Carcinogenesis, Vol 19, 1093-1102, Copyright © 1998 by Oxford University Press
AJ Gonzales, TL Goldsworthy and TR Fox
Dysregulated cell proliferation is one phenotypic change associated with
neoplasia. Key protein complexes involved in regulating cell division are
composed of cyclins, cyclin-dependent kinases (CDK) and CDK inhibitors
(CDI). Many virally transformed cells in culture exhibit disrupted
cyclin-CDK-CDI complexes, suggesting that such changes may play a
mechanistic role in viral transformation. To determine whether similar
alterations may be involved in chemical carcinogenesis we characterized
cyclin D1-CDK-CDI protein complexes in a non-tumorigenic mouse liver cell
line and investigated whether complexes were altered after transformation
with the genotoxic carcinogens N-methyl-N'-nitro-N- nitrosoguanidine (MNNG)
or 3-methylcholanthrene (MC). In non- tumorigenic mouse liver cells cyclin
D1 associated with CDK6, CDK4 or CDK2 to form binary (cyclin D1-CDK),
tertiary (cyclin D1-CDK-p27KIP1) or quaternary (cyclin D1-CDK-p21WAF1-PCNA)
complexes. After chemical transformation of mouse liver cells with either
MC or MNNG, select cyclin D1-CDK-CDI protein complexes were altered. In
MC-transformed cells formation of various binary, tertiary and quaternary
cyclin D1- CDK-(CDI) protein complexes was reduced, resulting in decreased
CDK4 kinase activity. Interestingly, CDK6 kinase activity was dramatically
elevated due to high levels of cyclin D3 in association with CDK6. In
MNNG-transformed cells select cyclin D1-CDK6-CDI and cyclin D1-CDK2-CDI
protein complexes were altered but CDK6 and CDK4 kinase activity remained
unaffected. Distinct changes in cyclin D1-CDK-CDI complexes found between
the two chemically transformed mouse liver cell lines suggest that each
cell line harbored unique mutations or alterations that differentially
contributed to stabilization of cyclin D1-CDK-CDI holoenzymes. p53 gene
mutations were not detected in the MC- or MNNG- transformed mouse liver
cell lines and thus were not involved in disrupting cyclin D1-CDK-CDI
protein complexes. In summary, this study presents evidence that D-type CDK
protein complexes can be altered physically and functionally after chemical
transformation with genotoxic carcinogens, suggesting that components of
the cell cycle machinery can be targeted during chemical carcinogenesis.
ARTICLES
Chemical transformation of mouse liver cells results in altered cyclin D-CDK protein complexes
Curriculum in Toxicology, University of North Carolina, Chapel Hill 27599-7270, USA.
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