Assignment of the heme axial ligand(s) for the ferric myoglobin (H93G) and heme oxygenase (H25A) cavity mutants as oxygen donors using magnetic circular dichroism

UV-visible absorption and magnetic circular dichroism (MCD) data are reported for the cavity mutants of sperm whale H93G myoglobin and human H25A heme oxygenase in their ferric states at 4 degreesC. Detailed spectral analyses of H93G myoglobin reveal that its heme coordination structure has a single water ligand at pH 5.0, a single hydroxide ligand at pH 10.0, and a mixture of species at pH 7.0 including five-coordinate hydroxide-bound, and six-coordinate structures. The five-coordinate aquo structure at pH 5 is supported by spectral similarity to acidic horseradish peroxidase (pH 3.1), whose MCD data are reported herein for the first time, and acidic myoglobin (pH 3.4), whose structures have been previously assigned by resonance Raman spectroscopy. The five-coordinate hydroxide structure at pH 10.0 is supported by MCD and resonance Raman data obtained here and by comparison with those of other known five-coordinate oxygen donor complexes. In particular, the MCD spectrum of alkaline ferric H93G myoglobin is strikingly similar to that of ferric tyrosinate-ligated human H93Y myoglobin, whose MCD data are reported herein for the first time, and that of the methoxide adduct of ferric protoporphyrin IX dimethyl ester (FeIIIPPIXDME). Analysis of the spectral data for ferric H25A heme oxygenase at neutral pH in the context of the spectra of other five-coordinate ferric heme complexes with proximal oxygen donor ligands, in particular the p-nitrophenolate and acetate adducts of FeIIIPPIXDME, is most consistent with ligation by a carboxylate group of a nearby glutamyl (or aspartic) acid residue.

[Studies on reduction of Au3+ by bacteria for preparing gold catalyst]

The strain D01, screened from different source bacterial strains, has relatively strong ability of adsorbing Au3+. The strain D01 was identified as Bacillus megatherium D01 and still grew well in the medium containing 600 mg/L Au3+. The results of electrochemical reaction indicated that the strain D01 had a strong ability of reduction. It could reduce the Au3+/alpha-Fe2O3(precursor of the gold catalyst) to highly dispersive Au0/alpha-Fe2O3 catalyst which could catalyze the reaction of CO + O2-->CO2.

Engineering human interferon alpha1c/86D with phage display technology

Human interferon-alpha1c/86D (IFNalpha1c/86D) was functionally displayed on the surface of the filamentous bacteriophage using a phagemid vector system (pCANTAB5E). The key amino acid residues involved in the receptor binding were further defined with phage displayed 6-mer peptide library and two neutralizing antibodies against linear epitopes on the IFN-alpha1b, indicating that residues 30, 33, 34, (AB-loop) and residues 124, 126, 127 (D helix, DE-loop) were more critical than the adjacent residues for recognition of receptor. In addition, a cassette mutagenesis library was generated by fully randomizing the sequence of the four positions 29, 31, 32 and 35 in AB-loop, and used to select phage-IFN variants with WISH-based panning method. Three phage-IFN variants were isolated to possess more antiviral activity in the range of 4-16-fold than parental phage-IFN after IPTG-induced soluble expression. The results suggest that phage displayed phage-IFN alpha1c/86D variants with increased specific activity might be obtained after purification procedures.

[Influence of the synthetic peptide recognized by neutralizing antibody on IFN-induced biological responses]

OBJECTIVE

The influence of synthetic peptide WLDPRH on IFN-induced biologic activity was studied.

METHODS

Based on our earlier studies in which two peptides were recognized by neutralizing antibody from the hexapeptide library displayed on the phage, one of the peptides synthesized, with amino acid sequence WLDPRH.

RESULTS

Computer-building approach showed that the synthetic peptide WLDPRH exhibited structural homology with LoopAB (29-35), the binding domain of type I IFN receptor. In the competitive ELISA studies, the synthetic peptide WLDPRH in 25 micrograms/ml could inhibit IFN binding neutralizing antibody 4C1. IFN-induced antiviral assay showed that the protective effects of suboptimal dose (20-70 pg/ml) of IFN were increased from 40% to 86% in the presence of the synthetic peptide WLDPRH and 1.4 micrograms/ml of the synthetic peptide WLDPRH was the lowest dose with the best protection. But potentiating effect on IFN-induced growth inhibition was fewer noticeable in 1.4 micrograms/ml of synthetic peptide.

CONCLUSION

The results indicated that synthetic peptide WLDPRH can mimic the structure and activity of Loop AB in the IFN molecule and can be applied to immunotherapy as well as the mimic minimolecular design of IFN.

Solid phase microextraction of pesticide residues from strawberries

A new solid phase microextraction method for the determination of pesticide residues in strawberries for 16 commonly used compounds was described. The strawberries were crushed and centrifuged. An aliquot of the well agitated aqueous supernatant (4 ml) was extracted with a fibre coated with polydimethylsiloxane (PDMS, 100 microns) for 45 min at room temperature. Identification and quantification were achieved using a gas chromatography-mass spectrometry (GC-MS) system and selective ion monitoring (SIM). The method was tested for the following pesticides: carbofuran, diethofencarb, penconazole, hexaconazole, metalaxyl, folpet, bromopropylate, dichlofluanid, alpha-endosulfan, beta-endosulfan, parathion ethyl, procymidone, iprodione, vinclozolin, myclobutanil and chlorothalonil. Limits of detection, repeatability and linearity for standard calibration in strawberries were obtained. Positive and negative effects of the matrix between the extracting solution of strawberries and water were observed. Stabilities of these compounds in the extracting solution of strawberries were determined. The solvent-free SPME procedure was found to be quicker and more cost effective than the solvent extraction methods commonly used.

[Expression of C-erbB-2 protein in breast cancer and its clinical significance]

In order to understand the expression of C-erbB-2 protein in breast cancer and its clinical significance, we examined the expression of C-erbB-2 protein in 106 breast carcinomas by using the immunohistochemical techniques LSAB. The results showed that the positive rate of C-erbB-2 expression was 63.21% (67/106). The overexpression of C-erbB-2 protein related negatively with survival. 81.63% of the cases with overexpression of C-erbB-2 protein survived < or = 5 years and 34.29% survived > 10 years. There were significant associations of C-erbB-2 overexpression with advanced clinical stage, high histological grade, and positive axillary node status in breast cancers. All of these findings suggested that overexpression of C-erbB-2 protein might be an important prognostic factor and the detection of C-erbB-2 protein might be arranged as a regular pathological examination in the cases of breast cancer.

[Study on the combination of isotachophoresis and high performance liquid chromatography for the separation of complex samples]

A method on the combination of isotachophoresis (ITP) and high performance liquid chromatography (HPLC) for the separation and analysis of the complex samples containing proteins and metals is proposed. The instrumental system consisted of a self-made Model OCEP-1 isotachophoresis analyser, main parts of Waters high performance liquid chromatograph and a self-made Model IHI-1 interface. The interface is simple and convenient to use. The injection volume of the interface was determined accurately with a neutralization titration method. In ITP experiment the leading electrolyte was 2.5 mmol/L HCl containing 30 mmol/L of 18-crown-6; the terminating electrolyte was 5 mmol/L Tris+Cl-(pH 6.0); ITP current, 40 microA; detection of metal ions, potential gradient detector. In HPLC experiment the column was a mu-Bondapak C18, reversed-phase column, 4 mm x 200 mm, 10 microns, 12.5 nm; the mobile phase A, V(isopropanol with 5% volume fraction):V(butanol) = 2:1 containing 2.2 mmol/L HCl (pH 2.63); the mobile phase B, V(isopropanol with 50% volume fraction):V(butanol) = 2:1; low pressure gradient elution, mobile phase B changed from 0 to 70% in 17.5 minutes; flow rate, 1.0 mL/min; detection wavelength 225 nm; temperature, 25 degrees C. The experimental results showed that proteins were interfered in the determination of the metals with ITP method. It also showed that HPLC with the use of C18 column can separate the proteins but not the metal ions. By using this new combination system, a complex sample of the proteins and metal ions was injected to the HPLC, the proteins Lys, BSA and OVA were well separated in HPLC, while NH4+, K+, Na+, and Ca2+ were less retained and eluted first. Then the latter was introduced into the system of the ITP with the aid of the interface for separation. Satisfactory results were obtained.

[Expression of P62c-myc protein in breast cancer and its clinical significance]

The objective of this study was to determine the clinical significance of P62c-myc protein expression in breast cancer. P62c-myc protein was detected in 107 patients with breast cancer by immunohistochemical techniques (LSAB). The results showed that the positive rate of P62c-myc protein expression was 63.55% (68/107). The overexpression of P62c-myc protein related negatively with survival. 94.00% of the cases with overexpression of P62c-myc protein survived < or = 5 years, 65.00% survived > 5 years-< 10 years, and 21.62% survived > or = 10 years. There were significant associations of P62c-myc expression with advance clinical stage, high histological grade, and positive axillary node status in breast cancers. All of these findings suggested that overexpression of P62c-myc might be an important prognostic factor, and the detection of P62c-myc protein might be arranged as a regular pathological examination in the cases of breast cancer.

Are complication rates for elective primary total hip arthroplasty in Ontario related to surgeon and hospital volumes? A preliminary investigation

OBJECTIVE

To test the hypothesis that complication rates for elective total hip replacement operations are related to surgeon and hospital volumes.

DESIGN

Retrospective population cohort study. STUDY COHORT: Patients who had undergone elective total hip replacement in Ontario during 1992 as captured in the Canadian Institute for Health Information database.

MAIN OUTCOME MEASURES

In-hospital complications, 1- and 3-year revision rates, 1- and 3-year infection rates, length of hospital stay, and 3-month and 1-year death rates.

RESULTS

Surgeons with patient volumes above the 80th percentile (more than 27 hip replacements annually) discharged patients approximately 2.4 days earlier (p < 0.05) than surgeons with volumes below the 40th percentile (less than 9 hip replacements annually) even after adjusting for discharge disposition, hospital volume, patient age, sex, comorbidity and diagnosis. Complication rates requiring hospital readmission and death rates did not differ by surgeon or hospital volume (p > 0.05).

CONCLUSIONS

There is no evidence to support regionalization of elective hip replacement surgery in Ontario based on adverse clinical outcomes. Surgeons who perform a large number of total hip replacements are discharging patients earlier than less experienced surgeons, without any-demonstrable increase in complications leading to hospital readmission. The explanation for this observation remains unknown and will require further study.

Effects of the feeding process of Ixodes scapularis (Acari: Ixodidae) on embryonic development of its parasitoid, Ixodiphagus hookeri (Hymenoptera: Encyrtidae)

The chalcid wasp Ixodiphagus hookeri (Howard) is a parasitoid of several ixodid ticks including the blacklegged tick, Ixodes scapularis Say. We evaluated effects of the feeding process of nymphal I. scapularis on the embryonic development of I. hookeri. Potentially wasp-parasitized nymphal I. scapularis were collected on Prudence Island, RI. Subsamples of the questing nymph cohort were allowed to feed on laboratory white mice. Both the body length and the scutal length of ticks were measured individually for questing nymphs and for feeding nymphs that were removed from hosts at time intervals of 12, 24, 36, 48, and 72 h after attachment. The diameters of wasp eggs they contained were also measured for each designated time interval. There was a positive relationship between the mean scutal index (ratio between body length and scutal length) of ticks and the mean diameter of wasp eggs during 72 h of tick feeding (P < 0.05). Moreover, it appeared that within 24 h of tick attachment, the scutal index of ticks remained unchanged. However, after that period, the scutal index increased significantly (P < 0.05). Diameters of wasp eggs increased continuously during tick feeding and at 72 h after attachment, enclosed eggs and completely formed larvae were found in several ticks. We conclude that factors related to the feeding process of nymphal I. scapularis are necessary to initiate the embryonic development of wasps.

[Functional phage display of human interferon alpha lc/86D]

We have successfully displayed human interferon-alpha lc/86D(IFN-alpha lc/86D) on the surface of the filamentous bacteriophage using a phagemid vector system (pCANTAB5E). The IFN-alpha lc/86D cDNA was fused to a DNA sequence encoding the amino-terminal domain of pIII, a minor coat protein exposed at one end of the phage. Fusion gene was packaged into phagemid particles upon superinfection with M13K07 helper phage. Expression of IFN-alpha lc/86D was verified by its reactivity with IFN-alpha l specific neutralizing antibodies and the phage displayed IFN-alpha lc86D was found to possess antiviral biological activity on VSV challenged WISH cells comparable to that of human recombinant IFN-alpha lb. These results demonstrate that IFN-alpha lc/86D can be displayed on phage in a correctly folded and functionally active form, and this system can be applicable to the sorting of a large repertoire of phage-displayed IFN-alpha lc/86D variants.

Reservoir competence of the meadow vole (Rodentia: Cricetidae) for the Lyme disease spirochete Borrelia burgdorferi

The reservoir competence of the meadow vole, Microtus pennsylvanicus Ord, for the Lyme disease spirochete Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner was established on Patience Island, RI. Meadow voles were collected from 5 locations throughout Rhode Island. At 4 of the field sites, M. pennsylvanicus represented only 4.0% (n = 141) of the animals captured. However, on Patience Island, M. pennsylvanicus was the sole small mammal collected (n = 48). Of the larval Ixodes scapularis Say obtained from the meadow voles on Patience Island, 62% (n = 78) was infected with B. burgdorferi. Meadow voles from all 5 locations were successfully infected with B. burgdorferi in the laboratory and were capable of passing the infection to xenodiagnostic I. scapularis larvae for 9 wk. We concluded that M. pennsylvanicus was physiologically capable of maintaining B. burgdorferi infection. However, in locations where Peromyscus leucopus (Rafinesque) is abundant, the role of M. pennsylvanicus as a primary reservoir for B. burgdorferi was reduced.

[Treatment of "bayonet" deformity of knee from poliomyelitis]

The "bayonet" deformity from poliomyelitis is a peculiar type of deformity of knee. From January 1986 through December 1994, 23 cases of this type of knee deformity were corrected by surgery. The operative procedures performed were suprachondylar osteotomy of femur or subplateau osteotomy of tibia. The patients were followed up from 1 to 5 years, with an average of 3 years. The result rated excellent to good was 95.6%. The features of this disorder and the main points in the surgical procedure were discussed.

[Three-dimensional volumetric display--a new application of frequency up-conversion]

This paper discusses the present research situation and the application prospect of 3-D volumetric display technology. The possible usability and science significance of frequency up-conversion in 3-D volumetric display field are also demonstrated systematically. In ZBLAN: Pr, Yb glasses, we primarily demonstrated and achieved a new application of frequency up-conversion three dimensional volumetric display, using the two-frequency up-conversion of the rare earth ions. The efficiency of luminescence of Pr was enhanced much by the energy transfer between Pr and Yb ions.

The diazoxide derivative IDRA 21 enhances ischemic hippocampal neuron injury

The diazoxide derivative IDRA 21 and other positive modulators of (AMPA)-type glutamate receptors are considered potential memory-enhancing agents. However, AMPA receptor activation contributes to CA1 hippocampal neuron damage from global ischemia in rodents, raising the possibility that 7-chloro-3-methyl-3-4-dihydro-2H-1,2,4 benzothiadiazine S,S-dioxide (IDRA 21) or drugs with similar actions may worsen ischemic neuronal injury. Here we demonstrate that glutamate plus IDRA 21 kills cultured rat hippocampal neurons by AMPA receptor activation, and, in vivo, 12 and 24 mg/kg of IDRA 21 given orally increases CA1 neuron loss produced by 10 minutes of global ischemia. Treating patients with drugs that potentiate AMPA receptor activation will have to consider these potential effects, particularly when coexistent with conditions in which excessive activation of AMPA receptors may occur (eg, stroke, seizures).

[Repair of large articular cartilage defect of hip with allograft of skull periosteum]

It is very difficult to repair large articular cartilage defect of the hip. From May 1990 to April 1994, 47 hips in 42 patients of large articuler cartilage defects were repaired by allograft of skull periosteum. Among them, 14 cases, whose femoral heads were grade. IV necrosis, were given deep iliac circumflex artery pedicled iliac bone graft simultaneously. The skull periosteum had been treated by low tempreturel (-40 degrees C) before and kept in Nitrogen (-196 degrees C) till use. During the operation, the skull periosteum was sutured tightly to the femoral head and sticked to the accetabulum by medical ZT glue. Thirty eight hips in 34 patients were followed up for 2-6 years with an average of 3.4 years. According to the hip postoperative criteria of Wu Zhi-kang, 25 cases were excellent, 5 cases very good, 3 cases good and 1 case fair. The mean score increased from 6.4 before operation to 15.8 after operation. The results showed, in compare with autograft of periosteum for biological resurface of large articular defect, this method is free of donor-site morbidity. Skull periosteum allograft was effective for the treatment of large articular cartilage defects in hip.

Production and characterization of monoclonal anti-idiotypic antibody exhibiting a catalytic activity similar to carboxypeptidase A

A new approach for producing catalytic anti-idiotypic antibody was developed. A monoclonal anti-idiotypic antibody which was induced against carboxypeptidase A (CPA) showed the catalytic activity similar to the original antigen. The activity of the catalytic antibody was investigated. Rabbits were immunized by bovine pancreas carboxypeptidase A. The antiserum was purified and used as antigen to immunize BALB/c mice to induce monoclonal anti-idiotypic antibodies. Screened for enzymatic activities, the monoclonal antibody 32C3 showed esterase activity. The hydrolysis of hippuryl-DL-phenyllactic acid by McAb 32C3 followed the enzymatic kinetics. In our experimental system, Kcat value was 0.0123 min-1 and Km was 0.04M. The acceleration rate was 1750 times compared to the rate of self-hydrolysis of the substrate. This hydrolysis reaction can be competitively inhibited by hydrocinnamic acid. This method could be effective to obtain catalytic antibodies with the characters close to natural enzymes.

Prolonged STAT1 activation related to the growth arrest of malignant lymphoma cells by interferon-alpha

Multiple biologic effects of interferon-alpha (IFN-alpha), including cell growth inhibition and antiviral protection, are initiated by tyrosine phosphorylation of STAT proteins. Although this signal pathway has been intensively investigated, the relevance of STAT signal persistence has received scant attention. Using paired isogenic lymphoma cells (Daudi), which either are sensitive or resistant to growth inhibition by IFN-alpha, we found comparable initial tyrosine phosphorylation of multiple STAT proteins; however, the phosphorylation durations and associated DNA-binding activities diverged. Phosphorylation and DNA-binding capacity of STAT1 decreased after 4 to 8 hours in resistant cells, as compared with 24 to 32 hours in sensitive cells, whereas phosphorylation of STAT3 and STAT5b was briefer in both lines. Functional significance of the prolonged STAT1 signal, therefore, was explored by experimental interruption of tyrosine phosphorylation, either by premature withdrawal of the IFN-alpha or deferred addition of pharmacologically diverse antagonists: staurosporine (protein kinase inhibitor), phorbol 12-myristate 13-acetate (growth promoter), or aurintricarboxylic acid (ligand competitor). Results indicated that an approximately 18-hour period of continued STAT1 phosphorylation was associated with growth arrest, but that antiviral protection developed earlier. These differences provide novel evidence of a temporal dimension to IFN-alpha signal specificity and show that duration of STAT1 activation may be a critical variable in malignant cell responsiveness to antiproliferative therapy.

A small proline-rich protein, spr1: specific marker for squamous lung carcinoma

We have identified a small proline-rich protein, spr1, which is a sensitive and specific marker for distinguishing squamous cancer from the other cell types of lung carcinoma. A rabbit antiserum against a 15-amino-acid peptide of the C-terminus of spr1 was prepared. The specificity of this antiserum was demonstrated in normal squamous tissues by Western blotting and immunohistochemical analysis. Expression of spr1 in 63 cases of formalin-fixed and paraffin-embedded human bronchogenic carcinoma was studied by immunohistochemical staining. For these 63 cases of bronchogenic carcinoma previously diagnosed by hematoxylin/eosin (H/E) staining, the number of spr1-positive cases/total number of H/E cases of each cell type of lung cancer were as follows: 20/20 of squamous carcinoma, 2/18 of adenocarcinoma, 4/14 of large-cell carcinoma, and 0/11 of small-cell lung carcinoma. Squamous differentiation evidenced by spr1 expression was substantiated by the presence of squamous features observed under transmission electron microscopy (TEM). We conclude that spr1 is a sensitive and specific marker for squamous bronchogenic carcinoma.

[Repair of cartilage defect in joint with transplantation of cryopreserved homologous embryonic periosfeum of rabbits]

In order to repair cartilage defect in joint with transplantation of cryopreserved homologous embryonic periosteum, 30 rabbits were used and divided into two groups. A 4 mm x 7 mm whole thickness cartilage defect was made in the patellar groove of femur of each rabbit. The homologous embryonic rabbit skull periosteum (ERSP), preserved in two-step freezing schedule, was transplanted onto the cartilage defect of joints of one group and autogenous periosteal graft was done in the joint defect of the other group. The knees were not immobilized, following operation and 16 weeks later, the newly formed tissue in the defects were assessed by gross observation, histochemical examination and biochemical analysis. The results showed that new hyaline-like cartilage was formed in the cryopreserved ERSP grafted knee, and had no significant difference from that of the knee receiving autogenous periosteal graft, but had significant difference from that of the fresh ERSP grafted knee and the non-grafted knee. Furthermore, the new hyaline-like cartilage had the biochemical characteristics of a fibrous cartilage. The conclusion was that this method might be feasible to repair articular cartilage defects.

MMAC1/PTEN mutations in primary tumor specimens and tumor cell lines

A candidate tumor suppressor gene, MMAC1/PTEN, located in human chromosome band 10q23, was recently identified based on sequence alterations observed in several glioma, breast, prostate, and kidney tumor specimens or cell lines. To further investigate the mutational profile of this gene in human cancers, we examined a large set of human tumor specimens and cancer cell lines of many types for 10q23 allelic losses and MMAC1 sequence alterations. Loss of heterozygosity (LOH) at the MMAC1 locus was observed in approximately one-half of the samples examined, consistent with the high frequency of 10q allelic loss reported for many cancers. Of 124 tumor specimens exhibiting LOH that have been screened for MMAC1 alterations to date, we have detected variants in 13 (approximately 10%) of these primary tumors; the highest frequency of variants was found in glioblastoma specimens (approximately 23%). Novel alterations identified in this gene include a missense variant in a melanoma sample and a splicing variant and a nonsense mutation in pediatric glioblastomas. Of 76 tumor cell lines prescreened for probable LOH, microsequence alterations of MMAC1 were detected in 12 (approximately 16%) of the lines, including those derived from astrocytoma, leukemia, and melanoma tumors, as well as bladder, breast, lung, prostate, submaxillary gland, and testis carcinomas. In addition, in this set of tumor cell lines, we detected 11 (approximately 14%) homozygous deletions that eliminated coding portions of MMAC1, a class of abnormality not detected by our methods in primary tumors. These data support the occurrence of inactivating MMAC1 alterations in multiple human cancer types. In addition, we report the discovery of a putative pseudogene of MMAC1 localized on chromosome 9.

The role of MMAC1 mutations in early-onset breast cancer: causative in association with Cowden syndrome and excluded in BRCA1-negative cases

Cowden syndrome (CS) is an autosomal dominant disorder associated with the development of hamartomas and benign tumors in a variety of tissues, including the skin, thyroid, breast, endometrium, and brain. It has been suggested that women with CS are at increased risk for breast cancer. A locus for CS was recently defined on chromosome 10 in 12 families, resulting in the identification of the CS critical interval, between the markers D10S215 and D10S541. More recently, affected individuals in four families with CS have been shown to have germ-line mutations in a gene known as "PTEN," or "MMAC1," which is located in the CS critical interval on chromosome 10. In this study, we report three novel MMAC1 mutations in CS and demonstrate that MMAC1 mutations are associated with CS and breast cancer. Furthermore, we also show that certain families and individuals with CS do not have mutations in the coding sequence of MMAC1. Finally, we did not detect MMAC1 mutations in a subpopulation of individuals with early-onset breast cancer, suggesting that germ-line mutations in this gene do not appear to be common in this group.

Human mitogen-activated protein kinase kinase 4 as a candidate tumor suppressor

Mitogen-activated protein kinases function in signal transduction pathways that are involved in controlling key cellular processes in many organisms. A mammalian member of this kinase family, MKK4/JNKK1/SEK1, has been reported to link upstream MEKK1 to downstream stress-activated protein kinase/JNK1 and p38 mitogen-activated protein kinase. This mitogen-activated protein kinase pathway has been implicated in the signal transduction of cytokine- and stress-induced apoptosis in a variety of cell types. Here, we report that two human tumor cell lines, derived from pancreatic carcinoma and lung carcinoma, harbor homozygous deletions that eliminate coding portions of the MKK4 locus at 17p, located approximately 10 cM centromeric of p53. In addition, in a set of 88 human cancer cell lines prescreened for loss of heterozygosity, we detected two nonsense and three missense sequence variants of MKK4 in cancer cell lines derived from human pancreatic, breast, colon, and testis cells. In vitro biochemical assays revealed that, when stimulated by MEKK1, four of the five altered MKK4 proteins lacked the ability to phosphorylate stress-activated protein kinase. Thus, the incidence of coding mutations of MKK4 in the set of cell lines is 6 of 213 (approximately 3%). These findings suggest that MKK4 may function as a suppressor of tumorigenesis or metastasis in certain types of cells.