CPI
The role of protein kinase C
(PKC) in the regulation of contraction has been controversial. Recently,
CPI-17, a PKC-potentiated inhibitor protein of PP1, has been cloned and shown
to be specifically expressed in SMC. In this study, we over-expressed CPI-17
and its mutants in NIH3T3 cells, which do not express CPI-17, and examined its
effect on the contractile property. For the measurement of tension, NIH3T3
cells were collected by trypsinization, mixed with type I collagen and made
into a ring preparation (reconstituted ring: RR). The isometric tension
developments were measured using this RR and a force transducer. The
application of phorbol dibutyrate (PDBu; 0.3 microM) to RR transfected by
CPI-17 induced a contraction that reached 2-3 times greater that the 10%
FBS-induced contraction, while PDBu relaxed the RR transfected with vector
alone (control) or CPI-17 mutants (T38A and T38E). The PDBu-induced contraction
of the CPI-17 transfected RR could be inhibited by 3 microM GF109203X (PKC
inhibitor) but not by 3 microM Y27632 (rho kinase inhibitor). The application
of PDBu during contraction induced by 1 microM bradykinin induced further
contraction in CPI-17 transfected RR, while it induced a complete relaxation in
control RR. These results indicated that CPI-17 is a molecular switch that
reverses the PKC mediated effect on contraction. The limited expression of
CPI-17 to SMC may explain the previous observation that the effects of PKC
stimulation were quite different in SMC from those of other cell types.
PMID: 14727519 [PubMed - indexed for MEDLINE]