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© The Rockefeller University Press,
0021-9525/2003/2/589 $5.00
The Journal of Cell Biology, Volume 160, Number 4, 589-596
Article |
A tumor-associated ß1 integrin mutation that abrogates epithelial differentiation control
Address correspondence to Fiona M. Watt, Keratinocyte Laboratory, Cancer Research UK London Reasearch Institute, 44 Lincoln's Inn Fields, London WC2A 3PX, UK. Tel.: 44-20-7269-3528. Fax: 44-20-7269-3078. E-mail: fiona.watt{at}cancer.org.uk
SCC4 human keratinocytes are derived from a squamous cell carcinoma of the tongue and undergo very little spontaneous differentiation. Introduction of a wild-type ß1 integrin subunit into SCC4 cells stimulates differentiation, suggesting either that the cells have a defect in the integrin signaling pathways that control differentiation or that the ß1 subunit itself is defective. Here we describe a heterozygous mutation in the SCC4 ß1 subunit. The mutation, T188I, maps to the I-like domain. It results in constitutive activation of ligand binding, irrespective of the partner
subunit, in solid phase assays with recombinant protein and in living cells. The mutation promotes cell spreading, but not proliferation, motility, or invasiveness. It results in sustained activation of Erk MAPK independent of cell spreading. When introduced into SCC4 keratinocytes, the wild-type ß1 integrin stimulates differentiation, whereas the mutant is inactive. Activation of ß1 integrins in normal keratinocytes also suppresses differentiation. These results establish, for the first time, mutation as a mechanism by which integrins can contribute to neoplasia, because the degree of differentiation in epithelial cancers is inversely correlated with prognosis. They also provide new insights into how integrins regulate keratinocyte differentiation.
Key Words: integrin; keratinocyte; differentiation; adhesion; tumor
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