Bronchovascular bundle thickening on CT as a predictor of survival and brain metastasis in patients with stage IA peripheral small cell lung cancer.

AIM: To determine if bronchovascular bundle (BVB) thickening on pretreatment computed tomography (CT) images helps predict survival in patients with peripheral small cell lung cancer (pSCLC) ≤3 cm. MATERIALS AND METHODS: The pretreatment CT examinations of 79 histopathologically proven pSCLC ≤3 cm (TNM stage I, 21; II, 13; III, 22; IV, 23) were reviewed retrospectively. The CT characteristics of the nodule and associated findings, including BVB thickening, were evaluated. Progression-free survival (PFS), overall survival (OS), and brain metastasis-free survival were compared with the presence of BVB thickening using Kaplan-Meier and Cox regression analysis. RESULTS: Among the 79 patients, 34 (43%) had BVB thickening. BVB thickening was prevalent in patients with mediastinal lymph node metastasis (50.9% versus 22.7%; p=0.024) and distant metastasis (60.9% versus 35.7%; p=0.049). Out of the 21 patients with TNM stage IA disease, the 16 patients (76.2%) without BVB thickening showed better PFS, OS, and brain metastasis-free survival (mean, 1,762 versus 483 days; p=0.019: 2,243 versus 1,328 days; p=0.038: 2,274 versus 1,287 days; p=0.038, respectively). Multivariate Cox regression analysis showed that the absence of BVB thickening (hazard ratio [HR], 7.806; 95% CI, 1.241-49.091; p=0.029) and surgery (HR, 0.075; 95% CI, 0.008-0.746; p=0.027) were independent and useful prognostic factors for PFS. CONCLUSIONS: BVB thickening was found more frequently in patients with advanced-stage pSCLC ≤3 cm, and the PFS was more favourable in patients without BVB thickening, with a similar tendency to that of OS and brain metastasis-free survival, in stage IA pSCLC.

Lateral Femoral Cutaneous Nerve Radiofrequency Ablation for Long-term Control of Refractory Meralgia Paresthetica.

BACKGROUND: Meralgia paresthetica is a term used to describe a clinical pain syndrome related to the compression or irritation of the lateral femoral cutaneous nerve (LFCN). The LFCN is a pure sensory nerve that is susceptible to compression injury. The most common compression locations are: as it courses from the lumbosacral plexus, through the abdominal cavity, under the inguinal ligament, and into the subcutaneous tissue of the thigh. METHODS: This case series is a retrospective single-center review of six patients with medically intractable meralgia paresthetica who were treated with radiofrequency ablation. To be considered for radiofrequency ablation, the patient must have been unsuccessful with medical management alone for more than two months and have a clinical diagnosis of meralgia paresthetica. Temporary relief of pain of 50% or greater was considered a positive result. Average pain scores were measured pre- and postprocedure, along with one-, two-, three-, and six-month intervals postoperation. RESULTS: All patients demonstrated immediate relief in self-reported pain scores, averaging a 75.5% reduction in pain. At the one-, two-, three-, and six-month follow-ups, patients averaged a reduction of 60.0%, 58.0%, 51.4%, and 40.5%, respectively. Both the postop and one-month follow-up pain scores were lower, statistically significantly so (P < 0.05), whereas the two-, three-, and six-month follow-ups were not statistically different from pretreatment scores. CONCLUSIONS: Although our study was small, radiofrequency ablation showed a clear reduction in average pain scores in a subset of patients who had failed standard medical therapy with a reduction in pain at one-month follow-up with relief of symptoms sometimes lasting longer than 12 months.

Public Health Efforts Can Impact Adoption of Current Susceptibility Breakpoints, but Closer Attention from Regulatory Bodies Is Needed.

Microbiological testing, including interpretation of antimicrobial susceptibility testing results using current breakpoints, is crucial for clinical care and infection control. Continued use of obsolete Enterobacteriaceae carbapenem breakpoints is common in clinical laboratories. The purposes of this study were (i) to determine why laboratories failed to update breakpoints and (ii) to provide support for breakpoint updates. The Los Angeles County Department of Public Health conducted a 1-year outreach program for 41 hospitals in Los Angeles County that had reported, in a prior survey of California laboratories, using obsolete Enterobacteriaceae carbapenem breakpoints. In-person interviews with hospital stakeholders and customized expert guidance and resources were provided to aid laboratories in updating breakpoints, including support from technical representatives from antimicrobial susceptibility testing device manufacturers. Forty-one hospitals were targeted, 7 of which had updated breakpoints since the prior survey. Of the 34 remaining hospitals, 27 (79%) assumed that their instruments applied current breakpoints, 17 (50%) were uncertain how to change breakpoints, and 10 (29%) lacked resources to perform a validation study for off-label use of the breakpoints on their systems. Only 7 hospitals (21%) were familiar with the FDA/CDC Antibiotic Resistance Isolate Bank. All hospitals launched a breakpoint update process; 16 (47%) successfully updated breakpoints, 12 (35%) received isolates from the CDC in order to validate breakpoints on their systems, and 6 (18%) were planning to update within 1 year. The public health intervention was moderately successful in identifying and overcoming barriers to updating Enterobacteriaceae carbapenem breakpoints in Los Angeles hospitals. However, the majority of targeted hospitals continued to use obsolete breakpoints despite 1 year of effort. These findings have important implications for the quality of patient care and patient safety. Other public health jurisdictions may want to utilize similar resources to bridge the patient safety gap, while manufacturers, the FDA, and others determine how best to address this growing public health issue.

Early development of de novo hepatocellular carcinoma after direct-acting agent therapy: Comparison with pegylated interferon-based therapy in chronic hepatitis C patients.

Patients with chronic hepatitis C who achieve a sustained viral response after pegylated interferon therapy have a reduced risk of hepatocellular carcinoma, but the risk after treatment with direct-acting antivirals is unclear. We compared the rates of early development of hepatocellular carcinoma after direct-acting antivirals and after pegylated interferon therapy. We retrospectively analysed 785 patients with chronic hepatitis C who had no history of hepatocellular carcinoma (211 treated with pegylated interferon, 574 with direct-acting antivirals) and were followed up for at least 24 weeks after antiviral treatment. De novo hepatocellular carcinoma developed in 6 of 574 patients receiving direct-acting antivirals and in 1 of 211 patients receiving pegylated interferon. The cumulative incidence of early hepatocellular carcinoma development did not differ between the treatment groups either for the whole cohort (1.05% vs 0.47%, P = .298) or for those patients with Child-Pugh Class A cirrhosis (3.73% vs 2.94%, P = .827). Multivariate analysis indicated that alpha-fetoprotein level >9.5 ng/mL at the time of end-of-treatment response was the only independent risk factor for early development of hepatocellular carcinoma in all patients (P < .0001, hazard ratio 176.174, 95% confidence interval 10.768-2882.473) and in patients treated with direct-acting agents (P < .0001, hazard ratio 128.402, 95% confidence interval 8.417-1958.680). In conclusion, the rate of early development of hepatocellular carcinoma did not differ between patients treated with pegylated interferon and those treated with direct-acting antivirals and was associated with the serum alpha-fetoprotein level at the time of end-of-treatment response.

Stimulation of the human RAD51 nucleofilament restricts HIV-1 integration in vitro and in infected cells.

Stable HIV-1 replication requires the DNA repair of the integration locus catalyzed by cellular factors. The human RAD51 (hRAD51) protein plays a major role in homologous recombination (HR) DNA repair and was previously shown to interact with HIV-1 integrase (IN) and inhibit its activity. Here we determined the molecular mechanism of inhibition of IN. Our standard in vitro integration assays performed under various conditions promoting or inhibiting hRAD51 activity demonstrated that the formation of an active hRAD51 nucleofilament is required for optimal inhibition involving an IN-DNA complex dissociation mechanism. Furthermore we show that this inhibition mechanism can be promoted in HIV-1-infected cells by chemical stimulation of the endogenous hRAD51 protein. This hRAD51 stimulation induced both an enhancement of the endogenous DNA repair process and the inhibition of the integration step. Elucidation of this molecular mechanism leading to the restriction of viral proliferation paves the way to a new concept of antiretroviral therapy based on the enhancement of endogenous hRAD51 recombination activity and highlights the functional interaction between HIV-1 IN and hRAD51.

Curcumin in vitro Neuroprotective Effects Are Mediated by p62/keap-1/Nrf2 and PI3K/AKT Signaling Pathway and Autophagy Inhibition.

Oxidative stress and autophagy are potential mechanisms associated with cerebral ischemia/reperfusion injury (IRI) and is usually linked to inflammatory responses and apoptosis. Curcumin has recently been demonstrated to exhibit anti-inflammatory, anti-oxidant, anti-apoptotic and autophagy regulation properties. However, mechanism of curcumin on IRI-induced oxidative stress and autophagy remains not well understood. We evaluated the protective effects and potential mechanisms of curcumin on cerebral microvascular endothelial cells (bEnd.3) and neuronal cells (HT22) against oxygen glucose deprivation/reoxygenation (OGD/R) in vitro models that mimic in vivo cerebral IRI. The cell counting kit-8 (CCK-8) and lactate dehydrogenase (LDH) activity assays revealed that curcumin attenuated the OGD/R-induced injury in a dose-specific manner. OGD/R induced elevated levels of inflammatory cytokines TNF-alpha, IL-6 as well as IL-1beta, and these effects were notably reduced by curcumin. OGD/R-mediated apoptosis was suppressed by curcumin via upregulating B-cell lymphoma-2 (Bcl-2) and downregulating Bcl-associated X (Bax), cleaved-caspase3 and TUNEL apoptosis marker. Additionally, curcumin increased superoxide dismutase (SOD) and glutathione (GSH), but suppressed malondialdehyde (MDA) and reactive oxygen species (ROS) content. Curcumin inhibited the levels of autophagic biomarkers such as LC3 II/LC3 I and Beclin1. Particularly, curcumin induced p62 accumulation and its interactions with keap1 and promoted NF-E2-related factor 2 (Nrf2) translocation to nucleus, accompanied by increased NADPH quinone dehydrogenase (Nqo1) and heme oxygenase 1 (HO-1). Treatment of curcumin increased phosphorylation-phosphatidylinositol 3 kinase (p-PI3K) and p-protein kinase B (p-AKT). The autophagy inhibitor 3-methyladenine (3-MA) activated the keap-1/Nrf2 and PI3K/AKT pathways. This study highlights the neuroprotective effects of curcumin on cerebral IRI.

Synthesis of proline-derived dipeptides and their catalytic enantioselective direct aldol reactions: catalyst, solvent, additive and temperature effects.

A series of dipeptides of L-proline-L-amino acid and L-proline-D-amino acid were synthesized to evaluate the catalytic effect for asymmetric direct aldol reactions. In the direct aldol reaction, a catalyst of L-proline-L-amino acid achieves better enantioselectivity than the corresponding L-proline-D-amino acid catalyst. Solubility of the dipeptide catalysts in the solvents is a key point for achieving a better yield of the direct aldol reaction, while hydrogen bonding of solvent does not play an important role in attaining better enantioselectivity and yield. Yield and enantioselectivity of the direct aldol reaction in water were improved by NMM and SDS additives, but the results that were done in plain DMSO were even better.

Catalysis of ATP-dependent homologous DNA pairing and strand exchange by yeast RAD51 protein.

The RAD51 gene of Saccharomyces cerevisiae is required for genetic recombination and DNA double-strand break repair. Here it is demonstrated that RAD51 protein pairs circular viral single-stranded DNA from phi X 174 or M13 with its respective homologous linear double-stranded form. The product of synapsis between these DNA partners is further processed by RAD51 to yield nicked circular duplex DNA, which indicates that RAD51 can catalyze strand exchange. The pairing and strand exchange reaction requires adenosine triphosphate, a result consistent with the presence of a DNA-dependent adenosine triphosphatase activity in RAD51 protein. Thus, RAD51 is a eukaryotic recombination protein that can catalyze the strand exchange reaction.

Cripto-1 overexpression is involved in the tumorigenesis of gastric-type and pancreatobiliary-type intraductal papillary mucinous neoplasms of the pancreas.

Human Cripto-1, a membrane-bound protein, plays an important role during early embryogenesis and has oncogenic properties, including cell transformation and enhancement of invasion. Cripto-1 is up-regulated in various malignant tissues and premalignant lesions. However, Cripto-1 expression in intraductal papillary mucinous neoplasms (IPMNs) has yet to be reported. This study aimed to investigate Cripto-1 expression in IPMNs and evaluate the expression patterns according to the histological grade or phenotypic subclassification. Cripto-1 expression was evaluated by immunohistochemistry using 37 IPMN tissue samples and real-time RT-PCR analysis of seven frozen samples. Cripto-1 was up-regulated in 59.5% of IPMNs. Cripto-1 was positively stained in 3 of 4 (75%) adenomas, 12 of 19 (63.2%) borderline neoplasms, 5 of 11 (45.5%) non-invasive carcinomas and 2 of 3 (66.7%) invasive carcinomas. There was no correlation between Cripto-1 overexpression and the histological grade (P>0.05). Cripto-1 expression was significantly increased in pancreatobiliary- (4/5, 80%) and gastric-type (13/19, 68.4.2%) IPMNs compared with those of the intestinal type (2/10, 20%; P<0.01). Cripto-1 mRNA expression was higher in gastric- and pancreatobiliary-type IPMNs than in intestinal ones, supporting the immunohistochemical results. It is concluded that Cripto-1 overexpression is involved in the tumorigenesis of gastric- and pancreatobiliary-type IPMNs.

Changes of aqueous vascular endothelial growth factor and pigment epithelium-derived factor following intravitreal bevacizumab for macular oedema secondary to branch retinal vein occlusion.

BACKGROUND: To investigate sequential changes of aqueous vascular endothelial growth factor (VEGF) and pigment epithelium-derived factor (PEDF) in macular oedema secondary to branch retinal vein occlusion (BRVO) following intravitreal injection of bevacizumab (IVB). METHODS: We recruited 10 healthy controls and 40 patients with BRVO. Aqueous levels of VEGF and PEDF were measured by ELISA at the time of IVB and 6 weeks later. Non-response to IVB was defined as showing persistent macular oedema based on reduction of central macular thickness by less than 20% from baseline measurements by optical coherence tomography and vision improvement by <0.3 log MAR at 6 weeks after IVB. Fluorescein angiography was performed after resolution of foveal haemorrhage. We compared aqueous levels of VEGF and PEDF between responders and non-responders. RESULTS: The aqueous levels of VEGF and PEDF were significantly higher in 16 non-responders than in 24 responders at baseline measurements (491 +/- 231 pg/mL vs. 250 +/- 112 pg/mL, P < 0.001; 32 +/- 4 ng/mL vs. 25 +/- 5 ng/mL, P < 0.001, respectively). Six weeks after IVB, the aqueous levels of VEGF and PEDF were still higher in non-responders than in responders (388 +/- 141 pg/mL vs. 104 +/- 40 pg/mL, P < 0.001; 30 +/- 8 ng/mL vs. 18 +/- 5 ng/mL, P < 0.001, respectively). Fluorescein angiography revealed that non-responders showed higher frequencies of macular ischaemia and ischaemic BRVO. CONCLUSIONS: Our results indicate that aqueous VEGF levels are associated with persistent macular oedema secondary to ischaemic BRVO following IVB.

Improving neural network prediction of effluent from biological wastewater treatment plant of industrial park using fuzzy learning approach.

Three types of adaptive network-based fuzzy inference system (ANFIS) in which the online monitoring parameters served as the input variable were employed to predict suspended solids (SS(eff)), chemical oxygen demand (COD(eff)), and pH(eff) in the effluent from a biological wastewater treatment plant in industrial park. Artificial neural network (ANN) was also used for comparison. The results indicated that ANFIS statistically outperforms ANN in terms of effluent prediction. When predicting, the minimum mean absolute percentage errors of 2.90, 2.54 and 0.36% for SS(eff), COD(eff) and pH(eff) could be achieved using ANFIS. The maximum values of correlation coefficient for SS(eff), COD(eff), and pH(eff) were 0.97, 0.95, and 0.98, respectively. The minimum mean square errors of 0.21, 1.41 and 0.00, and the minimum root mean square errors of 0.46, 1.19 and 0.04 for SS(eff), COD(eff), and pH(eff) could also be achieved.

The metabolic syndrome increases cardiovascular mortality in Taiwanese elderly.

BACKGROUND: The prevalence of the metabolic syndrome (MetS) is high among the elderly. However, evidence that mortality increases with MetS is rare. In this study, we investigated the relationship between MetS, cardiovascular disease (CVD) and all cause mortality in the elderly. MATERIALS AND METHODS: A total 10 547 participants, aged 65 years and older, of baseline cohort were recruited from four nationwide Health Screening Centres in Taiwan from 1998 to 1999. The metabolic syndrome was defined according to the America Heart Association/National Heart Lung Blood Institute definition. Cox proportional hazards regression analyses were used to estimate the relative risks (RRs) of CVD and all cause mortality for those with MetS for up to 8 years of follow-up. RESULTS: The baseline prevalence of MetS was 50.1% (45.6% in men and 54.4% in women, respectively). A total of 1312 participants died; of these, 300 participants died from CVD. Adjusted for age, gender, smoking, total cholesterol and estimated glomerular filtration rate, the RRs for CVD and all cause mortality among participants with MetS were 1.48 (95% confidence interval = 1.16-1.90) and 1.16 (1.03-1.30), respectively, for participants compared to those without MetS. The mean RRs for CVD, however, ranged from 1.21 to 5.31 among different combinations of MetS components. CONCLUSION: The elderly with MetS, compared to those without MetS, had a higher CVD and all cause mortality in Taiwan. Furthermore, different combinations of MetS components posed different risks to the mortality, which deserves further research in the future.

DLX3 c.561_562delCT mutation causes attenuated phenotype of tricho-dento-osseous syndrome.

The distal-less homeobox gene DLX3 is expressed in a variety of tissues including placenta, skin, hair, teeth, and bone. Mutation of DLX3 (c.571_574delGGGG) causes the tricho-dento-osseous syndrome (TDO), characterized by abnormal hair, teeth, and bone. Evaluation of a kindred segregating the DLX3 c.561_562delCT mutation revealed distinct changes in the hair, teeth, and bones as has been observed with the DLX3 c.571_574delGGGG mutation. Previously, the DLX3 c.561_562delCT mutation was associated with autosomal dominant amelogenesis imperfecta with taurodontism. The present study shows that the DLX3 c.560_561delCT mutation causes an attenuated TDO phenotype with less severe hair, tooth, and bone manifestations compared with individuals having the DLX3 c.571_574delGGGG mutation. Careful phenotyping of individuals with allelic DLX3 mutations reveals marked differences in phenotypic severity indicating that the carboxy-terminus of the DLX3 protein is critical in determining its function during development in these different tissues.

Chromosomal integration of LTR-flanked DNA in yeast expressing HIV-1 integrase: down regulation by RAD51.

HIV-1 integrase (IN) is the key enzyme catalyzing the proviral DNA integration step. Although the enzyme catalyzes the integration step accurately in vitro, whether IN is sufficient for in vivo integration and how it interacts with the cellular machinery remains unclear. We set up a yeast cellular integration system where integrase was expressed as the sole HIV-1 protein and targeted the chromosomes. In this simple eukaryotic model, integrase is necessary and sufficient for the insertion of a DNA containing viral LTRs into the genome, thereby allowing the study of the isolated integration step independently of other viral mechanisms. Furthermore, the yeast system was used to identify cellular mechanisms involved in the integration step and allowed us to show the role of homologous recombination systems. We demonstrated physical interactions between HIV-1 IN and RAD51 protein and showed that HIV-1 integrase activity could be inhibited both in the cell and in vitro by RAD51 protein. Our data allowed the identification of RAD51 as a novel in vitro IN cofactor able to down regulate the activity of this retroviral enzyme, thereby acting as a potential cellular restriction factor to HIV infection.

Changes of aqueous vascular endothelial growth factor and interleukin-6 after intravitreal triamcinolone for branch retinal vein occlusion.

BACKGROUND: To investigate sequential changes of aqueous vascular endothelial growth factor (VEGF) and interleukin (IL)-6 in macular oedema secondary to branch retinal vein occlusion after single intravitreal injection of triamcinolone acetonide (IVTA). METHODS: We recruited 10 healthy controls and 30 patients at Chonnam National University Hospital, Gwangju, Korea. Aqueous and plasma levels of VEGF and IL-6 were measured by enzyme-linked immunosorbent assay at the time of IVTA and 3 months later. Non-response to IVTA was defined as showing persistent macular oedema based on a reduction of central macular thickness by less than 20% from baseline measurements by optical coherence tomography and vision improvement by less than 0.3 logMAR. Fluorescein angiography was performed 6 months after IVTA. We compared aqueous levels of VEGF and IL-6 between responders and non-responders. RESULTS: The aqueous levels of VEGF and IL-6 were significantly higher in 12 non-responders than in 18 responders at baseline measurements (511 +/- 245 pg/mL vs. 230 +/- 108 pg/mL, P < 0.001; 38 +/- 31 pg/mL vs. 16 +/- 13 pg/mL, P < 0.001, respectively). Aqueous levels of VEGF were still higher in non-responders (312 +/- 64 pg/mL) 3 months after IVTA, and aqueous levels of VEGF in responders returned to normal (86 +/- 21 pg/mL, P < 0.001). Aqueous levels of IL-6 normalized in all patients 3 months after IVTA. Fluorescein angiography revealed that non-responders showed higher frequencies of macular ischaemia and ischaemic branch retinal vein occlusion. CONCLUSIONS: IL-6-independent VEGF secretion may contribute to persistent macular oedema associated with ischaemic BRVO after IVTA.

Whole-body positron emission tomography with 18F-fluorodeoxyglucose is an effective method to detect extra-pelvic recurrence in uterine sarcomas.

PURPOSE OF INVESTIGATION: To assess the clinical use of F-18-fluorodeoxyglucose positron emission tomography (FDG-PET) in the post-therapy surveillance of uterine sarcoma. METHODS: Eight whole-body FDG-PET studies were performed in seven women with previously treated uterine sarcoma. Conventional image studies (computed tomography) and physical examinations were performed for follow-up. All FDG-PET studies were indicated to localize suspected recurrences noted by conventional methods. RESULTS: The per case sensitivity of the FDG-PET studies and CT scans was 85.7% (6/7) and 100% (7/7), respectively (p = 0.174). FDG-PET was able to detect seven extrapelvic metastastic sites below the diaphragm (7/7, sensitivity: 100%), including the liver, spleen, paraaortic lymph node, spine and paracolic gutter, as well as pulmonary lesions in five patients, while the CT scan detected only three lesions (3/7, sensitivity: 42.9%; p = 0.070). FDG-PET detected only four recurrent pelvic lesions (4/6) and CT scan detected six (6/6) recurrent pelvic lesions (66.7% vs 100%, p = 0.455). CONCLUSIONS: The FDG-PET showed a better detection rate than the abdominal CT scan for extrapelvic metastatic lesions and a similar detection rate as well as abdominal CT scan. FDG-PET can serve as a useful detection tool for patients with uterine sarcomas because nearly 80% of recurrence involve an extrapelvic site.

Etoposide and illegitimate DNA double-strand break repair in the generation of MLL translocations: new insights and new questions.

Faithful repair of chromosomal double-strand breaks (DSBs) is central to genome integrity and the suppression of genome rearrangements including translocations that are a hallmark of leukemia, lymphoma, and soft-tissue sarcomas [B. Elliott, M. Jasin, Double-strand breaks and translocations in cancer, Cell. Mol. Life Sci. 59 (2002) 373-385; D.C. van Gent, J.H. Hoeijmakers, R. Kanaar, Chromosomal stability and the DNA double-stranded break connection, Nat. Rev. Genet. 2 (2001) 196-206]. Chemotherapy agents that target the essential cellular enzyme topoisomerase II (topo II) are known promoters of DSBs and are associated with therapy-related leukemias. There is a clear clinical association between previous exposure to etoposide and therapy-related acute myeloid leukemia (t-AML) characterized by chromosomal rearrangements involving the mixed lineage leukemia (MLL) gene on chromosome band 11q23 [C.A. Felix, Leukemias related to treatment with DNA topoisomerase II inhibitors, Med. Pediatr. Oncol. 36 (2001) 525-535]. Most MLL rearrangements initiate within a well-characterized 8.3 kb region that contains both putative topo II cleavage recognition sequences and repetitive elements leading to the logical hypothesis that MLL is particularly susceptible to aberrant cleavage and homology-mediated fusion to repetitive elements located on novel chromosome partners. In this review, we will discuss the findings and implications of recent attempts to confirm this hypothesis.

Binding of insertion/deletion DNA mismatches by the heterodimer of yeast mismatch repair proteins MSH2 and MSH3.

DNA-mismatch repair removes mismatches from the newly replicated DNA strand. In humans, mutations in the mismatch repair genes hMSH2, hMLH1, hPMS1 and hPMS2 result in hereditary non-polyposis colorectal cancer (HNPCC) [1-8]. The hMSH2 (MSH for MutS homologue) protein forms a complex with a 160 kDa protein, and this heterodimer, hMutSalpha, has high affinity for a G/T mismatch [9,10]. Cell lines in which the 160 kDa subunit of hMutSalpha is mutated are specifically defective in the repair of base-base and single-nucleotide insertion/deletion mismatches [9,11]. Genetic studies in S. cerevisiae have suggested that MSH2 functions with either MSH3 or MSH6 in mismatch repair, and, in the absence of the latter two genes, MSH2 is inactive [12,13]. MSH6 encodes the yeast counterpart of the 160 kDa subunit of hMutSalpha [12,13]. As in humans, yeast MSH6 forms a complex with MSH2, and the MSH2-MSH6 heterodimer binds a G/T mismatch [14]. Here, we find that MSH2 and MSH3 form another stable heterodimer, and we purify this heterodimer to near homogeneity. We show that MSH2-MSH3 has low affinity for a G/T mismatch but binds to insertion/deletion mismatches with high specificity, unlike MSH2-MSH6.

Enhancement of MSH2-MSH3-mediated mismatch recognition by the yeast MLH1-PMS1 complex.

DNA mismatch repair has a key role in maintaining genomic stability. Defects in mismatch repair cause elevated spontaneous mutation rates and increased instability of simple repetitive sequences, while mutations in human mismatch repair genes result in hereditary nonpolyposis colorectal cancers. Mismatch recognition represents the first critical step of mismatch repair. Genetic and biochemical studies in yeast and humans have indicated a requirement for MSH2-MSH3 and MSH2-MSH6 heterodimers in mismatch recognition. These complexes have, to some extent, overlapping mismatch binding specificities. MLH1 and PMS1 are the other essential components of mismatch repair, but how they function in this process is not known. We have purified the yeast MLH1-PMS1 heterodimer to near homogeneity, and examined its effect on MSH2-MSH3 binding to DNA mismatches. By itself, the MLH1-PMS1 complex shows no affinity for mismatched DNA, but it greatly enhances the mismatch binding ability of MSH2-MSH3.