Cholesterol-mediated regulation of HMG-CoA reductase in microsomes from human skin fibroblasts and rat liver

3-Hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase activity was determined in microsomes from human skin fibroblasts and rat liver that had been variously manipulated in vivo or in tissue culture to up- and down-regulate the enzyme. The cholesterol content of these microsomal preparations was then altered by depletion to or enrichment from either cholesterol-free or cholesterol-rich lipid vesicles. Microsomes from human skin fibroblasts responded to cholesterol depletion by increasing HMG-CoA reductase activity and by decreasing it in response to cholesterol enrichment. This was independent of the initial enzyme activity or the tissue culture conditions. Alterations in cholesterol content of rat liver microsomes in vitro failed to demonstrate any significant changes in HMG-CoA reductase activity whether the microsomes started with low enzyme activity (cholesterol-fed rats) or with high enzyme activity (cholestyramine-treated rats). The results are discussed in relation to previously published data and in respect to differences in the control of the human skin fibroblast and rat liver enzymes.Key words: cholesterol, HMG-CoA reductase, microsomes, fibroblasts, rat liver.

Download Full-text

Effect of ketanserin tartrate on HMG CoA reductase and LDL receptor activity in cultured human skin fibroblasts

European Journal of Clinical Pharmacology ◽

10.1007/bf00315099 ◽

1990 ◽

Vol 39 (3) ◽

pp. 217-220 ◽

Cited By ~ 2

Author(s):

M. Suzukawa ◽

H. Nakamura

Keyword(s):

Human Skin ◽

Ldl Receptor ◽

Skin Fibroblasts ◽

Receptor Activity ◽

Human Skin Fibroblasts ◽

Hmg Coa Reductase ◽

Coa Reductase

Download Full-text

Effects of beta-blockers on HMG CoA reductase and LDL receptor activity in cultured human skin fibroblasts

Cardiovascular Drugs and Therapy ◽

10.1007/bf00051132 ◽

1996 ◽

Vol 10 (1) ◽

pp. 67-74 ◽

Cited By ~ 5

Author(s):

Hiroshi Yoshida ◽

Michio Suzukawa ◽

Toshitsugu Ishikawa ◽

Hideki Shige ◽

Eisuke Nishio ◽

...

Keyword(s):

Human Skin ◽

Beta Blockers ◽

Ldl Receptor ◽

Skin Fibroblasts ◽

Receptor Activity ◽

Human Skin Fibroblasts ◽

Hmg Coa Reductase ◽

Coa Reductase

Download Full-text

Sterol Synthesis and HMG CoA Reductase Activity in Cultured Skin Fibroblasts from Heterozygous Familial Hypercholesterolemic Patients with Abnormally Thick Achilles Tendon

The Journal of Japan Atherosclerosis Society ◽

10.5551/jat1973.6.1_89 ◽

1978 ◽

Vol 6 (1) ◽

pp. 89-93

Author(s):

Toshihiro HABA ◽

Ryozo TATAMI ◽

Kosei UEDA ◽

Ryosei UEDA ◽

Tomio KAMETANI ◽

...

Keyword(s):

Achilles Tendon ◽

Reductase Activity ◽

Skin Fibroblasts ◽

Sterol Synthesis ◽

Hmg Coa Reductase ◽

Cultured Skin ◽

Coa Reductase

Download Full-text

Conditions that result in the mobilization and influx of Ca2+ into rat hepatocytes induce the rapid loss of 3-hydroxy-3-methylglutaryl-CoA reductase activity that is not reversed by phosphatase treatment

Biochemical Journal ◽

10.1042/bj2690373 ◽

1990 ◽

Vol 269 (2) ◽

pp. 373-379 ◽

Cited By ~ 13

Author(s):

V A Zammit ◽

A M Caldwell

Keyword(s):

Enzyme Activity ◽

Okadaic Acid ◽

Reductase Activity ◽

Total Activity ◽

Ionophore A23187 ◽

Hmg Coa Reductase ◽

Pronounced Increase ◽

Phosphorylation State ◽

Total Enzyme Activity ◽

Coa Reductase

We investigated the effects of conditions that induce Ca2+ mobilization from intracellular stores and Ca2+ influx into hepatocytes on the expressed and total (fully dephosphorylated) activities of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase. Vasopressin and phenylephrine when added alone had small or negligible effects on the phosphorylation state of the enzyme, as judged from the expressed/total activity ratio. However, when added in combination with glucagon, they elicited appreciable increases in the phosphorylation of the enzyme. Glucagon on its own had no effect either on phosphorylation state or on total HMG-CoA reductase activity during 40 min of incubation. Under conditions of sustained Ca2+ influx (i.e. vasopressin or phenylephrine plus glucagon), there was a marked loss of total HMG-CoA reductase activity. This effect was more pronounced when vasopressin was used; 50% of the enzyme activity was lost within 40 min. The involvement of Ca2+ in these effects was verified directly by the use of ionophore A23187. Its addition to hepatocytes resulted both in a very pronounced increase in the phosphorylation state of the enzyme and in the loss of 50% of the total activity within 30 min. There was no correlation between the ability of any set of conditions to increase the phosphorylation of the enzyme and the subsequent loss of total HMG-CoA reductase activity. The latter parameter appeared to be directly related, however, to the maintenance of prolonged Ca2+ influx, as indicated by the continued activation of glycogen phosphorylase, measured in the same cells. The lack of a causal relationship between increased phosphorylation and loss of total activity was demonstrated directly by studies in which okadaic acid was used to induce phosphorylation of HMG-CoA reductase in hepatocytes by inhibition of phosphatase 1 and 2A activities. This was not accompanied by any loss of total enzyme activity. Neither did okadaic acid enhance the loss of reductase induced by A23187 when the two agents were added together. It is concluded that altered Ca2+ fluxes in hepatocytes in vivo, under conditions of acute or chronic stress (such as may be associated with trauma or diabetes respectively), may be involved in the regulation of the expression of HMG-CoA reductase activity through alteration of enzyme concentration in the liver.

Download Full-text

The rate of sphingomyelin synthesis de novo is influenced by the level of cholesterol in cultured human skin fibroblasts

Biochemical Journal ◽

10.1042/bj3350285 ◽

1998 ◽

Vol 335 (2) ◽

pp. 285-291 ◽

Cited By ~ 32

Author(s):

Petra LEPPIMÄKI ◽

Robert KRONQVIST ◽

J. Peter SLOTTE

Keyword(s):

Palmitic Acid ◽

Human Skin ◽

De Novo ◽

Cholesterol Content ◽

Skin Fibroblasts ◽

Cholesterol Depletion ◽

Human Skin Fibroblasts ◽

Cellular Cholesterol ◽

Cholesterol Levels ◽

A Cell

Plasma membrane sphingomyelin (SM) is known to affect the cellular distribution of cholesterol. The aim of this work was to examine how SM homoeostasis in human skin fibroblasts is affected by alterations in the level of cholesterol in the cell. The cellular cholesterol level was decreased by exposing cells to 2-hydroxypropyl-β-cyclodextrin, and increased by exposing cells to cholesterol–methyl-β-cyclodextrin inclusion complexes. A lowering of the cellular unesterified cholesterol content by 20% was shown to increase the incorporation of [14C]palmitic acid into SM by 70%. Subsequently, the cellular SM mass was shown to be increased (24% increase after a 24 h period). Since l-cycloserine completely abolished the increased incorporation of [14C]palmitic acid into SM in cholesterol-depleted cells, we concluded that the de novo synthesis of the sphingosine backbone of SM was activated in cholesterol-depleted cells. This conclusion was further verified by performing a cell-free assay of serine C-palmitoyltransferase (SPT) in cholesterol-depleted cells, which showed that the activity of the enzyme was increased by 30% after cholesterol depletion. Most of the newly synthesized SM in cholesterol-depleted cells was susceptible to degradation by sphingomyelinase, indicating that it was transported efficiently to the cell surface. Loading of fibroblasts with cholesterol had essentially the opposite effects on SM homoeostasis to those of cholesterol depletion, i.e. 20–30% decreased incorporation of [14C]palmitic acid into SM and decreased activity of SPT. The results of this study show that cellular cholesterol levels have marked effects on the homoeostasis of SM.

Download Full-text