A tumor-associated β1 integrin mutation that abrogates epithelial differentiation control

SCC4 human keratinocytes are derived from a squamous cell carcinoma of the tongue and undergo very little spontaneous differentiation. Introduction of a wild-type beta1 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 01 subunit itself is defective. Here we describe a heterozygous mutation in the SCC4 beta1 subunit. The mutation, T1881, maps to the I-like domain. It results in constitutive activation of ligand binding, irrespective of the partner a 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 MAN independent of cell spreading. When introduced into SCC4 keratinocytes, the wild-type beta1 integrin stimulates differentiation, whereas the mutant is inactive. Activation of beta1 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.