Growth and Cell Cycle Abnormalities of Fibroblasts From Tangier Disease Patients

Abstract

—We have investigated the abnormal proliferation and morphology of fibroblasts from patients with Tangier disease (TD), a high density lipoprotein (HDL) deficiency syndrome that is characterized by impairment of HDL ₃ -mediated lipid efflux and G _i -protein–mediated signaling via phosphatidylinositol-specific phospholipase C (PI-PLC) and phospholipase D (PLD). TD fibroblasts displayed a 30% to 50% reduced in vitro growth rate and a 1.6-fold increased cell surface area. The response to different mitogens was diminished, and asynchronously growing TD fibroblasts showed 4.4±0.3% S-phase and 19.1±0.5% G ₂ /M-phase cells compared with 9.7±0.6% and 7.8±0.5%, respectively, in controls. Monensin, but not brefeldin A, induced an S- and G ₂ /M-phase distribution in control cells similar to that found in TD fibroblasts. This effect of monensin was accompanied by an increase of ceramide levels in controls, whereas TD fibroblasts already had a 2.5-fold increased basal ceramide concentration. Incubation of control cells with C2 ceramide and threo -1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP) mimicked the effect of monensin on the cell cycle. The inhibition of neither G _i protein function by pertussis toxin nor PLD by butanol resulted in a G ₂ /M-phase arrest. Propranolol, known to increase phosphatidic acid levels, was ineffective in reversing the G ₂ /M-phase arrest in TD fibroblasts. In addition, cDNA sequences and mRNA expression of the participants of PI-PLC or PLD signaling, ie, G-protein subunits α _i 1, α _i 2, and α _i 3; phosphatidylinositol transfer proteins-α and -β; and ADP ribosylation factors 1 and 3 were found to be normal. Thus, growth and cell cycle abnormalities in TD fibroblasts are likely to be related to impaired Golgi function and sphingolipid signaling rather than inoperative G-protein signal transduction. Because PDMP was also found to decrease HDL ₃ -mediated lipid efflux in control but not TD fibroblasts, similar pathways seem to be involved in the disturbances of lipid transport and growth retardation.