ABSTRACT
Melanosomes are pigment cell-specific lysosome-related organelles in which melanin pigments are synthesized and stored. Melanosome maturation requires delivery of melanogenic cargoes via tubular transport carriers that emanate from early endosomes and that require BLOC-1 for their formation. Here we show that phosphatidylinositol-4-phosphate (PtdIns4P) and the type II PtdIns-4-kinases (PI4KIIα and PI4KIIß) support BLOC-1-dependent tubule formation to regulate melanosome biogenesis. Depletion of either PI4KIIα or PI4KIIß with shRNAs in melanocytes reduced melanin content and misrouted BLOC-1-dependent cargoes to late endosomes/lysosomes. Genetic epistasis, cell fractionation, and quantitative live-cell imaging analyses show that PI4KIIα and PI4KIIß function sequentially and non-redundantly downstream of BLOC-1 during tubule elongation toward melanosomes by generating local pools of PtdIns4P. The data show that both type II PtdIns-4-kinases are necessary for efficient BLOC-1-dependent tubule elongation and subsequent melanosome contact and content delivery during melanosome biogenesis. The independent functions of PtdIns-4-kinases in tubule extension are downstream of likely redundant functions in BLOC-1-dependent tubule initiation.
Subject(s)
1-Phosphatidylinositol 4-Kinase , Endosomes , Melanins , Melanosomes , 1-Phosphatidylinositol 4-Kinase/metabolism , Endosomes/metabolism , Intracellular Signaling Peptides and Proteins/metabolism , Melanins/metabolism , Melanocytes/metabolism , Melanosomes/metabolism , Phosphatidylinositol Phosphates/metabolism , Protein TransportABSTRACT
Glutamic acid decarboxylase 65kD autoantibody (GAD65Ab) is frequently detected in patients with refractory epilepsy and stiff person syndrome. In contrast to T1D, the pathological role of GAD65Ab in neurological disorders is still debatable. As a result, the implementation of possible immunotherapy is usually delayed. This report presents 2 cases of GAD65Ab-associated brain autoimmunity and their different management. We present clinical data and discuss management based on available evidence in the reviewed literature. Both cases presented with acute on chronic neurological symptoms and were GAD65Ab positive. Case 1, a 30-year-old man with a history of early-onset type 1 diabetes mellitus at 14 months, followed by cryptogenic temporal epilepsy at 11 years of age, presented with intractable seizures. Case 2, a 48-year-old woman, presented with a history of recurrent severe headaches, cognitive impairment, decreased memory, and behavioral symptoms. GAD65Ab was detected in both patients' sera. Cerebrospinal fluid GAD65Ab was only checked and positive in case 1. Case 2 was diagnosed with limbic encephalitis, treated with immunotherapy, and showed a remarkable clinical improvement. Case 1 with refractory epilepsy failed multiple antiepileptic drugs and responsive-stimulator system treatments. He was finally diagnosed with autoimmune epilepsy. The delay in diagnosis resulted in a lost opportunity for early immunotherapy. In conclusion, autoantibody screening and early initiation of immunotherapy should be considered to manage GAD65Ab-associated neurological disorders.
ABSTRACT
Lamellar bodies (LBs) are lysosome-related organelles (LROs) of surfactant-producing alveolar type 2 (AT2) cells of the distal lung epithelium. Trafficking pathways to LBs have been understudied but are likely critical to AT2 cell homeostasis given associations between genetic defects of endosome to LRO trafficking and pulmonary fibrosis in Hermansky Pudlak syndrome (HPS). Our prior studies uncovered a role for AP-3, defective in HPS type 2, in trafficking Peroxiredoxin-6 to LBs. We now show that the P4-type ATPase ATP8A1 is sorted by AP-3 from early endosomes to LBs through recognition of a C-terminal dileucine-based signal. Disruption of the AP-3/ATP8A1 interaction causes ATP8A1 accumulation in early sorting and/or recycling endosomes, enhancing phosphatidylserine exposure on the cytosolic leaflet. This in turn promotes activation of Yes-activating protein, a transcriptional coactivator, augmenting cell migration and AT2 cell numbers. Together, these studies illuminate a mechanism whereby loss of AP-3-mediated trafficking contributes to a toxic gain-of-function that results in enhanced and sustained activation of a repair pathway associated with pulmonary fibrosis.
Subject(s)
Adaptor Protein Complex 3/genetics , Adaptor Proteins, Signal Transducing/genetics , Adenosine Triphosphatases/genetics , Alveolar Epithelial Cells/metabolism , Hermanski-Pudlak Syndrome/genetics , Phospholipid Transfer Proteins/genetics , Pulmonary Fibrosis/genetics , Transcription Factors/genetics , Adaptor Protein Complex 3/metabolism , Adaptor Proteins, Signal Transducing/metabolism , Adenosine Triphosphatases/metabolism , Alveolar Epithelial Cells/cytology , Animals , Biological Transport , Cell Line , Cell Movement , Disease Models, Animal , Endosomes/metabolism , Female , Gene Expression Regulation , Hermanski-Pudlak Syndrome/metabolism , Hermanski-Pudlak Syndrome/pathology , Humans , Lung/metabolism , Lung/pathology , Lysosomes/metabolism , Male , Mice , Mice, Inbred C57BL , Peroxiredoxin VI/genetics , Peroxiredoxin VI/metabolism , Phosphatidylserines/metabolism , Phospholipid Transfer Proteins/metabolism , Primary Cell Culture , Pulmonary Fibrosis/metabolism , Pulmonary Fibrosis/pathology , Signal Transduction , Transcription Factors/metabolism , YAP-Signaling Proteins , rab GTP-Binding Proteins/genetics , rab GTP-Binding Proteins/metabolismABSTRACT
The Carcinoembryonic Antigen-Related Cell Adhesion Molecule (CEACAM) family of proteins plays a significant role in regulating peripheral insulin action by participating in the regulation of insulin metabolism and energy balance. In light of their differential expression, CEACAM1 regulates chiefly insulin extraction, whereas CEACAM2 appears to play a more important role in regulating insulin secretion and overall energy balance, including food intake, energy expenditure and spontaneous physical activity. We will focus this review on the role of CEACAM2 in regulating insulin metabolism and energy balance with an overarching goal to emphasize the importance of the coordinated regulatory effect of these related plasma membrane glycoproteins on insulin metabolism and action.
