Antisense-mediated Specific Inhibition of PI 20 Protein Expression Prevents Gr to S-Phase Transition

A pentadecadeoxyribonucleotide (5-AAAGCCCCCCACCAC), com-plementary to a splice junction site of mRNA for human proliferation-associated nucleolar protein PI 20, inhibited expression of the PI 20 gene and the mitogen-induced proliferation of human lymphocytes. The inhibition of PI 20 gene expression and proliferation was concentration dependent and reached 90% at 200 MM, as measured by [3H]thymidine uptake and by densitometric scanning of Northern (mRNA) and Western (protein) blots of PI 20. Inhibition was not observed in cells treated with the correspondent nonsense oligomer. PI 20 antisense oligomer treatment prevented S-phase entry of mitogen-stimulated lymphocytes, as determined by flow cytometric analysis, but did not block G0-G1 transition assessed by morphological blast transformation and induction of I3H]uridine incorporation. Results of this study suggest that PI 20 expression may be required for the upregulation of nucleolar function necessary for cell proliferation.