Injection of proteins into primary rat hepatocytes by erythrocyte-mediated techniques

Microinjection of endogenous and exogenous proteins into primary cultures of rat hepatocytes and the degradation of the injected proteins

1. A method to microinject proteins into cells through packaging proteins to erythrocyte ghosts (erythrocyte-mediated microinjection) was modified partially in order to apply the method to primary cultures of rat hepatocytes. 2. Degradation of the microinjected proteins was examined employing the improved method. The mean half-life of the injected endogenous liver protein was 20 hr. The data suggested that the injected proteins are degraded through both lysosomal and non-lysosomal proteolytic pathways probably depending on their structure. 3. The present method to microinject exogenous proteins into primary cultures of rat hepatocytes can be employed usefully for the investigations of protein metabolism in liver.

Degradation of horseradish peroxidase after microinjection into mammalian cells

Horseradish peroxidase (HRP) has been microinjected into mammalian cells in tissue culture by the erythrocyte ghost-mediated technique. This protein was selected because it can be localized and quantified after injection by cytochemical and spectrophotometric methods. HRP labeled by reductive methylation retained full catalytic activity, was efficiently loaded into erythrocyte ghosts, and did not associate to a significant degree with ghost membranes. A combination of cytochemical staining and autoradiography established that HRP injected into rat L6 myoblasts, HE(39)L human diploid fibroblasts, or HeLa cells was intracellular and uniformly distributed throughout the cell, while cell lysis techniques showed that the catalytically active HRP was not membrane bound. Inactivation of labeled HRP after injection paralleled the disappearance of the 40-kDa polypeptide, and was always more rapid than its overall degradation. This difference was associated with a pool of water-insoluble radioactivity in the injected cells. This material was of smaller molecular size than the native protein: many labeled peptides were detected in the range of 10 to 38 kDa. By the use of inhibitors of autophagic proteolysis or lysosomal function it was established that HRP degradation was not subjected quantitatively to the same regulatory processes as the average endogenous protein labeled in the same cultures.

Immunotargeting of erythrocyte-bound streptokinase provides local lysis of a fibrin clot

The creation of an anticollagen antibody-erythrocyte-streptokinase complex has been described. Immobilization of both proteins on erythrocyte membrane has been performed using an avidin-biotin interaction. Modification of streptokinase with (6-biotinylamido)hexanoic acid N-hydroxysuccinimide ester at the concentration of 1.1 mM (20% modification of protein amino groups) provides effective (up to 90%) attachment of streptokinase to an avidin-carrying erythrocyte surface. The loss of streptokinase activity due to modification under these conditions is not significant. The maximal attachment of streptokinase was equal to about 50 ng per 10(6) erythrocytes, i.e., about 5 X 10(5) molecules of streptokinase per erythrocyte. The presence of streptokinase in the incubation mixture inhibited the attachment of antibodies by about 50%. Nevertheless, co-immobilization of anticollagen antibody (1.0 X 10(5) molecules per cell) and streptokinase (2.8 X 10(5) molecules per cell) on the erythrocyte surface provided firm and specific binding of such erythrocytes to a collagen-coated surface (1.6 X 10(6) bound cells per 1 cm2 on a collagen-coated surface against 0.006 X 10(6) bound cells on a bovine serum albumin-coated surface). Targeting of such erythrocytes led to local lysis of a fibrin clot in the target zone. The properties described offer in principle the possibility of the application of this or a similar system of fibrinolytic agent targeting for the preventive therapy of rethrombosis during surgical manipulations on vessels.

Autophagy and lysosomal proteolysis in the liver

Autophagy is defined as any process whereby cellular macromolecules destined for degradation gain access to the lysosomes. A review is presented on the physiological significance, mechanisms and regulation of autophagy in hepatocytes, concentrating on the issue of regulation. The article ends by discussing techniques available for future research.

Targeting of enzyme immobilized on erythrocyte membrane to collagen-coated surface

It is suggested to use 'enzyme(s)-erythrocyte-antibody' complex for modulation of the microenvironment in definite compartments of blood circulation. A model system including peroxidase, human erythrocytes and anti-collagen antibodies was chosen to illustrate the principle. Peroxidase was conjugated to the erythrocyte surface via periodate-oxidized enzyme carbohydrate moiety; biotinylated antibodies were linked by avidin to the biotinylated erythrocytes. The properties of the immunocomplexes obtained have been investigated in an artificial system simulating an injured blood vessel wall. The advantages in using erythrocyte-mediated immunoenzyme complexes for enzyme (drug) targeting are discussed.

Microinjection of cultured cells using red-cell-mediated fusion and osmotic lysis of pinosomes: a review of methods and applications

Proteins and other macromolecules can be injected into cultured cells by several different methods. Here we review the strengths and limitations of two of these methods, red-cell-mediated microinjection and osmotic lysis of pinosomes, and indicate how they may be successfully applied to the study of cultured cells.