Oncogenic stimulation recruits cyclin-dependent kinase in the cell cycle start in rat fibroblast.
The rat fibroblast NRK cells are transformed reversibly by a combination of growth factors. When stimulated with serum, NRK cells rely on cyclin-dependent kinase 4 (Cdk4) for their S phase entry. However, when stimulated with serum containing oncogenic growth factors, they come to rely on either Cdk4 or Cdk6, and their S phase entry cannot be blocked unless both Cdk4 and Cdk6 are immunodepleted. Such change of dependence does not occur in the NRK cell mutants defective in an oncogenic signal pathway and, therefore, deficient in anchorage-independent cell cycle start ability, correlating Cdk6 dependence with this remarkable, cancer-associated phenotype. However, both Cdk4 and Cdk6 are activated upon serum stimulation, and neither the amounts of Cdk6, Cdk4, cyclin D1, and cyclin-dependent kinase inhibitors nor the activities or subcellular localization of Cdk6 and Cdk4 are significantly influenced by oncogenic stimulation. Thus, oncogenic stimulation invokes Cdk6 to participate in a critical step of the cell cycle start in a rat fibroblast, but by a mechanism seemingly unrelated to the regulation of the kinase. Given that many hematopoietic cells employ predominantly Cdk6 for the cell cycle start and perform anchorage-independent growth by nature, our results raise the possibility that the oncogenic stimulation-induced anchorage-independent cell cycle start of NRK is elicited by a mechanism similar to the one used for hematopoietic cell proliferation.
Jinno
S
S
Department of Biochemistry, Graduate School of Medicine, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan.
Hung
S C
SC
Yamamoto
H
H
Lin
J
J
Nagata
A
A
Okayama
H
H
D000818:Animals; D002453:Cell Cycle; D002460:Cell Line; D003470:Culture Media; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D004789:Enzyme Activation; D005347:Fibroblasts / Q000166:cytology / Q000201:enzymology; D006133:Growth Substances / Q000378:metabolism; D009857:Oncogenes; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins; D051381:Rats; D013347:Subcellular Fractions / Q000201:enzymology
D003470:Culture Media; D006133:Growth Substances; D011518:Proto-Oncogene Proteins; D017346:Protein Serine-Threonine Kinases; C495903:Cdk4 protein, rat; C495913:Cdk6 protein, rat; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6; D018844:Cyclin-Dependent Kinases