Simultaneous changes in the function and expression of beta 1 integrins during the growth arrest of poorly differentiated colorectal cells (LISP-1)

Abstract

Cells usually lose adhesion and increase proliferation and migration during malignant transformation. Here, we studied how proliferation can affect the other two characteristics, which ultimately lead to invasion and metastasis. We determined the expression of β1 integrins, as well as adhesion and migration towards laminin-1, fibronectin, collagens type I and type IV presented by LISP-1 colorectal cancer cells exposed to 2.5% dimethyl sulfoxide (DMSO), an agent capable of decreasing proliferation in this poorly differentiated colorectal cell line. Untreated cells (control), as shown by flow cytometry and monoclonal antibodies, expressed α2 (63.8 ± 11.3% positive cells), (93.3 ± 7.0%), α5 (50.4 ± 12.0%) and α6 (34.1 ± 4.9%) integrins but not α1, α4, αv or β4. Cells adhered well to laminin-1 (73.4 ± 6.0% and fibronectin (40.0 ± 2.0%) substrates but very little to collagens. By using blocking monoclonal antibodies, we showed that α2, α3 and α6 mediated laminin-1 adhesion, but neither α3 nor α5 contributed to fibronectin adherence. DMSO arrested cells at G0/G1 (control: 55.0 ± 2.4% vs DMSO: 70.7 ± 2.5%) while simultaneously reducing α5 (24.2 ± 19% and α6 (14.3 ± 10.8%) expression as well as c-myc mRNA (7-fold), the latter shown by Northern blotting. Although the adhesion rate did not change after exposure to DMSO, α3 and α5 played a major role in laminin-1 and fibronectin adhesion, respectively. Migration towards laminin-1, which was clearly increased upon exposure to DMSO (control: 6 ± 2 cells vs DMSO: 64 ± 6 cells), was blocked by an antibody against α6. We conclude that the effects of DMSO on LISP-1 proliferation were accompanied by concurrent changes in the expression and function of integrins, consequently modulating adhesion/migration, and revealing a complex interplay between function/expression and the proliferative state of cells.