C. Mollers et al., HIGH-DENSITY-LIPOPROTEIN AND LOW-DENSITY LIPOPROTEIN-MEDIATED SIGNAL-TRANSDUCTION IN CULTURED HUMAN SKIN FIBROBLASTS, Cellular signalling, 7(7), 1995, pp. 695-707
The signalling mechanisms whereby high-density lipoproteins (HDL) and
low-density lipoproteins (LDL) affect a number of cellular functions i
n fibroblasts are unclear. This study has analyzed the influence of HD
L(3) and LDL on the phosphatidylinositol specific phospholipase C path
way in human skin fibroblasts. Exposure of myo-[2-H-3]-inositol prelab
elled fibroblasts to HDL(3) or LDL elicited major increases in IP1 and
minor increases in IP2 and IP3 within 30 s. In fura-2 loaded suspende
d fibroblasts, HDL(3) and LDL increased intracellular Ca2+ concentrati
ons ([Ca2+](i)) with comparable rapid, transient kinetics. The dose-pr
ofiles for HDL(3)- and LDL-induced increases in [Ca2+](i) were also co
mparable, with half-maximally and maximally effective concentrations b
eing approximate to 15 mu g/mL and approximate to 50 mu g/mL, respecti
vely. HDL(3)- and LDL-induced increases in [Ca2+](i) were diminished b
y approximate to 60% (vs. control fibroblasts) in thapsigargin-pretrea
ted fibroblasts, indicating that release of Ca2+ from intracellular po
ols is the major contributor toward lipoprotein-induced increases in [
Ca2+](i). Pertussis toxin-pretreatment of cells completely abolished l
ipoprotein induced Ca2+-transient, indicating the involvement of a gua
nine nucleotide-binding protein in the signalling process. In [3H]-pal
mitic acid-prelabelled fibroblasts, both HDL(3) and LDL were observed
to stimulate production of DAG. Activation of protein kinase C (PKC) w
as analysed by determining the cytosol-to-membrane translocation of bo
th enzymatic activity and immunoreactivity of specific PKC isoforms (a
lpha, delta, epsilon, and zeta). Stimulation with HDL(3) and LDL evoke
d a rapid (within 2.5 min) translocation of PKC activity, with PKC alp
ha and PKC epsilon being the isoforms translocated. It is concluded th
at HDL(3) and LDL acutely stimulate a phosphoinositide-specific phosph
olipase C pathway in human skin fibroblasts. However, the specific cel
l membrane events mediating this signal transduction remain to be furt
her elucidated.