Specific chemopreventive agents trigger proteasomal degradation of G1 cyclins: implications for combination therapy.
OBJECTIVE
There is a need to identify cancer chemoprevention mechanisms. We reported previously that all-trans-retinoic acid (RA) prevented carcinogenic transformation of BEAS-2B immortalized human bronchial epithelial cells by causing G(1) arrest, permitting repair of genomic DNA damage. G(1) arrest was triggered by cyclin D1 proteolysis via ubiquitin-dependent degradation. This study investigated which chemopreventive agents activated this degradation program and whether cyclin E was also degraded.


METHODS
This study examined whether: (a) cyclin E protein was affected by RA treatment; (b) cyclin degradation occurred in derived BEAS-2B-R1 cells that were partially resistant to RA; and (c) other candidate chemopreventive agents caused cyclin degradation.


RESULTS
RA treatment triggered degradation of cyclin E protein, and ALLN, a proteasomal inhibitor, inhibited this degradation. Induction of the retinoic acid receptor beta, growth suppression, and cyclin degradation were each inhibited in BEAS-2B-R1 cells. Transfection experiments in BEAS-2B cells indicated that RA treatment repressed expression of wild-type cyclin D1 and cyclin E, but ALLN inhibited this degradation. Mutation of threonine 286 stabilized transfected cyclin D1, and mutations of threonines 62 and 380 stabilized transfected cyclin E, despite RA treatment. Specific chemopreventive agents triggered cyclin degradation. Nonclassical retinoids (fenretinide and retinoid X receptor agonists) and a synthetic triterpenoid (2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid) each suppressed BEAS-2B growth and activated this degradation program. However, a vitamin D3 analog (RO-24-5531), a cyclooxygenase inhibitor (indomethacin), and a peroxisome proliferator-activated receptor gamma agonist (rosiglitazone) each suppressed BEAS-2B growth, but did not cause cyclin degradation. BEAS-2B-R1 cells remained responsive to nonclassical retinoids and to 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid.


CONCLUSIONS
Specific chemopreventive agents activate cyclin proteolysis. Yet, broad resistance did not occur after acquired resistance to a single agent. This provides a therapeutic rationale for combination chemoprevention with agents activating non-cross-resistant pathways.
Dragnev
Konstantin H
KH
Norris Cotton Cancer Center, and Department of Medicine, Dartmouth Medical School, Hanover, New Hampshire 03755, USA.
Pitha-Rowe
Ian
I
Ma
Yan
Y
Petty
W Jeffrey
WJ
Sekula
David
D
Murphy
Bryan
B
Rendi
Mara
M
Suh
Nanjoo
N
Desai
Neil B
NB
Sporn
Michael B
MB
Freemantle
Sarah J
SJ
Dmitrovsky
Ethan
E
D016588:Anticarcinogenic Agents / Q000627:therapeutic use*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D001980:Bronchi / Q000166:cytology; D018929:Cell Culture Techniques; D002455:Cell Division; D002460:Cell Line; D019938:Cyclin D1 / Q000096:biosynthesis / Q000378:metabolism; D019927:Cyclin E / Q000378:metabolism; D056746:Cyclin G; D056766:Cyclin G1; D016213:Cyclins / Q000378:metabolism*; D004249:DNA Damage; D004305:Dose-Response Relationship, Drug; D004847:Epithelial Cells / Q000378:metabolism; D016193:G1 Phase; D006801:Humans; D015151:Immunoblotting; D007976:Leupeptins / Q000494:pharmacology; D009154:Mutation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D061988:Proteasome Inhibitors; D012176:Retinoids / Q000737:chemistry; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013912:Threonine / Q000737:chemistry; D014158:Transcription, Genetic; D014162:Transfection; D014212:Tretinoin / Q000378:metabolism
D016588:Anticarcinogenic Agents; C534702:CCNG1 protein, human; D019927:Cyclin E; D056746:Cyclin G; D056766:Cyclin G1; D016213:Cyclins; D007976:Leupeptins; D061988:Proteasome Inhibitors; D012176:Retinoids; C063261:acetylleucyl-leucyl-norleucinal; D019938:Cyclin D1; D013912:Threonine; D014212:Tretinoin; D046988:Proteasome Endopeptidase Complex