Pleiotropic drug resistance in cystic fibrosis fibroblasts: Increased resistance to cyclic AMP

Abstract

In previous studies, cystic fibrosis (CF) fibroblasts were demonstrated to be resistant to the cytotoxic effects of ouabain, dexamethasone, and the sex hormones, dihydrotestosterone, 17beta-estradiol, and progesterone. We now show that CF fibroblasts also exhibit greatly increased resistance to the cytotoxic effects of exogenous dibutyryl cyclic AMP (cAMP), as well as to isoproterenol and theophylline, drugs which are known to increase endogenous levels of cAMP. CF cells were also shown to have normal amounts of (3H)cAMP binding to protein kinase as well as normal amounts of cAMP-stimulated protein kinase activity. Phosphodiesterase in CF cells was also found to be stimulated by cAMP to the same degree as in normal cells. These findings suggest that there is no detectable protein kinase deficiency in CF cells. cf cells thus appear to be unlike some cAMP-resistant mutants described by others which are defective in protein kinase activity and cAMP regulation of phosphodiesterase levels. The cross-resistance of CF fibroblasts to ouabain, steroid hormones, and cAMP may provide a unique opportunity to study the biochemical events involved in the metabolism of these drugs as well as the basic biochemical defect in a common human genetic disease.

Killing of Fibroblasts by Dexamethasone or Dibutyryl Adenosine 3′,5′-Monophosphate Is Not a Valid Test for Cystic Fibrosis

“…This selective effect of dexamethasone has been proposed as the basis of a diagnostic test for the disease in fetuses and in individuals heterozygous for the trait (2). Our results do not agree with the findings reported in (1)(2)(3)(4). Our results do not agree with the findings reported in (1)(2)(3)(4).…”

“…Their procedure (1)(2)(3)(4)12) has been to add enough cells to each experimental dish to produce 75 to 100 colonies. Their procedure (1)(2)(3)(4)12) has been to add enough cells to each experimental dish to produce 75 to 100 colonies.…”

“…Epstein, Breslow, and their co-workers have reported (1)(2)(3)(4) that both dexamethasone and dibutyryl adenosine 3',5'-monophosphate (cyclic AMP) kill cultured fibroblasts derived from skin of normal individuals at concentrations (10-10 to 10-7M) at which they have little effect on the viability of fibroblasts from individuals with cystic fibrosis (CF). This selective effect of dexamethasone has been proposed as the basis of a diagnostic test for the disease in fetuses and in individuals heterozygous for the trait (2).…”

A Review. Cystic Fibrosis at Forty—Quo Vadis?

“…Until now, no other laboratory has published an attempt to replicate these findings (64). The phenomenon is not explained by differences in protein kinase activity, phosphodiesterase activity, CAMP binding sites, steroid binding sites, or Na/K ATPase activity, or its inhibition by ouabain (22).…”

“…Epstein and Breslow have reported that CF fibroblasts are more resistant to the toxic effects of dexamethasone (21), ouabain (in potassium-free medium) (20), sex steroids (S), dibutyryl cyclic AMP, isoproterenol and theophylline than normal cells (22); fibroblasts from obligate heterozygotes for CF are intermediate (6). One cell line obtained from the amniotic fluid of a mother who previously had a child with CF and later fibroblasts from the skin of the aborted fetus showed increased resistance similar to homozygotes (6).…”