Analysis of protein incorporation of radioactive isotopes in the Chinese hamster ovary cell cycle by electronic sorting and gel microelectrophoresis

P48: a novel nuclear protein possibly associated with aging and mortality

The synthesis ([35S]-incorporation) of stress proteins (sps, i.e., 24, 25, 70, 90 Mr) and of nuclear protein 48 (p48) was investigated in the heart and bone marrow cells of three groups of male Fischer 344 rats following administration of isoproterenol (IPR). Two groups of rats, young ad libitum (Y/AL-3 1/2 months) and old/AL (O/AL-28 months), had full access to rat chow; a third group of old diet restricted (O/DR-28 months) rats was maintained on a diet restricted intake of 40% of the Y/AL animals. Sp synthesis in the bone marrow (25, 70, 90 Mr) and heart (24, 70, 90 Mr) nuclei of O/AL was significantly reduced, as compared with Y/AL and O/DR rats, following their induction with IPR. A unique sp24 was expressed in heart following IPR dosing. A 1 mg/kg dose of IPR was lethal for O/AL, but not for Y/AL or O/DR animals. This lethal dose induced synthesis of p48 in heart and bone marrow nuclei of O/AL rats only. P48 existed in isoform states in bone marrow, and when a lethal dose of IPR was administered in this tissue, it was expressed in O/AL rats in a cell-cycle regulated pattern. Stress proteins and other non-sps were seen as cell cycle regulated following IPR administration. P48 in bone marrow and heart nuclei from O/AL rats showed an antigenic response identical to that of p48 in HL60 nuclei. The presence of p48 is correlated with mortality and with an ad libitum diet in old rats, since it is absent in old diet restricted animals; therefore, DR may impede the expression of p48 through a mechanism(s) that is undisclosed at this time.

The effect of aging and dietary restriction on the retinoylation of nuclear matrix proteins in rats

The labeling in vivo of young ad libitum (Y/AL) and old diet restricted (O/DR) rats with [3H]retinoic acid (RA) for 6 hours, and the exposure of electrophoretically separated nuclear matrix proteins from bone marrow tissue on film for 48 days revealed the presence of eleven retinoylated proteins. Dosing with RA (100 mg/kg body weight) for 96 hours and exposure to [3H]RA enhanced the levels of radioactive incorporation of several nuclear matrix proteins, including p51, and p55, similarly in Y/AL and O/DR rats. Dosing of old ad libitum (O/AL) rats with [3H]RA for 6 hours showed the incorporation of six proteins following 48 days of exposure on film. Long-term dosing of RA (96 hours) did not increase [3H]RA incorporation in these proteins, including p51 and p55, in O/AL rats. Increasing the level of RA by two-fold (200 mg/kg body weight) in Y/AL and O/DR rats elicited an increase in the incorporation levels of [3H]RA in five proteins. This dose response following increased levels of RA was not seen in the retinoylated proteins of O/AL animals. Analysis by the Western blotting technique showed p51 and p55 from rat bone marrow cells to have the same immunochemical determinates with proteins of identical molecular masses in HL60 cells. The levels of retinoylation of nuclear matrix proteins in O/DR animals, altered by age- and diet-dependent factors, suggests a condition that is more reminiscent of Y/AL than of O/AL animals.

Retinoic acid-induced stress protein synthesis in the mouse

We have previously demonstrated that stress proteins (SPs) are synthesized in tissues in which malformations are later observed following treatment with the developmental toxicant, retinoic acid (RA), on day 11 of gestation (GD 11). These proteins were not synthesized in tissues which did not present with malformations near partuition. The purpose of the present investigation was to determine if this correlation between early SP synthesis and later malformation was present at other times during gestation. CD-1 strain mice were dosed orally with corn oil or 100 mg/kg body weight RA on GD 10 or 13. Some of the mice in each group were given an intraperitoneal injection of 3H-leucine to label embryonic protein synthesis one hour after dosing with RA. These animals were sacrificed 1.5 hour later, and embryonic protein synthesis was determined by two-dimensional gel electrophoresis followed by autoradiography. Other animals in each group were sacrificed on day 17 of gestation, and fetuses were examined for the presence of malformations. Following treatment with RA on day 10 of gestation, malformations were observed in the forelimbs, the hindlimbs and the tail; heart defects were not observed. SPs of 20-25,000 and 90,000 relative molecular mass (Mr) were synthesized in the forelimb bud and tail; in addition, a second low molecular weight (20-25,000) and a 84,000 Mr SPs were synthesized in forelimb buds. No SPs were synthesized in the hindlimb bud or the heart. Following RA treatment on GD 13, cleft palate was observed in 58% of fetuses; no other malformations were found. Proteins of 34,000, 84,000 and 90,000 Mr were synthesized in craniofacial tissue; SPs were not observed in forelimb bud, hindlimb bud, heart or tail tissues at this time. Therefore, it appears that there may be a correlation between tissue-specific SP synthesis early in organogenesis and the presence of a malformation later in gestation.

The homology of a novel polypeptide with stress protein characteristics in embryonic mice brain and in the hypothalamus of caloric restricted rats as determined by ultramicro western blotting

A novel protein (p34) was observed in polyacrylamide gel fluorographs of gestation day 13 embryonic mouse brain following retinoic acid dosing of dams. Another p34 polypeptide with identical gel migratory characteristics was seen in the hypothalamus of old caloric restricted rats after "food deprivation stress". Western blotting, employing an ultramicro trans-blot cell developed in our laboratory, detected identical immunochemical determinants between these proteins, verifying their homology. Peptide mapping and Western blotting further validated the uniqueness of p34 compared with other stress proteins including heme oxygenase.

The temporal relationships of synthesis and phosphorylation in stress proteins 70 and 90 in aged caloric restricted rats exposed to bleomycin

A single intraperitoneal injection of the human therapeutic drug bleomycin (BL) was administered to three groups of male Fischer 344 rats at time 0, and the incorporation of [35S]methionine ("synthesis") and phosphorylation patterns of stress proteins (sps/hsps) from bone marrow cells were analyzed over time by two-dimensional electrophoresis and fluorography. Two groups of rats, young ad libitum (Y/AL--3 months) and old ad libitum (O/AL--28 months), had free access to rat chow, and a third group of old rats (O/CR--28 months) were maintained on a caloric restricted intake (60% of the AL diet). The administration of BL in Y/AL, O/AL and O/CR animals activated the 35S-labeling of sp 90 which reached a peak at 4 hours. Labeling of sp 90 was significantly greater in Y/AL compared to O/AL, and the incorporation pattern of O/CR was intermediate to Y/AL and O/AL animals. All labeling of sp 90 in each group had disappeared by 10 hours after BL administration. Stress protein 70x (inducible form) in these three animal groups displayed a similar pattern of 35S-incorporation, but the amount of labeling was less than that of sp 90. No labeling of sp 70x remained by 13 hours after BL administration. Phosphorylation ([32P] phosphate incorporation) of sp 90 reached a maximum level at 2 hours in all animals, and 32P-labeling in Y/AL was significantly increased over O/AL and O/CR with an intermediate level found in O/CR animals. The turnover rate (phosphorylation/dephosphorylation) of sp 90 induced by BL was significantly suppressed and temporarily extended in O/AL as compared with O/CR, which implied that CR not only increased incorporation of sp 90, but also enhanced a utilization of the phosphate pool very similar to that seen in Y/AL animals.

Comparative studies of synthesis, phosphorylation, DNA binding and proteolytic characteristics of a novel protein during phases of the mouse spleen cell cycle

1. Cultured mouse spleen cells were exposed to the mitogen Concanavalin A followed by isoproterenol, and nuclei were electronically sorted from seven partitions of the cell cycle. 2. Several nuclear proteins, including stress proteins, which were cell-cycle-stage specific, were elicited by isoproterenol as determined by micro-electrophoresis and fluorography. 3. Two novel S-phase proteins (X0 and X') demonstrated differing synthesis and phosphorylation patterns during the cell-cycle phases. 4. X' showed DNA binding characteristics and proteolytic properties (hydrolyzing X0 or beta-galactosidase); both proteins were cell-cycle regulated.

A nuclear protein associated with lethal heat shock of HL-60 cells

The responses to stress in living cells are well known. Thermal stress causes decreased protein synthesis as well as rapid induction of heat shock proteins (hsps), or alternately termed stress proteins (sps). The exposure of cultured promyelocytic leukemia cells (HL-60) to a 45 degrees C lethal heat shock for 1 h elicited synthesis and phosphorylation of a polypeptide M(r) 48,000 and pI 7.5 (p 48) as visualized by two-dimensional polyacrylamide gel ultra-microelectrophoresis. p 48, which was not observed at sublethal temperatures (39 and 41 degrees C), was synthesized during all phases of the cell cycle but was phosphorylated only in G0 + G1 and S-phases. The appearance of p 48 was marked by a concomitant and reciprocal reduction in hsps or sps 70 and 90. Distinct protease V8 fragment maps of p 48, hsps 70 and 90 in conjunction with immunochemical determination indicated vast differences in their primary structures. These facts suggest that p 48 was not formed from coalesced breakdown products of hsps 70 or 90. Western blotting showed that p 48 possessed the same immunochemical determinants as two other proteins with the same molecular mass but different isoelectric points. In an association assay, p 48 was shown to bind with actins and hsp 90 from HL-60 nuclei.

Target tissue specificity of retinoic acid-induced stress proteins and malformations in mice

Retinoic acid (RA) is teratogenic in rodents and also induces the synthesis of stress proteins in fetal mouse limb buds. To determine if the RA induction of stress proteins is target tissue specific, pregnant CD-1 mice were gavaged with 100 mg/kg RA on day 11 of gestation, and nuclei isolated from tissues susceptible to RA-induced malformations (target tissues) as well as nuclei isolated from nontarget tissues were examined for stress protein synthesis and malformations. Forelimb and hindlimb (target tissues), as well as heart and tail (nontarget tissues), were removed from embryos 2.5 hours after RA treatment (1.5 hr after [3H]leucine labeling). Cell nuclei were isolated, stained with a DNA specific fluorochrome, propidium iodide, and sorted from the G0 + G1 and G2 + M phases of the cell cycle. Forelimb and hindlimb target tissues showed the synthesis in these embryonic nuclear proteins of an 84,000 relative molecular mass (Mr) protein and a 90,000 Mr protein following RA treatment. Two 20,000-25,000 Mr stress proteins were also labeled both in forelimb and hindlimb. Forelimb and hindlimb from untreated dams showed no stress protein labeling. Neither heart nor tail, nontarget tissues, showed any stress protein labeling following RA treatment. Classical teratological evaluation of embryos treated on GD 11 and sacrificed on GD 17 showed that 100% of the fetuses had forelimb and/or hindlimb malformations, while no malformations were observed in either the heart or tail. Based on the correlation of teratological anomalies with the identification of stress proteins in target tissue only, we postulate that stress proteins may be involved in the teratogenic process. Further work is necessary to establish whether a causal relationship exists.

Comparative immunochemical and structural similarities of five stress proteins from various tissue types

1. Incorporation of radioactive phosphate or leucine by stress proteins from rodent lymphoma, submaxillary and liver nuclei were observed in two-dimensional gels following chemical and environmental stress. 2. The stress proteins were isolated from second-dimension gels and their similarities compared. Mol. wt determinations, immunochemical blotting and protease V8 peptide mapping confirmed the identical nature of the stress proteins possessing identical Mr, but from diverse tissue types. 3. These data imply that highly similar stress proteins exist in diverse tissues, are conserved during evolution, and possess some elemental and essential function.

Retinoic acid induction of stress proteins in fetal mouse limb buds

Retinoic acid (RA) is teratogenic in rodent embryos. Several teratogens have been shown to induce the synthesis of a subset of heat shock proteins (stress proteins) in Drosophila. To determine if RA induces the synthesis of these proteins in rodent embryos, pregnant ICR mice were dosed with 100 mg/kg RA on Day 11 of gestation. Forelimb buds were removed from embryos 2.5 hr post-RA-treatment and nuclei were isolated, stained, and sorted from stages of the cell cycle. Nuclear proteins were extracted and analyzed by two-dimensional polyacrylamide gel electrophoresis. Nuclear proteins with molecular weights of approximately 84 and 25 kDa were synthesized in embryos in the G0 + G1 phase after pregnant dams were treated with RA. Isoelectric points, molecular weights, immunochemical blotting, and polypeptide mapping demonstrated that these proteins are indistinguishable from stress proteins isolated under a variety of conditions from rat submaxillary glands and mouse lymphoma cells. These results suggest that treatment with RA induces the synthesis of a subset of stress proteins; the role of these proteins in the teratogenic effects of RA is not known.