Two-dimensional polyacrylamide gel electrophoresis analysis of phosphorylated, membrane-localized ras p21 proteins

Relative steady-state expression of the different post-translational products of p21-H-ras from normal rat tissues. A 2D-western immunoblot study

Proteins extracts from rat cell lines or tissues expressing normal or activated c-H-ras genes, or normal N-ras gene were submitted to westernblot analysis with an anti-H, K, N p21-ras antibody. This showed that p21-H-ras products resolved into four spots (a, b, c, d) that are readily distinguishable from the normal p21-N-ras products (spots e, f, g), and also from two other products (spots a', b') present in extracts from cells which overexpress a Val12-mutated H-ras gene. Considering metabolic isotopic labeling and cell fractionation, we were able to establish the correspondance of spots a, b, c, d with the known steps of the sequential post-translational processing (farnesylation, further carboxymethylation and ultimate palmitoylation) of p21-H-ras. The palmitoylated product predominates in normal brain and still more in normal adult liver tissues, whereas its relative level decreases in proliferating liver cells.

Immunodetection of the p21-ras products in human normal and preneoplastic tissues and solid tumors: a review

Immunohistochemical detection of p21-ras to identify and characterize preneoplastic or neoplastic lesions in human tissues is reviewed. Information concerning the commercially available antibodies is presented. Antibodies DWP, Ras-10, Y13-259, YA6-172, NCC-001, and NCC-004 are fully documented with respect to their behavior in appropriate specificity tests and appear to be reliable reagents. After reviewing the data we have identified three groups of tissues or organs with respect to positive immunostaining for p21-ras as the significant criterion of malignancy. These three groups comprise (1) tissues for which no definite conclusion could be drawn (colon, lung, bladder, ovary, and neural and odontogenic tissues) despite occasional claims to the contrary, (2) tissues for which conclusions were negative (pancreas and stomach), and (3) tissues for which p21-ras staining positively discriminated malignant from normal tissues (liver, uterus, and salivary gland). Immunohistochemically detectable levels of products from a mutated ras gene could be demonstrated in a fraction of the samples from colon, lung, and bladder carcinomas, as well as in some histologically normal tissues adjacent to a colon carcinoma. The possibility that a higher relative intensity of the immunostaining reaction for p21-ras might discriminate malignant tissues from normal tissues or benign lesions in breast, pancreas, stomach, lung, uterus, or thyroid samples is suggested. Further studies now appear warranted and a strategy is proposed to validate the conclusions reached thus far.

Post-translational processing of p21ras is two-step and involves carboxyl-methylation and carboxy-terminal proteolysis

We have studied the post-translational processing of p21ras proteins. The primary translation product pro-p21 is cytosolic and is rapidly converted to a cytosolic form (c-p21) of higher mobility on SDS-PAGE. c-p21 is converted in turn to the membrane-bound mature palmitoylated form (m-p21) of slightly higher mobility. These processing steps are accompanied by increases in isoelectric point and in hydrophobicity as judged by Triton X-114 partitioning. Although the increases in electrophoretic mobility and hydrophobicity precede acylation we show that mutation of Cys186, which has been shown to block acylation, also abolishes the pro-p21 to c-p21 conversion. Thus the Cys186 residue is involved in the processing steps prior to acylation. We have identified two processing events which contribute to the pro-p21 conversion. Site-directed mutagenesis to insert tryptophan, which is not present in the wild type, followed by metabolic labelling with [3H]tryptophan has allowed us to map a proteolytic processing event which removes the three C-terminal residues. In addition, both the c-p21 and m-p21 forms are carboxyl-methylated. Approximately one methyl group is incorporated per molecule of p21 at steady state, which can partially account for the increase in isoelectric point. Unlike palmitate, methyl group turnover is not observed.