Reactive Cellular Changes in Anal Cytology Smears and Its Relation to Future Dysplastic Changes in HIV+ Subjects

Introduction/Objective

The incidence of anal squamous cell carcinoma is increasing in high risk populations. There is no consensus regarding screening for anal squamous cell carcinoma. Anal pap smears are interpreted using the Bethesda System for cervical cytology. Significant challenges exist for anal cytology that do not apply to cervicovaginal cytology.

Methods/Case Report

We retrospectively reviewed the anal cytology smears performed in our institution between 2012- 2019. The smears with reactive cytology changes (RCCs) were retrieved, and corresponding follow up smears were reviewed.

Results (if a Case Study enter NA)

A total of 39 cytology smears with positive RCCs with no dysplasia diagnosis were obtained. All were HIV+. 32 cases were male and 7 females. The overall mean age was: 37.77 + 11.94 SD (range: 23-65 years). The mean age for men was 36.53 + 11.51 and 43.43 + 13.13 for women. Although this mean age was higher for women, the age difference was statistically insignificant (p=0.7, alpha=0.05). Four of the women patients had concomitant cervicovaginal cytology all of which were negative. Only 1 female had a follow up study which was negative. Of the 39 cases, 26 cases (25 men and 1 woman or a total of 66.7%) had followed up smears versus 13 (33.3%) cases with no follow up. A total of 7 out of the 26 follow ups were negative for dysplasia (26.92%). Of the 26 follow ups, a total of 18 (69.23%) were found to have progressed to either ASCUS (15 or 57.69%) or LSIL (3 or 11.53%). One ASCUS was diagnosed as possible high grade. The mean time to convert to dysplasia was 2.06 + 1.25 years (range 1-5 years). Half of the dysplastic cases developed in a 1 year period.

Conclusion

Patients who have reactive changes on anal cytology should be monitored for possible development of anal neoplasia.

General quantitative treatment for the binding of divalent antibodies to antigens immobilized on a solid phase

A general expression for the binding isotherm of divalent antibodies to antigens bound to solid lattices with excluded volume effects is derived by using a statistical mechanical approach. The method is based on matrix generation of the partition function for the system, from which the degree of saturation of the antigen lattice may be computed directly. The saturation function has a simple form that under appropriate conditions reduces to forms derived previously for simpler cases (such as monovalent binding with and without excluded volume effects). Solution by numerical techniques of a simple secular equation for each concentration of antibody allows computation of the saturation function. Thus, the binding expression derived is easily fit to any set of binding data obtained and results in the determination of such parameters as intrinsic affinity constants, length of excluded space (and hence molecular size), and number of sites. It predicts that under conditions wherein divalent binding is favored over univalent binding, biphasic adsorption isotherms will be obtained.

Immunoglobulin E antibodies from pancreatic cancer patients mediate antibody-dependent cell-mediated cytotoxicity against pancreatic cancer cells

In addition to allergy and parasitic infections, immunoglobulin E (IgE) has been shown recently to possess anti-viral and anti-cancer effects. We investigated serum levels of IgE, its low-affinity receptor, soluble CD23 (sCD23) in patients with pancreatic cancer and the effect of IgE against pancreatic cancer cells. Twelve patients were evaluated for pancreatic cancer by imaging and confirmed by biopsy. Fifteen healthy volunteers served as controls. Serum Igs (IgG, IgM, IgA, IgE) and sCD23 levels were determined (enzyme-linked immunosorbent assay, nephelometry) and the presence of cancer-specific IgE was assessed (fluorescence microscopy, Western blot). IgE anti-cancer activity was determined by antibody-dependent cell-mediated cytotoxicity (ADCC). Serum levels of IgE and sCD23 were elevated significantly in patients with pancreatic cancer versus controls, whereas no differences were observed in other Ig isotypes (IgG, IgM, IgA). Flow cytometry and immunofluorescence microscopy demonstrated similar presence of IgG and IgE pancreatic cancer Igs. However, Western blot analysis indicated differences in IgG and IgE antigen-specific antibodies; IgE antibody recognized a 50 kD protein. ADCC studies demonstrated that serum and purified IgE-mediated cytotoxicity against pancreatic cancer cells, effects which were reversed with anti-IgE neutralizing antibody and IgE depletion (immunoaffinity); greater cytotoxicity was observed in patient serum when compared with healthy controls. These data suggest that IgE and sCD23 may serve as useful biomarkers for patients with pancreatic cancer and may be important in the immune response to this disease in that IgE-directed therapy may help to direct treatment.

Peptides from the amino terminal mdm-2-binding domain of p53, designed from conformational analysis, are selectively cytotoxic to transformed cells

We have synthesized three peptides from the mdm-2 binding domain of human p53, residues 12-26 (PPLSQETFSDLWKLL), residues 12-20, and 17-26. To enable transport of the peptides across the cell membrane and at the same time to maximize the active mdm-2 binding alpha-helical conformation for these peptides, each was attached at its carboxyl terminus to the penetratin sequence, KKWKMRRNQFWVKVQRG, that contains many positively charged residues that stabilize an alpha-helix when present on its carboxyl terminal end. All three peptides were cytotoxic to human cancer cells in culture, whereas a control, unrelated peptide attached to the same penetratin sequence had no effect on these cell lines. The same three cytotoxic peptides had no effect on the growth of normal cells, including human cord blood-derived stem cells. These peptides were as effective in causing cell death in p53-null cancer cells as in those having mutant or normal p53. Peptide-induced cell death is not accompanied by expression of apoptosis-associated proteins such as Bax and waf(p21). Based on these findings, we conclude that the antiproliferative effects of these p53-derived peptides are not completely dependent on p53 activity and may prove useful as general anticancer agents.

Differences in patterns of activation of MAP kinases induced by oncogenic ras-p21 and insulin in oocytes

Oncogenic ras (Val 12-containing)-p21 protein induces oocyte maturation by a pathway that is blocked by peptides from effector domains of ras-p21, i.e., residues 35-47 (that block Val 12-p21-activated raf) and 96-110 and 115-126, which do not affect the ability of insulin-activated cellular p21 to induce maturation. Oncogenic p21 binds directly to jun-N-terminal kinase (JNK), which is blocked by the p21 96-110 and 115-126 peptides. This finding predicts that oncogenic p21, but not insulin, induces maturation by early and sustained activation of JNK. We now directly confirm this prediction by showing that oncogenic p21 induces activating phosphorylation of JNK (JNK-P) and of ERK (MAP kinase) (MAPK-P), whose levels correlate with oocyte maturation. p21 peptides 35-47 and 96-110 block formation of JNK-P and MAPK-P, further confirming this correlation and suggesting, unexpectedly, that raf-MEK-MAPK and JNK-jun pathways strongly interact on the oncogenic p21 pathway. In contrast, insulin activates only low levels of JNK-P, and, surprisingly, we find that insulin induces only low levels of MAPK-P, indicating that insulin and activated normal p21 utilize MAP kinase-independent signal transduction pathways.

Plasmid expression of a peptide that selectively blocks oncogenic ras-p21-induced oocyte maturation

PURPOSE

We have previously found that a synthetic peptide corresponding to ras-p21 residues 96 110 (PNC2) selectively blocks oncogenic (Val 12-containing) ras-p21 protein-induced oocyte maturation. With a view to introducing this peptide into ras-transformed human cells to inhibit their proliferation, we synthesized an inducible plasmid that expressed this peptide sequence. Our purpose was to test this expression system in oocytes to determine if it was capable of causing selective inhibition of oncogenic ras-p21.

METHODS

We injected this plasmid and a plasmid expressing a control peptide into oocytes either together with oncogenic p21 or in the presence of insulin (that induces maturation that is dependent on normal cellular ras-p21) in the presence and absence of the inducer isopropylthioglucose (IPTG).

RESULTS

Microinjection of this plasmid into oocytes together with Val 12-p21 resulted in complete inhibition of maturation in the presence of inducer. Another plasmid encoding the sequence for the unrelated control peptide, X13, was unable to inhibit Val 12-p21-induced maturation. In contrast, PNC2 plasmid had no effect on the ability of insulin-activated normal cellular or wild-type ras-p21 to induce oocyte maturation, suggesting that it is selective for blocking the mitogenic effects of oncogenic (Val 12) ras p21.

CONCLUSION

We conclude that the PNC2 plasmid selectively inhibits oncogenic ras-p21 and may therefore be highly effective in blocking proliferation of ras-induced cancer cells. Also, from the patterns of inhibition, by PNC2 and other ras- and raf-related peptides, of raf- and constitutively activated MEK-induced maturation, we conclude that PNC2 peptide inhibits oncogenic ras p21 downstream of raf.

Jun NH2-terminal kinase phosphorylation of p53 on Thr-81 is important for p53 stabilization and transcriptional activities in response to stress

The p53 tumor suppressor protein plays a key role in the regulation of stress-mediated growth arrest and apoptosis. Stress-induced phosphorylation of p53 tightly regulates its stability and transcriptional activities. Mass spectrometry analysis of p53 phosphorylated in 293T cells by active Jun NH2-terminal kinase (JNK) identified T81 as the JNK phosphorylation site. JNK phosphorylated p53 at T81 in response to DNA damage and stress-inducing agents, as determined by phospho-specific antibodies to T81. Unlike wild-type p53, in response to JNK stimuli p53 mutated on T81 (T81A) did not exhibit increased expression or concomitant activation of transcriptional activity, growth inhibition, and apoptosis. Forced expression of MKP5, a JNK phosphatase, in JNK kinase-expressing cells decreased T81 phosphorylation while reducing p53 transcriptional activity and p53-mediated apoptosis. Similarly transfection of antisense JNK 1 and -2 decreased T81 phosphorylation in response to UV irradiation. More than 180 human tumors have been reported to contain p53 with mutations within the region that encompasses T81 and the JNK binding site (amino acids 81 to 116). Our studies identify an additional mechanism for the regulation of p53 stability and functional activities in response to stress.

Common conformational effects of p53 mutations

The tumor suppressor gene p53 has been identified as the most frequent target of genetic alterations in human cancers. Most of these mutations occur in highly conserved regions in the DNA-binding core domain of the p53 protein, suggesting that the amino acid residues in these regions are critical for maintaining normal p53 structure and function. We previously used molecular dynamics calculations to demonstrate that several amino acid substitutions in these regions that are induced by environmental carcinogens and found in human tumors produce certain common conformational changes in the mutant proteins that differ substantially from the wild-type structure. In order to determine whether these conformational changes are consistent for other p53 mutants, we have now used molecular dynamics to determine the structure of the DNA-binding core domain of seven other environmentally induced, cancer-related p53 mutants, namely His 175, Asp 245, Asn 245, Trp 248, Met 249, Ser 278, and Lys 286. The results indicate that all of these mutants differ substantially from the wild-type structure in certain discrete regions and that some of these conformational changes are similar for these mutants as well as those determined previously. The changes are also consistent with experimental evidence for alterations in structure in p53 mutants determined by epitope detectability using monoclonal antibodies directed against these regions of predicted conformational change.

Identification, using molecular dynamics, of an effector domain of the ras-binding domain of the raf-p74 protein that is uniquely involved in oncogenic ras-p21 signaling

By comparing the average structures, computed using molecular dynamics, of the ras-binding domain of raf (RBD) bound to activated wild-type ras-p21 and its homologous inhibitory protein, rap-1A, we formerly identified three domains of the RBD that changed conformation between the two complexes, residues 62-76, 97-110, and 111-121. We found that one synthetic peptide, corresponding to RBD residues 97-110, selectively inhibited oncogenic ras-p21-induced oocyte maturation. In this study, we performed molecular dynamics on the Val 12-ras-p21-RBD complex and compared its average structure with that for the wild-type protein. We find that there is a large displacement of a loop involving these residues when the structures of the two complexes are compared. This result corroborates our former finding that the RBD 97-110 peptide inhibits only signal transduction by oncogenic ras-p21 and suggests that oncogenic p21 uses this loop to interact with raf in a unique manner.

Induction of oocyte maturation by jun-N-terminal kinase (JNK) on the oncogenic ras-p21 pathway is dependent on the raf-MEK signal transduction pathway

PURPOSE

We have previously found that microinjection of activated MEK (mitogen activated kinase kinase) and ERK (mitogen-activated protein; MAP kinase) fails to induce oocyte maturation, but that maturation, induced by oncogenic ras-p21 and insulin-activated cell ras-p21, is blocked by peptides from the ras-binding domain of raf. We also found that jun kinase (JNK), on the stress-activated protein (SAP) pathway, which is critical to the oncogenic ras-p21 signal transduction pathway, is a strong inducer of oocyte maturation. Our purpose in this study was to determine the role of the raf-MEK-MAP kinase pathway in oocyte maturation and how it interacts with JNK from the SAP pathway.

METHODS

We microinjected raf dominant negative mutant mRNA (DN-raf) and the MEK-specific phosphatase, MKP-T4, either together with oncogenic p21 or c-raf mRNA, into oocytes or into oocytes incubated with insulin to determine the effects of these raf-MEK-MAP kinase pathway inhibitors.

RESULTS

We found that oocyte maturation induced by both oncogenic and activated normal p21 is inhibited by both DN-raf and by MKP-T4. The latter more strongly blocks the oncogenic pathway. Also an mRNA encoding a constitutively activated MEK strongly induces oocyte maturation that is not inhibited by DN-raf or by MKP-T4. Surprisingly, we found that oocyte maturation induced by JNK is blocked both by DN-raf and MKP-T4. Furthermore, we discovered that c-raf induces oocyte maturation that is inhibited by glutathione-S-transferase (GST), which we have found to be a potent and selective inhibitor of JNK.

CONCLUSION

We conclude that there is a strong reciprocal interaction between the SAP pathway involving JNK and the raf-MEK-MAP kinase pathway and that oncogenic ras-p21 can be preferentially inhibited by MEK inhibitors. The results imply that blockade of both MEK and JNK-oncogenic ras-p21 interactions may constitute selective synergistic combination chemotherapy against oncogenic ras-induced tumors.

Molecular modeling of mammalian cytochrome P450s

The cytochrome P450s are a superfamily of hemoprotein enzymes responsible for the metabolism of a wide variety of xenobiotic and endogenous compounds. The individual P450s exhibit unique substrate specificity and stereoselectivity profiles which reflect corresponding differences in primary sequence and tertiary structure. In the absence of an experimental structure models for mammalian P450s have been generated by their homology with bacterial P450s of known structure. The rather low sequence identity between target and template proteins renders P450 modeling a challenging task. However, the substrate recognition properties of several P450s are consistent with recently developed working models. This review summarizes the major concepts and current approaches of molecular modeling of P450s.

Glutathione-S-Transferase as a selective inhibitor of oncogenic ras-p21-induced mitogenic signaling through blockade of activation of jun by jun-N-terminal kinase

We have identified the intracellular detoxification enzyme, glutathione-S-transferase (GST), as a potent inhibitor of the activation of jun by its kinase, jun-N-terminal kinase (JNK), in vitro. All three major isozymes (alpha, mu, and pi) bind to JNK-jun complexes and inhibit activation of jun by JNK. We now find that GST inhibits JNK-induced oocyte maturation in vivo and strongly inhibits oocyte maturation induced by oncogenic ras-p21 protein, but not by insulin-activated normal cellular p21 protein. These results correlate with the finding that oncogenic, but not insulin-activated normal, p21 induces high levels of activated JNK. GST also strongly blocks induction of oocyte maturation by protein kinase C (PKC) which is a critical downstream target of oncogenic but not normal ras-p21. Thus, we have established a new function for GST as a potent physiological inhibitor of the ras-JNK-jun pathway.

Conformational and molecular basis for induction of apoptosis by a p53 C-terminal peptide in human cancer cells

A p53-derived C-terminal peptide induced rapid apoptosis in breast cancer cell lines carrying endogenous p53 mutations or overexpressed wild-type (wt) p53 but was not toxic to nonmalignant human cell lines containing wt p53. Apoptosis occurred through a Fas/APO-1 signaling pathway involving increased extracellular levels of Fas/FasL in the absence of protein synthesis, as well as activation of a Fas/APO-1-specific protease, FLICE. The peptide activity was p53-dependent, and it had no effect in three tumor cell lines with null p53. Furthermore, the C-terminal peptide bound to p53 protein in cell extracts. Thus, p53-dependent, Fas/APO-1 mediated apoptosis can be induced in breast cancer cells with mutant p53 similar to the recently described Fas/APO-1 induced apoptosis by wt p53. However, mutant p53 without p53 peptide does not induce a Fas/APO-1 activation or apoptosis. Docking of the computed low energy conformations for the C-terminal peptide with those for a recently defined proline-rich regulatory region from the N-terminal domain of p53 suggests a unique low energy complex between the two peptide domains. The selective and rapid induction of apoptosis in cancer cells carrying p53 abnormalities may lead to a novel therapeutic modality.

Inhibition of oncogenic and activated wild-type ras-p21 protein-induced oocyte maturation by peptides from the guanine-nucleotide exchange protein, SOS, identified from molecular dynamics calculations. Selective inhibition of oncogenic ras-p21

In the preceding paper we performed molecular dynamics calculations of the average structures of the SOS protein bound to wild-type and oncogenic ras-p21. Based on these calculations, we have identified four major domains of the SOS protein, consisting of residues 631-641, 676-691, 718-729, and 994-1004, which differ in structure between the two complexes. We have now microinjected synthetic peptides corresponding to each of these domains into Xenopus laevis oocytes either together with oncogenic (Val 12)-p21 or into oocytes subsequently incubated with insulin. We find that the first three peptides inhibit both oncogenic and wild-type p21-induced oocyte maturation, while the last peptide much more strongly inhibits oncogenic p21 protein-induced oocyte maturation. These results suggest that each identified SOS region is involved in ras-stimulated signal transduction and that the 994-1004 domain is involved uniquely with oncogenic ras-p21 signaling.

Identification of a glutathione-S-transferase effector domain for inhibition of jun kinase, by molecular dynamics

We have recently found that the glutathione-S-transferase pi-isozyme (GST-pi), a cellular detoxification enzyme, potently and selectively inhibits activation of jun protein by its upstream kinase, jun kinase (JNK). This newly identified regulatory activity of GST-pi is strongly inhibited by a group of agents that inhibit its enzymatic activity. Since loss of enzymatic activity in general does not correlate with loss of regulatory activity, it is likely that inhibitor binding induces changes in the structure of one or more domains of GST that block its interaction with JNK. To identify regions of GST that change conformation on the binding of inhibitors, we have performed molecular dynamics calculations on GST-pi to compute its average structure in the presence and absence of the inhibitor, glutathione sulfonate. Superposition of the two average structures reveals that several regions change local structure depending upon whether the inhibitor is bound or not bound. Two of these regions, residues 36-50 and 194-201, are highly exposed. We have synthesized peptides corresponding to these two segments and find that the 194-201 sequence strongly inhibits the ability of GST-pi to block the in vitro phosphorylation of jun by JNK. These results suggest that this region of GST-pi is critical to its functioning as a newly discovered regulator of signal transduction.

Molecular dynamics analysis of the structures of ras-guanine nucleotide exchange protein (SOS) bound to wild-type and oncogenic ras-p21. Identification of effector domains of SOS

The X-ray crystal structure of the ras oncogene-encoded p21 protein bound to SOS, the guanine nucleotide exchange-promoting protein, has been determined. We have undertaken to determine if there are differences between the three-dimensional structures of SOS bound to normal and oncogenic (Val 12-p21) proteins. Using molecular dynamics, we have computed the average structures for both complexes and superimposed them. We find four domains of SOS that differ markedly in structure: 631-641, 676-691, 718-729, and 994-1004. Peptides corresponding to these sequences have been synthesized and found to be powerful modulators of oncogenic p21 in cells as described in an accompanying paper. We find that the SOS segment from 809-815 makes contacts with multiple domains of ras-p21 and can facilitate correlated conformational changes in these domains.

Identification of the site of inhibition of oncogenic ras-p21-induced signal transduction by a peptide from a ras effector domain

We have previously found that a peptide corresponding to residues 35-47 of the ras-p21 protein, from its switch 1 effector domain region, strongly inhibits oocyte maturation induced by oncogenic p21, but not by insulin-activated cellular wild-type p21. Another ras-p21 peptide corresponding to residues 96-110 that blocks ras-jun and jun kinase (JNK) interactions exhibits a similar pattern of inhibition. We have also found that c-raf strongly induces oocyte maturation and that dominant negative c-raf strongly blocks oncogenic p21-induced oocyte maturation. We now find that the p21 35-47, but not the 96-110, peptide completely blocks c-raf-induced maturation. This finding suggests that the 35-47 peptide blocks oncogenic ras at the level of raf; that activated normal and oncogenic ras-p21 have differing requirements for raf-dependent signaling; and that the two oncogenic-ras-selective inhibitory peptides, 35-47 and 96-110, act at two different critical downstream sites, the former at raf the latter at JNK/jun, both of which are required for oncogenic ras-p21 signaling.

Common conformational effects in the p53 protein of vinyl chloride-induced mutations

The tumor suppressor gene p53 has been identified as the most frequent site of genetic alterations in human cancers. Vinyl chloride, a known human carcinogen, has been associated with specific A --> T transversions at codons 179, 249, and 255 of the p53 gene. The mutations result in amino acid substitutions of His --> Leu at residue 179, Arg --> Trp at residue 249, and He --> Phe at residue 255 in highly conserved regions of the DNA-binding core domain of the p53 protein. We previously used molecular dynamics calculations to demonstrate that the latter two mutants contain certain common regions that differ substantially in conformation from the wild-type structure. In order to determine whether these conformational changes are consistent for other p53 mutants, we have now used molecular dynamics to determine the structure of the DNA-binding core domain of the Leu 179 p53 mutant. The results indicate that the Leu 179 mutant differs substantially from the wild-type structure in certain discrete regions that are similar to those noted previously in the other p53 mutants. One of these regions (residues 204-217) contains the epitope for the monoclonal antibody PAb240, which is concealed in the wild-type structure, but accessible in the mutant structure, and another region (residues 94-110) contains the epitope for the monoclonal antibody PAb1620, which is accessible in the wild-type structure, but concealed in the mutant structure. Immunologic analyses of tumor tissue known to contain this mutation confirmed these predicted conformational shifts in the mutant p53 protein.

Regulation of JNK signaling by GSTp

Studies of low basal Jun N-terminal kinase (JNK) activity in non-stressed cells led us to identify a JNK inhibitor that was purified and identified as glutathione S-transferase Pi (GSTp) and was characterized as a JNK-associated protein. UV irradiation or H2O2 treatment caused GSTp oligomerization and dissociation of the GSTp-JNK complex, indicating that it is the monomeric form of GSTp that elicits JNK inhibition. Addition of purified GSTp to the Jun-JNK complex caused a dose-dependent inhibition of JNK activity. Conversely, immunodepleting GSTp from protein extracts attenuated JNK inhibition. Furthermore, JNK activity was increased in the presence of specific GSTp inhibitors and a GSTp-derived peptide. Forced expression of GSTp decreased MKK4 and JNK phosphorylation which coincided with decreased JNK activity, increased c-Jun ubiquitination and decreased c-Jun-mediated transcription. Co-transfection of MEKK1 and GSTp restored MKK4 phosphorylation but did not affect GSTp inhibition of JNK activity, suggesting that the effect of GSTp on JNK is independent of the MEKK1-MKK4 module. Mouse embryo fibroblasts from GSTp-null mice exhibited a high basal level of JNK activity that could be reduced by forced expression of GSTp cDNA. In demonstrating the relationships between GSTp expression and its association with JNK, our findings provide new insight into the regulation of stress kinases.

Inhibition of human cytochrome P450 1A2 by flavones: a molecular modeling study

Cytochrome P450 1A2 metabolizes a number of important drugs, procarcinogens, and endogenous compounds. Several flavones, a class of phytochemicals consumed in the human diet, have been shown to differentially inhibit human P450 1A2-mediated methoxyresorufin demethylase. A molecular model of this P450 was constructed in order to elucidate the molecular basis of the P450-flavone interaction. Flavone and its 3,5,7-trihydroxy and 3,5,7-trimethoxy derivatives were docked into the active site to assess their mode of binding. The site is hydrophobic and includes several residues that hydrogen bond with substituents on the flavone nucleus. The binding interactions of these flavones in the modeled active side are consistent with their relative inhibitory potentials, namely 3,5,7-trihydroxylflavone > flavone > 3,5,7-trimethoxylflavone, toward P450 1A2-mediated methoxyresorufin demethylation.

MEKK1/JNK signaling stabilizes and activates p53

Activation of the tumor suppressor p53 by stress and damage stimuli often correlates with induction of stress kinases, Jun-NH2 kinase (JNK). As JNK association with p53 plays an important role in p53 stability, in the present study we have elucidated the relationship between the JNK-signaling pathway and p53 stability and activity. Expression of a constitutively active form of JNKK upstream kinase, mitogen-activated protein kinase kinase kinase (DeltaMEKK1), increased the level of the exogenously transfected form of p53 in p53 null (10.1) cells as well as of endogenous p53 in MCF7 breast cancer cells. Increased p53 level by forced expression of DeltaMEKK1 coincided with a decrease in p53 ubiquitination in vivo and with prolonged p53 half-life. Computerized modeling of the JNK-binding site (amino acids 97-116; p7 region) enabled us to design mutations of exposed residues within this region. Respective mutations (p53(101-5-8)) and deletion (p53(Deltap7)) forms of p53 did not exhibit the same increase in p53 levels upon DeltaMEKK1 expression. In vitro phosphorylation of p53 by JNK abolished Mdm2 binding and targeting of p53 ubiquitination. Similarly, DeltaMEKK1 expression increased p53 phosphorylation by immunopurified JNK and dissociated p53-Mdm2 complexes. Transcriptional activity of p53, as measured via mdm2 promoter-driven luciferase, exhibited a substantial increase in DeltaMEKK1-expressing cells. Cotransfection of p53 and DeltaMEKK1 into p53 null cells potentiated p53-dependent apoptosis, suggesting that MEKK1 effectors contribute to the ability of p53 to mediate programmed cell death. Our results point to the role of MEKK1-JNK signaling in p53 stability, transcriptional activities, and apoptotic capacity as part of the cellular response to stress.

Direct identification of unexpected serum antibodies against red cell antigens

A new method to detect the identity of unexpected antibodies in the sera of prospective transfusion recipients is presented. The method is based on a macroscopic hemagglutination inhibition assay. In this assay, incubation of phenotypically defined test red blood cells with patient sera containing non-agglutinating antibodies to one or more specific antigen systems block monoclonal IgM induction of red cell agglutination. Since the specificities of the IgM antibodies are known, the identity of the patient's antibody(ies) can be directly determined. This method, which uses only reagents that are commercially available, is specific and eliminates the use of the indirect antiglobulin test (IAT) and the use of elimination panels.

Molecular markers of carcinogenesis

The protein products of oncogenes and tumor suppressor genes play critical roles in the development of many cancers. The expression of a number of these proteins can be detected in extracellular fluids such as blood. This article reviews the literature on the application of methods for the detection of the proteins of oncogenes and tumor suppressor genes in the blood of humans with cancer or at risk for the development of cancer. The detection of these proteins in blood may be useful molecular markers of carcinogenesis that could play an important part in cancer diagnosis, prognosis, and prevention.

Molecular modeling of cytochrome P450 2B1: mode of membrane insertion and substrate specificity

A molecular model of a mammalian membrane-bound cytochrome P450, rat P450 2B1, was constructed in order to elucidate its mode of attachment to the endoplasmic reticulum and the structural basis of substrate specificity. The model was primarily derived from the structure of P450BM-3, which as a class II P450 is the most functionally similar P450 of known structure. However, model development was also guided by the conserved core regions of P450cam and P450terp. To optimally align the P450 2B1 and P450BM-3 sequences, multiple alignment was performed using sequences of five P450s in the II family, followed by minor adjustments on the basis of secondary structure predictions. The resulting P450 2B1 homology model structure was refined by molecular dynamics heating, equilibration, simulation, and energy minimization. The model suggests that the F-G loop serves as both a hydrophobic membrane anchor and entrance channel for hydrophobic substrates from the membrane to the P450 active site. To assess the mode of substrate binding, benzphetamine, testosterone, and benzo[a]pyrene were docked into the active site. The hydrophobic substrate-binding pocket is consistent with the preferences of this P450 toward hydrophobic substrates, while the presence of an acidic Glu-105 in this pocket is consistent with the preference of this P450 for the cationic substrate benzphetamine. This model is thus consistent with several known experimental properties of this P450, such as membrane attachment and substrate selectivity.

Selective inhibition of oncogenic ras-p21 in vivo by agents that block its interaction with jun-N-kinase (JNK) and jun proteins. Implications for the design of selective chemotherapeutic agents

We have obtained evidence that oncogenic and activated normal ras-p21 proteins utilize overlapping but distinct signal transduction pathways. Recently, we found that ras-p21 binds to both jun and its kinase, jun kinase (JNK). We now present evidence that suggests that oncogenic but not normal activated p21 depends strongly on early activation of JNK/jun. This early activation most likely involves direct interaction between oncogenic p21 and JNK/jun because p21 peptides that blocked the binding of p21 to JNK and jun strongly inhibited oncogenic p21-induced oocyte maturation while they did not inhibit insulin-activated normal cellular p21-induced maturation. Very similar results were also obtained for a newly characterized specific inhibitor of JNK which blocked oncogenic but not normal activated p21-induced oocyte maturation. We also found that both jun and JNK strongly enhanced oncogenic p21-induced oocyte maturation while they inhibited insulin-activated normal p21-induced oocyte maturation. These results suggest that the peptides and JNK inhibitor may be useful agents in selectively blocking the effects of oncogenic but not normal p21 in cells.

Molecular dynamics on complexes of ras-p21 and its inhibitor protein, rap-1A, bound to the ras-binding domain of the raf-p74 protein: identification of effector domains in the raf protein

We have computed the average structures for the ras-p21 protein and its strongly homologous inhibitor protein, rap-1A, bound to the ras-binding domain (RBD) of the raf protein, using molecular dynamics. Our purpose is to determine the differences in structure between these complexes that would result in no mitogenic activity of rap-1A-RBD but full activity of p21-RBD. We find that despite the similarities of the starting structures for both complexes, the average structures differ considerably, indicating that these two proteins do not interact in the same way with this vital target protein. p21 does not undergo major changes in conformation when bound to the RBD, while rap-1A undergoes significant changes in structure on binding to the RBD, especially in the critical region around residue 61. The p21 and rap-1A make substantially different contacts with the RBD. For example, the loop region from residues 55-71 of rap-1a makes extensive hydrogen-bond contacts with the RBD, while the same residues of p21 do not. Comparison of the structures of the RBD in both complexes reveals that it undergoes considerable changes in structure when its structure bond to p21 is compared with that bound to rap-1A. These changes in structure are due to displacements of regular structure (e.g., alpha-helices and beta-sheets) rather than to changes in the specific conformations of the segments themselves. Three regions of the RBD have been found to differ significantly from one another in the two complexes: the binding interface between the two proteins at residues 60 and 70, the region around residues 105-106, and 118-120. These regions may constitute effector domains of the RBD whose conformations determine whether or not mitogenic signal transduction will occur.

Inhibition of oncogenic and activated wild-type ras-p21 protein-induced oocyte maturation by peptides from the ras-binding domain of the raf-p74 protein, identified from molecular dynamics calculations

In the preceding paper we found from molecular dynamics calculations that the structure of the ras-binding domain (RBD) of raf changes predominantly in three regions depending upon whether it binds to ras-p21 or to its inhibitor protein, rap-1A. These three regions of the RBD involve residues from the protein-protein interaction interface, e.g., between residues 60 and 72, residues 97-110, and 111-121. Since the rap-1A-RBD complex is inactive, these three regions are implicated in ras-p21-induced activation of raf. We have therefore co-microinjected peptides corresponding to these three regions, 62-76, 97-110, and 111-121, into oocytes with oncogenic p21 and microinjected them into oocytes incubated in in insulin, which activates normal p21. All three peptides, but not a control peptide, strongly inhibit both oncogenic p21- and insulin-induced oocyte maturation. These findings corroborate our conclusions from the theoretical results that these three regions constitute raf effector domains. Since the 97-110 peptide is the strongest inhibitor of oncogenic p21, while the 111-121 peptide is the strongest inhibitor of insulin-induced oocyte maturation, the possibility exists that oncogenic and activated normal p21 proteins interact differently with the RBD of raf.

Conformation-dependent phosphorylation of p53

Phosphorylation of the p53 tumor suppressor protein is known to modulate its functions. Using bacterially produced glutathione S-transferase (GST)-p53 fusion protein and baculovirus-expressed histidine-tagged p53 ((His)p53), we have determined human p53 phosphorylation by purified forms of jun-N-kinase (JNK), protein kinase A (PKA), and beta subunit of casein kinase II (CKIIbeta) as well as by kinases present in whole cell extracts (WCEs). We demonstrate that PKA is potent p53 kinase, albeit, in a conformation- and concentration-dependent manner, as concluded by comparing full-length with truncated forms of p53. We further demonstrate JNK interaction with GST-p53 and the ability of JNK to phosphorylate truncated forms of GST-p53 or full-length (His)p53. Dependence of phosphorylation on conformation of p53 is further supported by the finding that the wild-type form of p53 (p53wt) undergoes better phosphorylation by CKIIbeta and by WCE kinases than mutant forms of p53 at amino acid 249 (p53(249)) or 273 (p53(273)). Moreover, shifting the kinase reaction's temperature from 37 degrees C to 18 degrees C reduces the phosphorylation of mutant p53 to a greater extent than of p53wt. Comparing truncated forms of p53 revealed that the ability of CKIIbeta, PKA, or WCE kinases to phosphorylate p53 requires amino acids 97-155 within the DNA-binding domain region. Among three 20-aa peptides spanning this region we have identified residues 97-117 that increase p53 phosphorylation by CKIIbeta while inhibiting p53 phosphorylation by PKA or WCE kinases. The importance of this region is further supported by computer modeling studies, which demonstrated that mutant p53(249) exhibits significant changes to the conformation of p53 within amino acids 97-117. In summary, phosphorylation-related analysis of different p53 forms in vitro indicates that conformation of p53 is a key determinant in its availability as a substrate for different kinases, as for the phosphorylation pattern generated by the same kinase.

Activation of c-Jun-NH2-kinase by UV irradiation is dependent on p21ras

We have demonstrated previously that Jun-NH2-kinase (JNK) activation in vitro is potentiated by association with the p21(ras) protein. To determine if in vivo activation of JNK also depends on p21(ras), we have used M1311 cells that carry the cDNA for the neutralizing antibody to p21(ras), Y13-259, under a dexamethasone-inducible promoter. The ability of UV to activate JNK gradually decreased over a 4-day period of cell growth in dexamethasone. This decrease coincides with weaker transcriptional activation measured via gel shift and chloramphenicol acetyltransferase assays. Peptides corresponding to amino acids 96-110 on p21(ras), which were shown to block Ras-JNK association, inhibited UV-mediated JNK activation in mouse fibroblast 3T3-4A cells as well as in M1311 cells, further supporting the role of p21(ras) in UV-mediated JNK activation. Overall, the present studies provide in vivo confirmation of the role p21(ras) plays in JNK activation by UV irradiation.

Effects of chemopreventive selenium compounds on Jun N-kinase activities

Activation of Jun-N-kinases (JNK) is stimulated by diverse agents including UV-irradiation, heat shock, tumor necrosis factor and osmotic shock. In the present study we have elucidated the effect of the organoselenium chemopreventive agent 1,4-phenylenebis(methylene)selenocyanate (p-XSC, on UV-mediated JNK activation. Using mouse fibroblasts as a model cell system we found that low concentrations (1-10 microM range) of p-XSC did not affect JNK activity, yet were capable of potentiating JNK activity when administered prior to UV-irradiation. While higher doses of p-XSC have minimal effect on JNK activation, when combined with UV, there is a dose-dependent decrease in JNK activation. Similar to its effects on JNK, p-XSC is a potent inducer of src-related tyrosine kinases. p-XSC mediated changes in JNK activation correlate with its ability to potentiate the association of JNK with p21ras, in a manner similar to that we have previously observed with GTP or sodium vanadate. That p-XSC can modulate JNK activities points to a possible mechanism by which it contributes to the cell's ability to cope with stress.

Diffuse large cell lymphoma of B-cell type associated with reactive hemophagocytosis

Some lymphomas, virtually all phenotypically of the T-cell type, have been associated with the phenomenon of hemophagocytosis. Only two B-cell lymphomas, one T-cell-rich and the other an angiocentric lymphoma, have been observed to exhibit this phenomenon. A case is reported of a diffuse large cell lymphoma of the B-cell type associated with reactive hemophagocytosis. Cytokines or other humoral factors produced by the lymphoma are a possible cause, and their effect is probably systemic. There is some evidence suggesting correlation of hemophagocytosis with tumor aggressiveness.

Computed three-dimensional structures for the ras-binding domain of the raf-p74 protein complexed with ras-p21 and with its suppressor protein, rap-1A

The three-dimensional structures of the ras-p21 protein and its protein inhibitor, rap-1A, have been computed bound to the ras-binding domain, RBD (residues 55-131), of the raf-p74 protein, a critical target protein of ras-p21 in the ras-induced mitogenic signal transduction pathway. The coordinates of RBD have been reconstructed from the stereoview of an X-ray crystal structure of this domain bound to rap-1A and have been subjected to energy minimization. The energy-minimized structures of both ras-p21 and rap-1A, obtained in previous studies, have been docked against RBD, using the stereo figure of the RBD-rap-1A complex, based on a six-step procedure. The final energy-minimized structure of rap-1A-RBD is identical to the X-ray crystal structure. Comparison of the ras-p21- and rap-1A-RBD complexes reveals differences in the structures of effector domains of ras-p21 and rap-1a, including residues 32-47, a domain that directly interacts with RBD, 60-66, 96-110, involved in the interaction of ras-p21 with jun kinase (JNK) and jun protein, and 115-126, involved in the interaction of p21 with JNK. The structure of the RBD remained the same in both complexes with the exception of small deviations in its beta-2 binding loop (residues 63-71) and residues 89-91, also involved in binding to rap-1A. The results suggest that the binding of these two proteins to RBD may allow them to interact with other cellular target proteins such as JNK and jun.

Oncogenic amino acid substitutions in the inhibitory rap-1A protein cause it to adopt a ras-p21-like conformation as computed using molecular dynamics

rap-1A is a membrane-bound G-protein in the ras superfamily that, like the ras-p21 protein, is activated by binding GTP in place of GDP. When activated, however, this protein inhibits the action of ras-p21, which is to induce mitogenesis in cells A chimeric protein containing RAS-p21 residues 1-65 and rap-1A residues 66-184 becomes ras-p21-like in its activity. The critical changes in sequence that result in this transformation are G26N, 127H, E30D, K31E, and E45V. All of these substitutions occur in or around a critical effector domain of p21 that is involved in interacting with GTPase activating protein (GAP), raf-p74 protein and inositol-3-hydroxy kinase. Using molecular dynamics, we have computed the average low energy structures for each of the three proteins, ras-p21, rap-1A and mutant rap1A, called rap-M, that contains these critical amino acid substitutions. We find that rap-M more closely superimposes on ras-p21 (rms deviation 1.9 A) than on wild-type rap-1A (rms deviation 3.4 A). In particular, the amino terminal domains (residues 3-59) of both RAS-p21 and rap-M are superimposable while they deviate when the average structures of these two proteins are superimposed on that of wild-type rap-1A. We have identified Pro 34 as a critical residue which may determine if the protein transforms cells or inhibits cell transformation. In addition, we have found that ras-p21 and rap-M proteins are superimposable in the region 96-110 except at Asp 105. The 96-110 domain of ras-p21 has been found to be involved in the binding of this protein to the nuclear transcription protein, jun and its kinase, jun kinase, JNK. Both segments differ in structure from that of the rap-1A segment at Asp 108, implicating this residue as also being important in determining the activity of the protein. Overall, the oncogenic substitutions introduced into the rap-1A protein cause it to adopt a conformation that is very similar to that of ras-p21 rather than wild-type rap-1A.

Conformational effects in the p53 protein of mutations induced during chemical carcinogenesis: molecular dynamic and immunologic analyses

The tumor suppressor gene p53 has been identified as the most frequent target of genetic alterations in human cancers. Vinyl chloride, a known human carcinogen that induces the rare sentinel neoplasm angiosarcoma of the liver, has been associated with specific A-->T transversions at the first base of codons 249 and 255 of the p53 gene. These mutations result in an Arg-->Trp amino acid substitution at residue 249 and an Ile-->Phe amino acid substitution at residue 255 in a highly conserved region in the DNA-binding core domain of the p53 protein. To determine the effects of these substitutions on the three-dimensional structure of the p53 protein, we have performed molecular dynamics calculations on this core domain of the wild-type and the Trp-249 and Phe-255 mutants to compute the average structures of each of the three forms. Comparisons of the computed average structures show that both mutants differ substantially from the wild-type structure in certain common, discrete regions. One of these regions (residues 204-217) contains the epitope for the monoclonal antibody PAb240, which is concealed in the wild-type structure but accessible in both mutant structures. In order to confirm this conformational shift, tumor tissue and serum from vinyl chloride-exposed individuals with angiosarcomas of the liver were examined by immunohistochemistry and enzyme-linked immunosorbent assay. Individuals with tumors that contained the p53 mutations were found to have detectable mutant p53 protein in their tumor tissue and serum, whereas individuals with tumors without mutations and normal controls did not.

Prediction of the three-dimensional structure of the rap-1A protein from its homology to the ras-gene-encoded p21 protein

rap-1A, an anti-oncogene-encoded protein, is a ras-p21-like protein whose sequence is over 80% homologous to p21 and which interacts with the same intracellular target proteins and is activated by the same mechanisms as p21, e.g., by binding GTP in place of GDP. Both interact with effector proteins in the same region, involving residues 32-47. However, activated rap-1A blocks the mitogenic signal transducing effects of p21. Optimal sequence alignment of p21 and rap-1A shows two insertions of rap-1A at ras positions 120 and 138. We have constructed the three-dimensional structure of rap-1A bound to GTP by using the energy-minimized three-dimensional structure of ras-p21 as the basis for the modeling using a stepwise procedure in which identical and homologous amino acid residues in rap-1A are assumed to adopt the same conformation as the corresponding residues in p21. Side-chain conformations for homologous and nonhomologous residues are generated in conformations that are as close as possible to those of the corresponding side chains in p21. The entire structure has been subjected to a nested series of energy minimizations. The final predicted structure has an overall backbone deviation of 0.7 A from that of ras-p21. The effector binding domains from residues 32-47 are identical in both proteins (except for different side chains of different residues at position 45). A major difference occurs in the insertion region at residue 120. This region is in the middle of another effector loop of the p21 protein involving residues 115-126. Differences in sequence and structure in this region may contribute to the differences in cellular functions of these two proteins.

Complexes of p21RAS with JUN N-terminal kinase and JUN proteins

RAS gene-encoded p21 protein has been found to increase in vitro phosphorylation of JUN via its kinase, JUN N-terminal kinase (JNK). This effect is mediated by increased phosphorylation of JNK in the presence of wild-type and oncogenic (Val-12) p21 protein in a dose-dependent manner. Oncogenic p21 protein is more potent in mediating this effect than its normal counterpart. Both normal and oncogenic p21 proteins bind to purified JNK and to JNK that is present in cell extracts from transformed fibroblasts and melanoma cells. Oncogenic and normal p21 proteins have also been found to bind to bacterially expressed JUN protein. This binding is dose dependent, enhanced by the presence of GTP, and depends on the presence of the first 89 amino acids of JUN (the delta domain), as it does not occur with v-jun. While the ability of both normal and oncogenic p21 proteins to bind JNK is strongly inhibited by a p21 peptide corresponding to aa 96-110, and more weakly inhibited by the p21 peptide corresponding to aa 115-126, p21-JUN interaction is inhibited by peptides corresponding to aa 96-110 and, to a lesser degree, by peptides corresponding to aa 35-47. The results suggest that the p21 protein interacts specifically with both JNK and JUN proteins.

Structural effects of the binding of GTP to the wild-type and oncogenic forms of the ras-gene-encoded p21 proteins

Molecular dynamics calculations have been performed to determine the average structures of ras-gene-encoded p21 proteins bound to GTP, i.e., the normal (wild-type) protein and two oncogenic forms of this protein, the Val 12- and Leu 61-p21 proteins. We find that the average structures for all of these proteins exhibit low coordinate fluctuations (which are highest for the normal protein), indicating convergence to specific structures. From previous dynamics calculations of the average structures of these proteins bound to GDP, major regional differences were found among these proteins [Monaco et al. (1995), J. Protein Chem., in press]. We now find that the average structures of the oncogenic proteins are more similar to one another when the proteins are bound to GTP than when they are bound to GDP [Monaco et al. (1995), J. Protein Chem., in press]. However, they still differ in structure at specific amino acid residues rather than in whole regions, in contradistinction to the results found for the p21-GDP complexes. Two exceptions are the regions 25-32, in an alpha-helical region, and 97-110. The two oncogenic (Val 12- and Leu 61-) proteins have similar structures which differ significantly in the region of residues 97-110. This region has recently been identified as being critical in the interaction of p21 with kinase target proteins. The differences in structure between the oncogenic proteins suggest the existence of more than one oncogenic form of the p21 protein that can activate different signaling pathways.

Comparison of the computed three-dimensional structures of oncogenic forms (bound to GDP) of the ras-gene-encoded p21 protein with the structure of the normal (non-transforming) wild-type protein

The ras-oncogene-encoded p21 protein becomes oncogenic if amino acid substitutions occur at critical positions in the polypeptide chain. The most commonly found oncogenic forms contain Val in place of Gly 12 or Leu in place of Gln 61. To determine the effects of these substitutions on the three-dimensional structure of the whole p21 protein, we have performed molecular dynamics calculations on each of these three proteins bound to GDP and magnesium ion to compute the average structures of each of the three forms. Comparisons of the computed average structures shows that both oncogenic forms with Val 12 and Leu 61 differ substantially in structure from that of the wild type (containing Gly 12 and Gln 61) in discrete regions: residues 10-16, 32-47, 55-74, 85-89, 100-110, and 119-134. All of these regions occur in exposed loops, and several of them have already been found to be involved in the cellular functioning of the p21 protein. These regions have also previously been identified as the most flexible domains of the wild-type protein and have been bound to be the same ones that differ in conformation between transforming and nontransforming p21 mutant proteins neither of which binds nucleotide. The two oncogenic forms have similar conformations in their carboxyl-terminal domains, but differ in conformation at residues 32-47 and 55-74. The former region is known to be involved in the interaction with at least three downstream effector target proteins. Thus, differences in structure between the two oncogenic proteins may reflect different relative affinities of each oncogenic protein for each of these effector targets. The latter region, 55-74, is known to be a highly mobile segment of the protein. The results strongly suggest that critical oncogenic amino acid substitutions in the p21 protein cause changes in the structures of vital domains of this protein.

Three-dimensional energy-minimized model of human type II "Smith" collagen microfibril

A procedure is described for constructing a three-dimensional model of fibril-forming human type II collagen based on the "Smith" microfibril model. This model is a complex of five individual collagen triple-helical molecules, and is based on known structural parameters for collagen. Both experimental and theoretical data were used as constraints to guide the modeling. The resulting fibril model for type II collagen is in agreement with both physical and chemical characteristics produced by experimental staining patterns of type II fibrils. Some advantages of the type II model are that the stereochemistry of all the sidechain groups is accounted for, and specific atomic interactions can now be studied. This model is useful for: development of therapeutics for collagen related diseases; development of synthetic collagen tissues; design of chemical reagents (i.e., tanning agents) to treat collagen-related products; and study of the structural and functional aspects of type II collagen. Described is the procedure by which the Smith microfibril of type II collagen was developed using molecular modeling tools, validation of the model by comparison to electron-microscopic images of fibril staining patterns, and some applications of this microfibril model.

Conformation of the transmembrane domain of the c-erbB-2 oncogene-encoded protein in its monomeric and dimeric states

The human c-erbB-2 oncogene is homologous to the rat neu oncogene, both encoding transmembrane growth factor receptors. Overexpression and point mutations in the transmembrane domain of the encoded proteins in both cases have been implicated in cell transformation and carcinogenesis. In the case of the neu protein, it has been proposed that these effects are mediated by conformational preferences for an alpha-helix in the transmembrane domain, which facilitates receptor dimerization, an important step in the signal transduction process. To examine whether this is the case for c-erbB-2 as well, we have used conformational energy analysis to determine the preferred three-dimensional structures for the transmembrane domain of the c-erbB-2 protein from residues 650 to 668 with Val (nontransforming) and Glu (transforming) at position 659. The global minimum energy conformation for the Val-659 peptide from the normal, nontransforming protein was found to contain several bends, whereas the global minimum energy conformation for Glu-659 peptide from the mutant, transforming protein was found to be alpha-helical. Thus, the difference in conformational preferences for these transmembrane domains may explain the difference in transforming ability of these proteins. The presence of higher-energy alpha-helical conformations for the transmembrane domain from the normal Val-659 protein may provide an explanation for the presence of a transforming effect from overexpression of c-erbB-2. In addition, docking of the oncogenic sequences in their alpha-helical and bend conformations shows that the all-alpha-helical dimer is clearly favored energetically over the bend dimer.

Conformational effects of environmentally induced, cancer-related mutations in the p53 protein

The tumor suppressor gene p53 has been identified as the most frequent target of genetic alterations in human cancers. A considerable number of environmentally induced, cancer-related p53 mutations in human tumors have been found in a highly conserved proline-rich sequence of the p53 protein encompassed by amino acid residues 147-158. Using conformational energy analysis based on ECEPP (Empirical Conformational Energy for Peptides Program), we have determined the low-energy three-dimensional structures for this dodecapeptide sequence for the human wild-type p53 protein and three environmentally induced, cancer-related mutant p53 proteins with His-151, Ser-152, and Val-154, respectively. The results suggest that the wild-type sequence adopts a well-defined low-energy conformation and that the mutant peptides adopt well-defined conformations that are distinctly different from the conformation of the wild-type peptide. These results are consistent with experimental conformational studies demonstrating altered detectability of antigenic epitopes in wild-type and mutant p53 proteins. These results suggest that the oncogenic effects of these environmentally induced, cancer-related, mutant p53 proteins may be mediated by distinct local conformational changes in the protein.

Interaction between cytochrome P450 2B1 and cytochrome bs: inhibition by synthetic peptides indicates a role for P450 residues Lys-122 and Arg-125

Binding of cytochrome b5 to rat cytochrome P450 2B1 was inhibited (by 75%) by a synthetic peptide corresponding to P450 residues 116-134. The role of Lys-122 and Arg-125 were evaluated using peptides in which one or both of these basic residues were replaced with Glu. The Lys-122 substitution nearly abolished while the Arg-125 replacement decreased (by 20%) the inhibitory potential of the peptide. Substitution of both residues resulted in a peptide with no inhibitory activity. These results thus indicate a role for a specific P450 region as well as two basic residues within this region in the cytochrome P450-cytochrome b5 interaction.

Specificity of the cytochrome P-450 interaction with cytochrome b5

The specificity of the interaction of cytochrome b5 with different forms of cytochrome P-450 was examined. Immunopurification of cytochromes P-450 1A1, 2B1 and 2E1 from rat liver microsomes resulted in co-purification of cytochrome b5 with cytochrome P-450 forms 2B1 and 2E1 but not 1A1. This specificity was evaluated in conjunction with multiple sequence alignment of the three cytochrome P-450s and a molecular model of the cytochrome P-450-cytochrome b5 complex [(1989) Biochemistry 28, 8201-8205]. These analyses suggest two basic residues in the arginine cluster region of P-450, which are present in P-450s 2B1 and 2E1 but are absent in P-450 1A1, as potential binding sites for cytochrome b5.