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Virus by Macropinocytosis. Jason Mercer and Ari Helenius Nature Cell Biology volume 11 May 2009. Anusara Daenthanasanmak ZIB 15.11.2010. Outline. Endocytosis Macropinocytosis Cellular factors and signalling pathways Viruses that internalized via macropinosomes Perspectives.

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Virus by Macropinocytosis

Jason Mercer and Ari Helenius

Nature Cell Biology volume 11

May 2009

Anusara Daenthanasanmak

ZIB 15.11.2010



  • Endocytosis
  • Macropinocytosis
  • Cellular factors and signalling pathways
  • Viruses that internalized via macropinosomes
  • Perspectives


  • Nature of the cargo
  • Cellular factors
  • Signal needed for activation
  • The fate of internalised material


  • Actin dependent endocytosis
  • Internalization of fluid and membrane
  • Plasma membrane ruffling


  • Inhomogenous in size and irregular in shape
  • Diameter of 0.5-10 µm
  • Increase cellular fluid 5-10 fold

Macropinocytosis versus phagocytosis

  • Role of particle
  • Fluid uptake
  • Cargo specificity
  • Cell-type specificity
  • Cellular machinery
  • Global versus membrane activation

Small GTPases

  • A family of hydrolase enzymes that can bind and hydrolyze guanosine triphosphate (GTP)
  • Small GTPases regulate a wide variety of processes in the cell, including growth, cellular differentiation, cell movement and lipid vesicle transport
  • Ras Superfamily GTPase play a crucial role
  • Ras superfamily is divided into eight main families Ras, Rad, Rab, Rap, Ran, Rho, Rheb, Rit, and Arf

Other factors

  • Na+/H+ exchangers
  • The inhibitors are sometimes used as the diagnostic test to identify Macropinocytosis
  • Depletion of cholesterol blocks both membrane ruffling and macropinocytosis

Macropinosome trafficking & maturation

  • Macropinosomes are sensitive to cytoplasmic pH
  • In human carcinoma A431 cells, most macropinosome recycle back to the cell surface
  • Trafficking seems to depend on cell type and mode of induction

Virus enter by endocytosis

  • Type of endocytosis used is determined by particle, size, choice of receptor, cell tropism and mode of transmission
  • Viruses are valuable tools for the study of endocytic mechanisms
  • Viruses can make use of Macropinocytosis; directly or indirectly

Experimental criteria for macropinocytosis of viruses

  • Ruffling
  • Fluid uptake
  • Actin
  • Rho GTPases
  • Na/H exchangers
  • Kinases – inhibitors of Pak1, PI(3)K and PKC kinases block entry
  • Other factors – dynamin-2, myosin II, microtubules and Arf6

Vaccinia virus

  • Poxvirus family, replicate in cytosol
  • Large, enveloped, double stranded DNA virus
  • Mature Vaccinia virions mimic the uptake of apoptotic bodies and enter cells using macropinocytosis
  • The uptake causes a rapid, transient increase of fluid phase markers
  • Inhibitor analysis shows that Pak1, PKC and PI(3)K are also needed
  • Na/H exchangers, myosin II and cholesterol are required

Vaccinia virus

C. Vaccinia virus mature virions induces systemic blebbing in HeLa cells

d. Focused ion beam-scanning electron microscopy (FIB-SEM): virions internalized next to retracting blebs


Adenovirus 3

  • Non-enveloped, double stranded DNA viruses
  • Human adenovirus serotype 3 (Ad3) is associated with epidemic conjunctivitis, fatal respiratory and systemic disease
  • Its entry into epithelial and haematopoietic cells by direct macropinocytosis by binding to CD46 activates Rac1
  • Ad3 induces clustering of αv-integrins triggering several cellular responses including activation of PI(3)K
  • The virus activates Pak1 and CtBP1 for closure of Ad3-macropinosome

Echovirus 1

  • Picornaviridae family
  • Small, non enveloped RNA virus
  • Causing meningoencephalitis, carditis and mild respiratory or enteric disease
  • EV1 bind α2β1-integrins and co-internalised into vacuolar that accumulate fluid-phase markers
  • Infection is dependent on actin dynamics and Rac1
  • It also requires cholesterol, Pak1, PI(3)K, PLC and Na/H exchanger

Coxsackievirus B

  • Picornavirus
  • CVB can cause myocarditis and hepatitis
  • Enter epithelia at tight junctions by stimulating the internalization of junctional membrane and virus itself into macropinosome
  • Internalized virions colocalize with fluid phase makers and the Rab5 effector
  • CVB entry requires the activity of Ras, Rab5 and Rab34 GTPase, Na/H exchangers and PKC

Herpes simplex virus 1

  • Large enveloped double stranded DNA virus
  • Cause mucosal blisters to deadly brain infections
  • HSV1 shows cell type dependent entry mechanisms
  • Macropinocytosis occurs in epidermal keratinocytes, HeLa and CHO cells
  • EM shows HSV1 virions to be in large, uncoated vesicles during the early stage of internalization
  • Inhibition of PI(3)K or RTKs prevent virus entry and infection

Human immunodeficiency virus

  • Enveloped, single stranded RNA lentivirus
  • HIV-1 are internalized by cell type-specific entry mechanisms
  • Marechal et al. (2001) showed direct Macropinocytosis in human macrophages and Brain microvascular endothelial cells (BMVECs) (Liu et al, 2002)
  • EM of HIV-1 infected BMVECs showed internalization into large cytoplasmic vacuoles with fluid phase makers
  • Macropinocytosis of HIV-1 into BMVECs is not a productive infection route, but rather for cell-to- cell transmission

HIV-1 virions enter large uncoated intracellular vacuoles into Macrophages (Marechal et al. J.virol 2001)


Adenovirus 2/5

  • Associate with respiratory infections
  • Ad2/5 binds to its receptor induces the integrin clustering needed for internalization
  • Ad2/5-induced macropinosomes are lysed and their contents released into the cytosol, required for escaping and infection
  • Ad2/5 triggered macropinocytosis depends on integrins, PKC, actin dynamics, Rac1, Na/H exchange and cholesterol, independent of dynamin

Rubella virus

  • Small, enveloped single-stranded RNA
  • Cause rash and fever
  • EM showed RV within clathrin-coated pits and vesicles and particles also colocalized with clathrin-mediated makers
  • RV enters cells by clathrin-mediated endocytosis, however, inhibition of Na/H exchange, actin or microtubule polymerization inhibits macropinocytosis


  • Are there several different types of macropinocytosis?
  • How many different viruses are using these pathways?
  • How do they trigger the relevant responses in different host cell types?
  • Why a virus might use macropinocytosis for immune evasion?
  • Macropinocytosis of apoptotic debris is known to suppress activation of innate immune responses
  • Ruffling and increased motility, in vivo infection, may allow viruses to spread more efficiently through epithelial layers, basal lamina and other obstacles