| dc.description.abstract | Previously we have found that green tea catechins, particularly EGCG, inhibit
growth and induce apoptosis of 3T3-L1 preadipocytes and such effects result from its
altering different phases of cell cycle. Using 3T3-L1 preadipose cell lines
transfected with pTargeTTM plasmid containing either wild type of cyclin-dependent
kinase 2 (CDK2) or CDK2-dominant negative (CDK2-dn) gene mutated from Asp145
of CDK2 to Asn145, we further examined whether CDK2 was essential in the EGCG
modulation of preadipocyte growth and apoptosis. As indicated by 50% increases in
cell number, 20% lower in G1 phase of cell cycle, and higher activity in
phosphorylating Histone H1, CDK2-overexpressed cells in the absence of EGCG
treatment grew faster than vector-transfected cells or CDK2-dn cells. At 20-100 µM,
EGCG, but not structurally-related EC, ECG, or EGC, reduced cell number by 30-50%
in wild type of cells and vector-transfected cells, and, to a lesser extent, in
CDK2-overexpressed cells; however, all catechins had no effect on CDK2-dn cells.
Also, EGCG arrested normal cells by 10% and, to a much lesser extent,
CDK2-overexpressed cells in G1 phase, but did not alter the G1 percentage of
CDK2-dn cell cycle. CDK2-dn cells displayed the similar extent of apoptosis, as
indicated by the appearance of DNA ladder and sub-G1 phase of cell cycle, when they
were treated with or without EGCG. CDK2 immunoprecipitates from normal,
vector-transfected, CDK2-transfected, or CDK2-dn cells treated with or without
EGCG contained the corresponding amounts of CDK2 inhibitors such as p18, p21, or
p27. We conclude that EGCG mediate growth and apoptosis of preadipocytes
through CDK2-dependent pathway and such pathway of EGCG action seems different
from other green tea catechins and may not rely on the binding between CDK2 and
CDK2 inhibitors. | en_US |