Eudoxia Hatzivassiliou | Aristotle University of Thessaloniki (original) (raw)

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Papers by Eudoxia Hatzivassiliou

Research paper thumbnail of Stress-Activated Protein Kinase Nuclear Factor{kappa}B, and Growth Factor Receptor Expression, Constitutive Activation of Epidermal Domain Is Similar to LMP1 in Domains to the CD40 Cytoplasmic Protein1 (LMP1) Transmembrane A Fusion of the EBV Latent Membrane

Research paper thumbnail of The PP4R1 subunit of protein phosphatase PP4 targets TRAF2 and TRAF6 to mediate inhibition of NF-κB activation

Cellular signalling, 2014

TRAFs constitute a family of proteins that have been implicated in signal transduction by immunom... more TRAFs constitute a family of proteins that have been implicated in signal transduction by immunomodulatory cellular receptors and viral proteins. TRAF2 and TRAF6 have an E3-ubiquitin ligase activity, which is dependent on the integrity of their RING finger domain and it has been associated with their ability to activate the NF-κB and AP1 signaling pathways. A yeast two-hybrid screen with TRAF2 as bait, identified the regulatory subunit PP4R1 of protein phosphatase PP4 as a TRAF2-interacting protein. The interaction of TRAF2 with PP4R1 depended on the integrity of the RING finger domain of TRAF2. PP4R1 could interact also with the TRAF2-related factor TRAF6 in a RING domain-dependent manner. Exogenous expression of PP4R1 inhibited NF-κB activation by TRAF2, TRAF6, TNF and the Epstein-Barr virus oncoprotein LMP1. In addition, expression of PP4R1 downregulated IL8 induction by LMP1, whereas downregulation of PP4R1 by RNA interference enhanced the induction of IL8 by LMP1 and TNF. PP4R1...

Research paper thumbnail of Epstein-Barr virus-transforming protein latent infection membrane protein 1 activates transcription factor NF- B through a pathway that includes the NF- B-inducing kinase and the I B kinases IKK  and IKK 

Proceedings of the National Academy of Sciences, 1998

Ser-36 is followed by its degradation and NF-B activation. In this report, we show that NF-B acti... more Ser-36 is followed by its degradation and NF-B activation. In this report, we show that NF-B activation by LMP1 or by each of its effector sites is mediated by a pathway that includes NIK, IKK␣, and IKK␤. Dominant negative mutants of NIK, IKK␣, or IKK␤ substantially inhibited NF-B activation by LMP1 or by each of its effector sites.

Research paper thumbnail of CYLD is a deubiquitinating enzyme that negatively regulates NF-κB activation by TNFR family members

Nature, 2003

Familial cylindromatosis is an autosomal dominant predisposition to tumours of skin appendages ca... more Familial cylindromatosis is an autosomal dominant predisposition to tumours of skin appendages called cylindromas. Familial cylindromatosis is caused by mutations in a gene encoding the CYLD protein of previously unknown function. Here we show that CYLD is a deubiquitinating enzyme that negatively regulates activation of the transcription factor NF-kappaB by specific tumour-necrosis factor receptors (TNFRs). Loss of the deubiquitinating activity of CYLD correlates with tumorigenesis. CYLD inhibits activation of NF-kappaB by the TNFR family members CD40, XEDAR and EDAR in a manner that depends on the deubiquitinating activity of CYLD. Downregulation of CYLD by RNA-mediated interference augments both basal and CD40-mediated activation of NF-kappaB. The inhibition of NF-kappaB activation by CYLD is mediated, at least in part, by the deubiquitination and inactivation of TNFR-associated factor 2 (TRAF2) and, to a lesser extent, TRAF6. These results indicate that CYLD is a negative regulator of the cytokine-mediated activation of NF-kappaB that is required for appropriate cellular homeostasis of skin appendages.

Research paper thumbnail of Induction of Apoptosis by Rewiring the Signal Transduction of Epstein-Barr Virus Oncoprotein LMP1 toward Caspase Activation

Journal of Virology, 2005

The Epstein-Barr virus latent membrane protein 1 (LMP1) is an oncoprotein which mimics activated ... more The Epstein-Barr virus latent membrane protein 1 (LMP1) is an oncoprotein which mimics activated tumor necrosis factor receptor family members. Here we demonstrate the principle that an inducible association of the LMP1 cytoplasmic carboxyl terminus with caspase-8 by a heterodimerizing agent causes apoptosis. This process depends on the catalytic activity of caspase-8 and the ability of LMP1 to oligomerize constitutively at the plasma membrane. Our data indicate that chemical inducers of the association of the LMP1 carboxyl terminus with caspase-8 can kill LMP1-expressing cells selectively. Such compounds could be used as chemotherapeutic agents for LMP1-associated malignancies.

Research paper thumbnail of Cellular signaling pathways engaged by the Epstein-Barr virus transforming protein LMP1

Frontiers in Bioscience, 2002

TABLE OF CONTENTS 1. Abstract 2. Introduction 3. Structural and functional elements of LMP1 4. Th... more TABLE OF CONTENTS 1. Abstract 2. Introduction 3. Structural and functional elements of LMP1 4. The NF-κB pathway 5. The AP1 pathway 6. The JAK/STAT pathway 7. LMP1 is a viral pseudoreceptor of the TNFR superfamily 8. Perspectives 9. Acknowledgments 10. References

Research paper thumbnail of Human ubiquitin specific protease 31 is a deubiquitinating enzyme implicated in activation of nuclear factor-κB

Cellular Signalling, 2006

TRAF2 mediates activation of the transcription factors NF-nB and AP1 by TNF. A yeast two-hybrid s... more TRAF2 mediates activation of the transcription factors NF-nB and AP1 by TNF. A yeast two-hybrid screen of a human cDNA library identified a ubiquitin specific protease homologue (USP31) as a TRAF2-interacting protein. Two cDNAs encoding for USP31 were identified. One cDNA encodes a 1035-amino acid long isoform of USP31 (USP31, long isoform) and the other a 485-amino acid long isoform of USP31 (USP31S1, short isoform). USP31 and USP31S1 share a common amino terminal region with homology to the catalytic region of known deubiquitinating enzymes. Enzymatic assays demonstrated that USP31 but not USP31S1 possess deubiquitinating activity. Furthermore, it was shown that USP31 has a higher activity towards lysine-63-linked as compared to lysine-48-linked polyubiquitin chains. Overexpression of USP31 in HEK 293T cells inhibited TNFa, CD40, LMP1, TRAF2, TRAF6 and IKKh-mediated NF-nB activation, but did not inhibit Smad-mediated transcription activation. In addition, both USP31 isoforms interact with p65/RelA. Our data support a role for USP31 in the regulation of NF-nB activation by members of the TNF receptor superfamily. D

Research paper thumbnail of Mutational analysis of TRAF6 reveals a conserved functional role of the RING dimerization interface and a potentially necessary but insufficient role of RING-dependent TRAF6 polyubiquitination towards NF-κB activation

Cellular Signalling, 2011

TRAF6 is an E3 ubiquitin ligase that plays a pivotal role in the activation of NF-κB by innate an... more TRAF6 is an E3 ubiquitin ligase that plays a pivotal role in the activation of NF-κB by innate and adaptive immunity stimuli. TRAF6 consists of a highly conserved carboxyl terminal TRAF-C domain which is preceded by a coiled coil domain and an amino terminal region that contains a RING domain and a series of putative zinc-finger motifs. The TRAF-C domain contributes to TRAF6 oligomerization and mediates the interaction of TRAF6 with upstream signaling molecules whereas the RING domain comprises the core of the ubiquitin ligase catalytic domain. In order to identify structural elements that are important for TRAF6-induced NF-κB activation, mutational analysis of the TRAF-C and RING domains was performed. Alterations of highly conserved residues of the TRAF-C domain of TRAF6 did not affect significantly the ability of the protein to activate NF-κB. On the other hand a number of functionally important residues (L77, Q82, R88, F118, N121 and E126) for the activation of NF-κB were identified within the RING domain of TRAF6. Interestingly, several homologues of these residues in TRAF2 were shown to have a conserved functional role in TRAF2-induced NF-κB activation and lie at the dimerization interface of the RING domain. Finally, whereas alteration of Q82, R88 and F118 compromised both the K63-linked polyubiquitination of TRAF6 and its ability to activate NF-κB, alteration of L77, N121 and E126 diminished the NF-κB activating function of TRAF6 without affecting TRAF6 K63-linked polyubiquitination. Our results support a conserved functional role of the TRAF RING domain dimerization interface and a potentially necessary but insufficient role for RING-dependent TRAF6 K63-linked polyubiquitination towards NF-κB activation in cells.

Research paper thumbnail of Constitutive CD40 signaling phenocopies the transforming function of the Epstein-Barr virus oncoprotein LMP1 in vitro

Leukemia Research, 2007

The oncoprotein LMP1 mimics an activated CD40 receptor, yet it is not known whether constitutive ... more The oncoprotein LMP1 mimics an activated CD40 receptor, yet it is not known whether constitutive CD40 signaling, like LMP1, is sufficient to transform cells. Here we demonstrate that constitutive activation of the CD40 pathway by a chimeric LMP1CD40 molecule resembles the transforming function of LMP1 in inducing loss of contact inhibition and anchorage independent growth of Rat1 fibroblasts. Rat1 transformation correlates with the expression level of LMP1CD40 and depends on its ability to oligomerize. Our data provide direct evidence for the oncogenic potential of the CD40 signaling pathway, which is also established as a model-mechanism for LMP1-induced transformation.

Research paper thumbnail of Stress-Activated Protein Kinase Nuclear Factor{kappa}B, and Growth Factor Receptor Expression, Constitutive Activation of Epidermal Domain Is Similar to LMP1 in Domains to the CD40 Cytoplasmic Protein1 (LMP1) Transmembrane A Fusion of the EBV Latent Membrane

Research paper thumbnail of The PP4R1 subunit of protein phosphatase PP4 targets TRAF2 and TRAF6 to mediate inhibition of NF-κB activation

Cellular signalling, 2014

TRAFs constitute a family of proteins that have been implicated in signal transduction by immunom... more TRAFs constitute a family of proteins that have been implicated in signal transduction by immunomodulatory cellular receptors and viral proteins. TRAF2 and TRAF6 have an E3-ubiquitin ligase activity, which is dependent on the integrity of their RING finger domain and it has been associated with their ability to activate the NF-κB and AP1 signaling pathways. A yeast two-hybrid screen with TRAF2 as bait, identified the regulatory subunit PP4R1 of protein phosphatase PP4 as a TRAF2-interacting protein. The interaction of TRAF2 with PP4R1 depended on the integrity of the RING finger domain of TRAF2. PP4R1 could interact also with the TRAF2-related factor TRAF6 in a RING domain-dependent manner. Exogenous expression of PP4R1 inhibited NF-κB activation by TRAF2, TRAF6, TNF and the Epstein-Barr virus oncoprotein LMP1. In addition, expression of PP4R1 downregulated IL8 induction by LMP1, whereas downregulation of PP4R1 by RNA interference enhanced the induction of IL8 by LMP1 and TNF. PP4R1...

Research paper thumbnail of Epstein-Barr virus-transforming protein latent infection membrane protein 1 activates transcription factor NF- B through a pathway that includes the NF- B-inducing kinase and the I B kinases IKK  and IKK 

Proceedings of the National Academy of Sciences, 1998

Ser-36 is followed by its degradation and NF-B activation. In this report, we show that NF-B acti... more Ser-36 is followed by its degradation and NF-B activation. In this report, we show that NF-B activation by LMP1 or by each of its effector sites is mediated by a pathway that includes NIK, IKK␣, and IKK␤. Dominant negative mutants of NIK, IKK␣, or IKK␤ substantially inhibited NF-B activation by LMP1 or by each of its effector sites.

Research paper thumbnail of CYLD is a deubiquitinating enzyme that negatively regulates NF-κB activation by TNFR family members

Nature, 2003

Familial cylindromatosis is an autosomal dominant predisposition to tumours of skin appendages ca... more Familial cylindromatosis is an autosomal dominant predisposition to tumours of skin appendages called cylindromas. Familial cylindromatosis is caused by mutations in a gene encoding the CYLD protein of previously unknown function. Here we show that CYLD is a deubiquitinating enzyme that negatively regulates activation of the transcription factor NF-kappaB by specific tumour-necrosis factor receptors (TNFRs). Loss of the deubiquitinating activity of CYLD correlates with tumorigenesis. CYLD inhibits activation of NF-kappaB by the TNFR family members CD40, XEDAR and EDAR in a manner that depends on the deubiquitinating activity of CYLD. Downregulation of CYLD by RNA-mediated interference augments both basal and CD40-mediated activation of NF-kappaB. The inhibition of NF-kappaB activation by CYLD is mediated, at least in part, by the deubiquitination and inactivation of TNFR-associated factor 2 (TRAF2) and, to a lesser extent, TRAF6. These results indicate that CYLD is a negative regulator of the cytokine-mediated activation of NF-kappaB that is required for appropriate cellular homeostasis of skin appendages.

Research paper thumbnail of Induction of Apoptosis by Rewiring the Signal Transduction of Epstein-Barr Virus Oncoprotein LMP1 toward Caspase Activation

Journal of Virology, 2005

The Epstein-Barr virus latent membrane protein 1 (LMP1) is an oncoprotein which mimics activated ... more The Epstein-Barr virus latent membrane protein 1 (LMP1) is an oncoprotein which mimics activated tumor necrosis factor receptor family members. Here we demonstrate the principle that an inducible association of the LMP1 cytoplasmic carboxyl terminus with caspase-8 by a heterodimerizing agent causes apoptosis. This process depends on the catalytic activity of caspase-8 and the ability of LMP1 to oligomerize constitutively at the plasma membrane. Our data indicate that chemical inducers of the association of the LMP1 carboxyl terminus with caspase-8 can kill LMP1-expressing cells selectively. Such compounds could be used as chemotherapeutic agents for LMP1-associated malignancies.

Research paper thumbnail of Cellular signaling pathways engaged by the Epstein-Barr virus transforming protein LMP1

Frontiers in Bioscience, 2002

TABLE OF CONTENTS 1. Abstract 2. Introduction 3. Structural and functional elements of LMP1 4. Th... more TABLE OF CONTENTS 1. Abstract 2. Introduction 3. Structural and functional elements of LMP1 4. The NF-κB pathway 5. The AP1 pathway 6. The JAK/STAT pathway 7. LMP1 is a viral pseudoreceptor of the TNFR superfamily 8. Perspectives 9. Acknowledgments 10. References

Research paper thumbnail of Human ubiquitin specific protease 31 is a deubiquitinating enzyme implicated in activation of nuclear factor-κB

Cellular Signalling, 2006

TRAF2 mediates activation of the transcription factors NF-nB and AP1 by TNF. A yeast two-hybrid s... more TRAF2 mediates activation of the transcription factors NF-nB and AP1 by TNF. A yeast two-hybrid screen of a human cDNA library identified a ubiquitin specific protease homologue (USP31) as a TRAF2-interacting protein. Two cDNAs encoding for USP31 were identified. One cDNA encodes a 1035-amino acid long isoform of USP31 (USP31, long isoform) and the other a 485-amino acid long isoform of USP31 (USP31S1, short isoform). USP31 and USP31S1 share a common amino terminal region with homology to the catalytic region of known deubiquitinating enzymes. Enzymatic assays demonstrated that USP31 but not USP31S1 possess deubiquitinating activity. Furthermore, it was shown that USP31 has a higher activity towards lysine-63-linked as compared to lysine-48-linked polyubiquitin chains. Overexpression of USP31 in HEK 293T cells inhibited TNFa, CD40, LMP1, TRAF2, TRAF6 and IKKh-mediated NF-nB activation, but did not inhibit Smad-mediated transcription activation. In addition, both USP31 isoforms interact with p65/RelA. Our data support a role for USP31 in the regulation of NF-nB activation by members of the TNF receptor superfamily. D

Research paper thumbnail of Mutational analysis of TRAF6 reveals a conserved functional role of the RING dimerization interface and a potentially necessary but insufficient role of RING-dependent TRAF6 polyubiquitination towards NF-κB activation

Cellular Signalling, 2011

TRAF6 is an E3 ubiquitin ligase that plays a pivotal role in the activation of NF-κB by innate an... more TRAF6 is an E3 ubiquitin ligase that plays a pivotal role in the activation of NF-κB by innate and adaptive immunity stimuli. TRAF6 consists of a highly conserved carboxyl terminal TRAF-C domain which is preceded by a coiled coil domain and an amino terminal region that contains a RING domain and a series of putative zinc-finger motifs. The TRAF-C domain contributes to TRAF6 oligomerization and mediates the interaction of TRAF6 with upstream signaling molecules whereas the RING domain comprises the core of the ubiquitin ligase catalytic domain. In order to identify structural elements that are important for TRAF6-induced NF-κB activation, mutational analysis of the TRAF-C and RING domains was performed. Alterations of highly conserved residues of the TRAF-C domain of TRAF6 did not affect significantly the ability of the protein to activate NF-κB. On the other hand a number of functionally important residues (L77, Q82, R88, F118, N121 and E126) for the activation of NF-κB were identified within the RING domain of TRAF6. Interestingly, several homologues of these residues in TRAF2 were shown to have a conserved functional role in TRAF2-induced NF-κB activation and lie at the dimerization interface of the RING domain. Finally, whereas alteration of Q82, R88 and F118 compromised both the K63-linked polyubiquitination of TRAF6 and its ability to activate NF-κB, alteration of L77, N121 and E126 diminished the NF-κB activating function of TRAF6 without affecting TRAF6 K63-linked polyubiquitination. Our results support a conserved functional role of the TRAF RING domain dimerization interface and a potentially necessary but insufficient role for RING-dependent TRAF6 K63-linked polyubiquitination towards NF-κB activation in cells.

Research paper thumbnail of Constitutive CD40 signaling phenocopies the transforming function of the Epstein-Barr virus oncoprotein LMP1 in vitro

Leukemia Research, 2007

The oncoprotein LMP1 mimics an activated CD40 receptor, yet it is not known whether constitutive ... more The oncoprotein LMP1 mimics an activated CD40 receptor, yet it is not known whether constitutive CD40 signaling, like LMP1, is sufficient to transform cells. Here we demonstrate that constitutive activation of the CD40 pathway by a chimeric LMP1CD40 molecule resembles the transforming function of LMP1 in inducing loss of contact inhibition and anchorage independent growth of Rat1 fibroblasts. Rat1 transformation correlates with the expression level of LMP1CD40 and depends on its ability to oligomerize. Our data provide direct evidence for the oncogenic potential of the CD40 signaling pathway, which is also established as a model-mechanism for LMP1-induced transformation.