1. Endocytosis - Exocytosis
BIOLOGY, Faculty of Pharmacy
László KŐHIDAI,
Med. Habil. MD, PhD., Assoc. Prof. Department of Genetics, Cell- and Immunobiology Semmelweis University

4. Endocytosis Phagocytosis – solid Pinocytosis – liquid (general)
Uptake of substances
Transport of protein or lipid components of compartments
Metabolic or division signaling
Defense to microorganisms

5. Phagocytosis (1) Predominant cells: unicellular cells macrophages
osteoslats
throphoblasts
Functions:
uptake of food partickles
immuneresponses
elimination of aged cells (RBC)

6. Phagocytosis (2) Required: signal
membrane receptor (Fc receptor for Ab)
formation of pseudopodium
cortical actin network
The formed vesicle: phagosome (hetero-; auto-)

7. Endocytosis Clathrin-coated vesicles Non-clathrin coated vesicles
Macropinocytosis
Potocytosis

8. Clathrin coated
pits/vesicles

9. Function of clathrin coated vesicles
Receptor mediated endocytosis
Selective uptake of molecules
(low environmental conc.)
Membrane receptors
Concentration of ligand (1000x)

10. Components of coated vesicles

11. Receptor-mediated endocytosis of LDL

12. Sorting signals of secreted and membrane
proteins to transport vesicles

13. Selective incorporation
of membrane proteins
Into the coated vesicles

14. Endosomal-Lysosomal compartment Structure
tubular, vesicular
acidic pH - vacuolar H+ ATP-ase - proton pump
early-endosome (EE) and late-endosomes (LE) and lysosomes (L)
EE pH= 6; LE pH=5
in EE no lysosomal membrane proteins or enzymes (in contrast LE)

15. Endosomal-Lysosomal compartment Function
sorting
transport
degradation
removal of clathrin layer
formation of EE
in the EE:
dissociation of receptor-ligand complex - receptor-recycling (e.g. LDL, transferrin)
receptor-ligand complex transported together - receptor down regulation (e.g. EGF)

16. Pathway of LDL
insulin or other
hormones –
in receptor
mediated
endocytosis

17. Fate of LDL
internalized by
receptor-mediated
endocytosis

18. The transferrin-cycle

19. Late endosome lysosomes
early endosomes, TGN and autophagosomes feed late endosomes
lysosomal enzymes M-6-P signal is changed, the phosphate group is cleaved - receptors can not bind enzymes
the enzyme content of vacuoles is in the lumen
lysosomes

22. Dissociation of receptor-ligand complex in
late endosomes

23. De Duve, Ch.
Nobel-prize
Lysosomes (TEM)

24. Lysosomes enzymes - acidic hydrolases
e.g. protease, nuclease, glycosidase, phosphatese
more than 40 types of enzymes
membrane proteins - highly glycosilated protects from the enzymes
transport molecules of the membranes - transports the products of proteolytic cleavage into the cytoplasm
the waste products are released or stored in the cytoplasm (inclusion - residual body)

25. LAMP = lysosome associated membrane proteins
integrant membrane proteins of
the lysosome
LAMP-2 – tarnsport of cholesterol
LAMP-2 defficiency- autophagy

26. Autophagy - Autophagosome
intake of own components
regulates the number of organells
toxic effects can also induce it

27. Formation of autophagosome E

28. Non-clathrin coated vesicles
There is no receptor or clathrin in the membrane
The uptake of substances is less selective
Primairly liquide-phase endocytosis

29. Macropinocytosis Ruffling of the surface membrane forms inclusions
These „vacuoles” have no membrane
Size mm - the mass/surface ratio is very good
Significance:
Liquide-phase pinocytosis
Taking probes from the
environment
– antigene recognition
in macrophages
Film produced by F. Vilhardt and M. Grandahl.

30. Caveolae 50-80 nm, bottle-like infoldings of the surface membrane
endothels, adipocytes
caveolin
potocytosis - caveolae close but not internalized,
the materials enter the cytoplasm by a special carrier molecule e.g. vitamine B4
some other caveolae enter the cell !!!

31. Caveolae

32. Caveolin oligomers and caveolae assembly
101 AA
33 AA
44 AA N C

34. Functions of dynamin Clathrin-mediated endocytosis Membrane retrieval
Endosome-
to-Golgi
transport
Secretory
vesicle
formation
in TGF
Caveolae
Fluid phase
endocytosis

35. Dynamin in the cell

36. Structure of dynamin Interaction with membranes Interaction with
cytosceleton
Activation of GTP-ase domain

37. Dynamin requires GTP hydrolysis to pinching off
coated vesicles
The not-hydrolysable GTP-gS is added
Dots represent binding of anti-dynamin antibodies
The long neck shows that however the coated pit was formed,
in the absence of GTP hydrolysis its pinching off is absence

38. Carrier mediated proteolysis
some molecules can enter lysosome directly from the cytoplasm
the signal of entry: KFERQ (Lys-Phe-Glu-Arg-Gln)

39. Proteasome non-lysosomal cleavage of proteins
cylindric, multienzyme complex
parts: ATP binding-, substrate binding-, regulator-domain
location: close to the external part of ER-translocon
ubiquitin - degradation-signal - is required
the non-properly folded or damaged proteins
regulator - eliminator - role e.g. cyclins
cystic fibrosis - Cl- fac. transp. is affected as the responsible membrane protein is broken down in proteosome

40. Proteasomes

41. Ubiquitation - proteasome

42. „Exocytotic” processes

43. The mannose-6-P pathway and lysosomal enzymes

44. Exocytosis in TEM

45. Apical and basolateral targeting in epithelial cell

46. Transcytosis the ligands walk around the endosomal compartment
ligands transported from one surface to the other
e.g. immunoglobulins of the colostrum cross the intestinal epithelium by transcytosis

47. Release of neurotransmitters