Autoregulatory Negative Feedback Loop Research Articles

A Narrative Review of the <i>TP53</i> and Its Product the p53 Protein

The main purpose of this paper was to generate a narrative review related to the current knowledge of the <em>TP53</em> gene and its product, the p53 protein. It was also attempted to elucidate the different p53 reactivation strategies of great interest, as various small molecules are being studied to reactivate mutant p53. PubMed and ScienceDirect were searched for p53, mutant p53, and wild-type p53 limited by the title filter through the end of 2022. The collected articles were studied, evaluated and summarized. In the short (p) arm of chromosome 17, there is a special place for <em>TP53</em>.<em> </em>(17p.13.1). It is made up of 19,180 bp, which includes thirteen exons, (elevem exons, two alternative exons), and ten introns. <em>TP53 </em>is mutated in most types of human cancers resulting in aggressive cancer proliferation, immune system evasion, genomic instability, invasion, and metastasis. Under stress-free conditions, p53 function is negatively regulated by <em>HDM2, </em>a p53 target gene, which binds to it and establishes an auto-regulatory negative feedback loop that promotes proteasomal-dependent degradation. In these conditions, p53 maintains at low levels and normalizes biological operations as the master regulator of cell fate. However, under conditions of stress such as DNA damage, hypoxia, oxidative stress, oncogene expression, nutrient deprivation, ribosomal dysfunction, or telomere attrition the p53 selection pathway will be cell type-specific and depend on the type and severity of the cell damage. Post-translational modifications such as phosphorylation and acetylation, which induce the expression of p53 target genes, contribute to the p53 selection pathway. In these conditions, p53 tetramerized and stabilized in the nucleus and activated, and its levels increased in the cell due to blocking the interaction with<em> MDM2. </em>Valuable findings have been discovered that elucidate the biological, biochemical, immunological, physiological, and pathological roles of p53 and its fundamental roles in cancer biology and genetics. The information gathered here should contribute to a better understanding of the impact of p53 deregulation on cancer and new research aimed at finding new anticancer strategies capable of reactivating the cancer suppressive function of WT and/or blocking the function of mutant p53 in order to improve cancer therapy and prognosis.

A Narrative Review of the <i>TP53</i> and Its Product the p53 Protein

The main purpose of this paper was to generate a narrative review related to the current knowledge of the <em>TP53</em> gene and its product, the p53 protein. It was also attempted to elucidate the different p53 reactivation strategies of great interest, as various small molecules are being studied to reactivate mutant p53. PubMed and ScienceDirect were searched for p53, mutant p53, and wild-type p53 limited by the title filter through the end of 2022. The collected articles were studied, evaluated and summarized. In the short (p) arm of chromosome 17, there is a special place for <em>TP53</em>.<em> </em>(17p.13.1). It is made up of 19,180 bp, which includes thirteen exons, (elevem exons, two alternative exons), and ten introns. <em>TP53 </em>is mutated in most types of human cancers resulting in aggressive cancer proliferation, immune system evasion, genomic instability, invasion, and metastasis. Under stress-free conditions, p53 function is negatively regulated by <em>HDM2, </em>a p53 target gene, which binds to it and establishes an auto-regulatory negative feedback loop that promotes proteasomal-dependent degradation. In these conditions, p53 maintains at low levels and normalizes biological operations as the master regulator of cell fate. However, under conditions of stress such as DNA damage, hypoxia, oxidative stress, oncogene expression, nutrient deprivation, ribosomal dysfunction, or telomere attrition the p53 selection pathway will be cell type-specific and depend on the type and severity of the cell damage. Post-translational modifications such as phosphorylation and acetylation, which induce the expression of p53 target genes, contribute to the p53 selection pathway. In these conditions, p53 tetramerized and stabilized in the nucleus and activated, and its levels increased in the cell due to blocking the interaction with<em> MDM2. </em>Valuable findings have been discovered that elucidate the biological, biochemical, immunological, physiological, and pathological roles of p53 and its fundamental roles in cancer biology and genetics. The information gathered here should contribute to a better understanding of the impact of p53 deregulation on cancer and new research aimed at finding new anticancer strategies capable of reactivating the cancer suppressive function of WT and/or blocking the function of mutant p53 in order to improve cancer therapy and prognosis.

A HD-ZIP transcription factor specifies fates of multicellular trichomes via dosage-dependent mechanisms in tomato.

Hair-like structures are shared by most living organisms. The hairs on plant surfaces, commonly referred to as trichomes, form diverse types to sense and protect against various stresses. However, it is unclear how trichomes differentiate into highly variable forms. Here, we show that a homeodomain leucine zipper (HD-ZIP) transcription factor named Woolly controls the fates of distinct trichomes in tomato via a dosage-dependent mechanism. The autocatalytic reinforcement of Woolly is counteracted by an autoregulatory negative feedback loop, creating a circuit with a high or low Woolly level. This biases the transcriptional activation of separate antagonistic cascades that lead to different trichome types. Our results identify the developmental switch of trichome formation and provide mechanistic insights into the progressive fate specification in plants, as well as a path to enhancing plant stress resistance and the production of beneficial chemicals.

Suppressive Role of ACVR1/ALK2 in Basal and TGFβ1-Induced Cell Migration in Pancreatic Ductal Adenocarcinoma Cells and Identification of a Self-Perpetuating Autoregulatory Loop Involving the Small GTPase RAC1b.

Pancreatic ductal adenocarcinoma (PDAC) cells are known for their high invasive/metastatic potential, which is regulated in part by the transforming growth factor β1 (TGFβ1). The involvement of at least two type I receptors, ALK5 and ALK2, that transmit downstream signals of the TGFβ via different Smad proteins, SMAD2/3 and SMAD1/5, respectively, poses the issue of their relative contribution in regulating cell motility. Real-time cell migration assays revealed that the selective inhibition of ALK2 by RNAi or dominant-negative interference with a kinase-dead mutant (ALK2-K233R) strongly enhanced the cells’ migratory activity in the absence or presence of TGFβ1 stimulation. Ectopic ALK2-K233R expression was associated with an increase in the protein levels of RAC1 and its alternatively spliced isoform, RAC1b, both of which are implicated in driving cell migration and invasion. Conversely, the RNAi-mediated knockdown or CRISPR/Cas9-mediated knockout of RAC1b resulted in the upregulation of the expression of ALK2, but not that of the related BMP type I receptors, ALK3 or ALK6, and elevated the phosphorylation of SMAD1/5. PDAC is a heterogeneous disease encompassing tumors with different histomorphological subtypes, ranging from epithelial/classical to extremely mesenchymal. Upon treatment of various established and primary PDAC cell lines representing these subtypes with the ALK2 inhibitor, LDN-193189, well-differentiated, epithelial cell lines responded with a much stronger increase in the basal and TGFβ1-dependent migratory activity than poorly differentiated, mesenchymal ones. These data show that (i) ALK2 inhibits migration by suppressing RAC1/RAC1b proteins, (ii) ALK2 and RAC1b act together in a self-perpetuating the autoregulatory negative feedback loop to mutually control their expression, and (iii) the ALK2 antimigratory function appears to be particularly crucial in protecting epithelial subtype cells from becoming invasive, both spontaneously and in a TGFβ-rich tumor microenvironment.

Circadian molecular clock disruption in chronic pulmonary diseases.

The circadian clock is the biochemical oscillator with a near 24-h period that is responsible for generating the circadian rhythms in peripheral organs including the lung. Mounting evidence suggests that circadian clock disruption during chronic lung diseases plays an essential role in augmented oxidative stress, inflammatory response, metabolic imbalances, hypoxia/hyperoxia, mucus secretion, dysregulated autophagy, and alters pulmonary function. Here, we review circadian clock disruption and discuss candidate clock genes that are altered at the transcriptional or translational level in chronic pulmonary diseases. This review aims to provide the current knowledge and understanding of the circadian molecular clock disruption in chronic pulmonary diseases which will further advance the development of novel clock-based therapeutics in the future.

Physiological tissue-specific and age-related reduction of mouse TDP-43 levels is regulated by epigenetic modifications.

ABSTRACTThe cellular level of TDP-43 (also known as TARDBP) is tightly regulated; increases or decreases in TDP-43 have deleterious effects in cells. The predominant mechanism responsible for the regulation of the level of TDP-43 is an autoregulatory negative feedback loop. In this study, we identified an in vivo cause-effect relationship between Tardbp gene promoter methylation and specific histone modification and the TDP-43 level in tissues of mice at two different ages. Furthermore, epigenetic control was observed in mouse and human cultured cell lines. In amyotrophic lateral sclerosis, the formation of TDP-43-containing brain inclusions removes functional protein from the system. This phenomenon is continuous but compensated by newly synthesized protein. The balance between sequestration and new synthesis might become critical with ageing, if accompanied by an epigenetic modification-regulated decrease in newly synthesized TDP-43. Sequestration by aggregates would then decrease the amount of functional TDP-43 to a level lower than those needed by the cell and thereby trigger the onset of symptoms.

Activation and negative feedback regulation of SlHY5 transcription by the SlBBX20/21-SlHY5 transcription factor module in UV-B signaling.

In tomato (Solanum lycopersicum) and other plants, the photoreceptor UV-RESISTANCE LOCUS 8 regulates plant UV-B photomorphogenesis by modulating the transcription of many genes, the majority of which depends on the transcription factor ELONGATED HYPOCOTYL 5 (HY5). HY5 transcription is induced and then rapidly attenuated by UV-B. However, neither the transcription factors that activate HY5 transcription nor the mechanism for its attenuation during UV-B signaling is known. Here, we report that the tomato B-BOX (BBX) transcription factors SlBBX20 and SlBBX21 interact with SlHY5 and bind to the SlHY5 promoter to activate its transcription. UV-B-induced SlHY5 expression and SlHY5-controlled UV-B responses are normal in slbbx20 and slbbx21 single mutants, but strongly compromised in the slbbx20 slbbx21 double mutant. Surprisingly, UV-B responses are also compromised in lines overexpressing SlBBX20 or SlBBX21. Both SlHY5 and SlBBX20 bind to G-box1 in the SlHY5 promoter. SlHY5 outcompetes SlBBX20 for binding to the SlHY5 promoter in vitro, and inhibits the association of SlBBX20 with the SlHY5 promoter in vivo. Overexpressing 35S:SlHY5-FLAG in the WT background inhibits UV-B-induced endogenous SlHY5 expression. Together, our results reveal the critical role of the SlBBX20/21-SlHY5 module in activating the expression of SlHY5, the gene product of which inhibits its own gene transcription under UV-B, forming an autoregulatory negative feedback loop that balances SlHY5 transcription in plants.

An autoregulatory negative feedback loop controls thermomorphogenesis in Arabidopsis.

Plant growth and development are acutely sensitive to high ambient temperature caused in part due to climate change. However, the mechanism of high ambient temperature signaling is not well defined. Here, we show that HECATEs (HEC1 and HEC2), two helix-loop-helix transcription factors, inhibit thermomorphogenesis. While the expression of HEC1 and HEC2 is increased and HEC2 protein is stabilized at high ambient temperature, hec1hec2 double mutant showed exaggerated thermomorphogenesis. Analyses of the four PHYTOCHROME INTERACTING FACTOR (PIF1, PIF3, PIF4 and PIF5) mutants and overexpression lines showed that they all contribute to promote thermomorphogenesis. Furthermore, genetic analysis showed that pifQ is epistatic to hec1hec2. HECs and PIFs oppositely control the expression of many genes in response to high ambient temperature. PIFs activate the expression of HECs in response to high ambient temperature. HEC2 in turn interacts with PIF4 both in yeast and in vivo. In the absence of HECs, PIF4 binding to its own promoter as well as the target gene promoters was enhanced, indicating that HECs control PIF4 activity via heterodimerization. Overall, these data suggest that PIF4-HEC forms an autoregulatory composite negative feedback loop that controls growth genes to modulate thermomorphogenesis.

Circadian rhythms of melatonin, cortisol, and clock gene expression in the hyperacute phase of wake-up stroke: study design and measurement.

Circadian rhythms of melatonin, cortisol, and clock gene expression in the hyperacute phase of wake-up stroke: study design and measurement.

Abstract 2971: Ellagic acid and its metabolite Urolithin A induce prostate cancer cell death in p53 dependent and independent manner

Abstract Carcinoma of the prostate (CaP) is the most common cancer in men and the second leading cause of cancer-related death in men worldwide. Treatment of early stages of CaP often involves the surgical removal of all or part of the prostate gland; whereas malignant cases of advanced CaP generally requires a combination of therapies including removal of the entire prostate, radiotherapy and androgen deprivation. However, significant number of CaP patients relapse the CaP as the disease becomes hormonal independent. Therefore, it is important to target cell death pathways that function independently of androgen signaling. p53 is a common tumor suppressor that mediates apoptosis, cell cycle arrest and DNA repair. Inactivation of p53 is common in CaP cells and this repression of p53 function diminishes androgen receptor signaling. The most common negative regulator of p53 is MDM2, which is itself a target gene of p53 to form an autoregulatory negative feedback loop. MDM2 inhibits p53 transcriptional activity through the induction of p53 polyubiquitination and degradation in the proteasome. This loss of p53 may permit CaP cells to undergo uncontrolled cell growth and cancer progression. Previous studies have shown that certain polyphenols, derived from natural products, possess anticancer activity that may be attributed to their repression of MDM2 ligase activity and activation of p53. Pomegranates, berries, and walnuts contain several bioactive compounds, including the Ellagitannins (ETs). ETs are polyphenolic compounds that are hydrolyzed in the stomach to form Ellagic acid (EA) which is itself metabolized in the gut microbiota to Urolithin A (UA). The purpose of this study was to investigate the influence of EA and UA on the p53-MDM2 signaling pathway in CaP cells. Three models of CaP cell lines were used because each harbor different p53 genotypes: LNCaP (p53+/+), 22RV1(p53-/+) and PC3 (p53-/-). Here we found that, when 22RV1 and LNCaP were treated with EA and UA, the interaction between p53 and MDM2 was disrupted. As a result, both EA and UA caused an increase in p53 protein levels and increased the steady-state concentration of p21, a main downstream target gene of p53 that mediates cell cycle arrest. In addition, EA and UA increased the levels of PUMA and NOXA proteins, both target genes of p53 which confer p53’s pro-apoptotic function. Moreover, we confirmed UA inhibits MDM2-mediated polyubiquitination and degradation of p53. Finally, the data show that EA and UA induce apoptosis in PC3 cells (p53-/-), indicating p53 independent role of these compounds. These results suggest that EA and UA may have potential anti-neoplastic activity in CaP cells that may be at least partially attributed to the stabilization and activation of p53. Citation Format: Yasir I. Mohammed Saleem, Mustafa Selim. Ellagic acid and its metabolite Urolithin A induce prostate cancer cell death in p53 dependent and independent manner [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2971.

Termination in Jasmonate Signaling by MYC2 and MTBs.

Jasmonic acid (JA) signaling can be switched off by metabolism of JA. The master regulator MYC2, interacting with MED25, has been shown to be deactivated by the bHLH transcription factors MTB1, MTB2, and MTB3. An autoregulatory negative feedback loop has been proposed for this termination in JA signaling.

Identification of TCERG1 as a new genetic modulator of TDP-43 production in Drosophila

TAR DNA-binding protein-43 (TDP-43) is a ubiquitously expressed DNA-/RNA-binding protein that has been linked to numerous aspects of the mRNA life cycle. Similar to many RNA-binding proteins, TDP-43 expression is tightly regulated through an autoregulatory negative feedback loop. Cell function and survival depend on the strict control of TDP-43 protein levels. TDP-43 has been identified as the major constituent of ubiquitin-positive inclusions in patients with Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Lobar Degeneration (FTLD). Several observations argue for a pathogenic role of elevated TDP-43 levels in these disorders. Modulation of the cycle of TDP-43 production might therefore provide a new therapeutic strategy. Using a Drosophila model mimicking key features of the TDP-43 autoregulatory feedback loop, we identified CG42724 as a genetic modulator of TDP-43 production in vivo. We found that CG42724 protein influences qualitatively and quantitatively the TDP-43 mRNA transcript pattern. CG42724 overexpression promotes the production of transcripts that can be efficiently released into the cytoplasm for protein translation. Importantly, we showed that TCERG1, the human homolog of the Drosophila CG42724 protein, also caused an increase of TDP-43 protein steady-state levels in mammalian cells. Therefore, our data suggest the possibility that targeting TCERG1 could be therapeutic in TDP-43 proteinopathies.

FTLD/ALS-linked TDP-43 mutations do not alter TDP-43’s ability to self-regulate its expression in Drosophila

TDP-43 is a major disease-causing protein in amyotrophic lateral sclerosis (ALS) and Frontotemporal Lobar Degeneration (FTLD). Today, >50 missense mutations in the TARDBP/TDP-43 gene have been described in patients with FTLD/ALS. However, the functional consequences of FTLD/ALS-linked TDP-43 mutations are not fully elucidated. In the physiological state, TDP-43 expression is tightly regulated through an autoregulatory negative feedback loop. Maintaining normal TDP-43 protein levels is critical for proper physiological functions of the cells. In the present study, we investigated whether the FTLD/ALS-associated mutations could interfere with TDP-43 protein’s capacity to modulate its own protein levels using Drosophila as an experimental model. Our data show that FTLD/ALS-associated mutant proteins regulate TDP-43 production with the same efficiency as the wild-type form of the protein. Thus, FTLD/ALS-linked TDP-43 mutations do not alter TDP-43’s ability to self-regulate its expression and consequently of the homeostasis of TDP-43 protein levels.

Transcription Factor Target Gene Network governs the Logical Abstraction Analysis of the Synthetic Circuit in Leishmaniasis

With the advent of synthetic biology in medicine many synthetic or engineered proteins have made their way to therapeutics and diagnostics. In this paper, the downstream gene network of CD14-TNF-EGFR pathway in leishmaniasis, a tropical disease, is reconstructed. Network analysis showed that NFkB links the signaling and gene network, used as a point of intervention through a synthetic circuit embedded within the negative autoregulatory feedback loop. A chimeric protein kinase C (PKC) is incorporated in the synthetic circuit, under the transcriptional regulation of Lac repressor and IPTG, as an inducer. The chimeric PKC_ζα via IκKb phosphorylation activates NFκB, and modulates the gene expression from an anti-inflammatory to a pro-inflammatory phenotype in in vitro L. major infected macrophage model. This is the first ever report of a synthetic device construction in leishmania.

Circadian processes in the RNA life cycle.

The circadian clock drives daily rhythms of multiple physiological processes, allowing organisms to anticipate and adjust to periodic changes in environmental conditions. These physiological rhythms are associated with robust oscillations in the expression of at least 30% of expressed genes. While the ability for the endogenous timekeeping system to generate a 24-hr cycle is a cell-autonomous mechanism based on negative autoregulatory feedback loops of transcription and translation involving core-clock genes and their protein products, it is now increasingly evident that additional mechanisms also govern the circadian oscillations of clock-controlled genes. Such mechanisms can take place post-transcriptionally during the course of the RNA life cycle. It has been shown that many steps during RNA processing are regulated in a circadian manner, thus contributing to circadian gene expression. These steps include mRNA capping, alternative splicing, changes in splicing efficiency, and changes in RNA stability controlled by the tail length of polyadenylation or the use of alternative polyadenylation sites. RNA transport can also follow a circadian pattern, with a circadian nuclear retention driven by rhythmic expression within the nucleus of particular bodies (the paraspeckles) and circadian export to the cytoplasm driven by rhythmic proteins acting like cargo. Finally, RNA degradation may also follow a circadian pattern through the rhythmic involvement of miRNAs. In this review, we summarize the current knowledge of the post-transcriptional circadian mechanisms known to play a prominent role in shaping circadian gene expression in mammals. This article is categorized under: RNA Processing > Splicing Regulation/Alternative Splicing RNA Processing > RNA Editing and Modification RNA Export and Localization > Nuclear Export/Import.

Splicing factors act as genetic modulators of TDP-43 production in a new autoregulatory TDP-43 Drosophila model.

TDP-43 is a critical RNA-binding factor associated with RNA metabolism. In the physiological state, maintaining normal TDP-43 protein levels is critical for proper physiological functions of the cells. As such, TDP-43 expression is tightly regulated through an autoregulatory negative feedback loop. TDP-43 is a major disease-causing protein in Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Lobar Degeneration (FTLD). Several studies argue for a pathogenic role of elevated TDP-43 levels in these disorders. Modulating the cycle of TDP-43 production might therefore provide a new therapeutic strategy. In this study, we developed a new transgenic Drosophila model mimicking the TDP-43 autoregulatory feedback loop in order to identify genetic modulators of TDP-43 protein steady-state levels in vivo. First, we showed that our TDP-43_TDPBR Drosophila model recapitulates key features of the TDP-43 autoregulatory processes previously described in mammalian and cellular models, namely alternative splicing events, differential usage of polyadenylation sites, nuclear retention of the transcript and a decrease in steady-state mRNA levels. Using this new Drosophila model, we identified several splicing factors, including SF2, Rbp1 and Sf3b1, as genetic modulators of TDP-43 production. Interestingly, our data indicate that these three RNA-binding proteins regulate TDP-43 protein production, at least in part, by controlling mRNA steady-state levels.

Modeling of a negative feedback mechanism explains antagonistic pleiotropy in reproduction in domesticated Caenorhabditis elegans strains.

Most biological traits and common diseases have a strong but complex genetic basis, controlled by large numbers of genetic variants with small contributions to a trait or disease risk. The effect-size of most genetic variants is not absolute and is instead dependent upon multiple factors such as the age and genetic background of an organism. In order to understand the mechanistic basis of these changes, we characterized heritable trait differences between two domesticated strains of C. elegans. We previously identified a major effect locus, caused in part by a mutation in a component of the NURF chromatin remodeling complex, that regulates reproductive output in an age-dependent manner. The effect-size of this locus changes from positive to negative over the course of an animal’s reproductive lifespan. Here, we use a previously published macroscale model of the egg-laying rate in C. elegans to show that time-dependent effect-size is explained by an unequal use of sperm combined with negative feedback between sperm and ovulation rate. We validate key predictions of this model with controlled mating experiments and quantification of oogenesis and sperm use. Incorporation of this model into QTL mapping allows us to identify and partition new QTLs into specific aspects of the egg-laying process. Finally, we show how epistasis between two genetic variants is predicted by this modeling as a consequence of the unequal use of sperm. This work demonstrates how modeling of multicellular communication systems can improve our ability to predict and understand the role of genetic variation on a complex phenotype. Negative autoregulatory feedback loops, common in transcriptional regulation, could play an important role in modifying genetic architecture in other traits.

The influence of nuclear compartmentalisation on stochastic dynamics of self-repressing gene expression

Gene expression is an inherently noisy process. This noise is generally thought to be deleterious as precise internal regulation of biochemical reactions is essential for cell growth and survival. Self-repression of gene expression, which is the simplest form of a negative feedback loop, is commonly believed to be employed by cellular systems to decrease the stochastic fluctuations in gene expression. When there is some delay in autoregulation, it is also believed that this system can generate oscillations. In eukaryotic cells, mRNAs that are synthesised in the nucleus must be exported to the cytoplasm to function in protein synthesis, whereas proteins must be transported into the nucleus from the cytoplasm to regulate the expression levels of genes. Nuclear transport thus plays a critical role in eukaryotic gene expression and regulation. Some recent studies have suggested that nuclear retention of mRNAs can control noise in mRNA expression. However, the effect of nuclear transport on protein noise and its interplay with negative feedback regulation is not completely understood. In this paper, we systematically compare four different simple models of gene expression. By using simulations and applying the linear noise approximation to the corresponding chemical master equations, we investigate the influence of nuclear import and export on noise in gene expression in a negative autoregulatory feedback loop. We first present results consistent with the literature, i.e., that negative feedback can effectively buffer the variability in protein levels, and nuclear retention can decrease mRNA noise levels. Interestingly we find that when negative feedback is combined with nuclear retention, an amplification in gene expression noise can be observed and is dependant on nuclear translocation rates. Finally, we investigate the effect of nuclear compartmentalisation on the ability of self-repressing genes to exhibit stochastic oscillatory dynamics.

A novel P53/POMC/Gαs/SASH1 autoregulatory feedback loop activates mutated SASH1 to cause pathologic hyperpigmentation.

p53‐Transcriptional‐regulated proteins interact with a large number of other signal transduction pathways in the cell, and a number of positive and negative autoregulatory feedback loops act upon the p53 response. P53 directly controls the POMC/α‐MSH productions induced by ultraviolet (UV) and is associated with UV‐independent pathological pigmentation. When identifying the causative gene of dyschromatosis universalis hereditaria (DUH), we found three mutations encoding amino acid substitutions in the gene SAM and SH3 domain containing 1 (SASH1), and SASH1 was associated with guanine nucleotide‐binding protein subunit‐alpha isoforms short (Gαs). However, the pathological gene and pathological mechanism of DUH remain unknown for about 90 years. We demonstrate that SASH1 is physiologically induced by p53 upon UV stimulation and SASH and p53 is reciprocally induced at physiological and pathophysiological conditions. SASH1 is regulated by a novel p53/POMC/α‐MSH/Gαs/SASH1 cascade to mediate melanogenesis. A novel p53/POMC/Gαs/SASH1 autoregulatory positive feedback loop is regulated by SASH1 mutations to induce pathological hyperpigmentation phenotype. Our study demonstrates that a novel p53/POMC/Gαs/SASH1 autoregulatory positive feedback loop is regulated by SASH1 mutations to induce pathological hyperpigmentation phenotype.

Chtop (Chromatin target of Prmt1) auto-regulates its expression level via intron retention and nonsense-mediated decay of its own mRNA

Chtop (chromatin target of Prmt1) regulates various aspects of gene expression including transcription and mRNA export. Despite these important functions, the regulatory mechanism underlying Chtop expression remains undetermined. Using Chtop-expressing human cell lines, we demonstrate that Chtop expression is controlled via an autoregulatory negative feedback loop whereby Chtop binds its own mRNA to retain intron 2 during splicing; a premature termination codon present at the 5′ end of intron 2 leads to nonsense-mediated decay of the mRNA. We also show that Chtop interacts with exon 2 of Chtop mRNA via its arginine-glycine-rich (RG) domain, and with intron 2 via its N-terminal (N1) domain; both are required for retention of intron 2. In addition, we show that hnRNP H accelerates intron 2 splicing of Chtop mRNA in a manner dependent on Chtop expression level, suggesting that Chtop and hnRNP H regulate intron 2 retention of Chtop mRNA antagonistically. Thus, the present study provides a novel molecular mechanism by which mRNA and protein levels are constitutively regulated by intron retention.