ont color=blue>
November 2006 Incytes From MBC 10
ASCB
NEWSLETTER NOVEMBER 2006
INCYTES
from
MBC
November, Vol. 17, No. 11
4 Integrin and EGF Coordinately Regulate Electric Fieldmediated Directional Migration via Rac1
Christine E. Pullar, Brian S. Baier, Yoshinobu Kariya, Alan J. Russell, Basil A. J. Horst, M. Peter Marinkovich, and R. Rivkah Isseroff
Galvanotaxis is the directed migration of cells within an electric eld. Evidence has recently emerged
that a lateral electric eld is generated at wound sites driven by the transepithelial potential, which
creates a negative pole (cathode) at the center of the low-resistance wound. Sensing this electric
eld, skin keratinocytes extend lamellipodia towards the cathode and migrate into the wound site, but
the mechanisms governing galvanotaxis are largely unknown. The
64 integrin, which functions to
anchor static keratinocytes to the basement membrane, redistributes to the lamellipodia of migrating
cells in response to growth factors, such as EGF, that are released at the wound site. Using a
galvanotaxis chamber, the authors have studied the migration of wild-type keratinocytes,
4 integrin
null keratinocytes, and
4 integrinnull keratinocytes reconstituted with wild-type or mutant 4
integrins. Their results suggest that endogenously generated wound electric elds guide keratinoctyes
to move into the wound by synergizing with extracellular matrix and growth factors present in the wound millieu, and that this interaction is
dependent on
64 integrin. Understanding the mechanisms of galvanotaxis may ultimately generate novel wound-healing strategies.
Erv26p Directs ProAlkaline Phosphatase into Endoplasmic Reticulumderived COPII Transport Vesicles
Catherine A. Bue, Christine M. Bentivoglio, and Charles Barlowe
The concept that transmembrane receptors interact with adaptor molecules to direct cargo packaging into
clathrin-coated vesicles has long been established. More recently this concept has been extended to the
packaging of nascent secretory proteins into COPII vesicles for export from the endoplasmic reticulum (ER).
Some of these cargo receptors were identied as abundant ER vesicle (Erv) proteins through previous proteomic
analyses. Here, the authors characterize Erv26p, a 26-kD tetraspanning membrane protein with homologues in
Drosophila and mammals. Erv26p is efciently packaged into COPII vesicles, cycles between the ER and Golgi,
and is required for the efcient packaging and export of the type II transmembrane protein alkaline phosphatase
(ALP). Why should an integral membrane protein with a cytoplasmic tail that can interact directly with the COPII
machinery need a transmembrane cargo receptor? Mammalian ALP is a GPI-anchored protein expressed on the
cell surface; hence the authors speculate that yeast may have evolved a mechanism to divert ALP to the vacuole
such that its cytoplasmic domain functions in post-TGN sorting but not in ER export.
Gene Targeting of Cdc42 and Cdc42GAP Afrms the Critical Involvement of Cdc42 in Filopodia Induction, Directed Migration,
and Proliferation in Primary Mouse Embryonic Fibroblasts
Linda Yang, Lei Wang, and Yi Zheng
The function of the Rho-family GTPase Cdc42 has predominantly been probed by
expression of dominant-negative or constitutively active mutants, raising concerns
about the specicity of the observed effects. Indeed, recent analyses of in
vitro differentiated and immortalized embryonic stem cells decient in Cdc42 have
brought into question its role in lopodia formation, directed migration, and mitosis
(Czurcha et al. [2005] Mol. Biol. Cell 16:44734484; see InCytes, October 2005).
Here the authors have taken a different genetic approach and isolated embryonic
broblasts from mice (MEFs) homozygous for the conditional oxed allele of Cdc42
or a null allele of Cdc42GAP. Cdc42-null MEFs were then generated by retroviral
expression of Cre recombinase and selected for analysis by means of coexpressed GFP or YFP markers. In contrast to the previous study,
these primary MEFs of early passages had defects in lopodia induction, directed migration, and proliferation. The parallel analysis of these
loss- and gain-of-activity mutants provides strong evidence for the role of Cdc42 in these processes. Differences in the two studies may
reect cell typeselective functions for Cdc42, or the induction of compensatory mechanisms during clonal selection of stable cell lines.
The results highlight the value of different genetic approaches to studying cellular function of Rho-family GTPases.
The Mitochondrial Fission Protein hFis1 Requires the Endoplasmic Reticulum Gateway to Induce Apoptosis
Emilie Alirol, Dominic James, Denise Huber, Andrea Marchetto, Lodovica Vergani, Jean-Claude Martinou, and Luca Scorrano
In addition to their role in energy production, mitochondria play key roles in Ca
2+
signaling, apoptosis,
and aging. Mitochondria are dynamic organelles that continuously undergo fusion and ssion. Recent
evidence has linked components of the mitochondrial ssion machinerythe cytosolic dynamin-related
protein, Drp1, and its mitochondrial outer membrane receptor, Fis1to apoptosis, with the suggestion
that excess ssion can result in cytochrome c release and, hence, apoptosis. The authors report the
unexpected nding that a conservative point mutation (K148R) in the domain of Fis1 that protrudes into
the intermembrane space uncouples its ability to trigger excessive mitochondrial ssion from its ability
to cause apoptosis. Although wild-type Fis1-mediated apoptosis requires the multidomain, proapoptotic
Bcl-2 family members Bax and Bak, the authors show that this requirement is indirect and that Fis1-
induced apoptosis depends on Ca
2+
levels in the endoplasmic reticulum (ER), the so-called ER gateway
also controlled by Bax and Bak. These results suggest that Fis1 is a bifunctional protein that independently
regulates mitochondrial fragmentation and ER-mediated apoptosis.