Isolation and identification of basement membrane collagen purified from dissociated rabbit renal tubules

In the present study collagens were isolated and identified from morphologically pure basement membrane material. Preparations of rabbit renal tubules devoid of contaminating glomeruli were obtained by homogenization and sieving of kidney cortices. Cellular material was removed by sequential detergent solubilization and the purity of the resultant tubular basement membrane was verified by transmission electron microscopy. The collagenous component of this ultrastructurally pure starting material was isolated by limited pepsinization and salt precipitation. Polyacrylamide gel electrophoresis of this collagen under nonreducing conditions resulted in four major bands: 300,000 (γ component), 100,000 (100K), 80,000 (80K), and 50,000 (50K). Individual collagen fractions of each of these molecular weights were then isolated from preparative polyacrylamide gels. Identification by their electrophoretic properties and cyanogen bromide peptide patterns leads us to believe that: (i) the 100K is composed of the C chain of type IV collagen; (ii) the 80K and 50K are derived from the genetically distinct D chain of type IV collagen; (iii) the γ component is structurally related to the 100K, 80K, and 50K; and (iv) A and B chains (type V collagen) are not major components of rabbit renal tubular basement membranes.     

The Epstein-Barr Virus Protein BRLF1 Activates S Phase Entry through E2F1 Induction

The Epstein-Barr Virus (EBV) immediate-early protein BRLF1 is one of two transactivators which mediate the switch from latent to lytic replication in EBV-infected cells. DNA viruses often modulate the function of critical cell cycle proteins to maximize the efficiency of virus replication. Here we have examined the effect of BRLF1 on cell cycle progression. A replication-deficient adenovirus expressing BRLF1 (AdBRLF1) was used to infect normal human fibroblasts and various epithelial cell lines. BRLF1 expression induced S phase entry in contact-inhibited fibroblasts and in the human osteosarcoma cell line U-2 OS. AdBRLF1 infection produced a dramatic increase in the level of E2F1 but not E2F4. In contrast, the levels of Rb, p107, and p130 were decreased in AdBRLF1-infected cells. Electrophoretic mobility shift assays confirmed an increased level of free E2F1 in the AdBRLF1-infected human fibroblasts. Consistent with the previously described effect of E2F1, AdBRLF1-infected fibroblasts had increased levels of p53 and p21 and died by apoptosis. BRLF1-induced activation of E2F1 may be required for efficient EBV lytic replication, since at least one critical viral replication gene (the viral DNA polymerase) is activated by E2F (C. Liu, N. D. Sista, and J. S. Pagano, J. Virol. 70:2545-2555, 1996).     

Densimetric determination of carbohydrate content in glycoproteins.

Carbohydrates play important roles in activity, stability and pharmacokinetics of glycoproteins and the degree of glycosylation varies with proteins. In this communication, a simple method of determining the carbohydrate content was developed, which consists of measuring the density increments of a glycoprotein and its non-glycosylated counterpart, and then dividing the difference between the two values by the density increment of carbohydrates. The density increment was relatively constant for various sugars except for sialic acid, and hence assumed to be 0.39. Thus, we obtained carbohydrate contents of 38, 28, 8 and 7% for Chinese hamster ovary cell-expressed erythropoietin (EPO), stem cell factor (SCF), granulocyte-colony-stimulating factor (G-CSF), and platelet-derived growth factor (PDGF), respectively. These values are in close agreement with those determined by other methods.     

Two regulatory isozymes of glutamine synthetase from Bacillus caldolyticus, an extreme thermophile.

Two glutamine synthetases (EC 6.3.1.2) have been purified to homogeneity from $\text{B. caldolyticus}$ strain YTP, grown at 70° on a minimal, defined medium. The enzymes are virtually identical in size and molecular weight (12 sub-units of MW 50,000), but differ in their isoelectric points, electrophoretic mobility, net charge, inherent thermal stability, affinity for substrates, and activity responses to metal ions and pH. Of primary interest is the observation that the more acidic form (pI = 5.2), E_I, is strongly feedback-regulated by certain amino acids derived from glutamine (Gly, L-Ala, L- and D-ser) but not by L-Glu or AMP, whereas the less acidic form (pI = 5.5), E_II, is inhibited most strongly by L-Gln and AMP, but not by the above amino acids. Both enzymes are inhibited strongly by ADP, CTP, NAD, glucosamine-6-P, less strongly by nucleotide diphosphates and L-Trp, and are activated by nucleotide monophosphates other than AMP. These results suggest that overall regulation of glutamine synthetase by the full spectrum of end product metabolites derived from L-Gln is accomplished by regulatory isozymes in this extremely thermophilic organism.     

Coexisting angiomyolipoma and renal cell carcinoma in a kidney of an elderly woman: case report and review of the literature

Angiomyolipoma is a well described but relatively uncommon benign renal neoplasm composed of varying admixtures of mature adipose tissue, smooth muscle, and thick-walled blood vessels. The incidence of angiomyolipoma is about 0.3% overall. It frequently occurs in patients with tuberous sclerosis. Even more uncommon is the simultaneous occurrence of angiomyolipoma and renal cell cancer in the same kidney in a patient without tuberous sclerosis.