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Endocytotic Cycling of PM Proteins

Endocytotic Cycling of PM Proteins. Junxia An Xihua Chen. Annu.Rev.plant.biol.2005:221-251. Summarize. Comparison of plasma membrane localization in polarized animal and plant cells. Types of endosytosis Endosomal Cycling In Animals: An Overveiw

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Endocytotic Cycling of PM Proteins

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  1. Endocytotic Cycling of PM Proteins Junxia An Xihua Chen Annu.Rev.plant.biol.2005:221-251

  2. Summarize • Comparison of plasma membrane localization in polarized animal and plant cells. • Types of endosytosis • Endosomal Cycling In Animals: An Overveiw • Protein Components of Endocytotic Cycling Mechanisms

  3. Tight junction Vacuole Endosomes Golgi Lysosome N Mitochondrum Plastid

  4. Introduction • Eukaryotic cell respond to external signals by altering(改变) transcriptional(转录) output and regulating the abundance(含量) and distribution(分布) of PM proteins that comprise the functional interface with the external environment . Animals (Yeast) Plants

  5. Animals (Yeast) • PM protein removal and recompartmentalization is regulated by endocytosis and endocytotic cycling.

  6. Plants • PM localization of the PIN1 auxin efflux carrier complex and the KAT1 potassium channel are dynamically regulated has intensified efforts to conclusively demonstrate endocytotic recycling in plants. Picture

  7. Endosomal Cycling In Animals:An Overveiw • Endocytosis: • Take up extracellular substances and/or internalize PM proteins for transport to endosomes. • comprise Highly dynamic structures • Helps maintain homeostatic regulation • Endosomes • PM proteins Target into the lysosome/vacuole for degradation or recycled back to cell surface.(M6P) • Mammalian endocytosis regylates multiple physiological processes

  8. Types of endocytosis • Receptor-mediated endocytosis (受体介导) • Clathrin-dependent endocytosis (网格蛋白介导) • Clathrin-independent endocytosis(非网格蛋白介导) • Caveolae/lipid raft-mediated endocytosis (晶格镶嵌型脂筏) • Fluid-phase endocytosis (液相内吞) • Phagocytosis (吞噬)

  9. Receptor-mediated endocytosis RME (受体介导的内吞作用) • Ligand bind to a PM receptor (uptake proteins or protein complexes) from the cell surface, then internalized in the cell.

  10. Clathrin-mediated RME(网格蛋白介导的受体介导内吞作用) Steps: • Ligands bound to their receptors (AP2 adaptor complex; AP-180; ARF6GTPase) • Clustering(聚集) in clathrin-coat • Destined for degradation in lysosomes (M6p)

  11. Clathrin-independent processes • Caveolae/lipid raft-mediated endocytosis • Fluid-phase endocytosis • Phagocytosis (吞噬)

  12. FM4-64 FM4-64 GFP GNOM Tf-R(-Fe) Tf-R PCR Sorting endosome ERC MVB MVB 焦磷酸酶 L L TGN

  13. Elements Early endosomes/Sorting endosomes早胞内体；分选内体 • Localized at the peripherally(边缘) of the cell • Structures: tubular-vesicular • The first organelles to receive PM-derived cargo (LDL; transferrin Tf) (来自PM的) • First junction(分叉) in the REM, tow main destination: the PM and the late endosomes • The kinetics are fast with a half-life(t1/2) of about 2 minutes

  14. ERC 内体循环区室 • Associated with microtubules and exhibits a variable(可变) distribution • Do not contain ligands or receptors (lysosomal enzymes; LDL) • Marked by the presence of LDL-R and iron-free Tf bound to the Tf-R • The main intracellular cholesterol repository(胆固醇贮藏)

  15. ERC内体循环区室 • Tow kinetics(活动) have been described for ERC-to-PM recycling: • A fast rate which recycle almost completely back to the PM(t1/2=10 minutes) • A slower rate (t1/2=30 minutes); be sorted by lipid microdomains(微结构域) • Relatively long-lived organelle (longer than late endosomes)

  16. ERC内体循环区室 • Insulin-regulated trafficking of the glucose-transporter GLUT4(葡萄糖转移酶) • Response to increased insulin(胰岛素) concentration(浓缩), resulting in higher uptake of glucose in fat and muscle cells.

  17. IRAP GLUT4 ERC ERC Sorting endosome SE Insulin-responsive compartment

  18. Protein Components of Endocytotic Cycling Mechanisms • Adaptins and Adaptor Complexes • ARFs/ARF-GEF • Dynamins • Rab GTPase • SNAREs • Other Cytoskeletal Interaction • Other Proteins Contributing to PM Protein Cycling

  19. Adaptins and Adaptor Complexes • Mediate the selection of cargo molecules for inclusion(包括) into coated vesicles(衣被小泡) in the late secretory and endocytotic pathway. • One group consist of cargo adaptors are monomeric(单体) proteins (AP180; β-arrestins; GGAs) • Another group consists of heterotetrameric(异四聚体) AP complexes composed of adaptin subunits

  20. Adaptins and Adaptor Complexes • Little is known about adaptin function in plants. Only two adaptins and one monomeric adaptor homolog(同系物) from Arabidopsis(拟南芥) have been functionally characterized on the molecular level.

  21. ARFs/ARF-GEF • AFRs are rasrelated GTP-binding proteins that maintain organellar integrity(完整) and regulate intracellular(内) transport. • Six types of ARFs.

  22. ARFs/ARF-GEF • Under normal condition , cytosolic(胞液) GDP-bound ARFs are inactive. • A vesicle-associated GTPase activating protein (GAP) hydrolyzes GTP and releases the ARF protein, resulting in coat dissociation(游离) prior to vesicle.

  23. Dynamins 发动蛋白(not dyneins动力蛋白) • Dynamins constitute a family of GTP Phosphohydrolases (P-水解酶) that carry out diverse roles in eukaryotie membrane cycling. • A coiled-coil region(CC domain) serves as the GTPases, effector domain. Dynamins participate in membrane scission(切割) events by self-assembling into multimeric ring structures.

  24. The mechanism hypothesis of Rabs regulating endocytosis • The GTP-GDP cycle of Rabs might act as a timer switch(定时的开关） to regulate the functionality of a membrane domain. • Rabs act as GTP-activated switches that simply stabilize protein complexes required for transition events. • The ability of Rabs to link membranes to cytoskeletal motor proteins suggests that they can generate uniquely functional membrane subdiomains.

  25. SNAREs N-ethymaleimide-sensitive factor（N-乙基马来酰亚胺敏感因子） adoptor protein receptors are essential components of vesicle-trafficking machinery where they play a central role in membrane fusion events.

  26. Other Cytoskeletal Interaction • All endocytotic pathways of membrane protein internalization depend on interaction with the cytoskeleton. • Direct participation of F-actin in internalization events has been documented in animals and yeast.

  27. Other Proteins Contributing to PM Protein Cycling • Rho GTPases • Immunophilins(抑免蛋白） • Fatty acyl CoA

  28. Rho GTPases • Rho GTPases are membranes of a small but diverse protein familly involved in signaling and regulation of edocytotic traffic. • Rho-GTPases are not found in plants,but plant Rho-related GTPases comprise a plant-specific subfamily.

  29. Immunophilins(抑免蛋白） • Immunophilin-like proteins are likely involved in fundamental cellular processes. • Most immunophilins possess peptidyl prolyl（脯胺酰基） cis/trans-isomerase activity required for protein folding and modification.

  30. Fatty acyl CoA Fatty acyl CoA has been identified in cycling GLUT4 vesicles and has been implicated in membrane budding and fusion events.In another study,acyl CoA dehydrogenase(脱氢酶）was found to mediate intracellular retention of GLUT4 vesicles via association with IRAP.

  31. What do we know about endocytotic cycling in plants • Endocytosis（内吞作用） • Endocytotic compartments • Endosomal Sorting and Redirection

  32. Endocytosis • Recent studies indicate that endocytosis mediates the internalization and recycling of PM molecules,including membrane proteins and sterols in plants. • At least four forms of endocytosis operate in plants: clathrin independent and dependent, phagocytotic,fluid-phases and lipid raft-mediated endocytosis.

  33. Endocytotic compartments • Molecules may be transported into or out of the compartment through transport vesicles or, alternatively,the compartments itself may be modifyed and mature over time. • Plant endocytic compartment are not well characterizd and the term endosome is often used for any comparment containing an endocytosed material.

  34. Evidence for endocytotic recycling in plant • Auxin Transport Proteins And GNOM • The KAT1 Inward-Rectifying Potassium Channel(内流钾通道） • Other Examples

  35. Auxin Transport Proteins And GNOM Establishing plant polarity depends on the polar transport of the growth hormone auxin. The directionality of auxin transport is maintained by a polar transport apparatus that requires asymmetrically localized transporters and regulators. The PIN proteins are the best characterized of such asymmetrically localized auxin efflux regulators.

  36. The KAT1 Inward-Rectifying Potassium Channel（内流钾通道） The dogma(信号） that the high turgor of plant cells precludes endocytosis was recently challenged by evidence that the KAT K+ inward-rectifying channel is constitutively endocytosed from the guard cell Pms against high turgor pressure.

  37. CONCLUSION Recent experimental evidence suggests that plant cells respond to developmental programming and environmental condition by regulating the endocytosis of PM proteins. This evidence also suggests that some of the mechanisms underlying endocytotic cycling are conserved between plants and animals.

  38. Thank you

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