Abstract 115: Nuclear CaMKII is a Histone H3 Kinase that Remodels Chromatin During Cardiac Hypertrophy

2013 ◽  
Vol 113 (suppl_1) ◽  
Author(s):  
Salma Mahmoud ◽  
Muhammad Kunhi ◽  
Gillian H Little ◽  
Yan Bai ◽  
Woojin An ◽  
...  
Keyword(s):  
Cardiac Hypertrophy ◽  
Cardiac Muscle ◽  
Chromatin Remodeling ◽  
Cellular Proliferation ◽  
Recombinant Adenovirus ◽  
Phosphorylation Site ◽  
Histone H3 ◽  
Functional Link

Background and Purpose: Calcium/calmodulin-dependent protein kinase II (CaMKII) is a ubiquitous serine/threonine kinase implicated in pathological events such as cardiac hypertrophy. In this study we investigated the role of a specific nuclear isoform of CaMKII in chromatin remodeling and in transcriptional regulation in cardiac muscle. Methods: Comprehensive experimental approaches performed in primary cardiomyocyte cultures were used including chromatin immunoprecipitation assays (ChIP), q-PCR, chromatin remodeling assays, in vitro phosphorylation/transcription assays, production of recombinant adenovirus, siRNA technology, fluorescence microscopy and mass spectrometry. Results: We found that CaMKIIδB targets specific components of chromatin during cardiac hypertrophy and binds to nucleosomes through its association domain in a cooperative model. CaMKIIδB also increased chromatin relaxation, and this action was dependent on its kinase activity. The observation that CaMKIIδB interacts with chromatin suggested to us that histones maybe novel substrates of the kinase in cardiac muscle. To test this hypothesis, we performed in vitro kinase assays and found that histone H3 is a bona fide CaMKIIδB substrate and Ser-10 appears to be a predominant phosphorylation site. Increased histone H3 Ser-10 phosphorylation was observed following hypertrophic stimulation and was not associated with cellular proliferation, whereas depletion of CaMKIIδB significantly reduced histone H3 Ser-10 phosphorylation in primary cardiomyocytes. Interestingly, we found that H3 S10 phosphorylation and recruitment of CaMKIIδB occur at promoters of fetal cardiac genes. To establish the functional link between H3 phosphorylation by CaMKIIδB, chromatin remodeling and transcription activation, we developed an in vitro transcription system and using it we found that CaMKIIδB increased chromatin accessibility and mediated transcription of the Mef2 transcription factor. Conclusion: Taken together, these findings highlight a new role of CaMKIIδB as relevant histone H3 kinase and link for the first time epigenetic changes by CaMKII to cardiac hypertrophy.

scholarly journals The H3K36me2 writer-reader dependency in H3K27M-DIPG

2021 ◽  
Author(s):  
Jia-Ray Yu ◽  
Gary LeRoy ◽  
Devin Bready ◽  
Joshua D. Frenster ◽  
Ricardo Saldaña-Meyer ◽  
...  
Keyword(s):  
Cellular Proliferation ◽  
Histone H3 ◽  
Pediatric Brain Tumor ◽  
Diffuse Intrinsic Pontine Glioma ◽  
Therapeutic Interventions ◽  
Functional Pathway ◽  
Proliferation In Vitro

AbstractThe lysine-to-methionine mutation at residue 27 of histone H3 (H3K27M) is a driving mutation in Diffuse Intrinsic Pontine Glioma (DIPG), a highly aggressive form of pediatric brain tumor with no effective treatment and little chance of survival. H3K27M reshapes the epigenome through a global inhibition of PRC2 catalytic activity, the placement of methylation at lysine 27 of histone H3 (H3K27me2/3), promoting oncogenesis of DIPG. As a consequence, a histone modification H3K36me2, antagonistic to H3K27me2/3, is aberrantly elevated. Here, we investigate the role of H3K36me2 in H3K27M-DIPG by tackling its upstream catalyzing enzymes (writers) and downstream binding factors (readers). We determine that NSD1 and NSD2 are the key writers for H3K36me2. Loss of NSD1/2 in H3K27M-DIPG impedes cellular proliferation in vitro and tumorigenesis in vivo, and disrupts tumor-promoting gene expression programs. Further, we demonstrate that LEDGF and HDGF2 are the main readers that mediate the pro-tumorigenic effects downstream of NSD1/2-H3K36me2. Treatment with a chemically modified peptide mimicking endogenous H3K36me2 dislodges LEDGF/HDGF2 from chromatin and specifically inhibits the proliferation of H3K27M-DIPG. Together, our results indicate a functional pathway of NSD1/2-H3K36me2-LEDGF/HDGF2 as an acquired dependency in H3K27M-DIPG and suggest a possibility to target this pathway for therapeutic interventions.

scholarly journals MiR-26a-5p inhibits GSK3β expression and promotes cardiac hypertrophy in vitro

PeerJ ◽  
2020 ◽  
Vol 8 ◽  
pp. e10371
Author(s):  
Liqun Tang ◽  
Jianhong Xie ◽  
Xiaoqin Yu ◽  
Yangyang Zheng
Keyword(s):  
Cell Surface ◽  
Cardiac Hypertrophy ◽  
Surface Area ◽  
Myocardial Cell ◽  
Immunofluorescence Staining ◽  
Cell Surface Area ◽  
Direct Target

Background The role of miR-26a-5p expression in cardiac hypertrophy remains unclear. Herein, the effect of miR-26a-5p on cardiac hypertrophy was investigated using phenylephrine (PE)-induced cardiac hypertrophy in vitro and in a rat model of hypertension-induced hypertrophy in vivo. Methods The PE-induced cardiac hypertrophy models in vitro and vivo were established. To investigate the effect of miR-26a-5p activation on autophagy, the protein expression of autophagosome marker (LC3) and p62 was detected by western blot analysis. To explore the effect of miR-26a-5p activation on cardiac hypertrophy, the relative mRNA expression of cardiac hypertrophy related mark GSK3β was detected by qRT-PCR in vitro and vivo. In addition, immunofluorescence staining was used to detect cardiac hypertrophy related mark α-actinin. The cell surface area was measured by immunofluorescence staining. The direct target relationship between miR-26a-5p and GSK3β was confirmed by dual luciferase report. Results MiR-26a-5p was highly expressed in PE-induced cardiac hypertrophy. MiR-26a-5p promoted LC3II and decreased p62 expression in PE-induced cardiac hypertrophy in the presence or absence of lysosomal inhibitor. Furthermore, miR-26a-5p significantly inhibited GSK3β expression in vitro and in vivo. Dual luciferase report results confirmed that miR-26a-5p could directly target GSK3β. GSK3β overexpression significantly reversed the expression of cardiac hypertrophy-related markers including ANP, ACTA1 and MYH7. Immunofluorescence staining results demonstrated that miR-26a-5p promoted cardiac hypertrophy related protein α-actinin expression, and increased cell surface area in vitro and in vivo. Conclusion Our study revealed that miR-26a-5p promotes myocardial cell autophagy activation and cardiac hypertrophy by regulating GSK3β, which needs further research.

scholarly journals Piezo1-Mediated Mechanotransduction Promotes Cardiac Hypertrophy by Impairing Calcium Homeostasis to Activate Calpain/Calcineurin Signaling

Hypertension ◽  
2021 ◽  
Author(s):  
Yuhao Zhang ◽  
Sheng-an Su ◽  
Wudi Li ◽  
Yuankun Ma ◽  
Jian Shen ◽  
...  
Keyword(s):  
Cardiac Hypertrophy ◽  
Ion Channel ◽  
Calcium Homeostasis ◽  
Pressure Overload ◽  
Cell Physiology ◽  
Hypertrophic Growth ◽  
Molecular Features ◽  
Mechanosensitive Ion Channel

Hemodynamic overload induces pathological cardiac hypertrophy, which is an independent risk factor for intractable heart failure in long run. Beyond neurohumoral regulation, mechanotransduction has been recently recognized as a major regulator of cardiac hypertrophy under a myriad of conditions. However, the identification and molecular features of mechanotransducer on cardiomyocytes are largely sparse. For the first time, we identified Piezo1 (Piezo type mechanosensitive ion channel component 1), a novel mechanosensitive ion channel with preference to Ca 2+ was remarkably upregulated under pressure overload and enriched near T-tubule and intercalated disc of cardiomyocyte. By applying cardiac conditional Piezo1 knockout mice (Piezo1 fl/fl Myh6Cre+, Piezo1 Cko ) undergoing transverse aortic constriction, we demonstrated that Piezo1 was required for the development of cardiac hypertrophy and subsequent adverse remodeling. Activation of Piezo1 by external mechanical stretch or agonist Yoda1 lead to the enlargement of cardiomyocytes in vitro, which was blocked by Piezo1 silencing or Yoda1 analog Dooku1 or Piezo1 inhibitor GsMTx4. Mechanistically, Piezo1 perturbed calcium homeostasis, mediating extracellular Ca 2+ influx and intracellular Ca 2+ overload, thereby increased the activation of Ca 2+ -dependent signaling, calcineurin, and calpain. Inhibition of calcineurin or calpain could abolished Yoda1 induced upregulation of hypertrophy markers and the hypertrophic growth of cardiomyocytes in vitro. From a comprehensive view of the cardiac transcriptome, most of Piezo1 affected genes were highly enriched in muscle cell physiology, tight junction, and corresponding signaling. This study characterizes an undefined role of Piezo1 in pressure overload induced cardiac hypertrophy. It may partially decipher the differential role of calcium under pathophysiological condition, implying a promising therapeutic target for cardiac dysfunction.

scholarly journals HNRNPA2B1 promotes multiple myeloma progression by increasing AKT3 expression via m6A-dependent stabilization of ILF3 mRNA

2021 ◽  
Vol 14 (1) ◽  
Author(s):  
Fengjie Jiang ◽  
Xiaozhu Tang ◽  
Chao Tang ◽  
Zhen Hua ◽  
Mengying Ke ◽  
...  
Keyword(s):  
Multiple Myeloma ◽  
Cell Proliferation ◽  
Cellular Proliferation ◽  
Aberrant Expression ◽  
The Stability ◽  
Induced Apoptosis ◽  
Proliferation In Vitro

AbstractN6-methyladenosine (m6A) modification is the most prevalent modification in eukaryotic RNAs while accumulating studies suggest that m6A aberrant expression plays an important role in cancer. HNRNPA2B1 is a m6A reader which binds to nascent RNA and thus affects a perplexing array of RNA metabolism exquisitely. Despite unveiled facets that HNRNPA2B1 is deregulated in several tumors and facilitates tumor growth, a clear role of HNRNPA2B1 in multiple myeloma (MM) remains elusive. Herein, we analyzed the function and the regulatory mechanism of HNRNPA2B1 in MM. We found that HNRNPA2B1 was elevated in MM patients and negatively correlated with favorable prognosis. The depletion of HNRNPA2B1 in MM cells inhibited cell proliferation and induced apoptosis. On the contrary, the overexpression of HNRNPA2B1 promoted cell proliferation in vitro and in vivo. Mechanistic studies revealed that HNRNPA2B1 recognized the m6A sites of ILF3 and enhanced the stability of ILF3 mRNA transcripts, while AKT3 downregulation by siRNA abrogated the cellular proliferation induced by HNRNPA2B1 overexpression. Additionally, the expression of HNRNPA2B1, ILF3 and AKT3 was positively associated with each other in MM tissues tested by immunohistochemistry. In summary, our study highlights that HNRNPA2B1 potentially acts as a therapeutic target of MM through regulating AKT3 expression mediated by ILF3-dependent pattern.

Abstract 026: Role of Tank in the Regulation of Pathological Cardiac Hypertrophy

Hypertension ◽  
2016 ◽  
Vol 68 (suppl_1) ◽  
Author(s):  
Hongliang Li ◽  
Peng Zhang
Keyword(s):  
Cardiac Hypertrophy ◽  
Cardiac Dysfunction ◽  
Pressure Overload ◽  
Adaptor Protein ◽  
Negative Regulator ◽  
Akt Inhibitor ◽  
Aortic Banding ◽  
Pathological Cardiac Hypertrophy

TRAF associated NF-κB activator (TANK) is adaptor protein which was identified as a negative regulator of TRAF-, TBK1- and IKKi-mediated signal transduction through its interaction with them. Besides its important roles in the regulation of immune response, it has been reported that TANK contributes to the development of autoimmune nephritis and osteoclastogenesis. However, its functions in cardiovascular diseases especially cardiac hypertrophy is largely unknown. In the present study, we interestingly observed that TNAK expression is increased by 240% in human hypertrophic cardiomyopathy(HCM)tissue and 320% in mouse hypertrophic heart after aortic banding (AB), indicating that TANK may be involved in the pathogenesis of this diseases. Subsequently, cardiac-specific TANK knockout (TANK-KO) and transgenic(TANK-TG)mice were generated and subjected to AB for 4 to 8 weeks. Our results demonstrated that TANK deficiency prevented against cardiac hypertrophy and fibrosis induced by pressure overload,as evidenced by that the cardiomyocytes enlargement and fibrosis formation was reduced by about 34% and 43% compared with WT mice, respectively. Conversely, TANK-TG mice showed an aggravated effect on cardiac hypertrophy in response to pressure overload with 36% and 47% increase of cardiomyocytes enlargement and fibrosis formation compared with non-transgenic mice. More importantly, in vitro experiments further revealed that TANK overexpression which was mediated by adenovirus in the cardiomyocytes dramatically increased the cell size and the expression of hypertrophic markers, whereas TANK knockdown had an opposite function. Mechanistically, we discovered that AKT signaling was activated (230%) in the hearts of TANK-TG mice, while being greatly reduced in TNAK-KO hearts after aortic banding. Moreover, blocking AKT/GSK3β signaling with a pharmacological AKT inhibitor reversed cardiac dysfunction of TANK-TG mice. Collectively, our data show that TNAK acts as a novel regulator of pathological cardiac hypertrophy and may be a promising therapeutic targets.

scholarly journals Transcriptional Regulation of Genes by Ikaros Tumor Suppressor in Acute Lymphoblastic Leukemia

2020 ◽  
Vol 21 (4) ◽  
pp. 1377
Author(s):  
Pavan Kumar Dhanyamraju ◽  
Soumya Iyer ◽  
Gayle Smink ◽  
Yevgeniya Bamme ◽  
Preeti Bhadauria ◽  
...  
Keyword(s):  
Acute Lymphoblastic Leukemia ◽  
Tumor Suppressor ◽  
Chromatin Remodeling ◽  
Target Genes ◽  
Cellular Proliferation ◽  
Lymphoblastic Leukemia ◽  
Regulatory Elements ◽  
Binding Motif ◽  
Functional Inactivation

Regulation of oncogenic gene expression by transcription factors that function as tumor suppressors is one of the major mechanisms that regulate leukemogenesis. Understanding this complex process is essential for explaining the pathogenesis of leukemia as well as developing targeted therapies. Here, we provide an overview of the role of Ikaros tumor suppressor and its role in regulation of gene transcription in acute leukemia. Ikaros (IKZF1) is a DNA-binding protein that functions as a master regulator of hematopoiesis and the immune system, as well as a tumor suppressor in acute lymphoblastic leukemia (ALL). Genetic alteration or functional inactivation of Ikaros results in the development of high-risk leukemia. Ikaros binds to the specific consensus binding motif at upstream regulatory elements of its target genes, recruits chromatin-remodeling complexes and activates or represses transcription via chromatin remodeling. Over the last twenty years, a large number of Ikaros target genes have been identified, and the role of Ikaros in the regulation of their expression provided insight into the mechanisms of Ikaros tumor suppressor function in leukemia. Here we summarize the role of Ikaros in the regulation of the expression of the genes whose function is critical for cellular proliferation, development, and progression of acute lymphoblastic leukemia.

scholarly journals Role of Toxoplasma gondii Chloroquine Resistance Transporter in Bradyzoite Viability and Digestive Vacuole Maintenance

mBio ◽  
2019 ◽  
Vol 10 (4) ◽  
Author(s):  
Geetha Kannan ◽  
Manlio Di Cristina ◽  
Aric J. Schultz ◽  
My-Hang Huynh ◽  
Fengrong Wang ◽  
...  
Keyword(s):  
Toxoplasma Gondii ◽  
Chronic Infection ◽  
Chloroquine Resistance ◽  
Congenital Defects ◽  
Functional Link ◽  
Content Type ◽  
Chloroquine Resistance Transporter

ABSTRACT Toxoplasma gondii is a ubiquitous pathogen that can cause encephalitis, congenital defects, and ocular disease. T. gondii has also been implicated as a risk factor for mental illness in humans. The parasite persists in the brain as slow-growing bradyzoites contained within intracellular cysts. No treatments exist to eliminate this form of parasite. Although proteolytic degradation within the parasite lysosome-like vacuolar compartment (VAC) is critical for bradyzoite viability, whether other aspects of the VAC are important for parasite persistence remains unknown. An ortholog of Plasmodium falciparum chloroquine resistance transporter (CRT), TgCRT, has previously been identified in T. gondii. To interrogate the function of TgCRT in chronic-stage bradyzoites and its role in persistence, we knocked out TgCRT in a cystogenic strain and assessed VAC size, VAC digestion of host-derived proteins and parasite autophagosomes, and the viability of in vitro and in vivo bradyzoites. We found that whereas parasites deficient in TgCRT exhibit normal digestion within the VAC, they display a markedly distended VAC and their viability is compromised both in vitro and in vivo. Interestingly, impairing VAC proteolysis in TgCRT-deficient bradyzoites restored VAC size, consistent with a role for TgCRT as a transporter of products of digestion from the VAC. In conjunction with earlier studies, our current findings suggest a functional link between TgCRT and VAC proteolysis. This study provides further evidence of a crucial role for the VAC in bradyzoite persistence and a new potential VAC target to abate chronic Toxoplasma infection. IMPORTANCE Individuals chronically infected with the intracellular parasite Toxoplasma gondii are at risk of experiencing reactivated disease that can result in progressive loss of vision. No effective treatments exist for chronic toxoplasmosis due in part to a poor understanding of the biology underlying chronic infection and a lack of well-validated potential targets. We show here that a T. gondii transporter is functionally linked to protein digestion within the parasite lysosome-like organelle and that this transporter is necessary to sustain chronic infection in culture and in experimentally infected mice. Ablating the transporter results in severe bloating of the lysosome-like organelle. Together with earlier work, this study suggests the parasite’s lysosome-like organelle is vital for parasite survival, thus rendering it a potential target for diminishing infection and reducing the risk of reactivated disease.

Baseline Nucleophosmin Status in Mutated(M) Versus Unmutated (U) Immunoglobulin B-CLL Is a Nuclear Reflection of Different Signal Transduction Physiology.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 5005-5005
Author(s):  
Jerina Boelens ◽  
Wim Van den Berghe ◽  
Guy Haegeman ◽  
Ann Janssens ◽  
Jan Philippe ◽  
...  
Keyword(s):  
Cellular Proliferation ◽  
Histone H3 ◽  
Routine Practice ◽  
Histone H4 ◽  
Total Histone ◽  
Environmental Signals ◽  
Erk Activation ◽  
Erk Phosphorylation ◽  
The Difference

Abstract Aim: The difference in prognosis between B-CLL patients with (M) and wihout (U) somatic hypermutations of the immunoglobulin genes has led to a search for surrogate markers in routine practice. cDNA-Microarray differentiation between M and U led to further analysis of Zap-70, fibromodulin and LPLase, all of which succesfully discriminate the majority of M vs U.. In 1 of 2 proteomic studies searching the difference between M and U B-CLL, nucleophosmin came out as uniformly absent in 6 U patients and present in all 6 with M B-CLL. Nucleophosmin is a nucleolar non-ribosomal protein, associated with cellular proliferation. It is implicated in carcinogenesis as a differentiation blocker in K562 myeloid leukemias where its degradation from a 35 to a 21 kD form accompanies phorbol ester induced differentiation. In K562 this degradation is dependent on P-Erk-translocation to the nucleus that by itself depends on prolonged Erk-activation. We have recently demonstrated that SDF-1, an important microenvironment factor in B-CLL, is capable of inducing prolonged Erk-activation in Zap-70+ but not in Zap-70- B-CLL cells in vitro. This prompted us to study the unstimulated expression of nucleophosmin and other nuclear proteins by Westen blot in 16 patients with B-CLL. Methods: Histones and other alkalic proteins were extracted from the nuclei (pellet fraction) upon treatment with 0.4 M HCl. Following precipitation in acetone, histones and proteins were resuspended in sample buffer and separated by SDS PAGE or acid urea gel electrophoresis. Subsequently, the proteins were electrotransferred to a nitrocellulose membrane. Western blot analysis was performed against nucleophosmin, histone H3 or H4, and final signal detection was revealed by enhanced chemiluminescence reaction. Results: The 35 kD nucleophosmin signal was uniformly expressed in all samples and related to total histone content, irrespective of mutation status, cytogenetics and stage of disease. However, a minor band at 21 kD reflecting degradation was present in 6/6 patients with U B-CLL and absent in 8/10 with M B-CLL. Pan-histone H3 and H4 antibodies revealed similar banding patterns for histone H3 in all patients, but the presence of a heavier (probably ubiquinated) double band for histone H4 in some. This ubiquinated fraction was important in 7/16, faint in 5/16 and absent in 4/16. Morphology was atypical in 4/7 with an important fraction, and typical in all others. 5/7 with important bands and 4/5 with faint bands were M B-CLL against only 1 out of 4 in the group with absence of ubiquitination bands. Discussion: In contrast to previous proteomic studies, we found the 35 kD form of nucleophosmin present in both M and U B-CLL. However, nucleophosmin metabolisation to the 21 kD form is observed preferentially in the U B-CLL. The increased baseline degradation of nucleophosmin in 6/6 U B-CLL all of whom are Zap-70+ can be explained as a downstream nuclear signal from constitutive increased Erk-phosphorylation upon environmental signals in Zap-70+ B-CLL.

VACM-1, a cul-5 gene, inhibits cellular growth by a mechanism that involves MAPK and p53 signaling pathways

2003 ◽  
Vol 285 (6) ◽  
pp. C1386-C1396 ◽  
Author(s):  
C. Van Dort ◽  
P. Zhao ◽  
K. Parmelee ◽  
B. Capps ◽  
A. Poel ◽  
...  
Keyword(s):  
Cell Lines ◽  
Cellular Proliferation ◽  
Phosphorylation Site ◽  
Chinese Hamster ◽  
Inhibitory Effect ◽  
Cellular Growth ◽  
P53 Expression ◽  
Mapk Phosphorylation ◽  
P53 Signaling

Vasopressin-activated Ca2+-mobilizing (VACM)-1 gene product is a 780-amino acid membrane protein that shares sequence homology with cullins, a family of genes involved in the regulation of cell cycle. However, when expressed in vitro, VACM-1 attenuates basal and vasopressin- and forskolin-induced cAMP production. Mutating the PKA-dependent phosphorylation site in the VACM-1 sequence (S730AVACM-1) prevents this inhibitory effect. To further examine the biological role of VACM-1, we studied the effect of VACM-1 and S730AVACM-1 proteins on cellular proliferation and gene expression in Chinese hamster ovary and COS-1 cells. Cellular proliferation of VACM-1-expressing cell lines was significantly lower compared with that of the vector-transfected cells, whereas it was significantly increased in S730AVACM-1-derived cell lines. Furthermore, expression of VACM-1 but not S730AVACM-1 protein retarded cytokinesis and prevented MAPK phosphorylation. Screening with the Human PathwayFinder-1 GEArray system and subsequent Western blot analysis demonstrated that VACM-1 induces p53 mRNA and protein expression. In summary, VACM-1 inhibits cellular growth by a mechanism that involves cAMP, MAPK phosphorylation, and p53 expression.

scholarly journals Differential phosphorylation signals control endocytosis of GPR15

2017 ◽  
Vol 28 (17) ◽  
pp. 2267-2281 ◽  
Author(s):  
Yukari Okamoto ◽  
Sojin Shikano
Keyword(s):  
Surface Density ◽  
Functional Role ◽  
Control Cell ◽  
Phosphorylation Site ◽  
Hek293 Cells ◽  
C Terminus ◽  
Differential Phosphorylation ◽  
G Protein Coupled

GPR15 is an orphan G protein–coupled receptor (GPCR) that serves for an HIV coreceptor and was also recently found as a novel homing receptor for T-cells implicated in colitis. We show that GPR15 undergoes a constitutive endocytosis in the absence of ligand. The endocytosis was clathrin dependent and partially dependent on β-arrestin in HEK293 cells, and nearly half of the internalized GPR15 receptors were recycled to the plasma membrane. An Ala mutation of the distal C-terminal Arg-354 or Ser-357, which forms a consensus phosphorylation site for basophilic kinases, markedly reduced the endocytosis, whereas phosphomimetic mutation of Ser-357 to Asp did not. Ser-357 was phosphorylated in vitro by multiple kinases, including PKA and PKC, and pharmacological activation of these kinases enhanced both phosphorylation of Ser-357 and endocytosis of GPR15. These results suggested that Ser-357 phosphorylation critically controls the ligand-independent endocytosis of GPR15. The functional role of Ser-357 in endocytosis was distinct from that of a conserved Ser/Thr cluster in the more proximal C-terminus, which was responsible for the β-arrestin– and GPCR kinase–dependent endocytosis of GPR15. Thus phosphorylation signals may differentially control cell surface density of GPR15 through endocytosis.

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