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Cell Biology International (2007) 31, 790–797 (Printed in Great Britain)

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Effect of reduced levels of the LDL receptor of Ehrlich ascites tumor cells on cholesterol uptake and cell proliferation: A coculture study with baby hamster kidney cells

E.W. Haeffner^a*, U. Wittmann^a, L. Kiesewetter^a, H.P. Zimmermann^b, M. Stöhr^c and E. Spiess^d

^aAbteilung Zelluläre und Molekulare Pathologie, Deutsches Krebsforschungszentrum, INF 280, 69120 Heidelberg, Germany
^bAbteilung Molekulare Biologie der Mitose, Deutsches Krebsforschungszentrum, INF 280, 69120 Heidelberg, Germany
^cAbteilung Zellbiologie, Deutsches Krebsforschungszentrum, INF 280, 69120 Heidelberg, Germany
^dAbteilung Invasion und Metastasierung, Deutsches Krebsforschungszentrum, INF 280, 69120 Heidelberg, Germany

Abstract

We have introduced a heterologous coculture model between Ehrlich ascites tumor (EAT) and baby hamster kidney cells (PtK2), and we have studied the influence of PtK2 cells and their newly synthesized cholesterol on uptake and tumor cell proliferation. PtK2 cells produce about five times more cholesterol as compared to EAT cells, and they support tumor cell growth in coculture experiments. This growth stimulation is reduced by 80% when EAT cells are cultured in PtK2 cell-derived medium in the presence of a monoclonal anti-low-density lipoprotein receptor (anti-LDLr) antibody. Freshly synthesized cholesterol by PtK2 cells is taken up by EAT cells in a time-dependent manner amounting to a threefold increase after 24h. Alternatively, cholesterol transfer to EAT cells is decreased between 28% and 35%, when PtK2 cell cholesterol synthesis is inhibited in the presence of mevinolin, the specific inhibitor of the hydroxy-3-methyl-glutaryl-coenzyme A (HMG-CoA) reductase. Furthermore, lower levels of EAT cell LDL receptor induced by antisense technology reduces cholesterol uptake and cell proliferation. These data demonstrate a metabolic interaction between normal and tumor cells mediated via the exchange of cholesterol, an important membrane constituent.

Key words: Coculture, HMG-CoA reductase, Cholesterol transfer, Antisense cDNA, Transfection, Anti-LDLr antibody, Tumor cell proliferation.

^*Corresponding author. c/o U. Zillmann, Zentrales Tierlabor, Deutsches Krebsforschungszentrum, INF 280, 69120 Heidelberg, Germany. Tel.: +49 6221 424262; fax: +49 6221 424258.

Received 22 June 2006/22 December 2006; accepted 17 January 2007