The Novel Structural Motif GlnGln in the Integrin Cytoplasmic Domain Regulates Cell Proliferation

doi:10.1074/jbc.270.42.24666

The Novel Structural Motif GlnGln in the Integrin Cytoplasmic Domain Regulates Cell Proliferation (*)

From the Department of Pathology, Yale University School of Medicine, New Haven, Connecticut 06520

^§ To whom correspondence should be addressed:
Dept. of Pathology, Yale University School of Medicine, P. O. Box 208023, 310 Cedar St., New Haven, CT 06520.
Tel.: 203-737-1454; languino{at}biomed.med.yale.edu.

Abstract

Alternative splicing of the integrin β subunit mRNA generates a variant form, β, with a unique cytoplasmic domain that differs from β for a 48-amino acid COOH-terminal sequence. The potential role of this unique sequence in modulating cellular functions was investigated using Chinese hamster ovary (CHO) cells transiently transfected with cDNAs coding for human integrin β or β subunits or mutants containing truncated forms of the β cytoplasmic domain. A differential effect of β and β on cell proliferation was observed. Expression of wild type β was associated with a 6-10-fold increase in cell proliferation in response to serum, as measured by [H]thymidine incorporation. In contrast, only a 2-fold increase in cell proliferation was observed in transfectants expressing comparable levels of β. Cells expressing the β mutant truncated at Leu and lacking the last 31 amino acids of the cytoplasmic domain showed a 12-fold proliferation increase in response to serum. However, three β deletion mutants, lacking the COOH-terminal 23, 13, and 8 amino acids, which all contained residues Gln-Gln of the variant cytoplasmic domain responded to serum stimulation with a 2-fold increase in [H]thymidine uptake. The effect of β expression on cell proliferation was not associated with changes in exposure of integrin functional epitopes, as judged by the finding that CHO transfectants expressing β, full-length or deletion mutants, or β equally adhered to a functionally inhibitory monoclonal antibody against human β integrin. Expression of β inversely correlated with the mitogenic potential of vascular cells. Absent on growing cultured endothelial cells, surface expression of β was induced in growth-arrested, tumor necrosis factor-stimulated endothelial cells. These findings suggest that integrin alternative splicing may provide an accessory mechanism to modulate cell type-specific growth regulatory pathways during vascular cell injury in vivo.

Footnotes

↵* This work was supported in part by American Cancer Society Grant IRG-IN 31-36 (to L. R. L.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
¹ The abbreviations used are:

CHO

Chinese hamster ovary

HUVEC

human umbilical vein endothelial cell(s)

DMEM

Dulbecco's modified Eagle's medium

FCS

fetal calf serum

TNF

tumor necrosis factor

nt

nucleotide(s)

FACS

fluorescence-activated cell sorting

PAGE

polyacrylamide gel electrophoresis.
²M. Fornaro, G. Tallini, and L. R. Languino, unpublished observations.
- Received July 5, 1995.
- Revision received August 8, 1995.