Downregulation of Transcription Factor Sp1 Suppresses Malignant Properties of A549 Human Lung Cancer Cell Line with Decreased beta 4-Galactosylation of Highly Branched N-Glycans

摘要

Dramatic changes in the glycan structures of cell surface proteins have been observed upon malignant transformation of cells as induced by the altered expression levels of glycosyltransferases. Such changes are closely associated with the malignant properties of cancer cells. Transcription factor Spl regulates the gene expression of various molecules including glycosyltransferases. Herein, we investigated whether or not Spl-downregulation affects to N-glycosylation of glycoproteins and malignant properties of A549 human lung cancer cell line. We established a stable clone whose Spl-expression level was reduced to 50% of a control clone by RNA interference. Lectin blotting revealed that the beta 4-galactosylation of highly branched N-glycans decreases mainly in cell adhesion molecule, E-cadherin. The analysis of underlying mechanism for decreased beta 4-galactosylation of N-glycans showed that the gene expression level of beta 4-galactosyltransferase (beta 4GalT) 1 decreases dramatically by downregulation of Spl without changes in those of beta 4GalT2 and N-acetylglu-cosaminyltransferase V. Mutations in the Spl-binding sites of the beta 4GalT1 gene promoter showed that the promoter activity decreases significantly, indicating that the gene expression is regulated by Spl. These results indicate that the beta 4-galactosylation of highly branched N-glycans decreases by downregulation of Spl through the reduced expression of the beta 4GalT1 gene. Furthermore, the Spl-downregulated cells showed the suppression of the anchorage-independent growth in soft agar and migratory activity when compared to the control cells. The present study demonstrates that downregulation of Spl suppresses the malignant properties of A549 cells through the decreased beta 4-galactosylation of highly branched N-glycans.