Biology Reference
In-Depth Information
10.1 Link Between Activation of Growth Factor Receptors
and Initiation of Centrosome Duplication: The Roles
of the Rho-ROCK II Pathway and STAT
Transcriptional Factors
When RTKs are activated by growth factor binding, they transmit the growth
signals to a number of different pathways, and cells commence cell cycling pro-
cesses. Because centrosome duplication is a cell cycle-dependent event, it is
reasonable to predict that the activated RTKs also signal to initiation of centro-
some duplication. It has been known that there is a close link between the acti-
vation of RTKs and initiation of centrosome duplication. For instance, in certain
cell types, addition of epidermal growth factor (EGF) can rather rapidly induce
physical separation of paired centrioles, which is an initial event of centrosome
duplication (Sherline and Mascardo
1982
). In the experimental system using
Chinese hamster ovary cells that are cell cycle-arrested by exposure to DNA
synthesis inhibitors, centrosomes continue to duplicate, resulting in generation of
C3 centrosomes (centrosome amplification), but when serum is depleted from the
media, centrosomes are no longer able to undergo duplication. Moreover, cen-
trosomes resume duplication and reduplication in those arrested cells upon addi-
tion of serum or EGFs to the media (Balczon et al.
1995
). It has also been known
that oncogenic (constitutive) activation of RTKs such as the Met receptor leads to
centrosome overduplication and amplification (Kanai et al.
2010
; Nam et al.
2010
;
Fukasawa
2011
).
What is the molecular pathway(s) that link the activation of RTKs occurring at cell
membrane to the initiation of centrosome duplication occurring near the nuclear
membrane? This question has recently been answered at least in part by the identi-
fication of ROCK II kinase as a key positive regulator of centrosome duplication
(Ma et al.
2006
) (Fig.
10.1
). ROCK II is one of two members of the ROCK Ser/Thr
kinase family. ROCK II is primed for activation by binding of GTP-bound Rho small
GTPase (Rho-GTP): Rho binding disrupts the interaction between the kinase domain
and autoinhibitory domain of ROCK II, freeing the kinase domain (Leung et al.
1996
;
Matsui et al.
1996
). Rho cycles between an active GTP-bound state and inactive
GDP-bound state, and many RTKs, when activated by the ligand binding, promote
the exchange for Rho-bound GDP to GTP via activating the Rho guanine nucleotide
exchange factors (Rho-GEFs) (Etienne-Manneville and Hall
2002
). ROCK II was
found to localize to centrosomes, and ectopic expression of the ROCK II mutant
that lacks the negative regulatory domain (hence its activity is independent from
Rho-binding) promotes initiation of centrosome duplication in a kinase activity and
centrosome localization-dependent manners. Moreover, depletion of ROCK II
results in significantly delayed initiation of centrosome duplication, indicating that
ROCK II plays a critical role in the timely initiation of centrosome duplication. Of
note, although the initiation of centrosome duplication is delayed in the ROCK II-
depleted cell, they eventually duplicate because of the functional replacement by
ROCK I, another member of the ROCK family, that shares *65 % overall identity
