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Biomedical subjects

M Spector

Publications and source records attributed to M Spector.

At least 55 records · Page 3Linked to original sources
PubMed1981

Stimulation of Ca2+ uptake and protein phosphorylation in tumor cells by fibronectin.

Suspensions derived from attached HeLa cells transported 45Ca2+ considerably faster than those derived from spinner cultures grown in liquid medium. Incubation of spinner cells with fibronectin or cold-insoluble globulin in the presence of 5% calf serum at 37 degrees C for 1 to 2 h greatly increased the rate of Ca2+ flux into the cells. Suspensions of cells transformed by Rous sarcoma virus transported Ca2+ much more slowly than cell suspensions of the parent strain of normal rat kidney. Incubation of the transformed cells or Ehrlich ascites tumor cells with fibronectin increased the rate of Ca2+ uptake, while no effect was seen on Ca2+ transport by this treatment of normal kidney cells grown in tissue cultures. A 45,500-dalton protein was found to interact firmly with Ca2+ that entered into attached HeLa cells or fibronectin-treated spinner cells. This Ca2+-associated protein was detected by lithium dodecyl sulfate gel electrophoresis at 0 degrees C after 30 s of exposure to radioactive Ca2+. In tumor cells without fibronectin treatment, the radioactive band was not seen under the same conditions, even after 10 min incubation with 45Ca2+. In fibronectin-treated tumor cells, addition of Ca2+ to buffered solutions resulted in increased phosphorylation of a protein in the 45,000-dalton region. The phosphorylated protein band which appears to be associated with the cytoskeleton can be resolved by isoelectric focusing into four polypeptide chains. The relation of these observations to the cascade of protein kinases involved in the phosphorylation of the beta-subunit of the (Na+-K+)-ATPase is discussed.

Animals↗
PubMed1981

A mouse homolog to the avian sarcoma virus src protein is a member of a protein kinase cascade.

Recent work has identified a cascade of membrane bound protein kinases in Ehrlich ascites tumor cells. These enzymes, designated PKL, PKS and PKM, are present in both Ehrlich tumor and mouse brain, but the cascade is active only in the tumor tissue. We have now purified a fourth protein kinase, PKF, that is also associated with this cascade. Protein kinase F prosphorylates PKL and is phosphorylated by PKS. The position of this kinase in the cascade is as follows, where the arrows denote phosphorylation: [Formula: see text] The phosphorylation by PKF, like phosphorylation by the other kinases, is at a tyrosine residue and causes the substrate kinase (PKL) to become active. The role of the tyrosine phosphorylation in activating these kinases is described in detail elsewhere. One result of activation of the cascade is the phosphorylation of the beta subunit of the Na+K+-ATPase, which causes inefficient Na+ pumping and is at last in part responsible for the high aerobic glycolysis of Ehrlich ascites tumor cells. By several criteria protein kinase F from Ehrlich cells is homologous to the src gene product (pp60src) from avian sarcoma viruses. Antiserum raised against PKF and sera from rabbits bearing rous sarcoma virus (RSV)-induced tumors quantitatively precipitate the same 60 kd phosphoprotein from cell lysates of three different RSV-transformed cell lines. Both proteins phosphorylate PKL and a 130 kd cytoskeletal protein (vinculin). The tryptic maps of these proteins are closely similar. Both proteins bind specifically to PKL covalently coupled to Sepharose. We used this latter observation to facilitate the purification of pp60 src from RSV-transformed cells.

Amino Acids↗
PubMed1981

Human stones.

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Adolescent↗
PubMed1981

Screening of solid and porous materials for pacemaker electrodes.

Several different materials, including one which was porous, were studied to assess their properties as pacemaker electrode tips. Leads were implanted in sheep for periods up to one year. Electrical measurements were made during the implant period and histopathological examination performed after sacrifice. Although titanium vapor-deposited carbon, and silver did not lower the chronic stimulation threshold below that of platinum, their electrical characteristics were within generally acceptable limits. Zinc evoked a severe tissue reactions and a high threshold. Porous titanium alloy electrodes demonstrated reduced dislodgement, more frequent attachment and a lower sensing impedance than other electrodes.

Alloys↗
PubMed1981

Radionuclide bone imaging of femoral prostheses with porous coatings.

Radionuclide bone imaging can be of value in assessing the osseous changes around porous-coated femoral prostheses. Scintimetry appears to be a promising method for determining if radiodensities seen in radiographs of long-term prostheses are indicative of accelerated bone turnover or represent stable osseous structures. In dogs, the periosteal reaction which often occurs within two months of joint surgery masks endosteal-intramedullary osseous changes, including bone ingrowth into the porous coating.

Animals↗
PubMed1981

Developmental aspects of calcium oxalate tubular deposits and calculi induced in rat kidneys.

We employed an experimental hyperoxaluric protocol involving the administration of 1 per cent ethylene glycol drinking water to rats to determine (i) the location and mechanism of retention of renal tubular calcium oxalate crystals, and (ii) how this tubular deposition is modified by magnesium deficiency and contributes to stone formation. Calcium oxalate monohydrate deposition was found predominantly within the lumina of proximal tubules, and was markedly accelerated by magnesium deficiency. Sheet- and strandlike mucoid appearing material attached the crystals to the luminal surface of the renal tubules. The structure of stones found in the renal pelvis suggested that tubular deposits aggregate to form the nidus of the calculus.

Animals↗
PubMed1980

Phosphorylation of the beta subunit of Na+K+-ATPase in Ehrlich ascites tumor by a membrane-bound protein kinase.

We have shown previously that proteoliposomes reconstituted with purified Na+K+-ATPase from Ehrlich ascites tumor cells, transport Na+ with low efficiency (Spector, M., O'Neal, S. and Racker, E. (1980) J. Biol. Chem., 255, 5504-5507). We now present evidence that this low efficiency (expressed in the ratio of Na+-transported/ATP-hydrolyzed) is caused by the phosphorylation of the beta subunit of the Na+K+-ATPase by an endogenous protein kinase. On addition of [gamma-32P]ATP, crude tumor plasma membrane preparations phosphorylated the beta subunit of the ATPase, whereas crude mouse brain plasma membranes did not. However, solubilized Na+K+-ATPase from either tumor or brain wre phosphorylated by purified protein kinase from the tumor plasma membrane and dephosphorylated by a phosphatase. In both cases, the phosphorylated enzyme was inefficient; the dephosphorylated enzyme was efficient after reconstitution into liposomes. During isolation of the Na+K+-ATPase from Ehrlich ascites tumor or mouse brain, an endogenous protease partially cleaved from the beta subunit a polypeptide of 29,000 daltons that contained the phosphorylation site. The proteolytic cleavage of the beta subunit was partially inhibited by phenylmethylsulfonyl fluoride and the major site of phosphorylation was then seen in the 53,000-dalton beta subunit of the enzyme. The isolated 29,000-dalton polypeptide from mouse brain ATPase was phosphorylated by tumor protein kinase with a stoichiometry of 1 mol of phosphate/mol of protein. When this 29,000-dalton polypeptide from mouse brain was incorporated into the tumor Na+K+-ATPase after mild proteolytic digestion, a marked increase in efficiency was observed after reconstitution of the Na+ pump.

Animals↗
PubMed1980

Reconstitution of the Na+K+ pump of Ehrlich ascites tumor and enhancement of efficiency by quercetin.

Plasma membranes from Ehrlich ascites tumor cells were solubilized by octylglucoside in the presence of phospholipids. The Na+K+-ATPase was purified from this extract by adsorption and elution from thio-Seph-arose 4B. The enzyme (specific activity, 7 mumoles of ATP hydrolyzed min-1 mg of protein -1) was reconstituted into liposomes by the octyglucoside dilution procedure. An ATP-dependent Na+ influx with low efficiency was observed. On addition of appropriate amounts of quercetin, the Na+ flux/ATP hydrolysis ratio was increased from 0.4 to 1.4.

Animals↗
PubMed1980

Hemopoiesis in demineralized bone allografts.

Demineralized allogeneic bone matrix (DBM), implanted in muscle, induces the formation of an ossicle within which histologically recognizable hemopoietic tissue develops. Analyses of rabbit ossicle marrow in a methylcellulose culture system demonstrated the presence of committed hemopoietic precursors; colony-forming units in culture (CFUC), erythroid colony-forming units (CFUE) and erythroid burst-forming units (BFUE) by six weeks post-implantation. The time courses of colony and burst formation by progenitor cells of ossicle and femoral marrow were similar. Induction of hemolytic anemia by phenylhydrazine hydrochloride at six weeks post-DBM implantation showed that the ossicle marrow was responsive to systemic erythropoietic stimuli. The DBM implant may provide a unique model for studying the development of hemopoietic microenvironments within bone.

Animals↗
PubMed1979

Characteristics of tissue growth into Proplast and porous polyethylene implants in bone.

(1) Bone does not form within internal pores of undistorted Proplast implants because of the small interconnecting pore size of the material; (2) the nonosseous, fibrous tissue which exists in the pores of Proplast implants in bone is not attached to the surrounding bone (i.e., Sharpey's fibers are not present). The load-bearing support which can be afforded by Proplast implants is limited by the incomplete bone ingrowth along the margins of the material and the tensile strength of Proplast.

Absorptiometry, Photon↗