title: Vitamin-K-dependent proteins in microsomes of primary Lewis lung tumors.
abstract: Microsomes isolated from Lewis lung (LL) primary tumors raised in C57BL/6 mice have been shown to (i) contain a 4-hydroxycoumarin (warfarin)-sensitive cycle of vitamin K metabolism which is at least qualitatively similar to that of liver, and (ii) catalyze the incorporation of NaH14 CO3 into endogenous protein in a vitamin-K hydroquinone-dependent reaction to produce gamma-carboxyglutamate. As in liver microsomes, LL microsomal reduction of vitamin K 2,3-epoxide to vitamin K was greatly enhanced by exogenous dithiols such as dithiothreitol, but under identical conditions the former was 10-fold faster. The R(+) and S(-) warfarin enantiomers were highly and equally effective inhibitors of both the liver and tumor vitamin K 2,3-epoxide reductases-the average I50 against the tumor enzyme was 0.25 microM. Partially purified reductases isolated by centrifugation of sodium-cholate-treated liver and LL tumor microsomes over a discontinuous sucrose gradient were also inhibited by the sulfhydryl reagent N-ethylmaleimide following their reduction by dithiothreitol. Like the activity of the epoxide reductase, that of the gamma-carboxylase was much lower in tumor than in liver microsomes and was only detectable in microsomes isolated from tumor-bearing mice previously administered S(-) warfarin. In view of the reported inhibition of LL tumor metastasis by warfarin and diet-induced vitamin-K deficiency, vitamin-K-dependent proteins may play a role in the spread and/or subsequent growth of LL cells.
mesh_terms: D000818:Animals; D004229:Dithiothreitol / Q000494:pharmacology; D008099:Liver / Q000378:metabolism; D008175:Lung Neoplasms / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008861:Microsomes / Q000378:metabolism*; D006899:Mixed Function Oxygenases / Q000032:analysis; D009362:Neoplasm Metastasis; D009363:Neoplasm Proteins / Q000032:analysis*; D014812:Vitamin K / Q000502:physiology*; D064417:Vitamin K Epoxide Reductases; D014859:Warfarin / Q000494:pharmacology
chemical_list: D009363:Neoplasm Proteins; D014812:Vitamin K; D014859:Warfarin; D006899:Mixed Function Oxygenases; D064417:Vitamin K Epoxide Reductases; D004229:Dithiothreitol