Irving Lieberman

Nonidentity of Fetuin and Protein Growth (Flattening) Factor

Fetuin, a fetal calf serum glycoprotein, appeared to possess activity with cultured mammalian cells similar to that of a protein growth factor partially purified from adult bovine and human sera. Column chromatography, however, yielded highly purified but inactive fetuin. These results leave open questions regarding the role of this interesting and readily purified protein.

Synthesis of the plasma membrane of the liver cell

Abstract The steps involved in the synthesis of a plasma (surface) membrane are completely unknown. For the newly-synthesized protein constituents of the membrane, four possibilities have been considered. First, newly-formed proteins are added directly to the membrane; second, they mix with a soluble pool and are then incorporated into the membrane; third, they are assembled into complex units that are then built into the membrance; and fourth, they are incorporated into a precursor membrance that is later converted into a plasma membrane. The work presented here shows that proteins may be formed several hours before they are built into the liver plasma membrane. Thus, a direct incorporation of all new protein can be ruled out. It is not yet possible, however, to distinguish among the remaining three possibilities.

Effect of probucol on development of diabetes mellitus in BB rats

Insulin-dependent diabetes mellitus (IDDM) results from an inflammatory process leading to destruction of the insulin-producing beta cells of the pancreas. Genetically mediated autoimmune processes are considered the most likely explanation for IDDM in humans, while viral infections, toxic agents, nutritional alterations and stress are also considered possibilities. The precise mechanisms by which autoimmunity, infections, toxins or other agents produce beta cell damage are not known. Toxin-induced diabetes in animals can be prevented by antioxidant therapy, while an agent that inhibits hydroxyl radical formation, desferrioxamine, extends the survival time of free allotypic islets in nonobese diabetic mice. The BB/W rat develops IDDM secondary to a pervasive autoimmune defect. This well-studied animal model develops IDDM with a highly predictable frequency and timing. This study describes the effects of the potent antioxidant, probucol, on the development of diabetes in BB rats by introducing it into standard rat chow at a 1% concentration at the time of weaning, and continuing this feeding schedule through 160 days of life. Control rats from split litters received standard chow only. Diabetes developed in 86.2% of the control rats at a mean age of 90.4 days. Probucol administration was associated with a reduction to 62% and a delay in diabetes diagnosis to 99.6 days. These very preliminary results suggest that probucol may be altering the inflammatory process, resulting in beta cell destruction in these genetically diabetes-prone rats.

Nature of the deoxyribonucleic acid made by isolated liver nuclei

Abstract To better study the nature of the process of deoxyribonucleotide incorporation by isolated nuclei from regenerating rat liver, improvements have been made in the assay mixture. The changes include the addition of a Ca2+ binder, ethylene glycol-bis -(2- aminoethyl ether )-N,N′- tetraacetate (EGTA), a high molecular weight compound such as dextran, and a greater concentration of buffer. The EGTA and increased buffer depress the hydrolysis of DNA during incubation of the nuclei at 37 °C. Under the new conditions, the initial rate of DNA synthesis is raised by about 3-fold. Additional evidence is given to show that the formation of DNA in vitro is by the elongation of the chains that were growing in vivo. The growing points of both strands of DNA appear to be advanced by the isolated nuclei. The approximate rates of advancement in vivo and in vitro were 1400 and 200 deoxynucleotides per min per strand, respectively.

On the possibility that the prereplicative increase in ornithine decarboxylase activity are related to DNA synthesis in liver

Romeoa1 o f part o f fiae liver o f the rat is no~ fol lowed rmmediate]y by an increase in DNA repficafion in the remnant ¢e,lts. Rather there is a prereplieafive period o f abou t 1.~ hr. It is reasonable to expect that critical changes must take place in the liver during this time in order for the nucM to enter the S period. The c r i t i c s ehange~ m a y cukrr~nate i n t h e s y n t h e s i s o f p ro teSns thai are needed for the replicative process. A2terations in tZNA and protein synthesis appear to be obligalory events o f the p~ereplicafive period after partial hepa tec tomy I1 ,2 ] . No other lNer change is known to be requisite to DNA fornaa.ion. The dearth o f infornaation 5s not due to a failure to find alterations in regenera~ng hver. On the contrary, it is a reflection o f the large number o f changes tha~ have been described end of the lack of a suilable means for selecting for intensive s tudy -those changes that show promise of being related Io the later ~2¢ntheziz of DNA. T]~e availability o f two new procedures that induce hepalic DNA synthesis in unoperated rms now offers a means for at leas~ tentafiveay ass~_gning a causal re~ation~Mp be-tween a prereplicative change and ~he replicmi,on of DNA. DNA formation can be reduced in the liver of the intact animal with a honnone-contabnkng ~o]ution (TAGH solution) I3] and by shifting rats from a protein-f,ree to a pr,otein-contaiMng diet ;[.

Effect of inhibitors of protein synthesis on DNA formation in liver

]. A n y prexep!icative change that takes place after partial hepa tec tomy bu t fain to occur after bofl~, oF the o ther stimuli can be or,eluded as being essential for DNA ~ynthesis. The appearance ,of the name ,change in all thlee sys-t.ems, on the other ~hand, is consistenl wi th a relationship be tween the change and the hndnction o f DNA xep]icafion.

A DNA polymerase in liver nuclei whose activity rises with DNA synthesis after partial hepatectomy

Abstract Three inhibitors of protein synthesis, cycloheximide, sparsomycin, and pactamycin, depressed to similar extents the formation of protein and DNA in the livers of partially hepatectomized rats at all the levels of the antibiotics tested. Inhibition of DNA replication was not due to reductions in the activities of the kinases that convert thymidine to TTP or of ribonucleotide reductase.

Effect of FK 506 on spontaneous diabetes in BB rats.

Abstract Rat liver nuclei contain at least two DNA polymerases that can be separated by extracting the nuclei with 5% Brij 58. The loosely-bound activity increases little or not at all after partial hepatectomy and is insensitive to cytosine arabinoside triphosphate (araCTP). The tightly-bound enzyme activity rises along with DNA replication and is inhibited by araCTP.

Synthesis of DNA after partial hepatectomy without changes in the lipid and glycogen contents of the liver

From days 30–120 after birth, 59 BB rats were treated with water (n = 20) or FK 506 in intragastric doses of 1 mg · kg−1 · day−1 (n = 19) or 2 mg · kg−1 day−1 (n = 20). Diabetes developed in 75,15, and 0% of the 3 groups, respectively. Animals protected from diabetes by FK 506 had normal intraperitoneal glucose tolerance tests, virtual absence histopathologically of autoimmune insulitis, and normal pancreatic insulin content. Forty-five to 75 days after stopping FK 506, ∼75% of the rats that were diabetes free at 120 days remained so.

Transcriptional and translational control of the biphasic increase in ornithine decarboxylase activity in liver.

Abstract Partial hepatectomy is not immediately followed by a rise in liver DNA synthesis. Rather there is an initial preparative period (13 h in the rats used in these studies) during which many alterations in liver chemistry occur. To study the mechanisms that control hepatic DNA synthesis, it is essential to distinguish between the changes that are and are not requisite for the entry of the liver cell into the replicative period. This report shows that two prereplicative changes that have received a good deal of attention, the accumulation of neutral lipid ( Ludewig et al. , 1939 ) and the fall in glycogen ( Stone, 1935 ), may be blocked without preventing the subsequent synthesis of DNA.