We previously reported that
zinc thiolate signaling contributes to hypoxic contraction of small, nonmuscularized arteries of the lung. The present studies were designed to investigate mechanisms by which
hypoxia-released
zinc induces contraction in isolated pulmonary endothelial cells and to delineate the signaling pathways involved in
zinc-mediated changes in the actin cytoskeleton. We used fluorescence-based imaging to show that
hypoxia induced time-dependent increases in actin stress fibers that were reversed by the
zinc chelator, N,N,N',N'-tetrakis-(2-pyridylmethyl)-ethylenediamine (
TPEN). We further showed that
hypoxia-induced phosphorylation of the
contractile protein myosin light chain (MLC) and assembly of actin stress fibers were each
TPEN sensitive.
Hypoxia and
zinc-induced inhibition of MLC
phosphatase (MLCP) were independent of the regulatory subunit (MYPT1) of MLCP, and therefore
hypoxia-released
zinc likely inhibits MLCP at its catalytic (PP1) subunit. Inhibition of PKC by
Ro-31-8220 and a dominant-negative construct of PKC-ε attenuated
hypoxia-induced contraction of isolated pulmonary endothelial cells. Furthermore,
zinc-induced phosphorylation of MLC (secondary to inhibition of MLCP) was PKC dependent, and
hypoxia-released
zinc promoted the phosphorylation of the PKC substrate, CPI-17. Collectively, these data suggest a link between
hypoxia, elevations in labile
zinc, and activation of PKC, which in turn acts through CPI-17 to inhibit MLCP activity and promote MLC phosphorylation, ultimately inducing stress fiber formation and endothelial cell contraction.