ogy. Our results suggest that alterations in Cx43 may serve as
survival factor for CE cells. In other biologic systems in which
cells are subjected to physical stress or injury, gap junction
coupling activation results in the mediation of injury or in-
In the CE, upregulation of Cx43 mRNA
and protein, via release of ciliary neurotrophic factor and its
receptor, promote CE cell survival during oxidative stress and
ex vivo corneal storage.
Also, point mechanical stimula
tion of CE cell monolayers results in a Cx43-dependent in-
crease in ATP release and calcium-wave propagation between
Therefore, Cx43 and GJIC provide a response in CE to
changes in cellular environment that is likely to represent a
The rapid rate at which CE responds to MMC suggests a
mechanism not reliant on changes in gene expression but
instead on posttranslation modiﬁcations of Cx43. Cx43 C-ter-
minal phosphorylation controls multiple aspects of this pro-
tein, including channel gating, subcellular localization, second-
ary structure, and stability.
Increased phosphorylation of
Cx43 C-terminal, for example is responsible for decreased
Site-speciﬁc Cx43 phosphorylation has also
been linked to internalization and degradation of this pro-
Casein kinase 1 is a likely candidate for an active par
ticipant in the response to MMC. Phosphorylation of Cx43 by
casein kinase 1 has been proposed to stimulate incorporation
of Cx43 into gap junction plaques,
and it appears to exert a
general role in regulating the stability of its numerous sub-
In addition, casein kinase 1 acutely responds to geno
toxic stress resulting in increased kinase activity, changes in
subcellular location, and increased mRNA and protein lev-
In conclusion, we have documented rapid changes in Cx43
in response to genotoxic stress and identiﬁed the changes in
binding partners and reduced degradation of Cx43. Mitomycin
C is widely used in ocular surgery, and we recently showed
that such treatment generates DNA cross-linking in CE.
however, may not be the only genotoxic agent to which these
cells are exposed. The high metabolic rate of the CE generates
reactive oxygen species, which are capable of DNA damage,
and as a possible consequence, CE exhibits an accumulation of
DNA modiﬁcations with increasing age.
The implications of
the stabilization of Cx43 and GJIC on CE cell homeostasis/
survival are yet to be fully elucidated but may serve to protect
against detrimental effects of natural DNA damage and acute
stress generated by agents such as MMC or ultraviolet light.
Future areas of interest include determining the functional
consequences of stabilized cell surface Cx43 and GJIC on CE
cell viability. One potential function inﬂuencing cell survival
may be to increase the intercellular transfer of cytoprotective
molecules that increase survival and function of intercon-
nected cells and/or disperse cytotoxic molecules and prevent
their accumulation in any one cell.
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IOVS, July 2011, Vol. 52, No. 8 CE Response to Genotoxic Stress Involves Cx43 5181