title: Apoptosis inducer NGFI-B is degraded by the proteasome and stabilized by treatment with EGF.
abstract: NGFI-B is a nuclear receptor and immediate early gene that is upregulated in many different tumour cell lines. As it is involved in cell death and survival, it has been suggested as a target for anti-cancer drugs. The protein level of NGFI-B is important for its functions and may be regulated through induction or stabilization. NGFI-B protein stability was studied using the protein synthesis inhibitor cycloheximide in CV1 cells transiently transfected with NGFI-B. Inhibiting the proteasome with MG132 stabilized NGFI-B, indicating that the proteasome is responsible for break-down of NGFI-B, as it is for many nuclear receptors. In order to determine regions responsible for the break-down of NGFI-B two N-terminal regions with high PEST-scores were deleted. Deletion of amino acids 122-195 containing a PEST-sequence which includes an ERK2 phosphorylation target, gave a more stable protein. In addition, treatment of the cells with the ERK2 activator EGF increased the stability of wild type NGFI-B. We then tested whether a mutation at threonine 142 influenced the stability of NGFI-B. We found that the phosphorylation-mimicking mutant NGFI-B T142E had an increased stability, while the non-phosphorylable mutant (T142A) showed similar stability to the wild type. Thus, EGF-stimulation of cells may be a mechanism for priming the cells for effects of NGFI-B by increasing its stability.
authors.affiliation: Department of Pharmaceutical Biosciences, University of Oslo, P.O. Box 1068 Blindern, N-0316 Oslo, Norway.
authors.forename: Bjørn O
authors.initials: BO
authors.lastname: Strøm
authors.forename: Ragnhild E
authors.initials: RE
authors.lastname: Paulsen
mesh_terms: D000818:Animals; D017209:Apoptosis; D002460:Cell Line; D002522:Chlorocebus aethiops; D004815:Epidermal Growth Factor / Q000494:pharmacology; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D009154:Mutation; D057105:Nuclear Receptor Subfamily 4, Group A, Member 1 / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000235:genetics; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D055550:Protein Stability; D059748:Proteolysis
chemical_list: D057105:Nuclear Receptor Subfamily 4, Group A, Member 1; D004815:Epidermal Growth Factor; D019950:Mitogen-Activated Protein Kinase 1; D046988:Proteasome Endopeptidase Complex