Ras oncogene directs expression of a differentially sialylated, functionally altered beta1 integrin.
Intense investigation has centered on understanding the regulation of integrin cell adhesion receptors. In the present study, we propose that variant N-glycosylation represents an important mechanism for regulation of beta1, but not beta3 or beta5 integrins. We find that expression of oncogenic ras in HD3 colonocytes causes increased alpha2-6 sialylation of beta1 integrins, whereas expression of dominant-negative ras induces decreased alpha2-6 sialylation, relative to cells with wild-type ras. In contrast, neither beta3 nor beta5 integrins are alpha2-6 sialylated, regardless of the state of ras activation. Results from RT-PCR analyses suggest that differential integrin sialylation is due to a ras-dependent alteration in the expression of ST6Gal I, the enzyme that adds alpha2-6-linked sialic acids. Cells that express differentially sialylated beta1 integrins exhibit altered adhesion to collagen I (a beta1 ligand), but not to vitronectin (a beta3 or beta5 ligand). Similarly, the enzymatic removal of cell surface sialic acids from control cells alters binding to collagen, but not to vitronectin. Finally, using a cell-free receptor/ligand-binding assay, we show that purified, desialylated alpha1beta1 integrins have diminished collagen-binding capability, providing strong evidence that sialic acids play a causal role in regulating beta1 integrin function.
Seales
Eric Clinton
EC
Department of Physiology and Biophysics, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
Jurado
Gustavo Adolfo
GA
Singhal
Anuj
A
Bellis
Susan Lynn
SL
D001483:Base Sequence; D002448:Cell Adhesion / Q000502:physiology; D002460:Cell Line; D002846:Chromatography, Affinity; D003106:Colon; D017931:DNA Primers; D004797:Enzyme-Linked Immunosorbent Assay; D005786:Gene Expression Regulation / Q000235:genetics*; D011905:Genes, ras / Q000235:genetics*; D005822:Genetic Vectors; D006801:Humans; D019012:Integrin beta1 / Q000235:genetics*; D007413:Intestinal Mucosa / Q000502:physiology*; D037102:Lectins; D009439:Neuraminidase; D043524:Peptide-N4-(N-acetyl-beta-glucosaminyl) Asparagine Amidase / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012794:Sialic Acids / Q000378:metabolism
D017931:DNA Primers; D019012:Integrin beta1; D037102:Lectins; D012794:Sialic Acids; D009439:Neuraminidase; D043524:Peptide-N4-(N-acetyl-beta-glucosaminyl) Asparagine Amidase