Structure, evolution, and regulation of chicken apolipoprotein A-I.

Rajavashisth, Tripathi B.; Dawson, Paul A.; Williams, D.; Shackleford, J E; Lebherz, Herbert G.; Lusis, Aldons J.

doi:10.1016/s0021-9258(18)48202-6

Cited by 77 publications

(17 citation statements)

References 44 publications

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“…In absolute terms, the total amount of apoA-I produced by the kidney, when expressed per organ basis, was approximately 25% of that of the liver. This result is difficult to reconcile with that of Rajavashisth et al (12) who found that the content of apoA-I mRNA (when expressed per organ basis) in chick kidney was only 3% of that found in the liver. We do not have a simple explanation for this discrepancy.…”

Section: Discussioncontrasting

confidence: 70%

“…There are no reports, however, on the secretion of apoB-containing lipoproteins by the mammalian kidney. The synthesis of apoA-I by chick kidney is not surprising, as this apolipoprotein is expressed in a variety of chick tissues (10)(11)(12)(13)(14)(15). A survey of several tissues in some mammalian species indicated that the apoA-I gene expression in organs other than liver and intestine is very low or negligible (23).…”

Section: Discussionmentioning

confidence: 99%

“…ApoA-I is the most abundant apolipoprotein present in chick plasma, where it is found not only in HDL but also in VLDL, IDL, and LDL (2,10). Although in the adult chick, liver and intestine represent the major sites of apoA-I synthesis and secretion, measurable amounts of apoA-I mRNA and apoA-I synthesis have been found in a variety of peripheral tissues including the kidney (11)(12)(13)(14)(15). As for apoB, little is known about the secretion of apoA-I-containing lipoproteins by chick kidney.…”

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confidence: 99%

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Secretion of apoB- and apoA-I-containing lipoproteins by chick kidney

Tarugi¹,

Ballarini²,

Pinotti³

et al. 1998

Journal of Lipid Research

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Previous studies showed that chick kidney is a site of synthesis of apolipoprotein (apo) B(B-100) and A-I. Aims of the present study were: a ) to compare apoB and apoA-I production in chick kidney and liver; b ) to investigate whether kidney apolipoproteins were secreted as constituents of lipoproteins; and c ) to define the cellular sites of renal apolipoprotein synthesis. Kidney and liver slices taken from the same animals were incubated with 35 S-labeled amino acids and radioactive apoB and apoA-I were immunoprecipitated from cell homogenate and incubation medium. The percentage of total protein radioactivity incorporated into cell plus medium apoB and apoA-I was 0.23 Ϯ 0.08 and 0.19 Ϯ 0.11 in kidney and 0.38 Ϯ 0.05 and 0.38 Ϯ 0.07 in liver, respectively ( P Ͻ 0.05 kidney vs. liver). 35 S-labeled medium lipoproteins were separated by density gradient ultracentrifugation and three major classes corresponding to VLDL ϩ IDL, LDL, and HDL were identified. Most of the apoB secreted by the liver was found in VLDL, IDL, and LDL whereas kidney apoB was found in VLDL, LDL and "light" HDL (d 1.070-1.130 g/ml). In both hepatic and renal lipoproteins apoA-I was found not only in HDL but also in the other lipoproteins. Immunohistochemical analysis of kidney sections showed that apoB and apoA-I were present almost exclusively in the epithelial cells of proximal and distal convoluted tubules. Thus apoB and apoA-I synthesized by the epithelial cells of the proximal and distal convoluted tubules of chick kidneys are secreted as constituents of lipoprotein particles floating within the density range of plasma lipoproteins. These observations suggest that in the chick, the kidneys may contribute to the plasma lipoprotein pool. -Tarugi, P., G. Ballarini, B. Pinotti, A. Franchini, E. Ottaviani, and S. Calandra. Secretion of apoB-and apoA-I-containing lipoproteins by chick kidney.

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Section: Discussioncontrasting

confidence: 70%

Section: Discussionmentioning

confidence: 99%

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Secretion of apoB- and apoA-I-containing lipoproteins by chick kidney

Tarugi¹,

Ballarini²,

Pinotti³

et al. 1998

Journal of Lipid Research

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“…In particular, chicken apoA-I is found in association with apoB lipoproteins in plasma, raising the possibility that presecretory chicken apoA-I may also associate with VLDL precursors intracellularly. Furthermore, chickens do not synthesize apoE and, because of the similar tissue distribution of chicken apoA-I and mammalian apoE, it has been suggested that chicken apoA-I may be the physiological equivalent of mammalian apoE (27).…”

Section: Discussionmentioning

confidence: 99%

“…However, the relevance of chicken hepatocytes to the study of mammalian apoA-I secretion and lipidation remains unclear, as chicken apoA-I, unlike mammalian apoA-I, has been shown to have a broad tissue distribution and is often found in circulation associated with apoB-containing lipoprotein particles. Because chickens lack apoE, it has been suggested that chicken apoA-I may function more like mammalian apoE (27).…”

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confidence: 99%

ApoA-I secretion from HepG2 cells: evidence for the secretion of both lipid-poor apoA-I and intracellularly assembled nascent HDL

Chisholm

Burleson

Shelness

et al. 2002

Journal of Lipid Research

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The goal of this study was to determine whether apolipoprotein A-I (apoA-I) is lipidated before secretion by HepG2 cells. ApoA-I was extracted from microsomes after radiolabeling with [ 35 S]Met/Cys. After ultracentrifugal flotation, d Ͻ 1.25 g/ml and d Ͼ 1.25 g/ml fractions were immunoprecipitated and analyzed by SDS-PAGE. Under steady state radiolabeling conditions, 20% of extracted microsomal apoA-I floated at d Ͻ 1.25 g/ml. Pulse-chase experiments demonstrated that the percentage of microsomal apoA-I associated with lipid peaked between 2 and 8 min postsynthesis. Density gradient ultracentrifugation, and nondenaturing gradient gel electrophoresis of HepG2 cell medium, indicated that 50% of secretory apoA-I existed as small HDL particles with a diameter of ϳ 7.5 nm. These and additional data suggested that ϳ 20% of newly secreted apoA-I is lipidated intracellularly and another 30% is secreted in lipid-free or lipid-poor form but acquires sufficient lipid to become small HDL within 1 h of secretion, with little further maturation over the time course of the incubation (2 h). These results indicate that a process exists for the presecretory intracellular assembly of apoA-I with lipid in HepG2 cells and that apoA-I is secreted in both lipid-poor and lipidated forms. -Chisholm, J. W., E. R. Burleson, G. S. Shelness, and J. S. Parks. ApoA-I secretion from HepG2 cells: evidence for the secretion of both lipid-poor apoA-I and intracellularly assembled nascent HDL.

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