Early hypomethylation of 2'-O-ribose moieties in hepatocyte cytoplasmic ribosomal RNA underlies the protein synthetic defect produced by CCl4.

Abstract

Abstract. Carbon tetrachloride (CCL) treatment of rats produces an early defect in methylation of hepatocyte ribosomal RNA, which occurs concurrently with a defect in the protein synthetic capacity of isolated ribosomes. The CCh-induced methylation defect is specific for the 2'-O-ribose position, and a corresponding proportional increase in mTG base methylation occurs in vivo. Undermethylated ribosomal subunits (rRNA) from CCl4-treated preparations can be methylated in vitro to a much greater extent than those from control preparations, and in vitro methylation restores their functional capacity. In vitro methylation of treated ribosomal subunits (which restores functional capacity) occurs at 2'-O-ribose positions (largely G residues). In contrast, in vitro methylation of control ribosomal subunits (which does not affect functional activity) represents base methylation as mTG, sites which are apparently methylated in treated preparations in vivo. Methylation/demethylation of 2'-O-ribose sites in rRNA exposed on the surface of cytoplasmic ribosomal subunits may represent an important cellular mechanism for controlling protein synthesis in quiescent hepatocytes, and it appears that CCL disrupts protein synthesis by inhibiting this 2'-O-ribose methylation.C ARBON tetrachloride (CCI4) ~ has long served as a model compound for study of hepatic injury (9,36,37,39,46). Like many other agents, CCL is metabolized via cytochrome P-450 (25, 39) to yield a free radical (34,44,45,50,51), which may mediate subsequent damage. A number of subcellular processes/compartments are affected (including lipid peroxidation and Ca ++ influx), and a well-described morphologic sequence ensues (39, 46), although the basic mechanisms underlying the cellular injury are not clear (3, 40 53).Early studies established the endoplasmic reticulum (ER) as the site of the first significant cellular changes (38,39,46). Altered ER structure occurs by 30 rain after oral CC14 administration (46, 47) and consists chiefly of a marked loss of ribosomes from rough ER ("degranulation') and a disaggregation of polysomes. Slightly later, other morphological changes in ER (such as tubular aggregates) can be detected.The major early functional defect involves protein synthesis (47); alterations in protein synthesis are specific for hepatocytes and parallel morphological alterations within the lobules (24). The nature of the protein synthetic defect is not

Ginseng essence, a medicinal and edible herbal formulation, ameliorates carbon tetrachloride-induced oxidative stress and liver injury in rats

“…Furthermore, supplementation with GE induced serum albumin levels in the CCl 4  + MGE and CCl 4  + HGE groups that were close to those of the CCl 4  + silymarin group (26.6 ± 2.4 g/L and 26.7 ± 3.1 g/L vs. 27.1 ± 2.2 g/L, respectively) and significantly higher than those of the CCl 4 group ( p  < 0.05). Previous studies have found that CCl 4 decreased serum total protein and albumin in carps [35], inhibited protein synthesis, and reduced ribosomal RNA methylation [36]. Administration of CCl 4 could inhibit the synthesis of albumin and other proteins in the liver, and result in significantly lower serum albumin level [37].…”

Alterations in nuclear scaffold constituents during carbon tetrachloride–induced liver regeneration

“…uitro translations were performed using a nucleasetreated rabbit reticulocyte lysate system (Bethesda Research Laboratories, Gaithersburg, MD), with 35s-methionine (New England Nuclear) and 1.2 pg poly(A)+ RNA. Previous experimentation (26) showed that mRNA was rate limiting under these conditions. Total incorporation was measured as described (26).…”

“…Previous experimentation (26) showed that mRNA was rate limiting under these conditions. Total incorporation was measured as described (26). Immunoprecipitations with solubilized translation products used a monoclonal antibody (G18) that recognized lamins A/C on immunoblots and anti-mouse-IgM- which is the reverse complement of nucleotide region 1210-1233 from human lamin A and C (16,29).…”

The hepatocyte protein synthesis defect induced by galactosamine involves hypomethylation of ribosomal RNA

“…), absorbance detector, fraction collector, radial compressed C,, u-bondapak reverse-phase column, a flow rate of 1 mlimin and a linear gradient of 0% to 30% acetonitrile from 0 to 40 min. Some analytical separations were as previously reported (4). These conditions were chosen to yield good separations of the major (and minor) methylated nucleosides; 0.3 ml fractions were collected and counted.…”

“…Perhaps the earliest metabolic defect in CC14-induced injury is a profound depression of PS (1)(2)(3). Recently, we found that CC1, injury is associated with an early hypomethylation of ribosomal RNA (rRNA) (4). For a variety of reasons, this methylation defect seems to be cyto-plasmic in nature and is specific for 2'-O-ribose moieties on purine nucleotides.…”