DYNAMICS OF THE INTERNALIZATION OF PHOSPHODIESTER OLIGODEOXYNUCLEOTIDES IN HL-60 CELLS

We have examined the cellular association and internalization of phosp hodiester (PO) oligodeoxynucleotides (oligos) with HL60 cells. At 4-de grees-C, a 15-mer PO homopolymer of thymidine (FOdT15) exhibits appare nt saturation binding (K(m) = 22 +/- 1 nM) that is competitive with th e binding of phosphorothioate (PS) oligos. The value of K(c) for SdC28 , a PS 28-mer homopolymer of cytidine, is 5 +/- 2 nM. SdC28 was used t o strip cell surface fluorescence: Internalized fluorescence accumulat ed in a (concentration)(time)-dependent fashion, consistent with a pin ocytotic mechanism. PS, and to a lesser extent, PO oligos inhibited th e rate of internalization of fluorescent albumin, also a marker of pin ocytosis. This was correlated with direct in vitro inhibition of prote in kinase C (PKC) beta1 by the PS and PO oligos. Furthermore, other PK C inhibitors (H7, staurosporine, DMSO, PKC pseudosubstrate polypeptide ) also inhibited intracellular accumulation of pinocytosed materials, perhaps by stimulating the exocytosis rate. In HL60 cells, the pinocyt otic internalization of charged oligos appears to be dependent on inta ct PKC kinase activity, which is inhibited in vitro by PS and PO oligo s.