2'-O-(2-METHOXY)ETHYL-MODIFIED ANTI-INTERCELLULAR ADHESION MOLECULE-1(ICAM-1) OLIGONUCLEOTIDES SELECTIVELY INCREASE THE ICAM-1 MESSENGER-RNA LEVEL AND INHIBIT FORMATION OF THE ICAM-1 TRANSLATION INITIATION COMPLEX IN HUMAN UMBILICAL VEIN ENDOTHELIAL-CELLS

Little is known about the mechanisms that account for inhibition of ge ne expression by antisense oligonucleotides at the level of molecular cell biology, For this purpose, we have selected potent 2'-O-(a-methox y) ethyl antisense oligonucleotides (IC50 = 2 and 6 nM) that target th e 5' cap region of the human intercellular adhesion molecule 1 (ICAM-1 ) transcript to determine their effects upon individual processes of m RNA metabolism in HUVECs. Given the functions of the 5' cap structure throughout mRNA metabolism, antisense oligonucleotides that target the 5' cap region of a target transcript have the potential to modulate o ne or more metabolic stages of the message inside the cell. In this st udy we found that inhibition of protein expression by these RNase H in dependent antisense oligonucleotides was not due to effects on splicin g or transport of the ICAM-1 transcript, but due instead to selective interference with the formation of the 80 S translation initiation com plex. Interestingly, these antisense oligonucleotides also caused an i ncrease in ICAM-1 mRNA abundance in the cytoplasm. These results imply that ICAM-1 mRNA turnover is coupled in part to translation.