Phosphorylation of human tristetraprolin in response to its interaction with the Cbl interacting protein CIN85.
BACKGROUND
Tristetraprolin (TTP) is the prototype member of a family of CCCH tandem zinc finger proteins and is considered to be an anti-inflammatory protein in mammals. TTP plays a critical role in the decay of tumor necrosis factor alpha (TNF) mRNA, among others, by binding AU-rich RNA elements in the 3'-untranslated regions of this transcript and promoting its deadenylation and degradation.


RESULTS
We used yeast two-hybrid analysis to identify potential protein binding partners for human TTP (hTTP). Various regions of hTTP recovered 31 proteins that fell into 12 categories based on sequence similarities. Among these, the interactions between hTTP and CIN85, cytoplasmic poly (A) binding protein (PABP), nucleolin and heat shock protein 70 were confirmed by co-immunoprecipitation experiments. CIN85 and hTTP co-localized in the cytoplasm of cells as determined by confocal microscopy. CIN85 contains three SH3 domains that specifically bind a unique proline-arginine motif (PXXXPR) found in several CIN85 effectors. We found that the SH3 domains of CIN85 bound to a PXXXPR motif located near the C-terminus of hTTP. Co-expression of CIN85 with hTTP resulted in the increased phosphorylation of hTTP at serine residues in positions 66 and 93, possibly due in part to the demonstrated association of mitogen-activated protein kinase kinase kinase 4 (MEKK4) to both proteins. The presence of CIN85 did not appear to alter hTTP's binding to RNA probes or its stimulated breakdown of TNF mRNA.


CONCLUSIONS
These studies describe interactions between hTTP and nucleolin, cytoplasmic PABP, heat shock protein 70 and CIN85; these interactions were initially discovered by two-hybrid analysis, and confirmed by co-immunoprecipitation. We found that CIN85 binding to a C-terminal motif within hTTP led to the increased phosphorylation of hTTP, possibly through enhanced association with MEKK4. The functional consequences to each of the members of this putative complex remain to be determined.
Kedar
Vishram P
VP
The Laboratory of Signal Transduction, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina, United States of America.
Darby
Martyn K
MK
Williams
Jason G
JG
Blackshear
Perry J
PJ
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D020816:Amino Acid Motifs; D002460:Cell Line; D003593:Cytoplasm / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D048768:MAP Kinase Kinase Kinase 4 / Q000378:metabolism; D018613:Microscopy, Confocal / Q000379:methods; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D039102:Poly(A)-Binding Proteins / Q000737:chemistry; D050721:Proto-Oncogene Proteins c-cbl / Q000378:metabolism*; D012313:RNA / Q000378:metabolism; D051816:Tristetraprolin / Q000494:pharmacology*; D020798:Two-Hybrid System Techniques
D048868:Adaptor Proteins, Signal Transducing; D018840:HSP70 Heat-Shock Proteins; D039102:Poly(A)-Binding Proteins; C433810:SH3KBP1 protein, human; D051816:Tristetraprolin; D012313:RNA; D050721:Proto-Oncogene Proteins c-cbl; D048768:MAP Kinase Kinase Kinase 4; C482779:MAP3K4 protein, human; C067419:CBL protein, human