The Npc1 mutation causes an altered expression of caveolin-1, annexin II and protein kinases and phosphorylation of caveolin-1 and annexin II in murine livers.
We have previously demonstrated (1) an increased expression of caveolin-1 in murine heterozygous and homozygous Niemann-Pick type C (NPC) livers, and (2) an increased concentration of unesterified cholesterol in a detergent insoluble caveolae-enriched fraction from homozygous livers. To define further the relationship between caveolin-1 function and the cholesterol trafficking defect in NPC, we examined the expression and distribution of additional caveolar and signal transduction proteins. The expression of annexin II was significantly increased in homozygous liver homogenates and the Triton X-100 insoluble floating fraction (TIFF). Phosphoamino acid analysis of caveolin-1 and annexin II from the homozygous TIFF demonstrated an increase in serine and tyrosine phosphorylation, respectively. To determine the basis for increased phosphorylation of these proteins, the expression and distribution of several protein kinases was examined. The expression of PKCalpha, PKCzeta and pp60-src (protein kinases) were significantly increased in both heterozygous and homozygous liver homogenates, while PKCdelta was increased only in homozygous livers. Of the protein kinases analyzed, only CK IIalpha was significantly enriched in the heterozygous TIFF. Finally, the concentration of diacylglycerol in the homozygous TIFF was significantly increased and this elevation may modulate PKC distribution and function. These results provide additional evidence for involvement of a caveolin-1 containing cellular fraction in the pathophysiology of NPC and also suggest that the Npc1 gene product may directly or indirectly, regulate the expression and distribution of signaling molecules.
Garver
W S
WS
Angel Charity for Children - Wings for Genetic Research, Section of Medical and Molecular Genetics, Steele Memorial Children's Research Center, The University of Arizona, College of Medicine, 1501 N. Campbell Avenue, Tucson, AZ 85724-5073, USA.
Hossain
G S
GS
Winscott
M M
MM
Heidenreich
R A
RA
D000818:Animals; D017306:Annexin A2 / Q000096:biosynthesis / Q000378:metabolism*; D051242:Caveolin 1; D022461:Caveolins; D002784:Cholesterol / Q000032:analysis; D004075:Diglycerides / Q000032:analysis; D004195:Disease Models, Animal; D005260:Female; D066298:In Vitro Techniques; D047908:Intracellular Signaling Peptides and Proteins; D008099:Liver / Q000378:metabolism*; D008297:Male; D008565:Membrane Proteins / Q000096:biosynthesis / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D000077296:Niemann-Pick C1 Protein; D009542:Niemann-Pick Diseases / Q000235:genetics; D017830:Octoxynol; D010743:Phospholipids / Q000032:analysis; D010766:Phosphorylation; D011494:Protein Kinases / Q000096:biosynthesis / Q000378:metabolism*; D011506:Proteins / Q000235:genetics*; D015398:Signal Transduction / Q000235:genetics; D012995:Solubility
D017306:Annexin A2; C495541:Cav1 protein, mouse; D051242:Caveolin 1; D022461:Caveolins; D004075:Diglycerides; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D000077296:Niemann-Pick C1 Protein; C106831:Npc1 protein, mouse; D010743:Phospholipids; D011506:Proteins; D017830:Octoxynol; D002784:Cholesterol; D011494:Protein Kinases