TY - JOUR
T1 - Measurement of apolipoprotein B in various cell lines
T2 - Correlation between intracellular levels and rates of secretion
AU - Bakillah, Ahmed
AU - Zhou, Zhangyin
AU - Luchoomun, Jayraz
AU - Hussain, M. Mahmood
PY - 1997/10
Y1 - 1997/10
N2 - We have standardized simple but sensitive enzyme-linked immunoassays to understand a relationship between intracellular levels and secretion rates of apoB. The assays were based on commercially available antibodies and were specific to human apoB. A monoclonal antibody, 1D1, was immobilized on microtiter wells and incubated with different amounts of low density lipoproteins to obtain a standard curve. Conditioned media were added to other wells in parallel, and the amount of apoB was quantitated from a linear regression curve. To standardize conditions for the measurement of intracellular apoB, cells were homogenized and solubilized with different concentrations of taurocholate. We found that 0.5% taurocholate was sufficient to solubilize all the apoB in HepG2, Caco-2, and McA-RH7777 cells. Next, a standard curve was prepared in the presence of taurocholate and used to determine intracellular levels of apoB in different cell lines. The intracellular levels (pmol/mg cell protein) and the rates of secretion (pmol/mg/h) of apoB100 were positively correlated (r2= 0.81, P = 0.0009) in HepG2 cells. Furthermore, a positive correlation (r2= 0.88, P < 0.0001) was found between intracellular and secreted apoB42 in stably transfected McA- RH7777 cells. In contrast, no correlation was observed for human apoB28 and apoB18 in stably transfected cells that were secreted either partially associated or completely unassociated with lipoproteins. These studies indicated that the rate of secretion of lipid-associated apoB, but not the lipid-free apoB, was tightly controlled.
AB - We have standardized simple but sensitive enzyme-linked immunoassays to understand a relationship between intracellular levels and secretion rates of apoB. The assays were based on commercially available antibodies and were specific to human apoB. A monoclonal antibody, 1D1, was immobilized on microtiter wells and incubated with different amounts of low density lipoproteins to obtain a standard curve. Conditioned media were added to other wells in parallel, and the amount of apoB was quantitated from a linear regression curve. To standardize conditions for the measurement of intracellular apoB, cells were homogenized and solubilized with different concentrations of taurocholate. We found that 0.5% taurocholate was sufficient to solubilize all the apoB in HepG2, Caco-2, and McA-RH7777 cells. Next, a standard curve was prepared in the presence of taurocholate and used to determine intracellular levels of apoB in different cell lines. The intracellular levels (pmol/mg cell protein) and the rates of secretion (pmol/mg/h) of apoB100 were positively correlated (r2= 0.81, P = 0.0009) in HepG2 cells. Furthermore, a positive correlation (r2= 0.88, P < 0.0001) was found between intracellular and secreted apoB42 in stably transfected McA- RH7777 cells. In contrast, no correlation was observed for human apoB28 and apoB18 in stably transfected cells that were secreted either partially associated or completely unassociated with lipoproteins. These studies indicated that the rate of secretion of lipid-associated apoB, but not the lipid-free apoB, was tightly controlled.
UR - http://www.scopus.com/inward/record.url?scp=0030777415&partnerID=8YFLogxK
U2 - 10.1007/s11745-997-0143-8
DO - 10.1007/s11745-997-0143-8
M3 - Article
C2 - 9358438
AN - SCOPUS:0030777415
SN - 0024-4201
VL - 32
SP - 1113
EP - 1118
JO - Lipids
JF - Lipids
IS - 10
ER -