxical and yet key counterweight to the selective advantage attained by cells as they experiment with genetic null states during tumorigenesis, the resultant balance then determining the observed biallelic mutation rate for a given tumor-suppressor gene.

Animals↗

PubMed2006

Theoretical proposal: allele dosage of MAP2K4/MKK4 could rationalize frequent 17p loss in diverse human cancers.

Although aneuploidy is a global genomic abnormality present in most human cancers, the clonal selection model best explains the action of select activating mutations in oncogenes and homozygous losses of tumor-suppressor genes. Simple gene dosage changes are difficult however, to incorporate into this model, in part due to negative feedback loops that govern major cancer mutational targets (e.g., TP53, PTCH, SMAD4) and essentially preclude a haploinsufficient phenotype. The 17p conundrum may offer a clue to reconciling this difficulty: In comparison to the moderate mutation rate of TP53, many tumors have a disproportionately high frequency of loss of 17p. This discrepancy, and similar discrepancies at other sites of LOH, has long been thought to be due to the presence of undiscovered yet frequently mutated tumor-suppressor genes. However, over 15 years of searching for this grail has distributed bountiful disappointment. It is perhaps time to seriously consider an alternative explanation. Located on 17p adjacent to the TP53 gene, MKK4 is one of the most consistently mutated genes across tumor types, and is located on one of the most frequently lost arms in the human genome. We theorized that a gene dosage-dependent phenotype of MKK4 could plausibly promote the emergence of 17p LOH and thereby the probability of evolving the biallelic inactivation of TP53. Using MKK4 somatic human knockout cancer cells, we observed the proof-of-principle in the downstream gene dosage-dependent phenotypes: heterozygous and homozygous knockouts were progressively deficient in Mkk4 protein, in stress-induced phosphorylation of Jnk, and the resultant upregulation of JUN mRNA. These observations highlight a lack of compensatory regulation when gene dosage changes perturb the Jnk-Jun relationship. Consideration of gene dosage changes specifically affecting members of positive feedback loops may permit integration of the aneuploidy process into a conventional model of clonal selection in tumorigenesis.

Cell Line, Tumor↗

PubMed2006

Polyamine depletion increases cytoplasmic levels of RNA-binding protein HuR leading to stabilization of nucleophosmin and p53 mRNAs.

Polyamines are essential for maintaining normal intestinal epithelial integrity, an effect that relies, at least in part, on their ability to keep low levels of nucleophosmin (NPM) and p53 mRNAs. The RNA-binding protein HuR associates with the p53 mRNA, as reported previously, and with the NPM mRNA, computationally predicted to be a target of HuR. Here, we show that HuR binds the NPM and p53 3'-untranslated regions and stabilizes these mRNAs in polyamine-depleted intestinal epithelial cells. Depletion of cellular polyamines by inhibiting ornithine decarboxylase with alpha-difluoromethylornithine dramatically enhanced the cytoplasmic abundance of HuR, whereas ectopic ornithine decarboxylase overexpression decreased cytoplasmic HuR; neither intervention changed whole-cell HuR levels. HuR was found to specifically bind the 3'-untranslated regions of NPN and p53 mRNAs. HuR silencing rendered the NPM and p53 mRNAs unstable and prevented increases in NPM and p53 mRNA and protein in polyamine-deficient cells. These results indicate that polyamines modulate cytoplasmic HuR levels in intestinal epithelial cells, in turn controlling the stability of the NPM and p53 mRNAs and influencing NPM and p53 protein levels.

3' Untranslated Regions↗

PubMed2006

Posttranscriptional derepression of GADD45alpha by genotoxic stress.

The growth arrest- and DNA damage-inducible gene GADD45alpha is potently upregulated in response to stress stimuli. Here, two RNA binding proteins, the mRNA decay-promoting AUF1 and the translational suppressor TIAR, were found to interact specifically with the 3' untranslated region (UTR) of the GADD45alpha mRNA in HeLa cells. These associations were prominent in unstimulated cells, decreasing dramatically after treatment with the genotoxin methyl methanesulfonate (MMS). Analysis of both endogenous and chimeric GADD45alpha mRNA revealed that in untreated cells AUF1 strongly reduced GADD45alpha mRNA stability, whereas TIAR potently inhibited GADD45alpha translation. After genotoxic stress, AUF1 and TIAR dissociated from the GADD45alpha mRNA, thereby allowing coordinated elevations in both GADD45alpha mRNA half-life and translation rate, respectively. We propose that the posttranscriptional derepression of GADD45alpha critically contributes to its potent upregulation after DNA damage.

3' Untranslated Regions↗

PubMed2006

En masse nascent transcription analysis to elucidate regulatory transcription factors.

Despite exhaustively informing about steady-state mRNA abundance, DNA microarrays have been used with limited success to identify regulatory transcription factors (TFs). The main limitation of this approach is that altered mRNA stability also strongly governs the patterns of expressed genes. Here, we used nuclear run-on assays and microarrays to systematically interrogate changes in nascent transcription in cells treated with the topoisomerase inhibitor camptothecin (CPT). Analysis of the promoters of coordinately transcribed genes after CPT treatment suggested the involvement of TFs c-Myb and Rfx1. The predicted CPT-dependent associations were subsequently confirmed by chromatin immunoprecipitation assays. Importantly, after RNAi-mediated knockdown of each TF, the CPT-elicited induction of c-Myb- and/or Rfx1-regulated mRNAs was diminished and the overall cellular response was impaired. The strategies described here permit the successful identification of the TFs responsible for implementing adaptive gene expression programs in response to cellular stimulation.

Binding Sites↗

PubMed2006

Targeted disruption of FANCC and FANCG in human cancer provides a preclinical model for specific therapeutic options.

BACKGROUND & AIMS: How specifically to treat pancreatic and other cancers harboring Fanconi anemia gene mutations has raised great interest recently, yet preclinical studies have been hampered by the lack of well-controlled human cancer models. METHODS: We endogenously disrupted FANCC and FANCG in a human adenocarcinoma cell line and determined the impact of these genes on drug sensitivity, irradiation sensitivity, and genome maintenance. RESULTS: FANCC and FANCG disruption abrogated FANCD2 monoubiquitination, confirming an impaired Fanconi anemia pathway function. On treatment with DNA interstrand-cross-linking agents, FANCC and FANCG disruption caused increased clastogenic damage, G2/M arrest, and decreased proliferation. The extent of hypersensitivity varied among agents, with ratios of inhibitory concentration 50% ranging from 2-fold for oxaliplatin to 14-fold for melphalan, a drug infrequently used in solid tumors. No hypersensitivity was observed on gemcitabine, etoposide, 3-aminobenzamide, NU1025, or hydrogen peroxide. FANCC and FANCG disruption also resulted in increased clastogenic damage on irradiation, but only FANCG disruption caused a subsequent decrease in relative survival. Finally, FANCC and FANCG disruption increased spontaneous chromosomal breakage, supporting the role of these genes in genome maintenance and likely explaining why they are mutated in sporadic cancer. CONCLUSIONS: Our human cancer cell model provides optimal controls to elucidate fundamental biologic features of individual Fanconi anemia gene defects and facilitates preclinical studies of therapeutic options. The impact of Fanconi gene defects on drug and irradiation sensitivity renders these genes promising targets for a specific, genotype-based therapy for individual cancer patients, providing a strong rationale for clinical trials.

Adenocarcinoma↗

PubMed2006

Esg1, expressed exclusively in preimplantation embryos, germline, and embryonic stem cells, is a putative RNA-binding protein with broad RNA targets.

In our earlier attempt to identify genes involved in the maintenance of cellular pluripotency, we found that KH-domain protein Embryonal stem cell-specific gene 1 (Esg1) showed similar expression patterns to those of Oct3/4 (Pou5f1), whereas the forced repression of Oct3/4 in mouse embryonic stem cells immediately downregulated the expression of Esg1. Here we further confirm this overlap by in situ hybridization and immunohistochemical analyses. Both Esg1 transcript and protein exist in the egg and preimplantation embryos. At embryonic day 3.5, blastocyst stage, however, ESG1 protein was more abundant in the inner cell mass (ICM) than in trophectoderm (TE), whereas Esg1 transcript was detected in both the ICM and the TE, particularly in the polar trophectoderm. The presence of an RNA-binding KH-domain in ESG1 led us to search for and identify 902 target transcripts by microarray analysis of immunoprecipitated ESG1 complex. Interaction of 20 target mRNA with ESG1, including Cdc25a, Cdc42, Ezh2, Nfyc and Nr5a2, was further validated by reverse transcriptase-polymerase chain reaction of the immunoprecipitation material, supporting the notion that ESG1 is an RNA-binding protein which associates with specific target transcripts.

Animals↗

PubMed2006

Translational repression by RNA-binding protein TIAR.

The RNA-binding protein TIAR has been proposed to inhibit protein synthesis transiently by promoting the formation of translationally silent stress granules. Here, we report the selective binding of TIAR to several mRNAs encoding translation factors such as eukaryotic initiation factor 4A (eIF4A) and eIF4E (translation initiation factors), eEF1B (a translation elongation factor), and c-Myc (which transcriptionally controls the expression of numerous translation regulatory proteins). TIAR bound the 3'-untranslated regions of these mRNAs and potently suppressed their translation, particularly in response to low levels of short-wavelength UV (UVC) irradiation. The UVC-imposed global inhibition of the cellular translation machinery was significantly relieved after silencing of TIAR expression. We propose that the TIAR-mediated inhibition of translation factor expression elicits a sustained repression of protein biosynthesis in cells responding to stress.

Eukaryotic Initiation Factors↗

PubMed2006

Translational control of cytochrome c by RNA-binding proteins TIA-1 and HuR.

Stresses affecting the endoplasmic reticulum (ER) globally modulate gene expression patterns by altering posttranscriptional processes such as translation. Here, we use tunicamycin (Tn) to investigate ER stress-triggered changes in the translation of cytochrome c, a pivotal regulator of apoptosis. We identified two RNA-binding proteins that associate with its approximately 900-bp-long, adenine- and uridine-rich 3' untranslated region (UTR): HuR, which displayed affinity for several regions of the cytochrome c 3'UTR, and T-cell-restricted intracellular antigen 1 (TIA-1), which preferentially bound the segment proximal to the coding region. HuR did not appear to influence the cytochrome c mRNA levels but instead promoted cytochrome c translation, as HuR silencing greatly diminished the levels of nascent cytochrome c protein. By contrast, TIA-1 functioned as a translational repressor of cytochrome c, with interventions to silence TIA-1 dramatically increasing cytochrome c translation. Following treatment with Tn, HuR binding to cytochrome c mRNA decreased, and both the presence of cytochrome c mRNA within actively translating polysomes and the rate of cytochrome c translation declined. Taken together, our data suggest that the translation rate of cytochrome c is determined by the opposing influences of HuR and TIA-1 upon the cytochrome c mRNA. Under unstressed conditions, cytochrome c mRNA is actively translated, but in response to ER stress agents, both HuR and TIA-1 contribute to lowering its biosynthesis rate. We propose that HuR and TIA-1 function coordinately to maintain precise levels of cytochrome c production under unstimulated conditions and to modify cytochrome c translation when damaged cells are faced with molecular decisions to follow a prosurvival or a prodeath path.

3' Untranslated Regions↗

PubMed2006

Signaling mechanisms underlying Abeta toxicity: potential therapeutic targets for Alzheimer's disease.

The accumulation of amyloid beta peptide (Abeta) is believed to be an early and critical event leading to synapse and neuronal cell loss in Alzheimer's Disease (AD). Abeta itself is toxic to neurons in vitro and the load of Abeta in vivo causes the loss of synapses and neurons in brain in animal models. Therefore, there has been considerable interest in elucidating the mechanism(s) of Abeta neurotoxicity. Here, we review the molecular signaling pathways involved in Abeta-induced cell death, including signaling through the neuronal nicotinic receptor and the Abeta-triggered generation of reactive oxygen species (ROS) leading to the activation of the c-jun N-terminal kinase (JNK), and the ensuing phosphorylation of p66Shc and inactivation of the Forkhead transcription factors. This focused review not only provides a better understanding of the signaling mechanisms involved in Abeta-induced cell death, but also underscores the potential of JNK, p66Shc, Forkhead proteins, p25/cdk5, and neuronal nicotinic receptor, as therapeutic targets for AD.

Alzheimer Disease↗

PubMed2005

Control of gene expression during T cell activation: alternate regulation of mRNA transcription and mRNA stability.

BACKGROUND: Microarray technology has become highly valuable for identifying complex global changes in gene expression patterns. The effective correlation of observed changes in gene expression with shared transcription regulatory elements remains difficult to demonstrate convincingly. One reason for this difficulty may result from the intricate convergence of both transcriptional and mRNA turnover events which, together, directly influence steady-state mRNA levels. RESULTS: In order to investigate the relative contribution of gene transcription and changes in mRNA stability regulation to standard analyses of gene expression, we used two distinct microarray methods which individually measure nuclear gene transcription and changes in polyA mRNA gene expression. Gene expression profiles were obtained from both polyA mRNA (whole-cell) and nuclear run-on (newly transcribed) RNA across a time course of one hour following the activation of human Jurkat T cells with PMA plus ionomycin. Comparative analysis revealed that regulation of mRNA stability may account for as much as 50% of all measurements of changes in polyA mRNA in this system, as inferred by the absence of any corresponding regulation of nuclear gene transcription activity for these groups of genes. Genes which displayed dramatic elevations in both mRNA and nuclear run-on RNA were shown to be inhibited by Actinomycin D (ActD) pre-treatment of cells while large numbers of genes regulated only through altered mRNA turnover (both up and down) were ActD-resistant. Consistent patterns across the time course were observed for both transcribed and stability-regulated genes. CONCLUSION: We propose that regulation of mRNA stability contributes significantly to the observed changes in gene expression in response to external stimuli, as measured by high throughput systems.

Cell Nucleus↗

PubMed2005

Antiapoptotic function of RNA-binding protein HuR effected through prothymosin alpha.

We report the antiapoptotic effect of RNA-binding protein HuR, a critical regulator of the post-transcriptional fate of target transcripts. Among the most prominent mRNAs complexing with HuR is that encoding prothymosin alpha (ProTalpha), an inhibitor of the apoptosome. In HeLa cells, treatment with the apoptotic stimulus ultraviolet light (UVC) triggered the mobilization of ProTalpha mRNA to the cytoplasm and onto heavier polysomes, where its association with HuR increased dramatically. Analysis of a chimeric ProTalpha mRNA directly implicated HuR in regulating ProTalpha production: ProTalpha translation and cytoplasmic concentration increased in HuR-overexpressing cells and declined in cells in which HuR levels were lowered by RNA interference. Importantly, the antiapoptotic influence engendered by HuR was vitally dependent on ProTalpha expression, since use of oligomers that blocked ProTalpha translation abrogated the protective effect of HuR. Together, our data support a regulatory scheme whereby HuR binds the ProTalpha mRNA, elevates its cytoplasmic abundance and translation, and thereby elicits an antiapoptotic program.

Antigens, Surface↗