An affinity labeling of ras p21 protein and its use in the identification of ras p21 in cellular and tissue extracts

A new approach to the prevention of breast cancer

While the role of oestrogens in breast cancer has been recognised for over a century, until recently our understanding of the mechanism by which they act has been limited, despite zealous efforts on the part of many investigators to seek for differences in oestrogen levels or metabolism in cancer patients. Since the initiation of breast cancer occurs many years before the detection of overt disease, it seems reasonable to suggest that these earlier studies may have been carried out at the wrong stage of the disease. Using a time invariant radiometric procedure, we have established that of the three principal sites of oestrogen metabolism at C-2, C-16α, and C-17, only C-16α hydroxylation is elevated in women with breast cancer. Further studies in women at high risk for breast cancer for familial reasons showed that they have an elevated rate of 16α-hydroxylation. Parallel studies in mice with high and low rates of spontaneous mammary tumour formation show a close parallelism between the extent of 16α-hydroxylation and tumour incidence. Studies of 16α-hydroxyoestrone, the product of 16α-hydroxylation, have demonstrated that it is a unique oestrogen, capable of binding irreversibly to the oestrogen receptor and permanently activating it. Studies on the effects of diet and drugs on the extent of C-2 and C-16α hydroxylation have shown that while the former reaction is easily increased or decreased, the latter is refractory to treatment and behaves like a constitutive enzyme. Thus, treatment with cimetidine, obesity, or high fat diets decrease the extent of C-2 hydroxylation, while high protein diets, hyperthyroidism, smoking, or dioxins increase C-2 hydroxylation. In contrast, 16α-hydroxylation is essentially unchanged in any of these conditions.

A link between increased C-2 hydroxylation and decreased levels of breast and endometrial cancer is suggested by epidemiological studies in smokers. Conversely, decreases in this reaction as in obesity are associated with increased risk for these tumours. The aim of these studies is to develop a safe prophylactic regimen which will increase C-2 hydroxylation, resulting in a decrease in active oestrogen and a lower tumour incidence.

Involvement of ras activation in toxic hair cell damage of the mammalian cochlea

To identify possible intracellular mediators of hair cell (HC) death due to ototoxins, we treated basal-turn, neonatal, rat HCs in vitro with several intracellular signaling inhibitors, prior to and during gentamicin exposure. The general guanine nucleotide-binding protein (G-protein) inhibitor, GDP-betaS (1 mM), provided potent HC protection, suggesting involvement of G-proteins in the intracellular pathway linking gentamicin exposure to HC death. ADP-betaS had minimal effect, indicating that the protection is specific to guanosine diphosphate (GDP)-binding, rather than a general reaction to nucleotides. Azido-GTP(32) photolabeling and gel electrophoresis indicated activation of an approximately 21 kDa G-protein in HCs after exposure to gentamicin. Spectroscopic analysis of peptide fragments from this band matched its sequence with H-Ras. The Ras inhibitors B581 (50 microM) and FTI-277 (10 microM) provided potent protection against damage and reduced c-Jun activation in HC nuclei, suggesting that activation of Ras is functionally involved in damage to these cells due to gentamicin.

Adenosine A(2A) receptors are colocalized with and activate g(olf) in rat striatum

In situ hybridization with cRNA probes showed A(2A) receptor and G(olf) mRNAs to be abundantly expressed in caudate putamen, nucleus accumbens, and olfactory tubercle, whereas G(s) mRNA shows a comparatively low expression in regions expressing A(2A) receptors. In caudate putamen, 49% of the medium-sized neuron-like cells exhibited a strong signal for adenosine A(2A) receptor mRNA, and 98% showed a strong signal for G(olf) mRNA. In contrast, G(s) mRNA was found in only 12% of the medium-sized neuron-like cells in caudate putamen. The coexpression of adenosine A(2A) receptor mRNA with that of G(olf) or G(s) mRNAs was studied with double in situ hybridization. A large majority (91-95%) of the neurons in caudate-putamen that contained adenosine A(2A) receptor mRNA also expressed G(olf) mRNA, whereas only 3 to 5% of the neurons with adenosine A(2A) receptor mRNA coexpressed G(s) mRNA. The A(2A) receptor agonist CGS 21680 [2-[p-(2-carbonylethyl)phenylethylamino-5'-N-ethylcarboxa midoadenosin e] dose dependently activated G(olf) subunits in striatal membranes as shown by photolabeling with [alpha-(32)P]m-acetylanilido-GTP followed by immunoprecipitation with a specific antibody against G(olf). Transfection of G(olf) cDNA into Chinese hamster ovary cells, which stably express human adenosine A(2A) receptors, led to an increased efficacy of CGS 21680, as evidenced by a stronger cAMP response, indicating that activation of G(olf) by A(2A) receptors leads to a biological signal. In conclusion, these results provide anatomical and biochemical evidence that adenosine A(2A) receptors stimulate G(olf) rather than G(s) in striatum.

Guanine nucleotide binding proteins in cultured renal epithelia: studies with pertussis toxin and aldosterone

The GTP-binding proteins from cultured A6 epithelia were examined in isolated membrane preparations. Binding of [35S]GTPgammaS revealed a class of binding sites with an apparent Kd value of 100 nM and a Bmax of 220 pmol/mg protein. Short-term aldosterone treatment of the cells did not modify the binding kinetics, whereas pertussis toxin (PTX) decreased Bmax by 50%. The mRNA levels for Galphai-3, Galpha0, Galphas, and Galphaq were not increased after aldosterone. The patterns of small Mr G proteins and of PTX-ribosylated proteins were identical in membranes of both control and aldosterone-treated cells. Cross-linking of [alpha-32P]GTP, in control membranes, showed either no labeling or a faint band of Mr 59.5 kDa. This protein became prominent after aldosterone, and its labeling decreased with spironolactone. Thus short-term aldosterone does not promote increased expression of known heterotrimeric G proteins in epithelial membranes but activates resident PTX-sensitive Gi proteins and stimulates the expression of a specific GTP-binding protein of Mr 59.5 kDa.

Proteins that interact with GTP in Streptomyces griseus and its possible implication in morphogenesis

By cross-linking with [alpha-32P]GTP or [gamma-32P]GTP with or without UV treatment, several proteins of Streptomyces griseus were shown to interact with GTP in specific ways. After gel electrophoresis, 19 bands of radioactivity were found; 12 bands were assigned as GTP-binding proteins and 6 bands as phosphorylated proteins. One band was assumed to be a guanylylated protein. The profile of radioactive bands was similar between cells prepared from liquid or solid culture, but markedly different between growth phases. A mutant (strain M-1) defective in aerial mycelium formation, which was originally found as a decoyinine-resistant isolate, was found to have a different profile of phosphorylated proteins.

Several small GTP-binding proteins are strongly down-regulated in simian virus 40 (SV40) transformed human keratinocytes and may be required for the maintenance of the normal phenotype

High resolution two-dimensional (2-D) gel electrophoresis in combination with the blot overlay nucleotide binding assay was used to reveal low molecular weight GTP-binding proteins expressed by primary cultured, normal human keratinocytes. Forty one small GTP-binding proteins (30 isoelectric focusing, IEF; and 11 nonequilibrium pH gradient electrophoresis, NEPHGE) ranging in molecular weights from 18,000 to 30,000 and isoelectric points from 4.4 to 8.0 were detected and mapped in the master human keratinocyte database. Four GTP-binding proteins were identified by 2-D gel immunoblotting and these correspond to rap1 and 2 and two forms of rab6. ras-Proteins are most likely present in the [alpha 32P]GTP 2-D gel blots but their levels may be too low to be detected by immunoblotting. Quantitative changes in the relative expression levels of [alpha 32P]GTP-binding proteins in normal proliferating and simian virus 40 (SV40) transformed human keratinocytes (K 14) were determined by scintillation counting of the radioactive spots excised from the nitrocellulose blots. The results showed that thirteen of these proteins were not expressed in transformed K14 keratinocytes, implying that they may play a role in the maintenance of the normal cell phenotype.

Mapping small GTP-binding proteins on high-resolution two-dimensional gels by a combination of GTP binding and labeling with in situ periodate-oxidized GTP

We compared two approaches to identify and map small GTP-binding proteins in combination with high-resolution two-dimensional (2-D) gel electrophoresis. The first approach involved direct GTP ligand binding after a renaturing transfer onto nitrocellulose. In the second, affinity labeling with in situ periodate-oxidized GTP was used in permeabilized cells (Peter, M. E., She, J., Huber, L. A. and Terhorst, C. Anal. Biochem. 1993, 210, 77-85). Analysis by 2-D gel electrophoresis revealed a number of distinct intracellular small GTP-binding proteins in Madine-darby canine kidney strain II cells (MDCKII). Using specific antibodies the electrophoretic coordinates of rab4, rap1a/b, and rap2 were identified for native as well as for crosslinked GTPases. These methods allow the identification of small GTP-binding proteins in total cell lysates and purified subcellular fractions, providing excellent markers throughout the course of differentiation and development.

Coordinated expression of intermediate biomarkers for tumorigenic transformation in RAS-transfected mouse mammary epithelial cells

Deregulated expression of the RAS oncogene is associated with tumorigenic transformation of mammary cells. Because of the complex, multiphasic nature of cancer progression, it is important to systematically identify the biomarkers specific for initiation, promotion, and progression of breast cancer. Mouse mammary epithelial cells (MMEC) were transfected with normal c-Ha-RAS proto oncogene (pH06N) and with mutant c-Ha-RAS oncogene (pH06T). The parental MMEC and the cloned transfectants pH06N1, pH06N2, pH06T1, and pH06T12 were evaluated for the acquisition of transformed characteristics by determining altered cellular metabolism of estradiol, increased ability for anchorage-independent growth, and ability to form tumors at the transplant site in athymic 'nude' mice. Persistent, functional integration of c-Ha-RAS was evidenced by the presence of a 1.2 kb c-Ha-RAS transcript in the four transfectants but not in MMEC. All the transfectants also exhibited a substantial increase in the binding of c-Ha-RAS p21 to [alpha-32P] GTP relative to MMEC (P less than 0.003). The relative extent of estradiol metabolism leading to the formation of 16 alpha-hydroxyestrone was increased (P less than 0.004) in all the four transfectants. These four transfectants also showed a 100-400 fold increase in colony forming efficiency in 0.33% agar, relative to MMEC (P less than 0.0009), and formed rapidly growing tumors within 3-5 weeks of transplantation. Our results demonstrate that i) persistent expression of normal and mutant c-Ha-RAS can bring about tumorigenic transformation of mouse mammary epithelial cells; and ii) alteration in estradiol metabolism and acquisition of anchorage-independent growth precede the emergence of a tumorigenic phenotype.(ABSTRACT TRUNCATED AT 250 WORDS)

Association of c-myc protein with enzymes of DNA replication in high molecular weight fractions from mammalian cells

Oncoprotein c-myc is expressed in proliferating but not quiescent mammalian cells, and its overexpression or inappropriate expression is associated with malignant transformation. However, in spite of an intense interest, the normal function of this protein has remained elusive. As a step towards the elucidation of the function of c-myc protein, we studied its distribution within several types of cells, including HL 60, K 562, COLO 320, and CHEF/18 cells. In all of the cells studied, c-myc protein was detected in high molecular weight protein fractions, in 350-600 Kd range, in gel-exclusion chromatography and sucrose gradient centrifugation. This distribution of c-myc protein coincided with the distribution of DNA polymerase alpha and several other enzymes necessary for DNA replication. The data suggest that c-myc product may be a component of the replitase complex of enzymes involved in nuclear DNA replication.

Novel GTP-binding proteins in plasma membranes and zymogen granule membranes from rat pancreas and in pancreatic AR 4-2J cell membranes

Photoaffinity labelling with [alpha-32P]GTP allowed to detect a 54 kDa GTP-binding protein in rat pancreatic plasma membranes and in pancreatic AR 4-2J cell membranes. Like the 42 and 48 kDa Gs alpha subunits and the 41 kDa Gi alpha subunit, this protein was absent from zymogen granule membranes. Contrastingly, a new 28 kDa GTP-binding protein (detected by [alpha-32P]GTP binding on immobilized proteins) and a 25 kDa protein (ADP-ribosylated by botulinum toxin D) were found in all three membrane preparations. This is to our knowledge the first report on GTP-binding proteins in zymogen granule membranes.

Cellular ras protooncogene expression in human mammary explant cultures. A potential marker for chemical carcinogenesis

The major findings of the present study can be summarized as follows: 1. The newly developed assay for quantitative determination of ras protooncogene expression which utilizes affinity labeling of ras p21 with [alpha-32P]GTP can effectively demonstrate the presence of ras protooncogene expression in explant cultures of human mammary tissues. 2. The prototype chemical carcinogens NMU and BP induce amplified expression of ras protooncogene in benign (noninvolved) human mammary TDLU. 3. The specific enhancement of ras expression by BP in TDLU (target tissue) but not in MF (nontarget tissue) for tumorigenesis indicates that the constitutive levels of ras protooncogene in the target tissue are responsive to carcinogenic insult. 4. The relative extent of ras protooncogene expression may constitute a sensitive marker for target tissue susceptibility to chemical carcinogenesis.

Proteins that interact with GTP during sporulation of Bacillus subtilis

During sporulation of Bacillus subtilis, several proteins were shown to interact with GTP in specific ways. UV light was used to cross-link [alpha-32P]GTP to proteins in cell extracts at different stages of growth. After electrophoresis, 11 bands of radioactivity were found in vegetative cells, 4 more appeared during sporulation, and only 9 remained in mature spores. Based on the labeling pattern with or without UV light to cross-link either [alpha-32P]GTP or [gamma-32P]GTP, 11 bands of radioactivity were apparent guanine nucleotide-binding proteins, and 5 bands appeared to be phosphorylated and/or guanylated. Similar results were found with Bacillus megaterium. Assuming that GTP might be a type of signal for sporulation, it could interact with and regulate proteins by at least three mechanisms.

Purification of nucleotide-linked peptide

Affinity labeling of nucleotide-binding enzymes/proteins with 32P-labeled nucleotides is a powerful technique to identify nucleotide-binding proteins as well as to radiolabel the specific binding site. We have used this approach for labeling a nucleotide-binding domain in DNA polymerase and have isolated peptides bearing the linked nucleotides. The method used for separating tryptic peptides on hydrophobic matrices with an acetonitrile gradient in 0.1% trifluoroacetic acid as eluent results in loss of radioactivity, presumably through dissociation of the cross-linked nucleotide. This can be averted by the use of a non-acidic medium in the peptide purification protocol. We have devised a relatively simple procedure to concentrate the nucleotide-linked peptides by chromatography on DEAE-Sephadex A25. Most neutral and basic peptides as well as free nucleotides are removed by eluting the DEAE-Sephadex column with 0.2 M ammonium bicarbonate. The nucleotide-linked peptide is then eluted with 0.6 M ammonium bicarbonate. Radioactivity in the collected fractions is conveniently determined by scintillation counting. Labeled peptide in the 0.6 M ammonium bicarbonate eluate can be purified on a C4 reversed-phase column with an acetonitrile gradient in phosphate buffer (pH 6.8). By this procedure, 32P-labeled nucleotide linked with protein/peptide can be quantitatively purified with minimum loss.