Altered phi regulation in 3t3 / cftr clones and their chemotherapeutic drug - selected derivatives. Wei, Li Yong, Mary M. Hoffman & Paul D. Roepe. Program in Molecular Pharmacology & Therapeutics, at the Raymond & Beverly Sackler Foundation Laboratory, Memorial Sloan -Kettering Cancer Center and Graduate Program in Pharmacology, Cornell University Medical College, 1275 York Avenue, New York, NY 10021
APStracts 3:0419C, 1996.
Recently (Wei et al., Biophys. J. 69: 883 - 895, 1995) 3T3 cells overexpressing the CFTR1 were found to exhibit chemotherapeutic drug resistance and other traits of multidrug resistant (MDR) cells. In the present work, NIH 3T3 / CFTR clones were selected with either doxorubicin or vincristine in incremental fashion to generate series of stable MDR cell lines that exhibit increasing levels of multidrug resistance. Thus, C3D6 (grown in the presence of 600 nM doxorubicin) was selected from C3D4 (grown in the presence of 400 nM), which was selected from C3D1 (grown in the presence of 100 nM), which was in turn selected from the original 3T3 / CFTR clone C3 (Stutts et al., J. Biol. Chem. 268: 20653 - 20658, 1993) that was not grown in the presence of chemotherapeutic drug. A similar series was generated via selection with vincristine. In both series, as well as series derived from a different CFTR clone, initial low - level drug selection increases CFTR expression without promoting MDR 1 or MRP expression. Upon continued selection at higher drug concentrations, CFTR mRNA levels decrease while MDR 1 mRNA levels concomitantly increase. At each incremental step of selection intracellular pH (pHi) increases (e.g., pHi of C3D6 > C3D4 > C3D1 > C3). Cl- / HCO3- exchange (AE) activity is significantly reduced in the drug - selected derivatives overexpressing MDR 1, but not the parental CFTR clones. The apparent set point of Na+ / H+ exchange (NHE) activity is significantly lower for the non drug - selected 3T3 / CFTR clones, relative to controls, but then increases upon initial selection with chemotherapeutic drug. Overexpression of MDR 1 in the higher level selectants does not appear to further perturb apparent NHE. These data further describe how CFTR and MDR proteins may affect pHi regulation. 

Received 28 June 1996; accepted in final form 4 December 1996.
APS Manuscript Number C368-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996