alphaB-crystallin is mutant B-RAF regulated and contributes to cyclin D1 turnover in melanocytic cells.
The serine/threonine kinase, B-RAF, is frequently mutated in melanoma and is required for cell proliferation. Proteasomal turnover of cyclins and cyclin-dependent kinase inhibitors via E3 ubiquitin ligases regulates cell cycle progression. We previously showed that B-RAF regulates Cks1, a co-factor for the F-box protein Skp2. Recently, a second F-box protein cofactor was identified, alphaB-crystallin, that binds Fbx4 and promotes cyclin D1 degradation. Here, we demonstrate that alphaB-crystallin is down-regulated in mutant B-RAF melanoma cells compared to melanocytes in a B-RAF and MEK-dependent manner. In a subset of lines, MEK inhibition was sufficient to up-regulate alphaB-crystallin protein levels; whereas in other lines combined MEK and proteasome inhibition was required. alphaB-crystallin knockdown partially stabilized cyclin D1 in melanocytes. Expression of alphaB-crystallin in mutant B-RAF melanoma cells did not promote cyclin D1 turnover under normal conditions, but did enhance turnover following etoposide-induced DNA damage. Together, these data show that alphaB-crystallin is highly expressed in melanocytes contributing, in part, to cyclin D1 turnover. Furthermore, alphaB-crystallin is down-regulated in a B-RAF-dependent manner in melanoma cells and its re-expression regulates cyclin D1 turnover after DNA damage.
Hu
Rong
R
Department of Cancer Biology, Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, PA, USA.
Aplin
Andrew E
AE
D001761:Bleomycin / Q000494:pharmacology; D002070:Butadienes / Q000494:pharmacology; D002478:Cells, Cultured; D019938:Cyclin D1 / Q000235:genetics / Q000378:metabolism*; D003513:Cycloheximide / Q000494:pharmacology; D004249:DNA Damage; D005047:Etoposide / Q000494:pharmacology; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology; D008544:Melanocytes / Q000166:cytology / Q000378:metabolism*; D008545:Melanoma / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D009570:Nitriles / Q000494:pharmacology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D048493:Proto-Oncogene Proteins B-raf / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects; D013329:Structure-Activity Relationship; D013752:Tetracycline / Q000494:pharmacology; D038203:alpha-Crystallin B Chain / Q000235:genetics / Q000378:metabolism*
D002070:Butadienes; D007976:Leupeptins; D050505:Mutant Proteins; D009570:Nitriles; D047428:Protein Kinase Inhibitors; D012333:RNA, Messenger; C113580:U 0126; D038203:alpha-Crystallin B Chain; D001761:Bleomycin; D019938:Cyclin D1; C105427:Zeocin; D005047:Etoposide; D003513:Cycloheximide; D048493:Proto-Oncogene Proteins B-raf; D013752:Tetracycline; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde