Type C Niemann-Pick disease fibroblasts and their transformed cell lines are hypersensitive to HMG-CoA reductase inhibitors

Elevated small GTPase activation influences the cell proliferation signaling control in Niemann-Pick type C fibroblasts

Niemann-Pick type C (NPC) disease is characterized at the cellular level by the intracellular accumulation of free cholesterol. We have previously identified a similar phenotype in cystic fibrosis (CF) cell models that results in the activation of the small GTPase RhoA. The hypothesis of this study was that NPC cells would also exhibit an increase in small GTPase activation. An examination of the active, GTP-bound form of GTPases revealed a basal increase in the content of the active-form Ras and RhoA small GTPases in NPC fibroblasts compared to wt controls. To assess whether this increase in GTP-bound Ras and RhoA manifests a functional outcome, the expression of the proliferation control proteins p21/waf1 and cyclin D were examined. Consistent with increased GTPase signaling, p21/waf1 expression is reduced and cyclin D expression is elevated in NPC fibroblasts. Interestingly, cell growth rate is not altered in NPC fibroblasts compared to wt cells. However, NPC sensitivity to statin treatment is reversed by addition of the isoprenoid geranylgeranyl pyrophosphate (GGPP), a modifier of RhoA. It is concluded that Ras and RhoA basal activation is elevated in NPC fibroblasts and has an impact on cell survival pathways.

Model SV40-transformed fibroblast lines for metabolic studies of human prosaposin and acid ceramidase deficiencies

Skin fibroblasts from patients with Farber disease (acid ceramidase deficiency) and from two siblings of the only known family affected with prosaposin deficiency were transformed by transfection with a plasmid carrying the SV40 large T antigen. The prosaposin-deficient transformed cell lines conserved their original metabolic defects, and in particular they were free of detectable immunoreactivity when using anti-saposin B and anti-saposin C antisera. Ultrastructurally, the cells contained heterogeneous lysosomal storage products. As found for their parental cell lines, the SV40-transformed fibroblasts exhibited deficient in vitro activities of lysosomal ceramidase and beta-galactosylceramidase, but a normal activity of acid sphingomyelinase. As observed for SV40-transformed fibroblasts from Farber disease, degradation of radioactive glucosylceramide or low density lipoprotein-associated radiolabelled sphingomyelin by the prosaposin-deficient cells in situ showed a clear impairment in the turnover of lysosomal ceramide. Ceramide storage in prosaposin-deficient cells was also demonstrated by ceramide mass determination. In contrast to acid ceramidase deficient cells, both the accumulation of ceramide and the reduced in vitro activity of acid ceramidase in cells from prosaposin deficiency could be corrected by addition of purified saposin D. The data confirm that prosaposin is required for lysosomal ceramide degradation, but not for sphingomyelin turnover. The SV40-transformed fibroblasts will be useful for pathophysiological studies on human prosaposin deficiency.