Content area
Full text
Angiogenesis (2011) 14:345354 DOI 10.1007/s10456-011-9218-0
ORIGINAL PAPER
TM4SF1: a tetraspanin-like protein necessary for nanopodia formation and endothelial cell migration
Andrew Zukauskas Anne Merley Dan Li Lay-Hong Ang
Tracey E. Sciuto Samantha Salman Ann M. Dvorak
Harold F. Dvorak Shou-Ching Shih Jaminet
Received: 19 April 2011 / Accepted: 17 May 2011 / Published online: 29 May 2011 Springer Science+Business Media B.V. 2011
Abstract Transmembrane-4-L-six-family-1 (TM4SF1) is a tetraspanin-like membrane protein that is highly and selectively expressed by cultured endothelial cells (EC) and, in vivo, by EC lining angiogenic tumor blood vessels. TM4SF1 is necessary for the formation of unusually long (up to a 50 lm), thin (*100300 nm wide), F-actin-poor
EC cell projections that we term nanopodia. Immuno-staining of nanopodia at both the light and electron microsopic levels localized TM4SF1 in a regularly spaced, banded pattern, forming TM4FS1-enriched domains. Live cell imaging of GFP-transduced HUVEC demonstrated that EC project nanopodia as they migrate and interact with neighboring cells. When TM4SF1 mRNA levels in EC were increased from the normal *90 mRNA copies/cell to *400 copies/cell through adenoviral transduction, EC projected more and longer nanopodia from the entire cell circumference but were unable to polarize or migrate effectively. When broblasts, which normally express
TM4SF1 at *5 copies/cell, were transduced to express TM4SF1 at EC-like levels, they formed typical TM4SF1-banded nanopodia, and broadened, EC-like lamellipodia. Mass-spectrometry demonstrated that TM4SF1 interacted with myosin-10 and b-actin, proteins involved in lopodia formation and cell migration. In summary, TM4SF1, like genuine tetraspanins, serves as a molecular organizer that interacts with membrane and cytoskeleton-associated proteins and uniquely initiates the formation of nanopodia and facilitates cell polarization and migration.
Keywords TM4SF1 Endothelial cell Nanopodia
Myosin-10 b-actin
Introduction
Tetraspanins are integral membrane proteins that localize to microdomains where they associate with other tetraspanins, integrins, immunoglobulin superfamily members, growth factor receptors, and proteoglycans [1]; they are thought to stabilize cell signaling complexes that regulate cell adhesion, proliferation and migration, and are important players in many biological processes including angiogenesis [2]. In addition to the thirty-nine genuine tetraspanins, a group of six membrane proteins (the L6 family) has been described; L6 proteins resemble tetraspanins with respect to topology but not homology [3].
Transmembrane-4-L-six-family-1 (TM4SF1) is the founding member of the L6 family. It was originally described in...