Suppression of the radiation-sensitive phenotype of hamster irs1 and irs2 strains selected for resistance to 3-aminobenzamide

PURPOSE

The radiosensitive hamster cell lines irs1 and irs2 have phenotypic similarities to cells defective in the early response to DNA-damaging agents as a result of mutations of the genes encoding poly(ADP-ribose)polymerase (PARP) or ataxia-telangiectasia mutated (ATM). Whether modification of PARP activity through selection of strains resistant to 3-aminobenzamide (3-AB) would affect the radiosensitive phenotype of irs1 and irs2 was examined.

MATERIALS AND METHODS

3-AB-resistant strains of irs1, irs2 and their parent line V79 were established and their sensitivity to DNA-damaging agents was measured. In some 3-AB-resistant strains, the radiation resistance of DNA synthesis and the induction of apoptosis were also assayed. Additionally, a number of aspects of PARP function were measured.

RESULTS

Independently selected 3-AB-resistant strains of irs2 showed nearly complete suppression of radiation sensitivity, sensitivity to topoisomerase inhibitors, and radioresistant DNA synthesis. 3-AB-resistant strains of irs1 showed partial suppression of phenotype while 3-AB-resistant strains of V79 had no sensitivity changes. The induction of apoptosis in 3-AB-resistant strains of irs2 required substantially higher radiation doses than for irs2 itself. 3-AB-resistant strains had no detectable alteration of PARP level or cleavage following ionizing irradiation and there were no mutations in the PARP gene.

CONCLUSIONS

Suppression of radiosensitivity associated with 3-AB resistance has important implications for mechanisms of tolerance to damage because it is able to override responses associated with specific genetic defects.

Acinetobacter meningitis following head trauma

A case of acinetobacter meningitis following head injury in a patient who developed cerebrospinal fluid otorrhea, and did not have any neurosurgical procedure, is presented. Previously reported cases are cited, with a review of the literature. Pefloxacin monotherapy is associated with a poor clinical response.

Mycobacterium fortuitum endocarditis and meningitis after balloon mitral valvotomy

Mycobacteria rarely cause endocardial infections. We describe the clinical course of a patient who developed endocarditis, and meningitis with Mycobacterium fortuitum following balloon mitral valvotomy. The patient was treated with amikacin and clarithromycin but did not respond. She developed haemolytic anaemia as the terminal event.

Mutator phenotype in Msh2-deficient murine embryonic fibroblasts

Embryonic fibroblast cell lines were established from mice deficient, heterozygous, or proficient for Msh2, one of the three known DNA mismatch repair genes involved in hereditary nonpolyposis colon cancer (HNPCC). Cell lines were established by transfection of primary mouse embryo fibroblasts with E7 and Ras oncogenes or mutant p53. Spontaneously immortalized cells derived from the primary cultures were also studied. To determine whether these cells developed a mutator phenotype similar to that found in colon cancer cells deficient in mismatch repair, we measured mutation rates, microsatellite instability, and sensitivities to a range of DNA-damaging agents. The mutator phenotype detected in the E7 and Ras or mutant p53-immortalized Msh2-/- mouse cells was similar to that found in human mismatch repair-deficient colorectal carcinoma cell lines. Mutation rates to ouabain resistance were increased 8-12-fold relative to lines from Msh2+/+ mice, and microsatellite instability was detectable in 12-18% of subclones derived from the Msh2-/- line but was undetectable in subclones developed from the Msh2+/+ line. Furthermore, E7 and Ras or spontaneously immortalized Msh2-/- cells were significantly more resistant to the cytotoxic effects of 6-thioguanine relative to Msh2+/+ cells. In contrast, these lines showed various responses to UV light and cis-platinum, suggesting that mismatch repair deficiency was not the sole determinant for sensitivity to these DNA-damaging agents. Particular attention was paid to the properties of cells heterozygous for the Msh2 mutant gene, which would mimic the situation of an HNPCC carrier. However, our studies failed to reveal any properties of these cells that might provide a growth advantage or predispose them for the acquisition of further mutations. This observation is consistent with the model that inactivation of the wild-type Msh2 allele is a critical step for tumorigenesis in HNPCC patients.

Infection caused by Cryptococcus neoformans var. gattii serotype B in an AIDS patient in India

Cryptococcus neoformans is an opportunistic pathogen infecting AIDS patients. However, infection caused by C. neoformans var. gattii in AIDS patients is reportedly rare. We report herein the first culture proven C. neoformans var. gattii serotype B infection in an AIDS patient in India.

Systemic lupus erythematosus in Indian patients: prognosis, survival and life expectancy

BACKGROUND

There have been several studies on survival patterns in Indian patients with systemic lupus erythematosus but it is still not clear as to which factors at diagnosis predict survival outcome. The impact of specific organ involvement, and of disease activity itself, needs to be studied further.

METHODS

We conducted a non-concurrent prospective study of 98 lupus patients between 1981 and 1993. The clinical symptoms, signs and investigation results at onset, and at subsequent visits, were abstracted from the case notes. A systemic lupus erythematosus disease activity index (SLEDAI) was constructed at the initial presentation and for each subsequent visit. Patients not attending for at least 6 months were traced by post. The quantitative data from the SLEDAI was used to construct a Markov chain mathematical expression designed to predict life expectancy.

RESULTS

The cumulative percentage survival at 1, 5 and 10 years was found to be 89%, 77% and 60%, respectively. The Markov chain predicted a life expectancy of 13.9 years. Central nervous system and renal involvement were poor prognostic factors. Proteinuria (> 0.5 g/day) caused a 50% reduction in life expectancy but increased disease activity at onset did not predispose to a poor outcome.

CONCLUSION

The survival of patients with systemic lupus erythematosus continues to be poor. Central nervous system and renal disease indicate a poor outcome. Hence, new treatment strategies must be evolved to improve the survival of such patients.

Epidemiological features of acquired immunodeficiency syndrome in southern India

AIDS was diagnosed in 187 men and 24 women (M:F = 8:1) from April 1987 till December 1994 at the Christian Medical College Hospital, Vellore. The doubling time of the occurrence of AIDS cases was 14 months; during 1987-90 there were an average of 5.7 cases per year; in 1991-93 there were 28 per year; in 1994 there were 104 cases. The mean age of patients was 33 yr for men and 31 for women. Among men, the primary mode of infection was heterosexual contact with female commercial sex workers. Among women, the most common source of infection was their husbands. There were 4 bisexuals and one homosexual subject who might have acquired infection by having sex with other men. There were 135 subjects from urban and 76 from rural communities. Most subjects belonged to the lower socio-economic classes. These data show that HIV infection had been very widespread in this region, both urban and rural.

Evaluation of an ELISA for the diagnosis of brucellosis

Brucela serology using ELISA and standard agglutination test was performed on 23 patients with prolonged fever where the test was requested, on 26 randomly chosen patients with prolonged fever where it was not requested and on 17 controls. ELISA was positive in 39.1, 26.9 and 0 per cent respectively in these groups. Brucellosis may often be unsuspected because of its varied clinical manifestations and may be a more important cause of fever than previously considered. Our data reaffirm that ELISA is superior to the standard agglutination test for the diagnosis of brucellosis.

Melioidosis In India: the tip of the iceberg?

Diagnosis of melioidosis by the isolation of Burkholderia pseudomallei from one or more body fluid/tissue specimens of 6 Indian subjects, 5 of whom had not travelled outside India, is reported. The places of residence of these 6 and one patient previously reported, namely Tripura (2), Kerala (2), Orissa (1), Tamil Nadu (1) and Maharashtra (1) are therefore potentially endemic for melioidosis. B.pseudomallei closely resembles common contaminant Pseudomonas sp. and are easily mis-identified in microbiology laboratories. We surmise that melioidosis is underdiagnosed and underreported in India and we alert clinicians, microbiologists and public health professionals to the possibility of melioidosis being far more common than previously recognised.

Molecular analysis of mutations in mutator colorectal carcinoma cell lines

The nature of mutations occurring in two colorectal carcinoma cell lines deficient in mismatch repair and displaying mutator phenotypes was determined. One of the lines (HCT116) exhibited a higher level of microsatellite instability than the second (DLD-1), although the rate of mutation at the selectable locus encoding the purine salvage enzyme hypoxanthine guanine phosphoribosyl transferase (HPRT) was equally elevated (about 350-450-fold relative to mismatch repair proficient cell lines). Transitions were the major class of mutations in the two mutator lines. In DLD-1 these mutations recurred at several sites that appeared to be hotspots. Frameshifts at a run of six guanine residues in the coding sequence for HPRT constituted 35% of mutations in HCT116. These frameshifts were highly unstable and reverted to wild type at high frequency. Larger deletions were also detected in HCT116. Although these deletions constituted a small proportion of mutations compared with the other types, our data suggest that the rate of deletion is elevated relative to mismatch repair proficient (hMLH1+) cell lines. These observations suggest that the gene(s) altered in DLD-1 may preferentially affect the repair of base mismatches while the alteration(s) in HCT116 may affect the repair of both mismatches and frameshifts.

Spontaneous regression of pulmonary mucormycosis

A case of pulmonary mucormycosis with spontaneous resolution is presented. The patient had no known underlying predisposing disease.

Mutator phenotypes in human colorectal carcinoma cell lines

Recent studies have revealed that tumors in patients with hereditary nonpolyposis colon cancer are associated with high-frequency alterations of microsatellite sequences. To investigate the mechanisms and consequences of this form of genetic instability, we identified three colorectal carcinoma cell lines that express dinucleotide-repeat instability like that found in hereditary nonpolyposis colon cancer tumors and show increased rates of spontaneous mutation at selectable loci. However, the pattern of hypermutation in these cell lines differed significantly. In one line (HCT116), microsatellite mutations occurred at a remarkably high rate (approximately 10(-2) mutations per cell per generation), whereas this rate was considerably lower in the two other lines (DLD-1 and HCT15). The rate of mutation at the locus encoding hypoxanthine guanine phosphoribosyltransferase was substantially elevated (200- to 600-fold) in all three tumor cell lines, yet the types of mutations arising differed. A specific frame-shift hotspot accounted for 24% of hypoxanthine guanine phosphoribosyltransferase mutations in HCT116. The frequency of mutations at this site was reduced significantly in DLD-1 and HCT15 lines. These data suggest that the mutatw phenotypes in the colorectal carcinoma cell lines could be the consequence of mutator genes affecting different repair or error-avoidance pathways.

Repair and misrepair of site-specific DNA double-strand breaks by human cell extracts

The rejoining by human cell extracts of a double-strand break induced by endonuclease treatment at one of several sites within a small DNA molecule was studied. Rejoining was found at each of 8 sites tested, but the rejoin efficiency varied with the nature of the break (e.g., breaks with cohesive ends were rejoined more efficiently than blunt-ended breaks). Extracts from primary and immortalized cell lines, as well as those from individuals with ataxia telangiectasia (A-T), showed the same pattern of relative rejoin efficiencies. However, mis-rejoining varied with the cell extract used, and was particularly elevated with two immortalized A-T cell lines. Mixing experiments showed that the mis-rejoining property of extracts could act in a semi-dominant fashion, depending on the individual efficiencies of the component extracts. The mis-rejoin mechanism involved deletion at sites of short direct repeats at various distances from the initial break site. A model of deletion formation (the strand-exposure and repair model) is restated to explain the sequence repeat dependence found, and is compared to models of homologous DNA recombination.