Disease relevance of Fabp4

• Apoe-/- mice with Ap2+/+ adipocytes and Ap2-/- macrophages generated by bone-marrow transplantation showed a comparable reduction in atherosclerotic lesions to those with total aP2 deficiency, indicating an independent role for macrophage aP2 in atherogenesis [1].
• We conclude KFABP can functionally compensate for the absence of AFABP, resulting in no major alterations in adipocyte metabolism or fat accumulation in response to short-term feeding of high-fat diets that result in moderate hyperinsulinemia [2].
• RESULTS: TNFalpha mRNA was increased in the retinas of experimental animals on P13 and P15, during the early stages of retinal neovascularization [3].
• By screening a random cyclic peptide phage display library, we have identified a novel peptide, P15, that abrogated CK2 phosphorylation by blocking the substrate in vitro [4].
• The recombinant ALBP was soluble in E. coli extracts and resistant to bacterial proteolysis [5].

High impact information on Fabp4

• These transcription factors coordinate the expression of genes involved in creating and maintaining the adipocyte phenotype including the insulin-responsive glucose transporter (GLUT4), stearoyl CoA desaturase 1 (SCD1), and the fatty acid binding protein (422/aP2) [6].
• Adipocyte differentiation involves the transcriptional activation of several genes in triglyceride metabolism, including the adipose P2 (aP2 or 422) gene that encodes the adipocyte lipid-binding protein ALBP [7].
• IPTG-induced expression of the 42-kDa isoform of C/EBP alpha in preadipocytes caused expression of several endogenous adipocyte-specific genes (genes encoding the 422 adipose P2 protein, glucose transporter 4, and C/EBP alpha) and the accumulation of cytoplasmic triglyceride [8].
• Cell-free transcription directed by the 422 adipose P2 gene promoter: activation by the CCAAT/enhancer binding protein [9].
• We conclude that the first 858 base pairs of 5'-flanking sequence of the 422 gene contains elements that mediate activation by dexamethasone and cAMP [10].

Biological context of Fabp4

• To the contrary, basal lipolysis decreased approximately 40% in ALBP/aP2 nulls as compared to wild-type littermates [11].
• There was no appreciable difference in the rate of fatty acid influx or esterification in adipocytes of wild-type and ALBP/aP2 null animals [11].
• The 5'-flanking sequence of the 422 gene contains potential regulatory regions for adipose-specific expression [10].
• We have isolated and characterized a fragment of the gene encoding adipose fatty acid-binding protein (gene 422) from a 3T3-L1 adipocyte genomic library [10].
• The complete nucleotide sequence of the cDNA insert in pAL422 revealed a single long open reading frame that encodes a 132 amino acid polypeptide (the 422 protein) of 14.6 kDa [12].

Anatomical context of Fabp4

• Consistent with a decrease in basal efflux, the non-esterified fatty acid (NEFA) level was nearly 3-fold greater in adipocytes from ALBP/aP2 nulls as compared to wild-type animals [11].
• Western blotting and immunofluorescence using monospecific antibodies demonstrated the coexistence of H-FABP and A-FABP in the lactating mammary gland [13].
• Computer-assisted analyses showed that the 422 protein shares 69% and 64% homology with myelin P2 proteins from rabbit and bovine peripheral nerves, respectively, as well as 23% and 30% homology with fatty-acid binding proteins from rat liver and intestine, respectively [12].
• Sequence analysis of the PPARgamma gene revealed that all four cell lines contain a previously unidentified point mutation in the ninth alpha-helix of the ligand binding domain at codon 422 (K422Q) [14].
• Analysis of adipose tissue from aP2 null animals generated by a targeted disruption revealed that the partial loss of ALBP expression in heterozygotes and complete lack of ALBP in the nulls was accompanied by a compensatory up-regulation of the keratinocyte lipid binding protein [15].

Associations of Fabp4 with chemical compounds

• However, in the presence of 10 microm oleate, A-FABP and E-FABP each bound to HSL with high affinity (Kd of 0.5 and 3 nM, respectively) in a approximately 1:1 molar stoichiometry, whereas liver FABP and intestinal FABP did not exhibit any association [16].
• The glycerol release from isproterenol-stimulated ALBP/aP2 null fat cells was similarly reduced by approximately 35% [11].
• The significant decrease in both basal and isoproterenol-stimulated lipolysis in adipose tissue of ALBP/aP2 null mice supports the model whereby intracellular lipid-binding proteins function as lipid chaperones, facilitating the movement of fatty acids out of the fat cell [11].
• ALBP/aP2 and KLBP exhibit similar binding affinities for most long-chain fatty acids; however, ALBP/aP2 exhibits a two to three-fold increased affinity for myristic, palmitic, oleic and linoleic acids, the predominant fatty acids of adipocytes [17].
• As measured by guanidinium hydrochloride denaturation, the stability of ALBP/aP2 is nearly 3 kcal/mol greater than that of KLBP [17].

Physical interactions of Fabp4

• I conclude that these nonconsensus Ap2-like elements and their cognitive binding protein play a major role in the expression of the CAII gene [18].
• In the liver, dietary t10,c12-CLA triggered the ectopic production of peroxisome proliferator-activated receptor gamma (PPARgamma), adipocyte lipid-binding protein and fatty acid transporter mRNAs and induced expression of the sterol responsive element-binding protein-1a and fatty acid synthase genes [19].
• Furthermore, Northern analysis clearly indicated that transcript levels of peroxisome proliferator-activated receptor gamma (PPARgamma) and adipose-type fatty acid binding protein (A-FABP) were well correlated with the levels of fat accumulation [20].
• Translocation of hormone-sensitive lipase bound to the adipocyte lipid binding protein to the lipid droplet seems to be an important step during lipolytic activation [21].
• Crystalline ALBP has a conformation which is essentially identical to that of intestinal fatty acid binding protein and myelin P2 protein [22].
• These results suggest that ligand-bound AFABP/aP2 binds to and attenuates JAK2 signaling and establishes a new role for AFABP/aP2 as a fatty acid sensor affecting cellular metabolism via protein-protein interactions [23].

Regulatory relationships of Fabp4

• In 3T3-L1 preadipocytes, simultaneous administration of a PPARdelta-selective ligand and MIX significantly enhanced the early expression of PPARgamma and ALBP/aP2, but only modestly promoted terminal differentiation as determined by lipid accumulation [24].

Other interactions of Fabp4

• The activation by A-FABP was dependent upon its fatty acid binding properties because a non-fatty acid binding mutant, R126Q, failed to activate HSL [16].
• In addition, forced expression of ACBP, ALBP, and KLBP in CV-1 cells resulted in a substantial accumulation of all three proteins in the nucleus [25].
• Treating differentiating 3T3-L1 preadipocytes with t10c12 CLA and conjugated nonadecadienoic acid (CNA, a 19-carbon CLA cognate) resulted in decreased intracellular triglyceride accumulation and mRNA levels of the adipogenic gene fatty acid synthase and adipocyte lipid binding protein [26].
• At the molecular level, activation of PPARdelta by fatty acids induced transcription of the genes encoding fatty acid transporter, adipocyte lipid-binding protein, and PPARgamma [27].
• It was further found that AFABP, but not acetylated AFABP, prevented cytochrome c, a well characterized peripheral membrane protein, from binding to membranes [28].

Analytical, diagnostic and therapeutic context of Fabp4

• As assessed by Western blot analysis, the level of KFABP protein in AFABP-KOs was approximately 40% of the level of AFABP in WT controls [2].
• In an effort to examine the portal region, we have used site-directed mutagenesis to introduce the mutations V32D/F57H into the murine ALBP cDNA [29].
• Adipocyte lipid-binding protein complexed with arachidonic acid. Titration calorimetry and X-ray crystallographic studies [30].
• Recombinant ALBP was purified to homogeneity using a combination of pH fractionation, gel filtration, and immobilized metal affinity chromatography [31].
• Expression, purification, and crystallization of the adipocyte lipid binding protein [31].

References