Regulation of ppp(A2'p)nA-dependent RNase levels during interferon treatment and cell differentiation

Abstract

The intracellular effector oligonucleotides ppp(A2′p)_nA (n= 2−≥4) regulate the breakdown of RNA by activating ppp(A2′p)_nA‐dependent RNase. Cellular levels of this RNase were demonstrated to be regulated during differentiation of murine embryonal carcinoma cells. An induction of this RNase by interferon was demonstrated in each of three differentiated cell types (F9 clone 9, PYS, and PSA 5E) by analyzing rRNA breakdown following the introduction of ppp(A2′p)_nA into the intact cells. In contrast, in three undifferentiated embryonal carcinoma cell lines (F9, PC13 clone 5, and Nulli 2A) there was little if any ppp(A2′p)_nA‐dependent RNase either with or without interferon pretreatment. These results were confirmed by affinity labeling of the RNase in cell‐free systems. Addition of the proteinase inhibitor, leupeptin, to the cell lysis buffer was necessary to stabilize the RNase against cleavage to discrete breakdown products. Moreover, during differentiation of PC13 clone 5 cells by retinoic acid and N⁶,O^2′‐dibutyryl‐adenosine 3′,5′‐monophosphate there was a gradual induction of ppp(A2′p)_nA‐dependent RNase. The expression of this RNase is, therefore, greatly enhanced during cell differentiation. In addition, the double‐stranded‐RNA‐dependent protein kinase was investigated and was found to be interferon‐inducible in all of the cell lines regardless of the state of cell differentiation.