Biosynthetic and growth abnormalities are associated with high level expression of cftr in heterologous cells. Schiavi, Susan C., Nana Abdelkader, Steven Reber, Sarah Pennington, Radha Narayana, John M. McPherson, Alan E. Smith, Henry Hoppe Iv, and Seng H. Cheng. Genzyme Corporation, One Mountain Road, Framingham, Massachusetts 01701-9322, U.S.A.
APStracts 2:0280C, 1995.
An inducible gene amplification system was utilized to study the effects of overexpression of cystic fibrosis transmembrane conductance regulator (CFTR) in vitro. BTS, a monkey kidney cell line expressing a temperature-sensitive simian virus 40 (SV40) Large-T antigen was stably transfected at the non-permissive temperature with a plasmid containing an SV40 origin of replication and the cDNA for either the wild-type CFTR or the mutant G551D-CFTR. Shift of the isolated cell lines to the permissive temperature resulted in induction and accumulation to high levels of the CFTR plasmid, mRNA and protein. However, high level expression of CFTR was transient in both BTS-CFTR and BTS-G551D cells due to a decrease in their respective levels of CFTR mRNA. As G551D-CFTR only exhibits residual Cl- channel activity suggests that the observed down-regulation with BTS-G551D cells may have been induced by either the physical presence of high amounts of CFTR or by some low threshold level of Cl- channel activity. Examination of cell growth properties revealed a correlation between high level expression of wild-type CFTR and growth arrest of the cells at G2/M. However, similar induction of the G551D-CFTR mutant showed only a slight growth inhibition and little enrichment of cells at G2/M. Cytofluorographic analysis further revealed that BTS-CFTR cells were significantly larger than parental BTS or BTS-G551D cells at all stages of the cell cycle. These results indicate that CFTR overexpression is capable of inducing its own down-regulation and that high levels of Cl- channel activity can result in increased cell volume and subsequent cell growth abnormalities. 

Received 25 April 1995; accepted in final form 18 July 1995.
APS Manuscript Number C229-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 July 1995.