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MARK/PAR1 kinase is a regulator of microtubule-dependent transport in axons.

Mandelkow EM, Thies E, Trinczek B, Biernat J, Mandelkow E - J. Cell Biol. (2004)

Bottom Line: The transport can be regulated through motor proteins, cargo adaptors, or microtubule tracks.This occurs without impairing the intrinsic activity of motors because the velocity during active movement remains unchanged.This transport inhibition can be rescued by phosphorylating tau with MARK.

View Article: PubMed Central - PubMed

Affiliation: Max-Planck Unit for Structural Molecular Biology, 22607 Hamburg, Germany. mandelkow@mpasmb.desy.de

ABSTRACT
Microtubule-dependent transport of vesicles and organelles appears saltatory because particles switch between periods of rest, random Brownian motion, and active transport. The transport can be regulated through motor proteins, cargo adaptors, or microtubule tracks. We report here a mechanism whereby microtubule associated proteins (MAPs) represent obstacles to motors which can be regulated by microtubule affinity regulating kinase (MARK)/Par-1, a family of kinases that is known for its involvement in establishing cell polarity and in phosphorylating tau protein during Alzheimer neurodegeneration. Expression of MARK causes the phosphorylation of MAPs at their KXGS motifs, thereby detaching MAPs from the microtubules and thus facilitating the transport of particles. This occurs without impairing the intrinsic activity of motors because the velocity during active movement remains unchanged. In primary retinal ganglion cells, transfection with tau leads to the inhibition of axonal transport of mitochondria, APP vesicles, and other cell components which leads to starvation of axons and vulnerability against stress. This transport inhibition can be rescued by phosphorylating tau with MARK.

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Recovery of plus-end transport of mitochondria by coexpression of tau and MARK2. (a and b) CHO cells stably expressing tau and cotransfected with YFP-MARK2 (a, yellow and open arrowhead). In cells not expressing MARK2, mitochondria are clustered around the MTOC (closed arrowheads, cell perimeters dotted white), whereas the cell expressing MARK2 (top left) shows redispersion because the block of transport is partially relieved. (c and d) Correlation between MARK2 expression and tau phosphorylation at KXGS motifs (12E8 antibody). (c) Distribution of YFP-MARK2 (yellow) and (d) the same cells contain tau with elevated phosphorylation (green). Arrows point to untransfected cell not showing phosphorylation of MARK2 and tau. (e) Comparison of distribution of mitochondria. In wild-type CHO cells ∼50% of the cytoplasm is populated by mitochondria. The fraction is reduced to ∼15% after transfection with tau, but nearly restored after additional transfection with MARK2. The inactive MARK2 mutant cannot rescue the clustering caused by tau.
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fig2: Recovery of plus-end transport of mitochondria by coexpression of tau and MARK2. (a and b) CHO cells stably expressing tau and cotransfected with YFP-MARK2 (a, yellow and open arrowhead). In cells not expressing MARK2, mitochondria are clustered around the MTOC (closed arrowheads, cell perimeters dotted white), whereas the cell expressing MARK2 (top left) shows redispersion because the block of transport is partially relieved. (c and d) Correlation between MARK2 expression and tau phosphorylation at KXGS motifs (12E8 antibody). (c) Distribution of YFP-MARK2 (yellow) and (d) the same cells contain tau with elevated phosphorylation (green). Arrows point to untransfected cell not showing phosphorylation of MARK2 and tau. (e) Comparison of distribution of mitochondria. In wild-type CHO cells ∼50% of the cytoplasm is populated by mitochondria. The fraction is reduced to ∼15% after transfection with tau, but nearly restored after additional transfection with MARK2. The inactive MARK2 mutant cannot rescue the clustering caused by tau.

Mentions: When trying to observe the detachment of MAPs experimentally one is faced with the dual consequences of phosphorylation by MARK: detachment of MAPs may clear the microtubule tracks and thus facilitate traffic, but bare microtubules are less stable and tend to disintegrate, thereby interrupting traffic altogether. In CHO cells (which have a low level of endogenous MAP4), transient transfection with MARK causes the rapid disintegration of microtubules (with subsequent cell death), and the level of phospho-MAP4 remains below detectability by immunofluorescence (Ebneth et al., 1999). If these cells are stably transfected with tau, MAP2c, or MAP4-BD in order to visualize the inhibition of traffic (e.g., by the clustering of mitochondria, as in Fig. 1, b, d, and f), microtubules are stabilized and cells remain viable. In this case the transfection of MARK suffices to make the phosphorylation of MAPs visible (Fig. 2, c and d; Ebneth et al., 1999). But it has been difficult to demonstrate how the phosphorylation of MAPs leads to the reversal of transport inhibition. The reason is that too much phosphorylation causes not only detachment of MAPs and clearance of the microtubule tracks, but also breakdown of microtubules, whereas too little phosphorylation does not rescue the transport inhibition. This means that one has to match the concentration of MAPs with the activity of MARK in a controlled fashion.


MARK/PAR1 kinase is a regulator of microtubule-dependent transport in axons.

Mandelkow EM, Thies E, Trinczek B, Biernat J, Mandelkow E - J. Cell Biol. (2004)

Recovery of plus-end transport of mitochondria by coexpression of tau and MARK2. (a and b) CHO cells stably expressing tau and cotransfected with YFP-MARK2 (a, yellow and open arrowhead). In cells not expressing MARK2, mitochondria are clustered around the MTOC (closed arrowheads, cell perimeters dotted white), whereas the cell expressing MARK2 (top left) shows redispersion because the block of transport is partially relieved. (c and d) Correlation between MARK2 expression and tau phosphorylation at KXGS motifs (12E8 antibody). (c) Distribution of YFP-MARK2 (yellow) and (d) the same cells contain tau with elevated phosphorylation (green). Arrows point to untransfected cell not showing phosphorylation of MARK2 and tau. (e) Comparison of distribution of mitochondria. In wild-type CHO cells ∼50% of the cytoplasm is populated by mitochondria. The fraction is reduced to ∼15% after transfection with tau, but nearly restored after additional transfection with MARK2. The inactive MARK2 mutant cannot rescue the clustering caused by tau.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172520&req=5

fig2: Recovery of plus-end transport of mitochondria by coexpression of tau and MARK2. (a and b) CHO cells stably expressing tau and cotransfected with YFP-MARK2 (a, yellow and open arrowhead). In cells not expressing MARK2, mitochondria are clustered around the MTOC (closed arrowheads, cell perimeters dotted white), whereas the cell expressing MARK2 (top left) shows redispersion because the block of transport is partially relieved. (c and d) Correlation between MARK2 expression and tau phosphorylation at KXGS motifs (12E8 antibody). (c) Distribution of YFP-MARK2 (yellow) and (d) the same cells contain tau with elevated phosphorylation (green). Arrows point to untransfected cell not showing phosphorylation of MARK2 and tau. (e) Comparison of distribution of mitochondria. In wild-type CHO cells ∼50% of the cytoplasm is populated by mitochondria. The fraction is reduced to ∼15% after transfection with tau, but nearly restored after additional transfection with MARK2. The inactive MARK2 mutant cannot rescue the clustering caused by tau.
Mentions: When trying to observe the detachment of MAPs experimentally one is faced with the dual consequences of phosphorylation by MARK: detachment of MAPs may clear the microtubule tracks and thus facilitate traffic, but bare microtubules are less stable and tend to disintegrate, thereby interrupting traffic altogether. In CHO cells (which have a low level of endogenous MAP4), transient transfection with MARK causes the rapid disintegration of microtubules (with subsequent cell death), and the level of phospho-MAP4 remains below detectability by immunofluorescence (Ebneth et al., 1999). If these cells are stably transfected with tau, MAP2c, or MAP4-BD in order to visualize the inhibition of traffic (e.g., by the clustering of mitochondria, as in Fig. 1, b, d, and f), microtubules are stabilized and cells remain viable. In this case the transfection of MARK suffices to make the phosphorylation of MAPs visible (Fig. 2, c and d; Ebneth et al., 1999). But it has been difficult to demonstrate how the phosphorylation of MAPs leads to the reversal of transport inhibition. The reason is that too much phosphorylation causes not only detachment of MAPs and clearance of the microtubule tracks, but also breakdown of microtubules, whereas too little phosphorylation does not rescue the transport inhibition. This means that one has to match the concentration of MAPs with the activity of MARK in a controlled fashion.

Bottom Line: The transport can be regulated through motor proteins, cargo adaptors, or microtubule tracks.This occurs without impairing the intrinsic activity of motors because the velocity during active movement remains unchanged.This transport inhibition can be rescued by phosphorylating tau with MARK.

View Article: PubMed Central - PubMed

Affiliation: Max-Planck Unit for Structural Molecular Biology, 22607 Hamburg, Germany. mandelkow@mpasmb.desy.de

ABSTRACT
Microtubule-dependent transport of vesicles and organelles appears saltatory because particles switch between periods of rest, random Brownian motion, and active transport. The transport can be regulated through motor proteins, cargo adaptors, or microtubule tracks. We report here a mechanism whereby microtubule associated proteins (MAPs) represent obstacles to motors which can be regulated by microtubule affinity regulating kinase (MARK)/Par-1, a family of kinases that is known for its involvement in establishing cell polarity and in phosphorylating tau protein during Alzheimer neurodegeneration. Expression of MARK causes the phosphorylation of MAPs at their KXGS motifs, thereby detaching MAPs from the microtubules and thus facilitating the transport of particles. This occurs without impairing the intrinsic activity of motors because the velocity during active movement remains unchanged. In primary retinal ganglion cells, transfection with tau leads to the inhibition of axonal transport of mitochondria, APP vesicles, and other cell components which leads to starvation of axons and vulnerability against stress. This transport inhibition can be rescued by phosphorylating tau with MARK.

Show MeSH
Related in: MedlinePlus