Cell Migration

1
Cell Migration

• Cell migration is critical for many processes
• embryonic development
• wound healing
• tumor cell metastasis
• Migration is a complex cycle requiring careful
  coordination of many cytoskeleton proteins
• One important protein is myosin II

Sandquist, J.C. 2006
2
Myosin II
bipolar myosin filament
F-actin

• Non-muscle myosin II is an ubiquitous motor
  protein that is able to bind and contract actin
  filaments
• Invertebrates such as Dictyostelium, Drosophila
  and yeast harbor only one gene that encodes
  myosin II heavy chain
• All vertebrates examined express at least two
  myosin II heavy chain isoforms (denoted IIA and
  IIB)

Sandquist, J.C. 2006
3
Myosin II
Direction of contraction
bipolar myosin filament
ATP
F-actin
ADP

• Non-muscle myosin II is an ubiquitous motor
  protein that is able to bind and contract actin
  filaments
• Invertebrates such as Dictyostelium, Drosophila
  and yeast harbor only one gene that encodes
  myosin II heavy chain
• All vertebrates examined express at least two
  myosin II heavy chain isoforms (denoted IIA and
  IIB)

Sandquist, J.C. 2006
4
Myosin II Isoforms May Perform Distinct Cellular
Functions

• Myosin IIA and IIB
• Display different assembly and enzymatic
  properties in vitro (Kelley et al., J. Cell Biol.
  1996)
• Exhibit differences in subcellular localization
  in motile cells (Kolega J., J. Cell Sci. 1998
  Maupin et al. J. Cell Sci. 1994 Rochlin et al.,
  J. Cell Sci. 1995))
• Isoforms exhibit unique phosphorylation events
  (Murakami et al., Biochemistry. 1998
  Straussman et al., J. Cell Sci. 2001)
• Null mice exhibit different phenotypes
  (Tullio et al., PNAS. 1997
  Conti et al., J. Biol Chem. 2004)

Do myosin IIA and IIB perform different functions
in cell migration?
5
Rho Kinase (ROCK) Regulates Myosin II Activity
Rho-GDP
Rho-GTP
Y-27632
Regulatory Light Chain (RLC)
ROCK
Myosin II Activation
RLC
MLCP

• Phosphorylation on RLC increases myosin II
  activity
• ROCK directly phosphorylates RLC and inhibits
  myosin light chain phosphatase (MLCP)
• Y-27632 is a small molecule inhibitor of ROCK

Sandquist, J.C. 2006
6
Summary

• IIA-depleted cells exhibit
• migration rate
• spreading/protrusion
• focal adhesions
• IIB-depleted cells exhibit
• migration rate
• spreading/protrusions
• altered focal adhesions

• How do IIA and IIB perform distinct functions?

Sandquist, J.C. 2006
7
Conclusions

• IIA and IIB perform distinct functions during
  wound migration
• IIA positively regulates adhesion and prohibits
  protrusive activity
• IIB is required for proper cell
  spreading/protrusion
• ROCK preferentially regulates IIA activity via
  regulation of IIA-RLC phosphorylation

Sandquist, J.C. 2006