Endogenous oligonucleotides of human milk and their possible biological function

Oligonucleotides (ON)4 to 60 nucleotides in length were isolated by ion-exc hange chromatography on a column with Fractogel TSK DEAE-650 (M) from human milk which was hydrolyzed with proteinase K. ON from 60 to 16 nucleotides were degraded by RNase A but were resistant to DNase I, and, thus, they wer e ribooligonucleotides. In the presence of [gamma-P-32]ATP, ON and heparin inhibited the phosphorylation of 38- and 20-kD milk proteins and failed to affect the phosphorylation of a 76-kD protein. Human milk is believed to co ntain polyanion-dependent and polyanion-independent protein kinases. The in fluence of the ON on the activity of the cytotoxic fraction of human milk a lpha-lactalbumin towards human mammary gland carcinoma MCF-7 cells was stud ied. The ON inhibited the cytostatic and cytotoxic effects of alpha-lactalb umin. Synthetic oligonucleotides and heparin had similar effects. The endog enous ON are suggested to be involved in the regulation of cytotoxic activi ty of human milk.