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Proteasomal degradation of human CYP1B1: effect of the Asn453Ser polymorphism on the post-translational regulation of CYP1B1 expression

Proteasomal degradation of human CYP1B1: effect of the Asn453Ser polymorphism on the post-translational regulation of CYP1B1 expression

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Authors

  • Silvio Bandiera
  • Simone Weidlich
  • Volker Harth
  • Peter Broede
  • Yun Ko
  • Thomas Friedberg

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    Original languageEnglish
    Pages435-443
    Number of pages9
    JournalMolecular Pharmacology
    Journal publication date2005
    Journal number2
    Volume67
    DOIs
    StatePublished

    Abstract

    Allelic variations in CYP1B1 are reported modulate the incidence of several types of cancer. To provide a mechanistic basis for this association, we investigated the impact of nonsilent allelic changes on the intracellular levels and post-translational regulation of CYP1B1 protein. When transiently expressed in COS-1 cells, either in the presence or absence of recombinant cytochrome P450 reductase, the cellular level of the CYP1B1.4 allelic variant (containing a Ser at the amino acid position 453; Ser453) was 2-fold lower compared with the other four allelic CYP1B1 proteins (containing Asn453), as analyzed by both immunoblotting and ethoxyresorufin O-deethylase activity. This difference was caused by post-translational regulation; as in the presence of cycloheximide, the rate of degradation of immunodetectable and enzymatically active CYP1B1.4 was distinctly faster than that of CYP1B1.1. Pulse-chase analysis revealed that the half-life CYP1B1.4 was a mere 1.6 h compared with 4.8 h for CYP1B1.1. The presence of the proteasome inhibitor MG132 [N-benzoyloxycarbonyl (Z)-Leu-Leuleucinal] increased the stability not only of immunodetectable CYP1B1, but also—unexpectedly given the size of the proteasome access channel—increased the stability of enzymatically active CYP1B1. The data presented herein also demonstrate that CYP1B1 is targeted for its polymorphism-dependent degradation by polyubiquitination but not phosphorylation. Our results importantly provide a mechanism to explain the recently reported lower incidence of endometrial cancer in individuals carrying the CYP1B1*4 compared with the CYP1B1*1 haplo-type. In addition, the mechanistic paradigms revealed herein may explain the strong overexpression of CYP1B1 in tumors compared with nondiseased tissues.

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