Acylation-stimulatory activity in hyperapobetalipoproteinemic fibroblasts: enhanced cholesterol esterification with another serum basic protein, BP II.

Abstract

Cultured fibroblasts from patients with familial hyperapobetalipoproteinemia (hyperapoB) were used to determine if a defect in lipid metabolism was present. Three basic proteins (BP I, BP H, and BP I) were isolated from normal human serum by preparative isoelectric focusing, preparative SDS/PAGE, and reversed-phase HPLC. The Mr and pI values of these proteins were 14,000 and 9.10 for BP I, 27,500 and 8.48 for BP H, and 55,000 and 8.73 for BP HI. These proteins differed significantly in their content of arginine, cysteine, proline, histidine, serine, and methionine. BP I appears to be the same protein as acylation-stimulating protein, In summary, the identification of another serum basic protein, BP H, led to the elucidation of another cellular defect in hyperapoB fibroblasts, enhanced cholesterol esterification, which may be related to the precocious atherosclerosis and abnormal lipoprotein metabolism seen in hyperapoB.

Abnormal Protein Tyrosine Phosphorylation in Fibroblasts from Hyperapobetalipoproteinemia Subjects

“…The percentage of the total protein that was immunochemically reactive to anti-C 3a des-Arg was as follows: peak I unretained (0.01%); peak I retained (0.03%); BP I (0.06%); BP II (0.07%); BP III (0.07%). Purified BP I, BP II, and BP III also did not react on Western blots to antibodies against C 3a des-Arg, light chain, prealbumin, apolipoprotein A-I, sterol carrier protein-2, or protein 422, a basic 15-kDa fatty acid binding protein from adipose tissue (8,28).…”

“…Six first degree relatives of three of the probands were also studied here: TL, sister of BO; WB and RB, father and brother of BB; and EY, KG, and JL, brother, daughter, and grandson of WY. All but one of the relatives (JL) had hyperapoB defined as an elevated LDL apoB level (Ͼ120 mg/dl) with a normal LDL cholesterol level (8).…”

“…Their M r and isoelectric points, respectively, were as follows: BP I, 14,000 and 9.10; BP II, 27,500 and 8.48; BP III, 55,000 and 8.73 (8). The amino acid compositions of each were distinct from each other (8). BP I appears to be a different protein from acylation-stimulatory protein, a basic protein that has similar metabolic effects; acylation-stimulatory protein has been reported to be the same protein as C 3a des-Arg (M r 8,000), a proteolytic cleavage product of C 3 , the third component of complement (15).…”

“…In hyperapoB cells, the defect in the response to the stimulation of triglyceride formation by BP I is also time-and concentrationdependent and appears related to a deficiency in a high affinity cell surface mechanism (19). Conversely, the abnormality in the overresponse of hyperapoB cells to BP II by enhanced cholesterol formation is concentration-dependent and saturable (7,8) and appears due to an increased interaction of BP II with the cell surface (19).…”

“…We isolated three basic proteins (BP) from normal human serum that we called BP I, BP II, and BP III, based on their electrophoretic migration (8). Their M r and isoelectric points, respectively, were as follows: BP I, 14,000 and 9.10; BP II, 27,500 and 8.48; BP III, 55,000 and 8.73 (8). The amino acid compositions of each were distinct from each other (8).…”