Ubiquitin-mediated proteasomal degradation of non-synonymous SNP variants of human ABC transporter ABCG2

2008 ◽  
Vol 411 (3) ◽  
pp. 623-631 ◽  
Author(s):  
Hiroshi Nakagawa ◽  
Ai Tamura ◽  
Kanako Wakabayashi ◽  
Kazuyuki Hoshijima ◽  
Masayuki Komada ◽  
...  
Keyword(s):  
Genetic Polymorphisms ◽  
Proteasomal Degradation ◽  
Immunoblot Analysis ◽  
Mrna Levels ◽  
Single Nucleotide ◽  
Protein Levels ◽  
Atp Binding Cassette Transporter ◽  
Novel Approach ◽  
293 Cells ◽  
The Individual

Clinical relevance is implicated between the genetic polymorphisms of the ABC (ATP-binding cassette) transporter ABCG2 (ABC subfamily G, member 2) and the individual differences in drug response. We expressed a total of seven non-synonymous SNP (single nucleotide polymorphism) variants in Flp-In-293 cells by using the Flp (flippase) recombinase system. Of these, ABCG2 F208S and S441N variants were found to be expressed at markedly low levels, whereas their mRNA levels were equal to those of the other SNP variants and ABCG2 WT (wild-type). Interestingly, protein expression levels of the ABCG2 F208S and S441N variants increased 6- to 12-fold when Flp-In-293 cells were treated with MG132, a proteasome inhibitor. Immunoprecipitation followed by immunoblot analysis showed that the ABCG2 F208S and S441N variant proteins were endogenously ubiquitinated in Flp-In-293 cells, and treatment with MG132 significantly enhanced the level of these ubiquitinated variants. Immunofluorescence microscopy demonstrated that MG132 greatly affected the ABCG2 F208S and S441N variants in terms of both protein levels and intracellular distribution. Immunoblot analysis revealed that those variants were N-glycosylated; however, their oligosaccharides were immature compared with those present on ABCG2 WT. The ABCG2 F208S and S441N variant proteins do not appear to be processed in the Golgi apparatus, but undergo ubiquitin-mediated protein degradation in proteasomes, whereas ABCG2 WT is sorted to the plasma membrane and then degraded via the lysosomal pathway. The present study provides the first evidence that certain genetic polymorphisms can affect the protein stability of ABCG2. Control of proteasomal degradation of ABCG2 would provide a novel approach in cancer chemotherapy to circumvent multidrug resistance of human cancers.

scholarly journals Viral FGARAT Homolog ORF75 of Rhesus Monkey Rhadinovirus Effects Proteasomal Degradation of the ND10 Components SP100 and PML

2016 ◽  
Vol 90 (17) ◽  
pp. 8013-8028 ◽  
Author(s):  
Alexander S. Hahn ◽  
Anna K. Großkopf ◽  
Doris Jungnickl ◽  
Brigitte Scholz ◽  
Armin Ensser
Keyword(s):  
Rhesus Monkey ◽  
De Novo ◽  
Human Herpesvirus ◽  
Proteasomal Degradation ◽  
Lytic Replication ◽  
Intrinsic Immunity ◽  
Protein Levels ◽  
Short Palindromic Repeat ◽  
Infected Cells ◽  
The Individual

ABSTRACTNuclear domain 10 (ND10) components restrict herpesviral infection, and herpesviruses antagonize this restriction by a variety of strategies, including degradation or relocalization of ND10 proteins. The rhesus monkey rhadinovirus (RRV) shares many key biological features with the closely related Kaposi's sarcoma-associated herpesvirus (KSHV; human herpesvirus 8) and readily infects cells of both human and rhesus monkey origin. We used the clustered regularly interspaced short palindromic repeat-Cas9 (CRISPR-Cas9) technique to generate knockout (ko) cells for each of the four ND10 components, PML, SP100, DAXX, and ATRX. These ko cells were analyzed with regard to permissiveness for RRV infection. In addition, we analyzed the fate of the individual ND10 components in infected cells by immunofluorescence and Western blotting. Knockout of the ND10 component DAXX markedly increased RRV infection, while knockout of PML or SP100 had a less pronounced effect. In line with these observations, RRV infection resulted in rapid degradation of SP100, followed by degradation of PML and the loss of ND10 structures, whereas the protein levels of ATRX and DAXX remained constant. Notably, inhibition of the proteasome but not inhibition ofde novogene expression prevented the loss of SP100 and PML in cells that did not support lytic replication, compatible with proteasomal degradation of these ND10 components through the action of a viral tegument protein. Expression of the RRV FGARAT homolog ORF75 was sufficient to effect the loss of SP100 and PML in transfected or transduced cells, implicating ORF75 as the viral effector protein.IMPORTANCEOur findings highlight the antiviral role of ND10 and its individual components and further establish the viral FGARAT homologs of the gammaherpesviruses to be important viral effectors that counteract ND10-instituted intrinsic immunity. Surprisingly, even closely related viruses like KSHV and RRV evolved to use different strategies to evade ND10-mediated restriction. RRV first targets SP100 for degradation and then targets PML with a delayed kinetic, a strategy which clearly differs from that of other gammaherpesviruses. Despite efficient degradation of these two major ND10 components, RRV is still restricted by DAXX, another abundant ND10 component, as evidenced by a marked increase in RRV infection and replication upon knockout of DAXX. Taken together, our findings substantiate PML, SP100, and DAXX as key antiviral proteins, in that the first two are targeted for degradation by RRV and the last one still potently restricts replication of RRV.

scholarly journals Functional Characterization of Tissue Inhibitor of Metalloproteinase-1 (TIMP-1) N- and C-Terminal Domains duringXenopus laevisDevelopment

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
M. A. Nieuwesteeg ◽  
J. A. Willson ◽  
M. Cepeda ◽  
M. A. Fox ◽  
S. Damjanovski
Keyword(s):  
Functional Characterization ◽  
Full Length ◽  
Tissue Inhibitor Of Metalloproteinase ◽  
Tissue Inhibitors Of Metalloproteinases ◽  
Mrna Levels ◽  
Ecm Remodeling ◽  
Protein Levels ◽  
Terminal Domain ◽  
The Individual ◽  
Terminal Domains

Extracellular matrix (ECM) remodeling is essential for facilitating developmental processes. ECM remodeling, accomplished by matrix metalloproteinases (MMPs), is regulated by endogenous tissue inhibitors of metalloproteinases (TIMPs). While the TIMP N-terminal domain is involved in inhibition of MMP activity, the C-terminal domain exhibits cell-signaling activity, which is TIMP and cell type dependent. We have previously examined the distinct roles of theXenopus laevisTIMP-2 and -3 C-terminal domains during development and here examined the unique roles of TIMP-1 N- and C-terminal domains in earlyX. laevisembryos. mRNA microinjection was used to overexpress full-length TIMP-1 or its individual N- or C-terminal domains in embryos. Full-length and C-terminal TIMP-1 resulted in increased lethality compared to N-terminal TIMP-1. Overexpression of C-terminal TIMP-1 resulted in significant decreases in mRNA levels of proteolytic genes including TIMP-2, RECK, MMP-2, and MMP-9, corresponding to decreases in MMP-2 and -9 protein levels, as well as decreased MMP-2 and MMP-9 activities. These trends were not observed with the N-terminus. Our research suggests that the individual domains of TIMP-1 are capable of playing distinct roles in regulating the ECM proteolytic network during development and that the unique functions of these domains are moderated in the endogenous full-length TIMP-1 molecule.

Diminished proteasomal degradation results in accumulation of Gfi1 protein in monocytes

Blood ◽  
2006 ◽  
Vol 109 (1) ◽  
pp. 100-108 ◽  
Author(s):  
Jurgen A. F. Marteijn ◽  
Laurens T. van der Meer ◽  
Liesbeth Van Emst ◽  
Theo de Witte ◽  
Joop H. Jansen ◽  
...  
Keyword(s):  
Ubiquitin Proteasome System ◽  
Proteasomal Degradation ◽  
Myeloid Differentiation ◽  
Mrna Levels ◽  
Monocytic Differentiation ◽  
Granulocytic Differentiation ◽  
Monocytic Cell ◽  
Protein Levels ◽  
Ubiquitin Proteasome ◽  
Monocytic Lineage

Abstract Gfi1 is a transcriptional repressor essential during myeloid differentiation. Gfi1−/− mice exhibit a block in myeloid differentiation resulting in the accumulation of an immature myelo-monocytic cell population and the complete absence of mature neutrophils. Even though mRNA levels of Gfi1 appear to be very low in monocytes, Gfi1 might play a role in the monocytic lineage as Gfi1−/− mice exhibit diminished monocyte-derived dendritic cells and disturbed cytokine production by macrophages in response to LPS. We show here that Gfi1 protein levels are mainly regulated by the ubiquitin-proteasome system. Upon forced monocytic differentiation of U937 cells, Gfi1 mRNA levels dropped but protein levels increased due to diminished proteasomal turnover. Similarly, Gfi1 mRNA levels are low in primary monocytes whereas the protein is clearly detectable. Conversely, Gfi1 mRNA levels are high in granulocytes but the protein is swiftly degraded by the proteasome in these cells. Chromatin immunoprecipitation experiments showed that Gfi1 binds to the promoter of several granulocyte-specific genes in primary monocytes, including C/EBPα, neutrophil elastase, and Gfi1 itself. The binding of the repressor Gfi1 to these promoters correlated with low expression of these genes in monocytes compared with granulocytes. Our data fit a model in which Gfi1 protein levels are induced in primary monocytes, due to diminished proteasomal degradation, to repress genes that play a role in granulocytic differentiation.

Short- and long-term mechanisms of tau regulation in PC12 cells

1995 ◽  
Vol 108 (8) ◽  
pp. 2857-2864 ◽  
Author(s):  
E. Sadot ◽  
J. Barg ◽  
D. Rasouly ◽  
P. Lazarovici ◽  
I. Ginzburg
Keyword(s):  
Nerve Growth Factor ◽  
Growth Factor ◽  
Pc12 Cells ◽  
Tau Protein ◽  
Immunoblot Analysis ◽  
Term Treatment ◽  
Mrna Levels ◽  
Short Term Treatment ◽  
Nerve Growth ◽  
Protein Levels

Induction by nerve growth factor of neurite outgrowth in PC12 cells is transcription-dependent and is associated with the accumulation of tau protein. It was recently shown that short-term treatment with staurosporine, a protein kinase alkaloid inhibitor, induced an elevation of tau protein levels and outgrowth of stable neurites. In this study, we analyzed the mechanism(s) by which nerve growth factor and staurosporine exert their effects on tau levels. We demonstrate that nerve growth factor affects tau mRNA stability, thus contributing to the observed increase in tau mRNA levels. On the other hand, tau mRNA levels were not affected by the treatment with staurosporine. We also demonstrate that the phosphorylation of tau protein was reduced after treatment of PC12 cells with nerve growth factor or staurosporine, as shown by immunoblot analysis using specific antibodies and alkaline phosphatase treatment. Thus, regulation of tau levels by nerve growth factor appears to be mediated by transcriptional, post-transcriptional and posttranslational steps, whereas the effect of staurosporine on tau levels may be attributed to its effect on the state of phosphorylation of the protein.

Gfi1 Protein Turnover Is Regulated by the Ubiquitin Ligase Triad1.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 1173-1173
Author(s):  
Laurens T. van der Meer ◽  
Jurgen A.F. Marteijn ◽  
Theo M. de Witte ◽  
Joop H. Jansen ◽  
Bert A. van der Reijden
Keyword(s):  
Ubiquitin Ligase ◽  
Half Life ◽  
Proteasome Inhibitors ◽  
Ring Finger ◽  
Ubiquitin Ligases ◽  
Proteasomal Degradation ◽  
Mrna Levels ◽  
Yeast Two Hybrid ◽  
Protein Levels ◽  
Two Hybrid

Abstract The transcriptional repressor Growth factor independence-1 (Gfi1) plays an essential role during various stages of hematopoiesis. It is crucial for the self-renewal and long-term reconstituting potential of stem cells, essential for neutrophilic differentiation, and it plays an important role in T-cell and dendritic cell development. Gfi1 has also been implicated in malignant hematopoeisis because the Gfi1 gene is a common proviral integration site in murine leukemia models. We recently found that Gfi1 protein levels are mainly regulated by the ubiquitin-proteasome system. Although Gfi1 mRNA levels are low in primary human monocytes, the protein levels are high due to low proteasomal degradation. Conversely, in mature granulocytes Gfi1 mRNA levels are high but protein levels are low due to strong proteasome-mediated turnover. Because Gfi1 plays an important role in normal and malignant hematopoiesis it will be of great interest to identify the ubiquitin ligases that regulate its turnover. Previously, we showed that the RING finger ubiquitin ligase Triad1 regulates myeloid cell proliferation. Using yeast-two-hybrid assays we found that Triad1 binds the zinc finger region of Gfi1. This interaction was confirmed in co-immunoprecipitation experiments. To study whether the turnover of Gfi1 is regulated by Triad1 we performed ubiquitination assays. To our suprise we found that instead of promoting ubiquitination, Triad1 inhibited Gfi1 protein ubiquitination, also in the presence of proteasome inhibitors. RNAi mediated down regulation of Triad1 protein levels stimulated Gfi1 ubiquitination. Importantly, expression of a Triad1 point mutant (H158A) that fails to bind the ubiquitin conjugating enzyme UbcH7 also inhibited Gfi1 ubiquitination. To study whether the observed diminished ubiquitination by Triad1 affected the turnover of Gfi1 we analyzed Gfi1 protein half-life using the protein synthesis inhibitor cycloheximide. This showed that Triad1 co-expression prolonged the half-life of Gfi1 significantly. We conclude that Triad1 inhibits Gfi1 ubiquitination, resulting in decreased turnover of the protein. As this inhibition also occurs in the presence of proteasome inhibitors and is independent of the ubiquitin ligase activity of Triad1, these data support a model in which Triad1 competes for Gfi1 binding with other ubiquitin ligases that do mark Gfi1 for proteasomal degradation. Currently, we are testing candidate ubiquitin ligases (RING finger and HECT proteins) that were found to associate with Gfi1 in yeast-two-hybrid assays to gain more insight in how the activity of this important transcription factor is regulated.

scholarly journals BRF1 Protein Turnover and mRNA Decay Activity Are Regulated by Protein Kinase B at the Same Phosphorylation Sites

2006 ◽  
Vol 26 (24) ◽  
pp. 9497-9507 ◽  
Author(s):  
Don Benjamin ◽  
Martin Schmidlin ◽  
Lu Min ◽  
Brigitte Gross ◽  
Christoph Moroni
Keyword(s):  
Protein Kinase ◽  
Mrna Decay ◽  
Protein Kinase B ◽  
Proteasomal Degradation ◽  
Mrna Levels ◽  
Cell Compartment ◽  
Protein Levels ◽  
Dependent Protein

ABSTRACT BRF1 posttranscriptionally regulates mRNA levels by targeting ARE-bearing transcripts to the decay machinery. We previously showed that protein kinase B (PKB) phosphorylates BRF1 at Ser92, resulting in binding to 14-3-3 and impairment of mRNA decay activity. Here we identify an additional regulatory site at Ser203 that cooperates in vivo with Ser92. In vitro kinase labeling and wortmannin sensitivity indicate that Ser203 phosphorylation is also performed by PKB. Mutation of both serines to alanine uncouples BRF1 from PKB regulation, leading to constitutive mRNA decay even in the presence of stabilizing signals. BRF1 protein is labile because of proteasomal degradation (half-life, <3 h) but becomes stabilized upon phosphorylation and is less stable in PKBα−/− cells. Surprisingly, phosphorylation-dependent protein stability is also regulated by Ser92 and Ser203, with parallel phosphorylation required at these sites. Phosphorylation-dependent binding to 14-3-3 is abolished only when both sites are mutated. Cell compartment fractionation experiments support a model in which binding to 14-3-3 sequesters BRF1 through relocalization and prevents it from executing its mRNA decay activity, as well as from proteasomal degradation, thereby maintaining high BRF1 protein levels that are required to reinstate decay upon dissipation of the stabilizing signal.

scholarly journals Mebendazole Exerts Potent Anti-Leukemic Effects By Downregulating Protein Levels of Hedgehog Transcription Factors GLI1 and GLI2

Blood ◽  
2018 ◽  
Vol 132 (Supplement 1) ◽  
pp. 5145-5145
Author(s):  
Fabian Freisleben ◽  
Hauke Stamm ◽  
Jana Muschhammer ◽  
Alexander Krispien ◽  
Vanessa Thaden ◽  
...  
Keyword(s):  
Transcription Factors ◽  
Board Of Directors ◽  
Cell Lines ◽  
Research Funding ◽  
Proteasomal Degradation ◽  
26S Proteasome ◽  
Mrna Levels ◽  
Dependent Manner ◽  
Advisory Committees ◽  
Protein Levels

Abstract The relevance of the Hedgehog signaling pathway in the pathophysiology of acute myeloid leukemia (AML) has been demonstrated by us and others. Inhibition of the downstream Hedgehog transcription factors GLI1 and GLI2 results in strong anti-leukemic effects. Therefore, Hedgehog pathway inhibitors represent a promising therapeutic approach in AML. Mebendazole is an anthelmintic drug commonly used for the treatment of various parasitic worm infections. Recently, mebendazole has been shown to exhibit strong anti-tumor effects in different cancer entities including AML. In the work presented here, we investigated the effect of mebendazole on expression and activity of GLI transcription factors and its anti-leukemic activity. To determine the effect of mebendazole on GLI transcription factors, we treated the AML cell lines MV4-11, MOLM-13, THP-1 and OCI-AML3 with different concentrations of mebendazole and analyzed its impact on GLI1 and GLI2 protein- and mRNA levels. Furthermore, GLI reporter assays (Cignal GLI Reporter (luc) Kit, Qiagen) were performed to determine the effect of mebendazole on the GLI1 and -2 transcriptional activity. Mebendazole strongly inhibited GLI1 and GLI2 signaling activity in a dose-dependent manner. Exemplarily, treatment with 500 nM mebendazole reduced the GLI1 and -2 transcriptional activity in all cell lines tested by 54.8 % (± 9.6) after 24h and 73.2 % (± 11.6) after 48h. We could demonstrate by Western Blotting that GLI1 and -2 protein levels were clearly reduced 24h and 48h after mebendazole exposure, whereas GLI1 and -2 mRNA levels did not decrease. These data suggest that mebendazole may increase degradation of GLI proteins via the proteasome pathway. Therefore, we evaluated the influence of the 26s proteasome inhibitor bortezomib on GLI levels after mebendazole treatment. Inhibiting the 26s proteasome with 2 nM, 5 nM and 10 nM of bortezomib increased GLI signaling activity by 13.6 % (± 8.0), 84.6 % (± 39.2) and 137.1 % (± 37.9), respectively. Furthermore, 10 nM bortezomib abolished the effect of mebendazole on GLI protein levels. Taken together, mebendazole increased the proteasomal degradation of GLI1 and GLI2. These observations were extended to samples from AML patients. After mebendazole treatment for 24h or 48h all analyzed patients had reductions of GLI1 protein levels as confirmed by Western blotting (n=4), whereas GLI1 and GLI2 mRNA levels were not changed (n=7), indicating that proteasomal degradation was operational in primary blasts as well. Evaluating the anti-leukemic effects of mebendazole, we also investigated its combination with the small molecule GLI inhibitor GANT61. We treated the AML cell lines MV4-11, MOLM-13, THP-1 and OCI-AML3 with combinations of mebendazole and GANT61 and analyzed cell proliferation, apoptosis and colony formation. Mebendazole treatment alone already resulted in decreased proliferation and colony forming capacity as well as increased apoptosis rates in a dose-dependent manner. The combination of mebendazole with the GLI inhibitor GANT61 synergistically increased the anti-proliferative effects of mebendazole on all 4 AML cell lines tested. Additionally, GANT61 further increased the effect of mebendazole on colony formation significantly. Incubation with 100 nM, 200 nM and 500 nM mebendazole inhibited the proliferation of primary blasts from AML patients by 15.1 % (± 7.5), 31.6 % (± 16.8) and 66.0 % (± 17.4), respectively (n=8). Moreover, the combination with GANT61 significantly increased these anti-proliferative effects. This work indicates that mebendazole exerts profound anti-leukemic effects by decreasing GLI1 and GLI2 intracellular levels by promoting its proteasomal degradation. Combining mebendazole with GLI1 and GLI2 inhibitors such as GANT61 enhances this effect considerably. These observations may lead to the introduction of novel treatment strategies in AML. Disclosures Stamm: Amgen Research (Munich) GmbH / Amgen Inc.: Patents & Royalties; Astellas GmbH: Other: Travel Grant. Wellbrock:Amgen Research (Munich) GmbH: Patents & Royalties. Fiedler:GSO: Other: support for meeting attendance; Gilead: Other: support for meeting attendance; Amgen: Other: support for meetíng attendance; Pfizer: Research Funding; Amgen: Research Funding; Amgen: Patents & Royalties; Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees; ARIAD/Incyte: Membership on an entity's Board of Directors or advisory committees, support for meeting attendance; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Daiichi Sankyo: Other: support for meeting attendance; JAZZ Pharmaceuticals: Other: support for meeting attendance; Teva: Other: support for meeting attendance.

Differential regulation of renal sodium-phosphate transporter by glucocorticoids during rat ontogeny

1999 ◽  
Vol 277 (5) ◽  
pp. C884-C890 ◽  
Author(s):  
Yigit S. Guner ◽  
Pawel R. Kiela ◽  
Hua Xu ◽  
James F. Collins ◽  
Fayez K. Ghishan
Keyword(s):  
Membrane Vesicles ◽  
Chronic Administration ◽  
Immunoblot Analysis ◽  
Mrna Levels ◽  
Adult Rats ◽  
Immunoreactive Protein ◽  
Ru 486 ◽  
Protein Levels ◽  
Weanling Rats ◽  
Adolescent Rats

The effects of chronic administration of methylprednisolone (MP) were studied on the ontogeny of the renal type II Na-Pi transporter (NaPi-2). Immunoblot analysis showed that MP did not alter the expression of NaPi-2 protein levels in suckling and weanling rats; however, there was an ∼50% decrease in adolescent and adult rats. There was no change in Na-dependent Pi uptake in brush-border membrane vesicles in suckling rats, but there was an almost twofold decrease in adolescent rats induced by MP treatment. MP administration did not alter mRNA levels in suckling or adolescent rats. Dual injections with the glucocorticoid receptor blocker RU-486 (mifepristone) and MP did not reverse the downregulation of NaPi-2 immunoreactive protein levels in adolescent rats. To control for RU-486 antagonism efficiency, Na/H exchanger isoform 3 (NHE3) protein levels were also assayed after injection with RU-486 and MP. As expected, NHE3 protein levels increased after MP injection; however, the increase was blocked in adolescent rats by RU-486. We conclude that there is an age-dependent responsiveness to glucocorticoids and that the marked decrease in NaPi-2 immunoreactive protein levels and activity in adolescent rats is due to posttranscriptional mechanisms.

Gfi1 Protein Levels Are Upregulated upon Myeloid Differentiation Due to Diminished Proteasomal Degradation.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 2710-2710
Author(s):  
Jurgen A.F. Marteijn ◽  
Laurens T. van der Meer ◽  
Theo de Witte ◽  
Joop H. Jansen ◽  
Bert van der Reijden
Keyword(s):  
Proteasome Inhibitors ◽  
Myeloid Cells ◽  
Proteasome Inhibition ◽  
Ubiquitin Proteasome System ◽  
Proteasomal Degradation ◽  
Myeloid Differentiation ◽  
Mrna Levels ◽  
Monocytic Differentiation ◽  
Hematopoietic Stem ◽  
Protein Levels

Abstract Granulocytes and monocytes play an essential role in the innate immune system and the inflammatory system. The generation of these differentiated myeloid cells from hematopoietic stem cells is a tightly regulated process in which transcription factors play an essential role. One of these transcription factors is Growth factor independence 1 (Gfi1). Gfi1 was originally identified as a proviral insertion site in murine leukemia models. Subsequently, it was shown that Gfi1 is essential for the self-renewal and long term reconstituting potential of hematopoietic stem cells and that it regulates T-cell development. In addition, Gfi1 knockout mice are severely neutropenic and exhibit a block in myeloid differentiation resulting in the accumulation of an atypical immature myelo-monocytic cell population. The observed defect in granulocytic differentiation in Gfi1 null mice is in line with Gfi1 point mutations described in patients suffering from severe congenital neutropenia. To further investigate the role of Gfi1 in myelopoiesis, we measured Gfi1 expression during both granulocytic and monocytic differentiation of HL60, NB4 and U937 cells. Upon differentiation of these cells with PMA or retinoic acid Gfi1 mRNA levels declined more than 3-fold. Interestingly, at the same time Gfi1 protein levels increased significantly suggesting that Gfi1 protein expression was regulated in a post-transcriptional manner. Since the ubiquitin proteasome system is one of the main pathways that control protein stability we tested whether Gfi1 was regulated by this system. Proteasome inhibition resulted in an accumulation of cellular Gfi1 protein levels. Moreover, ubiquitination experiments showed that Gfi1 is ubiquitinated and that proteasome inhibition resulted in an accumulation of ubiquitinated Gfi1 species indicating that ubiquitinated Gfi1 is targeted for 26S proteasomal degradation. To study Gfi1 degradation during myelopoiesis we developed a Gfi1 protein degradation assay. This showed that in vitro translated Gfi1 was quickly degraded in lysates from immature myeloid cells in a proteasome-dependent manner since the proteasome inhibitors MG132 and Velcade clearly blocked Gfi1 degradation. Importantly, Gfi1 was not degraded in lysates from differentiated myeloid cells. This suggests that the Gfi1 protein is no longer subject to proteasomal degradation upon terminal myeloid differentiation. To further study this, we treated undifferentiated U937 cells with proteasome inhibitors and observed a clear accumulation of endogenous Gfi1 protein levels, while endogenous protein levels in differentiated U937 did not further increase upon proteasome inhibition. Based on these results we conclude that Gfi1 is upregulated upon myeloid differentiation due to diminished proteasomal degradation despite diminished mRNA levels. Because total proteasome activity was comparable in immature and mature myeloid cells these data strongly suggest that an E3 ubiquitin ligase is responsible for the specific differential degradation. To determine Gfi1 protein stability in primary cells, we performed the degradation experiments with freshly isolated human hematopoietic subsets. This revealed a rapid degradation in immature CD34+ cells and a clear delayed degradation in CD14+ monocytes. Together these data indicate that the ubiquitin proteasome system is a key regulator of Gfi1 protein expression and that Gfi1 may play a role during both terminal granulocytic and monocytic differentiation.

Dexamethasone-regulated expression of pancreatic lipase and two related proteins in AR42J cells

1996 ◽  
Vol 270 (5) ◽  
pp. G746-G751 ◽  
Author(s):  
J. Kullman ◽  
C. Gisi ◽  
M. E. Lowe
Keyword(s):  
Pancreatic Lipase ◽  
Rapid Change ◽  
Immunoblot Analysis ◽  
Pancreatic Acinar Cell ◽  
Mrna Levels ◽  
Protein Levels ◽  
Ar42j Cells ◽  
Regulated Expression ◽  
Related Proteins ◽  
New Protein

The pancreas makes two pancreatic proteins [pancreatic lipase-related protein-1 (PLRP-1) and PLRP-2] with marked homology to pancreatic lipase (PL). To determine if a pancreatic acinar cell line, AR42J, also expresses PLRP-1 and PLRP-2, we examined the cells for the presence of PL, PLRP-1, and PLRP-2. RNA blot analysis with specific probes and immunoblot analysis with antipeptide antibodies demonstrated the presence of mRNA and protein for all three homologues in AR42J cells. Additionally, we showed that dexamethasone decreased PLRP-1 mRNA levels twofold and increased PLRP-2 mRNA 20-fold but had little effect on PL or colipase mRNA. Extracellular PLRP-2 protein levels increased threefold, and intracellular PLRP-2 protein levels increased about fourfold. The characteristics of the dexamethasone-induced increase in PLRP-2 mRNA, a rapid change requiring new protein synthesis independent of mRNA turnover, suggested that dexamethasone regulated transcription. We conclude that AR42J cells synthesize and secrete PL, PLRP-1, and PLRP-2 and that dexamethasone discoordinately regulates the expression of the three genes.

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