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Evidence for the involvement of ecto-5′-nucleotidase (CD73) in drug resistance

✍ Scribed by Peter Ujházy; Erica S. Berleth; Joelle M. Pietkiewicz; Haruhisa Kitano; Jeffrey R. Skaar; M. Jane Ehrke; Enrico Mihich

Publisher
John Wiley and Sons
Year
1996
Tongue
French
Weight
888 KB
Volume
68
Category
Article
ISSN
0020-7136

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✦ Synopsis

Increased ecto-5'-nucleotidase (e!ctod'NT) protein expression in several multidrug-resistant (MDR) cell lines, documented previously by our group, suggests that this enzyme is invdved in drug resistance. Here, Northern blot analysis of selected cell lines and their MDR variants positively correlated ea0-5"T protein with its mRNA expression. An inhibitor of ecto-5'NT enzymatic activity, a,g-methyleneadenosine 5'diphosphate (AMP-CP), was used to determine if functionally active enzyme had a role in drug resistance. AMP-CP (0.3 mM) reversed the resistance of ecto-5"T-positive MDR cells (MCF7I A6, L12IO/A) to doxorubicin, whereas it did not affect the doxorubicin sensitivity of the ecto-5'NT-negative parental cell lines or that of 2 ecto-5' NT-negative MDR cell lines ( H M / V C R and A2780/DX5). Furthermore, AMP-CP increased rhodamine uptake and inhibited rhodamine efflux from ecto-5'NT-positive MDR cells without affecting ecto-5'NT-negative MDR cells. The presence of exogenous adenosine (0.5 pM) circumvented AMP-CP-induced inhibition of rhodamine efflux from EL4/ADM cells. AMP-CP inhibited the growth of the ecto-5'NT-positive L I 2 I O/A MDR cells but had no effect on the growth of the parental cell line. Determination of intracellular ATP levels indicated that MDR cells which had increased ecto-5'NT expression also had a lower intracellular ATP level than their parental cells. Our results suggest that, in certain MDR cell lines, ecto-5' NT serves as a required accessory molecule in resistance mediated by ATP-dependent mechanisms and that growth-sustaining nucleosides are provided by this salvage pathway.

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