D cyclins in lymphocytes.
BACKGROUND
D cyclins are essential for the progression of cells through the G1 phase of the cell cycle. There are three distinct D cyclins. Cyclin D1 has been shown to be expressed by many different types of cells but not by lymphocytes. Cyclins D2 and D3 have been found in lymphocytes.


METHODS
We used high-resolution enzymatic amplification staining technology in conjunction with flow cytometry and confocal microscopy and with immunoblotting to reassess the expression of the D cyclins in human lymphocytes.


RESULTS
Using high-resolution technology for flow cytometry, we found all three D cyclins in quiescent human peripheral blood lymphocytes. Cyclin D1 was expressed in quiescent and activated cells at levels commensurate with those of actively proliferating tumor cell lines. Cyclin D1 was functional inasmuch as it was complexed with CDK4. In the quiescent cells, cyclin D1 was expressed in the cytoplasm but, after activation, was found in the nucleus.


CONCLUSIONS
These findings demonstrate that lymphocytes express cyclin D1 and necessitate a reappraisal of the hypothesis that the D cyclins subsume redundant activities with tissue-specific expression.
Kaplan
David
D
Department of Pathology, Case School of Medicine, Cleveland, Ohio 44106-4943, USA. drk5@cwru.edu
Meyerson
Howard
H
Husel
William
W
Lewandowska
Kristine
K
MacLennan
Grayden
G
D002460:Cell Line; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D016213:Cyclins / Q000378:metabolism*; D005434:Flow Cytometry; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D008213:Lymphocyte Activation; D008214:Lymphocytes / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D013194:Staining and Labeling
D016213:Cyclins; D011518:Proto-Oncogene Proteins; C495900:CDK4 protein, human; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases