ABSTRACT
Lysyl oxidase (LOX) catalyzes the oxidative deamination of lysine residues in collagen and elastin, key components of connective tissue. LOX is synthesized as an inactive 50 kD pre-proenzyme, and secreted to the extracellular matrix where it is cleaved into an active 32 kD LOX, and an 18kD free propeptide (LOX-PP), purportedly an inhibitor of fibroblast growth factor-2 (FGF-2) signaling. Given that adipocytes are distributed inside the connective tissue, it is likely that LOX-PP has an important regulatory role in adipogenesis, which has not been studied. Using NIH 3T3-L1 cells, we observed that FGF-2 inhibited adipogenesis, and LOX-PP promoted adipogenesis of 3T3-L1 cells in the presence of FGF-2; the expression of peroxisome proliferator-activated receptor (PPAR) γ and CCAAT-enhancer binding protein (C/EBP) α, two markers of adipogenesis, were enhanced in the presence of LOX-PP. We further observed that LOX-PP down-regulated AKT and ERK1/2, two proliferative signaling proteins down-stream of FGF-2 signaling. Similarly, inhibition of FGF-2 receptor signaling by canofin, a competitive inhibitor of FGF-2 receptor, promoted adipogenesis albeit less effective compared to LOX-PP. To further explore whether LOX-PP promoted adipogenesis through inhibition of FGF-2 signaling, site directed mutagenesis of LOX-PP, resulting in an Arg158 to Gln158 mutation which abolishes the inhibitory activity of LOX-PP to FGF-2 receptor, attenuated the adipogenic promoting properties of LOX-PP. In summary, for the first time, our data show that LOX-PP enhances adipogenesis at least partially through inhibition of FGF-2 receptor signaling. Our data suggest that LOX-PP may serve as a bona fide therapeutic target for regulating adipogenesis and adipose tissue development.
Subject(s)
Adipogenesis/physiology , Protein-Lysine 6-Oxidase/biosynthesis , Protein-Lysine 6-Oxidase/metabolism , 3T3-L1 Cells , Adipocytes/metabolism , Animals , CCAAT-Enhancer-Binding Protein-alpha/metabolism , Cell Proliferation/physiology , Collagen/metabolism , Elastin/metabolism , Enzyme Precursors/metabolism , Fibroblast Growth Factor 2/antagonists & inhibitors , Fibroblast Growth Factor 2/metabolism , Fibroblast Growth Factor 2/physiology , Lysine/metabolism , Mice , PPAR gamma/metabolism , Protein-Lysine 6-Oxidase/chemistry , Signal Transduction/physiologyABSTRACT
Technological advancement has increasingly exposed humans to magnetic fields (MFs). However, more insights are necessary into the potential toxicity of MF exposure as a result of genetic variations related to oxidative metabolism. Therefore, the following study has assessed an in vitro cytotoxic effect of static magnetic field (SMF) (5 mT) on cells with Val16Ala polymorphism (AA, VA, and VV) in the manganese superoxide dismutase gene. Homozygous Val16Ala-superoxide dismutase 2 (SOD2) genotypes present oxidative imbalance that is associated with risk to several chronic degenerative diseases (VV produces less efficient and AA more efficient SOD2 enzyme). Blood samples from healthy adult subject carriers with different Val16Ala-SOD2 genotypes were obtained and exposed to MF at different times (0, 1, 3, 6 h). The cytotoxic effect as well as oxidative stress was evaluated after incubation of 24 h at 37 °C. In addition, apoptosis induction has been analyzed by flow cytometry as well as Bcl-2-associated X protein (BAX), B-cell lymphoma 2 (BCL-2), and caspases 8 and 3 gene expression. SMF cytotoxic effect has been observed in AA cells at all times of exposure, whereas AV cells presented higher mortality only after 6 h of exposure at SMF. Higher apoptosis induction has been observed in AA cells when compared to VV and AV cells. These results suggest a toxicogenetic SMF effect related to an imbalance in SOD2 activity.
Subject(s)
Magnetic Fields/adverse effects , Polymorphism, Genetic , Superoxide Dismutase/genetics , Apoptosis , Cells, Cultured , Genotype , Humans , Leukocytes, Mononuclear/drug effects , Oxidation-Reduction , Oxidative Stress/drug effectsABSTRACT
BACKGROUND: Motor-driven transport along microtubules is a primary mechanism for moving and positioning organelles. How such transport is regulated remains poorly understood. For lipid droplets in Drosophila embryos, three distinct phases of transport can be distinguished. To identify factors regulating this transport, we biochemically purified droplets from individual phases and used 2D gel analysis to search for proteins whose amount on droplets changes as motion changes. RESULTS: By mass spectrometry, we identified one such protein as LSD2. Similar to its mammalian counterpart Perilipin, LSD2 is responsible for regulating lipid homeostasis. Using specific antibodies, we confirmed that LSD2 is present on embryonic lipid droplets. We find that lack of LSD2 causes a specific transport defect: Droplet distribution fails to undergo the dramatic changes characteristic of the wild-type. This defect is not due to a complete failure of the core transport machinery--individual droplets still move bidirectionally along microtubules with approximately normal velocities and kinetics. Rather, detailed biophysical analysis suggests that developmental control of droplet motion is lost. We show that LSD2 is multiply phosphorylated in a developmentally controlled manner. LSD2 phosphorylation depends on the transacting signal Halo, and LSD2 can physically interact with the lipid-droplet-associated coordinator Klar, identifying LSD2 as a central player in the mechanisms that control droplet motion. CONCLUSIONS: LSD2 appears to represent a new class of regulators, a protein that transduces regulatory signals to a separable core motor machinery. In addition, the demonstration that LSD2 regulates both transport and lipid metabolism suggests a link between lipid-droplet motion and lipid homeostasis.
