Purification and characterization of clathrin from bovine brain

The PI3K/AKT/mTOR signaling pathway inhibitors enhance radiosensitivity in cancer cell lines

INTRODUCTION

Radiotherapy is one of the most common types of cancer treatment modalities. Radiation can affect both cancer and normal tissues, which limits the whole delivered dose. It is well documented that radiation activates phosphatidylinositol 3-kinase (PI3K) and AKT signaling pathway; hence, the inhibition of this pathway enhances the radiosensitivity of tumor cells. The mammalian target of rapamycin (mTOR) is a regulator that is involved in autophagy, cell growth, proliferation, and survival.

CONCLUSION

The inhibition of mTOR as a downstream mediator of the PI3K/AKT signaling pathway represents a vital option for more effective cancer treatments. The combination of PI3K/AKT/mTOR inhibitors with radiation can increase the radiosensitivity of malignant cells to radiation by autophagy activation. Therefore, this review aims to discuss the impact of such inhibitors on the cell response to radiation.

Production and characterization of polyclonal and monoclonal antibodies to rat brain L-glutamate decarboxylase

Specific monoclonal and polyclonal antibodies to rat brain glutamate decarboxylase (GAD) were produced and characterized. Polyclonal antibodies against GAD were raised in rabbits by injecting a total of 70-210 micrograms of purified GAD i.m. The specificity of anti-GAD serum was established from a variety of tests including Ouchterlony immunodiffusion, immunoelectrophoresis, immunoprecipitation, dot immunoassay, ELISA tests and Western immunoblottings. In immunodiffusion and immunoelectrophoresis tests using partially purified GAD preparations and anti-GAD serum a single, sharp precipitin line corresponding to GAD activity was obtained. Quantitative immunoprecipitation of GAD activity was achieved using anti-GAD IgG and Staphylococcus aureus. Specificity of the antiserum was further indicated from a dot immunoassay and ELISA tests in which the intensity of the reaction product was proportional to the amount of GAD protein present. In the Western immunoblotting experiments using partially purified GAD preparations only two protein bands corresponding to the position of the two subunits of GAD were stained by anti-GAD IgG, further supporting the specificity of polyclonal antibodies against GAD. In addition to polyclonal antibodies, several specific GAD-antibodies-producing clones were also obtained by the hybridoma technique. The specificity of monoclonal antibodies against GAD were established from the following criteria: positive on ELISA test using homogeneous GAD as antigen; formation of GAD--anti-GAD IgG complex as indicated from gel filtration chromatography and sodium dodecyl sulfate polyacrylamide gel electrophoresis; and specific recognition of GAD subunit in a partially purified GAD preparation in Western immunoblotting test. Monoclonal antibodies were further characterized by immunohistochemical localization of known GABAergic neurons and their processes in the cerebellum and retina.

Association of clathrin with microsomes isolated from canine myocardium

We and others have observed specialized regions of sarcoplasmic reticulum membranes that resemble coated vesicles, in the I-band region of myocardial cells. These structures have been named "corbular" sarcoplasmic reticulum, and are distinct in appearance from Golgi-associated coated vesicles, in that they are larger and contain a flocculent material that has been identified as calsequestrin. Whereas it has been suggested that these structures have a role in cardiac calcium metabolism, their function(s) and the molecular identity of the characteristic "bristle" coat remain unknown. Microsomes enriched in sarcoplasmic reticulum were prepared from canine ventricular muscle by Polytron homogenization in pH 6.5 buffer, followed by differential centrifugation. Protein was released by incubation in 50 mM Tris/HCl, pH 8, followed by centrifugation. We found these extracts to be enriched in a protein that was identical to brain clathrin in mobility on a Sepharose 4B gel filtration column, final position of the native protein following nondenaturing electrophoresis, relative mobility in denaturing (sodium dodecyl sulfate) electrophoresis on 6% and 7.5% gels, and antigenicity to anti-clathrin IgG. These findings confirmed the presence of clathrin triskelions in the cardiac microsome extract. On this basis, we suggest that clathrin may be a component of the electron dense "coat" of corbular sarcoplasmic reticulum.

Ca2+-Mg2+-ATPase activity in brain coated microvesicles purified on immunosorbents

Coated microvesicle fractions isolated from ox forebrain cortex by the ultracentrifugation procedure of Pearse (1) and by the modified, less time consuming method of Keen et al (2) had comparable Ca2+ +Mg2+ dependent ATPase activities (about 9 mumol/h per mg protein). The Na+ +K+ +Mg2+ dependent ATPase activity was 3.2 mumol/h per mg (+/- 1.0, S.D., n = 3) when microvesicles were prepared according to (1) and 1.5 mumol/h per mg (+/- 1.0, S.D., n = 3) when prepared according to (2). Oligomycin, ruthenium red, and trifluoperazine, inhibitors of Ca2+ transport in mitochondria and erythrocyte membranes had no effect on Ca2+ +Mg2+ dependent ATPase from any of the preparations. As demonstrated both by ATPase assays and electron microscopy, coated microvesicles could be bound to immunosorbents prepared with poly-specific antibodies against a coated microvesicle fraction obtained by the method of Pearse (1). The binding could be inhibited by dissolved coat protein using partially purified clathrin. The fraction of coated vesicles eluted from the immunosorbent was purified relative to the starting material as judged by electron microscopy. The Ca2+ +Mg2+ ATPase activity and calmodulin content was copurified with the coated microvesicles and the specific activity of Na+ +K+ +Mg2+ ATPase was decreased. Na+ +K+ +Mg2+ dependent ATPase activity in the coated microvesicle fraction could be ascribed to membranes with the appearance of microsomes. These membranes were also bound to the immunosorbents, but the binding was not influenced by clathrin. The capacity of the immunosorbents for these membranes was less than for the coated microvesicles, resulting in a decrease of Na+ +K+ +Mg2+ dependent ATPase activity in the eluted coated microvesicle fraction. It was concluded that Ca2+ +Mg2+ ATPase activity is not a contamination from plasma membrane vesicles or mitochondrial membranes but seems to be an integral part of the coated vesicle membrane.