Elevated levels of
bile acids have been implicated in the abnormal morphogenesis of the colonic epithelium thus contributing to
colorectal cancer (CRC). Alternatively
sodium butyrate (NaB) produced by anaerobic fermentation of dietary fibre is regarded as being protective against
colon cancer.
Bile acids such as
deoxycholic acid (DCA) are thought to mediate some of their actions by differentially activating
protein kinase C (PKC). We examined the effects of DCA on the subcellular localisation of PKC-beta(1), -epsilon and -delta and whether these responses could be modulated by NaB. HCT116 cells endogenously express
PKC-epsilon and -delta but not
PKC-beta. DCA treatment results in endogenous
PKC-epsilon translocation but not PKC-delta after 1 hr. To study the subcellular localisation of PKC
isoforms in response to DCA in real time, PKC-beta(1),
PKC-epsilon and PKC-delta functionally intact
green fluorescent protein (GFP) fusion constructs were used. Stimulation with 300 microM DCA induces rapid translocation of PKC-beta(1)-GFP and
PKC-epsilon-GFP but not PKC-delta-GFP from the cytosol to the plasma membrane in 15 min. Interestingly, pretreatment with 4mM NaB does not modify the response of the PKC
isoenzymes to DCA as PKC-beta(1)-GFP and
PKC-epsilon-GFP translocates to the plasma membrane in 15 min whereas PKC-delta-GFP localisation remains unaltered. Immunofluorescence shows that PKC-beta(1)-GFP and
PKC-epsilon-GFP cells treated with DCA colocalise with the cytoskeletal elements actin and
tubulin adjacent to the plasma membrane. Our findings demonstrate that the differential activation of the PKC
isoenzymes by DCA may be of critical importance for the functional responses of colonic epithelial cells. Supplementary material for this article can be found on the International Journal of
Cancer website at http://www.interscience.wiley.com/jpages/0020-7136/suppmat/index.html.