Compartmentalization of cholesterol metabolism and cellular growth in cultured intestinal crypt cells

Growth of rat intestinal crypt derived cells IEC-6 ceased when the key enzyme of cholesterol synthesis, hydroxymethylglutaryl-CoA reductase, was blocked by the competitive inhibitor mevinolin. This effect was reversed by the addition of mevalonolactone. LDL suppressed reductase activity as well as cholesterol synthesis from [14C]octanoate and stimulated acyl-CoA cholesterol acyltransferase, but failed to support cell growth despite rapid receptor mediated degradation even in the presence of low mevalonolactone concentrations. Inhibition of cholesterol esterification by Sandoz-Compound 58-035 enhanced cell growth in the presence of mevinolin, but did not promote proliferation in the additional presence of low-density lipoproteins. HDL3 but not HDL2 or tetranitromethane-modified HDL3 totally reversed the mevinolin induced inhibition of cell growth. This rescue by HDL3 was overcome by an increased dose of mevinolin. HDL3 derepressed reductase, stimulated cholesterol synthesis and reduced cholesterol esterification, but did not reverse the cholesterol synthesis inhibition by mevinolin. It is concluded that IEC-6 cells preferentially use endogenously synthesized cholesterol for membrane formation rather than low-density lipoprotein cholesterol. High-density lipoproteins appear to normalize cell growth in the presence of mevinolin by inhibition of cholesterol esterification and probably by inducing the formation of non sterol products of mevalonate.