In the first part of the proposed studies we will examine further the mechanisms through which nutritional state regulates apo Beta synthesis and VLDL assembly. We will examine the mechanism through which sucrose feeding increases apo Beta secretion without affecting the hepatic content of apo Beta mRNA. We will test our hypothesis that sucrose feeding increases VLDL assembly by increasing the portion of apo Beta which enters the VLDL assembly pathway. Secondly, we will examine the mechanism through which fasting selectively decreases apo Beta synthesis by decreasing apo Beta mRNA concentrations. We will determine absolute rates of apo Beta mRNA transcription and degradation in both control and fasted rats. In the second part of the proposed studies we will further examine our hypothesis that integration into the endoplasmic reticular and binding to actin affords apo Beta a mechanism through which triglyceride can be concentrated in the endoplasmic reticulum and combined into a VLDL particle which buds off into the lumen in a manner similar to viruses. To examine this hypothesis further, specific sequences of human apo Beta100 cDNA shown by computer analysis to contain a putative actin binding domain, putative hydrophobic stop-transfer signals and the putative apo Beta48 junction will be inserted in-frame with a non-processed reporter protein (alpha-globin). The expression of the apo Beta-globin fusion proteins in different cell types having species, tissue and genetic specific traits will enable us to examine if the apo Beta sequences can make globin behave in a manner similar to apo Beta100 in regard to secretory processes expressed by these cells. The combined physiologic, cell and molecular biologic approaches should provide new insights into the mechanisms through which VLDL assembly is regulated.
|Davis, R A (1993) The endoplasmic reticulum is the site of lipoprotein assembly and regulation of secretion. Subcell Biochem 21:169-87|
|Thrift, R N; Drisko, J; Dueland, S et al. (1992) Translocation of apolipoprotein B across the endoplasmic reticulum is blocked in a nonhepatic cell line. Proc Natl Acad Sci U S A 89:9161-5|
|Davis, R A; Thrift, R N; Wu, C C et al. (1990) Apolipoprotein B is both integrated into and translocated across the endoplasmic reticulum membrane. Evidence for two functionally distinct pools. J Biol Chem 265:10005-11|
|Lang, C A; Davis, R A (1990) Fish oil fatty acids impair VLDL assembly and/or secretion by cultured rat hepatocytes. J Lipid Res 31:2079-86|
|Leighton, J K; Joyner, J; Zamarripa, J et al. (1990) Fasting decreases apolipoprotein B mRNA editing and the secretion of small molecular weight apoB by rat hepatocytes: evidence that the total amount of apoB secreted is regulated post-transcriptionally. J Lipid Res 31:1663-8|
|Davis, R A; Prewett, A B; Chan, D C et al. (1989) Intrahepatic assembly of very low density lipoproteins: immunologic characterization of apolipoprotein B in lipoproteins and hepatic membrane fractions and its intracellular distribution. J Lipid Res 30:1185-96|