The Role of Intestinal Fatty Acid Binding Proteins in Protecting Cells from Fatty Acid Induced Impairment of Mitochondrial Dynamics and Apoptosis

Background/Aims: The conformation, folding and lipid binding properties of the intestinal fatty acid binding proteins (IFABP) have been extensively investigated. In contrast, the functional aspects of these proteins are not understood and matter of debates. In this study, we aim to address the deleterious effects of FA overload on cellular components, particularly mitochondria; and how IFABP helps in combating this stress by restoring the mitochondrial dynamics. Methods: In the present study the functional aspect of IFABP under conditions of lipid stress was studied by a string of extensive in-cell studies; flow cytometry by fluorescence-activated cell sorting (FACS), confocal imaging, western blotting and quantitative real time PCR. We deployed ectopic expression of IFABP in rescuing cells under the condition of lipid stress. Again in order to unveil the mechanistic insights of functional traits, we arrayed extensive computational approaches by means of studying centrality calculations along with protein-protein association and ligand induced cluster dissociation. While addressing its functional importance, we used FCS and in-silico computational analyses, to show the structural distribution and the underlying mechanism of IFABP’s action. Results: Ectopic expression of IFABP in HeLa cells has been found to rescue mitochondrial morphological dynamics and restore membrane potential, partially preventing apoptotic damage induced by the increased FAs. These findings have been further validated in the functionally relevant intestinal Caco-2 cells, where the native expression of IFABP protects mitochondrial morphology from abrogation induced by FA overload. However, this native level expression is insufficient to protect against apoptotic cell death, which is rescued, at least partially in cells overexpressing IFABP. In addition, shRNA mediated IFABP knockdown in Caco-2 cells compromises mitochondrial dynamics and switches on intrinsic apoptotic pathways under FA-induced metabolic stress. Conclusion: To summarize, the present study implicates functional significance of IFABP in controlling ligand-induced damage in mitochondrial dynamics and apoptosis.

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Selective Cooperation between Fatty Acid Binding Proteins and Peroxisome Proliferator-Activated Receptors in Regulating Transcription

Molecular and Cellular Biology ◽

10.1128/mcb.22.14.5114-5127.2002 ◽

2002 ◽

Vol 22 (14) ◽

pp. 5114-5127 ◽

Cited By ~ 330

Author(s):

Nguan-Soon Tan ◽

Natacha S. Shaw ◽

Nicolas Vinckenbosch ◽

Peng Liu ◽

Rubina Yasmin ◽

...

Keyword(s):

Retinoic Acid ◽

Fatty Acid ◽

Binding Proteins ◽

Lipid Binding ◽

Fatty Acid Binding Proteins ◽

Peroxisome Proliferator ◽

Fatty Acid Binding ◽

Peroxisome Proliferator Activated Receptors ◽

Retinoic Acid Binding Proteins ◽

Crabp Ii

ABSTRACT Lipophilic compounds such as retinoic acid and long-chain fatty acids regulate gene transcription by activating nuclear receptors such as retinoic acid receptors (RARs) and peroxisome proliferator-activated receptors (PPARs). These compounds also bind in cells to members of the family of intracellular lipid binding proteins, which includes cellular retinoic acid-binding proteins (CRABPs) and fatty acid binding proteins (FABPs). We previously reported that CRABP-II enhances the transcriptional activity of RAR by directly targeting retinoic acid to the receptor. Here, potential functional cooperation between FABPs and PPARs in regulating the transcriptional activities of their common ligands was investigated. We show that adipocyte FABP and keratinocyte FABP (A-FABP and K-FABP, respectively) selectively enhance the activities of PPARγ and PPARβ, respectively, and that these FABPs massively relocate to the nucleus in response to selective ligands for the PPAR isotype which they activate. We show further that A-FABP and K-FABP interact directly with PPARγ and PPARβ and that they do so in a receptor- and ligand-selective manner. Finally, the data demonstrate that the presence of high levels of K-FABP in keratinocytes is essential for PPARβ-mediated induction of differentiation of these cells. Taken together, the data establish that A-FABP and K-FABP govern the transcriptional activities of their ligands by targeting them to cognate PPARs in the nucleus, thereby enabling PPARs to exert their biological functions.

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Ligand Entry into Fatty Acid Binding Protein via Local Unfolding instead of Gap Widening

10.1101/782664 ◽

2019 ◽

Author(s):

T Xiao ◽

Y Lu ◽

J Fan ◽

D Yang

Keyword(s):

Fatty Acids ◽

Fatty Acid ◽

Binding Proteins ◽

Lipid Binding ◽

Relaxation Dispersion ◽

Chemical Exchange Saturation Transfer ◽

Fatty Acid Binding Proteins ◽

Fatty Acid Binding ◽

Protein Cavity ◽

Local Unfolding

AbstractFatty acid binding proteins (FABPs) play an important role in transportation of fatty acids. Despite intensive studies, how fatty acids enter the protein cavity for binding is still controversial. Here, a gap-closed variant of human intestinal FABP was generated by mutagenesis, in which the gap is locked by a disulfide bridge. According to its structure determined here by NMR, this variant has no obvious openings as the ligand entrance and the gap cannot be widened by internal dynamics. Nevertheless, it still uptakes fatty acids and other ligands. NMR relaxation dispersion, chemical exchange saturation transfer and hydrogen-deuterium exchange experiments show that the variant exists in a major native state, two minor native-like state, and two locally unfolded states in aqueous solution. Local unfolding of either βB–βD or helix 2 can generate an opening large enough for ligands to enter the protein cavity, but only the fast local unfolding of helix 2 is relevant to the ligand entry process.Statement of SignificanceFatty acid binding proteins transport fatty acids to specific organelles in the cell. To enable the transport, fatty acids must enter and leave the protein cavity. In spite of many studies, how fatty acids enter the protein cavity remains controversial. Using mutagenesis and biophysical techniques, we have resolved the disagreement and further showed that local unfolding of the second helix can generate a transient opening to allow ligands to enter the protein cavity. Since lipid binding proteins are highly conserved in 3D structures and ligand binding, all of them may use the same local unfolding mechanism for ligand uptake and release.

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Functional analysis of peroxisome-proliferator-responsive element motifs in genes of fatty acid-binding proteins

Biochemical Journal ◽

10.1042/bj20031340 ◽

2004 ◽

Vol 382 (1) ◽

pp. 239-245 ◽

Cited By ~ 75

Author(s):

Christian SCHACHTRUP ◽

Tanja EMMLER ◽

Bertram BLECK ◽

Anton SANDQVIST ◽

Friedrich SPENER

Keyword(s):

Fatty Acids ◽

Fatty Acid ◽

Binding Proteins ◽

Lipid Binding ◽

Fatty Acid Binding Proteins ◽

Computer Search ◽

Peroxisome Proliferator ◽

Fatty Acid Binding ◽

Responsive Element

Retinoic acids and long-chain fatty acids are lipophilic agonists of nuclear receptors such as RXRs (retinoic X receptors) and PPARs (peroxisome-proliferator-activated receptors) respectively. These agonists are also ligands of intracellular lipid-binding proteins, which include FABPs (fatty acid-binding proteins). We reported previously that L (liver-type)-FABP targets fatty acids to the nucleus of hepatocytes and affects PPARα activation, which binds together with an RXR subtype to a PPRE (peroxisome-proliferator-responsive element). In the present study, we first determined the optimal combination of murine PPAR/RXR subtypes for binding to known murine FABP-PPREs and to those found by computer search and then tested their in vitro functionality. We show that all PPARs bind to L-FABP-PPRE, PPARα, PPARγ1 and PPARγ2 to A (adipocyte-type)-FABP-PPRE. All PPAR/RXR heterodimers transactivate L-FABP-PPRE, best are combinations of PPARα with RXRα or RXRγ. In contrast, PPARα heterodimers do not transactivate A-FABP-PPRE, best combinations are of PPARγ1 with RXRα and RXRγ, and of PPARγ2 with all RXR subtypes. We found that the predicted E (epidermal-type)- and H (heart-type)-FABP-PPREs are not activated by any PPAR/RXR combination without or with the PPAR pan-agonist bezafibrate. In the same way, C2C12 myoblasts transfected with promoter fragments of E-FABP and H-FABP genes containing putative PPREs are also not activated through stimulation of PPARs with bezafibrate applied to the cells. These results demonstrate that only PPREs of L- and A-FABP promoters are functional, and that binding of PPAR/RXR heterodimers to a PPRE in vitro does not necessarily predict transactivation.

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