ABSTRACT
Three carbohydrate-binding proteins with relative molecular masses of 35, 67, and 70 kDa (CBP35, CBP67, and CBP70) have been described to be present in nuclei of mammalian cells, where they are associated with nuclear ribonucleoprotein (RNP) complexes. CBP35 consists of two domains, an N-terminal domain that is homologous to certain regions of proteins of the heterogeneous nuclear RNP complex, and a C-terminal domain that is homologous to beta-galactoside-specific lectins. CBP35 has been proposed, like the glucose-specific lectin, CBP67, to guide RNP complexes through the nuclear pore. Here, we show that exposition of mature rats (6-8 months old) to stress results in binding of nuclear CBP35 to CBP67 which is retained on a column containing immobilized glucose. In contrast to mature animals, nuclear extracts from the livers of old rats (22-24 months old) displayed no detectable stress response.
Subject(s)
Aging/physiology , Antigens, Differentiation/physiology , Arousal/physiology , Carrier Proteins/physiology , Receptors, Cell Surface , Animals , Cell Nucleus/physiology , Galectin 3 , Liver/cytology , Male , Molecular Weight , Rats , Rats, WistarABSTRACT
Previous studies have demonstrated the existence of nuclear carbohydrate binding proteins in a variety of mammalian cells with molecular masses of 35,000, 67,000, and 70,000 (CBP35, CBP67, and CBP70), which are associated with nuclear ribonucleoprotein (RNP) complexes. CBP35 consists of two domains, an amino-terminal portion that is homologous to certain regions of proteins of the heterogeneous nuclear RNP complex, and a carboxyl-terminal portion homologous to beta-galactoside-specific lectins. CBP35 it has been proposed, like the glucose-specific lectin, CBP67, to guide RNP complexes through the nuclear pore. Here we show that the exposure of mature rats to stress induces an increase in nuclear CBP35 bound to CBP67 and retained on immobilized glucose. Nuclear extracts from the livers of old rats displayed no detectable stress response. This CBP35.CBP67 association detected in rat liver is considered with respect to the CBP35.CBP70 association recently observed in HL60 cell nuclear extracts.
Subject(s)
Aging/metabolism , Antigens, Differentiation/metabolism , Lectins/metabolism , Nuclear Proteins/metabolism , Ribonucleoproteins/metabolism , Stress, Physiological/metabolism , Animals , Galectin 3 , Humans , Male , Molecular Weight , Rats , Rats, WistarABSTRACT
A study of the antiviral 2',5'-oligoadenylate (2-5A) system in different tissues of rats of different age (newborn: 1-day old; young adult: 2-3 month old; middle-aged adult: 12-month old; and old: 32-33-month old) revealed that the activities of the 2-5A metabolic enzymes alter during aging and development. We demonstrate that soluble 2-5A synthase (2-5OAS) activity strongly increases after birth, reaching maximal levels in young adult and middle-aged adult animals, and then significantly decreases with age. In contrast, the activity of 2',3'-exoribonuclease which inactivates 2-5A increases by three-fold with age. The decrease in 2-5OAS activity and increase in 2-5A nuclease activity were found to result in a decrease in the cellular 2-5A content with age. The 2-5A-dependent ribonuclease (RNase L), which degrades viral RNA, also changes age-dependently. The amount and activity of this enzyme were determined in cross-linking experiments, in nitrocellulose binding assays; and in the ribosomal RNA cleavage assay. The livers of old rats display a 5-6-fold decrease in RNase L activity compared to the adult animal groups, while the amount of the enzyme does not change significantly during aging, with the exception of a drop by 30% in the nuclear matrix fraction. We conclude that the antiviral activity of the 2-5A system is impaired in old cells with the consequence that virus production cannot be efficiently suppressed.
