Tumor-promoting phorbol ester transiently down-modulates the p53 level and blocks the cell cycle.

Activation of the protein kinase C signaling pathway by tumor-promoting phorbol esters, such as 4 beta-phorbol 12-myristate 13-acetate (PMA), induced a decrease in the level of p53 mRNA in several serum-starved human cell lines. Also, the tumor-promoting phosphatase inhibitor okadaic acid induced a decrease in the p53 mRNA level in the cell lines. Normal diploid as well as various tumor cell lines were tested.

Numerous proteins phosphorylated on tyrosine and enhanced tyrosine kinase activities in vanadate-treated NIH 3T3 fibroblasts.

A monoclonal antibody that can immunoprecipitate proteins containing phosphotyrosine has been isolated and characterized. To identify proteins that can act as substrates for tyrosine kinases in intact cells, extracts of phosphate-labeled NIH cells that had been treated with the phosphotyrosyl phosphatase inhibitor, vanadate, were precipitated with the antibody, and the immunoprecipitates were analyzed by two-dimensional gel electrophoresis. Numerous proteins were specifically precipitated from vanadate-treated NIH 3T3 cells by the antibody.

Herpes simplex virus-induced changes of the keratin type intermediate filament in rat epithelial cells.

Herpes simplex virus type 1 (HSV-1) infection of human fibroblast cells grown in culture induces reorganization of the cytoskeleton fibrillar structures. Normal transport and insertion of HSV glycoproteins into the plasma membrane of the cells depend on the integrity of the microtubules. The natural host cells for HSV are epithelial cells, and an epithelial cell line established from rat palate was used in the present study.

Two-dimensional gel electrophoresis of myc gene products after cleavage by viral protease p15.

An analysis of myc-specific protein (p58myc), precipitated from cells transformed by virus OK10, by means of two-dimensional gel electrophoresis revealed the presence of two variants of p58myc differing in their isoelectric point. Both variants are completely cleaved by protease p15 as is the c-myc gene product precipitated from 16Q cells. The cleavage fragments of c-myc and v-myc protein do not differ in size but differ in their stability.

Induction of the metastatic phenotype in a mouse tumor model by 5-azacytidine, and characterization of an antigen associated with metastatic activity.

The murine Lewis lung carcinoma is a long-term grafted tumor that, after subcutaneous inoculation, forms metastases to the lungs. Forty-two cell lines were established from a primary tumor site and 40 were established from lung metastatic foci. Cloned sublines were established from the original 82 lines, and 2 sublines among 405 were found to be tumorigenic but not metastatic (T+/M-), whereas the remaining 403 sublines were both tumorigenic and metastatic (T+/M+).

Two cellular proteins that are precipitated by an antitumor-RSV rat serum.

Here we report studies on non-viral proteins specific for transformation precipitated by immune sera. These sera were from rats injected by PR-RSV transformed rat XC cells and from rabbits immunized by subcutaneous injections of cytoplasmic membranes from rat cells transformed by Fujinami avian sarcoma virus. Immune complexes were analyzed in one- or two-dimensional gel electrophoresis and by autoradiography.

Immunoprecipitation of membrane proteins of cultured human sarcoma cells.

Human sarcoma associated antigens (HSAA) have previously been identified by indirect immune fluorescence in human sarcoma cells in culture using sera from patients bearing different types of sarcoma. To further characterize these HSAA, surface proteins of cultured cells were labeled with 125Iodine, [3H]-glucosamine and [35S]-methionine and solubilized. After immunoprecipitation labeled proteins were detected in immune complexes by SDS polyacrylamide gel electrophoresis and autoradiography, which allowed comparison with antigens described by other groups.

Temperature-sensitive tumorigenicity of cells transformed by a mutant of Moloney sarcoma virus.

Normal rat kidney cells were nonproductively infected either with CP27, a mutant of Moloney sarcoma virus that is temperature-sensitive for maintenance of transformation, or with the parental wild-type virus. The nonproducer cells were inoculated into the tails of athymic nude mice that were subsequently incubated at 28 or 36 degrees C. CP27-infected cells induced tumors only at 28 degrees C, whereas cells infected with wild-type Moloney sarcoma virus were tumorigenic at both temperatures.

Regulation of protein synthesis initiation in HeLa cells deprived of single essential amino acids.

In HeLa cells deprived of valine, histidine, or methionine initiation of protein synthesis decreases rapidly and disaggregation of polyribosomes also occurs. The mechanism of inhibition does not seem to involve the supply of RNA in the cell, and thus it differs from the initiation of inhibition at elevated temperatures. Polyribosomes rapidly form again if the missing amino acid is restored, even in the presence of actinomycin D.