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Membrane expansion increases endocytosis rate during mitosis.

Raucher D, Sheetz MP - J. Cell Biol. (1999)

Bottom Line: Mitosis in mammalian cells is accompanied by a dramatic inhibition of endocytosis.We have found that the addition of amphyphilic compounds to metaphase cells increases the endocytosis rate even to interphase levels.Detergents and solvents all increased endocytosis rate, and the extent of increase was in direct proportion to the concentration added.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710, USA.

ABSTRACT
Mitosis in mammalian cells is accompanied by a dramatic inhibition of endocytosis. We have found that the addition of amphyphilic compounds to metaphase cells increases the endocytosis rate even to interphase levels. Detergents and solvents all increased endocytosis rate, and the extent of increase was in direct proportion to the concentration added. Although the compounds could produce a variety of different effects, we have found a strong correlation with a physical alteration in the membrane tension as measured by the laser tweezers. Plasma membrane tethers formed by latex beads pull back on the beads with a force that was related to the in-plane bilayer tension and membrane- cytoskeletal adhesion. We found that as cells enter mitosis, the membrane tension rises as the endocytosis rate decreases; and as cells exited mitosis, the endocytosis rate increased as the membrane tension decreased. The addition of amphyphilic compounds decreased membrane tension and increased the endocytosis rate. With the detergent, deoxycholate, the endocytosis rate was restored to interphase levels when the membrane tension was restored to interphase levels. Although biochemical factors are clearly involved in the alterations in mitosis, we suggest that endocytosis is blocked primarily by the increase in apparent plasma membrane tension. Higher tensions inhibit both the binding of the endocytic complex to the membrane and mechanical deformation of the membrane during invagination. We suggest that membrane tension is an important regulator of the endocytosis rate and alteration of tension is sufficient to modify endocytosis rates during mitosis. Further, we postulate that the rise in membrane tension causes cell rounding and the inhibition of motility, characteristic of mitosis.

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Measurement of  tether force. (a) Membrane  tether formed with laser tweezers on a HeLa cell in interphase. Bar, 5 μm. (b) Position  of the bead in the trap (r)  with time during the tether  formation. Inset, schematic  diagram illustrating the opposition of the force of the  trap (FB) and tether force  (FT) pulling the bead back towards the cell. That tether  force is not dependent on  tether length is confirmed in  c, the data given are single  static tether force measurements plotted against corresponding tether length. (d) A  single tether was pulled to  different lengths and the corresponding static tether force  was measured.
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Figure 3: Measurement of tether force. (a) Membrane tether formed with laser tweezers on a HeLa cell in interphase. Bar, 5 μm. (b) Position of the bead in the trap (r) with time during the tether formation. Inset, schematic diagram illustrating the opposition of the force of the trap (FB) and tether force (FT) pulling the bead back towards the cell. That tether force is not dependent on tether length is confirmed in c, the data given are single static tether force measurements plotted against corresponding tether length. (d) A single tether was pulled to different lengths and the corresponding static tether force was measured.

Mentions: In previous studies, we have found that the increase in endocytosis rate after secretion was correlated with a decrease in membrane tension indicating that a decrease in membrane tension in mitotic cells could increase tension. To measure apparent membrane tension, a polystyrene bead coated with rat IgG or ConA was attached to the cell plasma membrane and pulled away from the cell surface with laser tweezers to form a membrane tether as previously described (Dai and Sheetz, 1995b; Fig. 3 a). The force pulling the bead back to the cell (tether force) causes displacement of the bead from the center of the tweezers (Fig. 3 b, inset), and the displacement (r) is directly proportional to the tether force (Kuo and Sheetz, 1993). In the actual force measurements, there is a peak during initial tether extension because of viscous flow into the tether (Fig. 3 b). When extension ceases, force decreases to the plateau level representing the static tether force. In HeLa cells there was no detectable change in static tether force for tethers pulled at different lengths (Fig. 3 c). Similarly, when the same bead was used to form membrane tethers varying in length from 3 to 14 μm, static tether force did not change (Fig. 3 d) indicating that static tether force is independent of tether length. In general, static tether force is dependent on bending stiffness, in-plane tension, and membrane-cytoskeleton interaction (Waugh et al., 1992; Dai and Sheetz, 1995b; Hochmuth et al., 1996). However, our results (data not shown) and results from the previous studies show that bending stiffness is constant. Since bending stiffness is constant, the static tether force is related to the square root of membrane tension (Waugh et al., 1992; Hochmuth et al., 1996). In the membrane tension term as it is defined here (Sheetz and Dai, 1996), there are contributions from membrane-cytoskeleton adhesion and in-plane tension that can not be separated cleanly. Both of those terms are relevant to the process of endocytosis because the membrane must be curved and separated from the cytoskeleton.


Membrane expansion increases endocytosis rate during mitosis.

Raucher D, Sheetz MP - J. Cell Biol. (1999)

Measurement of  tether force. (a) Membrane  tether formed with laser tweezers on a HeLa cell in interphase. Bar, 5 μm. (b) Position  of the bead in the trap (r)  with time during the tether  formation. Inset, schematic  diagram illustrating the opposition of the force of the  trap (FB) and tether force  (FT) pulling the bead back towards the cell. That tether  force is not dependent on  tether length is confirmed in  c, the data given are single  static tether force measurements plotted against corresponding tether length. (d) A  single tether was pulled to  different lengths and the corresponding static tether force  was measured.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2132908&req=5

Figure 3: Measurement of tether force. (a) Membrane tether formed with laser tweezers on a HeLa cell in interphase. Bar, 5 μm. (b) Position of the bead in the trap (r) with time during the tether formation. Inset, schematic diagram illustrating the opposition of the force of the trap (FB) and tether force (FT) pulling the bead back towards the cell. That tether force is not dependent on tether length is confirmed in c, the data given are single static tether force measurements plotted against corresponding tether length. (d) A single tether was pulled to different lengths and the corresponding static tether force was measured.
Mentions: In previous studies, we have found that the increase in endocytosis rate after secretion was correlated with a decrease in membrane tension indicating that a decrease in membrane tension in mitotic cells could increase tension. To measure apparent membrane tension, a polystyrene bead coated with rat IgG or ConA was attached to the cell plasma membrane and pulled away from the cell surface with laser tweezers to form a membrane tether as previously described (Dai and Sheetz, 1995b; Fig. 3 a). The force pulling the bead back to the cell (tether force) causes displacement of the bead from the center of the tweezers (Fig. 3 b, inset), and the displacement (r) is directly proportional to the tether force (Kuo and Sheetz, 1993). In the actual force measurements, there is a peak during initial tether extension because of viscous flow into the tether (Fig. 3 b). When extension ceases, force decreases to the plateau level representing the static tether force. In HeLa cells there was no detectable change in static tether force for tethers pulled at different lengths (Fig. 3 c). Similarly, when the same bead was used to form membrane tethers varying in length from 3 to 14 μm, static tether force did not change (Fig. 3 d) indicating that static tether force is independent of tether length. In general, static tether force is dependent on bending stiffness, in-plane tension, and membrane-cytoskeleton interaction (Waugh et al., 1992; Dai and Sheetz, 1995b; Hochmuth et al., 1996). However, our results (data not shown) and results from the previous studies show that bending stiffness is constant. Since bending stiffness is constant, the static tether force is related to the square root of membrane tension (Waugh et al., 1992; Hochmuth et al., 1996). In the membrane tension term as it is defined here (Sheetz and Dai, 1996), there are contributions from membrane-cytoskeleton adhesion and in-plane tension that can not be separated cleanly. Both of those terms are relevant to the process of endocytosis because the membrane must be curved and separated from the cytoskeleton.

Bottom Line: Mitosis in mammalian cells is accompanied by a dramatic inhibition of endocytosis.We have found that the addition of amphyphilic compounds to metaphase cells increases the endocytosis rate even to interphase levels.Detergents and solvents all increased endocytosis rate, and the extent of increase was in direct proportion to the concentration added.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710, USA.

ABSTRACT
Mitosis in mammalian cells is accompanied by a dramatic inhibition of endocytosis. We have found that the addition of amphyphilic compounds to metaphase cells increases the endocytosis rate even to interphase levels. Detergents and solvents all increased endocytosis rate, and the extent of increase was in direct proportion to the concentration added. Although the compounds could produce a variety of different effects, we have found a strong correlation with a physical alteration in the membrane tension as measured by the laser tweezers. Plasma membrane tethers formed by latex beads pull back on the beads with a force that was related to the in-plane bilayer tension and membrane- cytoskeletal adhesion. We found that as cells enter mitosis, the membrane tension rises as the endocytosis rate decreases; and as cells exited mitosis, the endocytosis rate increased as the membrane tension decreased. The addition of amphyphilic compounds decreased membrane tension and increased the endocytosis rate. With the detergent, deoxycholate, the endocytosis rate was restored to interphase levels when the membrane tension was restored to interphase levels. Although biochemical factors are clearly involved in the alterations in mitosis, we suggest that endocytosis is blocked primarily by the increase in apparent plasma membrane tension. Higher tensions inhibit both the binding of the endocytic complex to the membrane and mechanical deformation of the membrane during invagination. We suggest that membrane tension is an important regulator of the endocytosis rate and alteration of tension is sufficient to modify endocytosis rates during mitosis. Further, we postulate that the rise in membrane tension causes cell rounding and the inhibition of motility, characteristic of mitosis.

Show MeSH
Related in: MedlinePlus