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Biomedical subjects

K Bhatia

Publications and source records attributed to K Bhatia.

At least 73 records · Page 4Linked to original sources
PubMed1996

HLA-DR2 haplotypic diversity in populations of South-East Asia, northern China, Melanesia and Australian aborigines using PCR-RFLP for DRB1, DRB5, DQA1 and DQB1. A novel DRB1 allele: DRB1*16022.

The polymorphism of the human leucocyte antigen HLA-DR2 and the heterogeneity of HLA-DR2 class II-related haplotypes (HLA-DRB1-DRB5-DQA1-DQB1) were investigated in four populations of east and south-east Asia (SEA) and five Melanesian populations using TaqI restriction fragment length polymorphism (RFLP) analysis, and the polymerase chain reaction (PCR) amplification-based techniques PCR-RFLP and sequence-specific oligonucleotide (SSO) typing. The haplotype DRB1*1502-DRB5*0101-DQA1*0102-DQB1*0601 was common in Malaysians, Javanese, Thursday Islanders, Madang, Goroka and the Australian Aborigines, while DRB1*16021-DRB5*0101-DQA1*0102-DQB1*0502 was common in the Thai and Thursday Islanders. DRB1*1501-DRB5*0101-DQA1*0102-DQB1*0602 was present at a high frequency in Northern Chinese, Goroka, Watut and Australian Aborigines. The study describes four rare or unusual haplotypes: HLA-DRB1*1501-DRB5*0101-DQA1*0101-DQB1*0601, DRB1*1502-DRB5*0101-DQA1*0101-DQB1*0502, DRB1*1502-DRB5*0102-DQA1* 0102-DQB1*0502 and DRB1*1501-DRB5*0101-DQA1*0101/2-DQB1*0503; the latter two were confirmed by segregation in two Javanese families. A new DR2 allele, initially detected by PCR-RFLP and confirmed by DNA sequencing as DRB1*16022 (previously designated DRB1*16Madang), was seen in a Madang individual. A new HLA-DR2 TaqI RFLP subtype, locally designated as DR15U, is also described. This RFLP subtype segregated in a Javanese family and correlated with a typically SEA haplotype, DRB1*1502-DRB5*0102-DQA1*0101-DQB1*0501. The allele HLA-DR16Thai, determined by TaqI DRB RFLP, was found by PCR-RFLP and SSO typing to correlate with a unique SEA haplotype, HLA-DRB1*16021-DRB5*0101-DQA1*0102-DQB1*0502, and was observed in the Thai, Malaysian, Thursday Islander, Javanese and Northern Chinese populations.

Alleles↗
PubMed1996

Glucose-6-phosphate dehydrogenase deficiency mutations in Papua New Guinea.

We characterize the molecular basis of two G6PD deficiency variants from Papua New Guinea (PNG) and use the information to examine the extent of molecular heterogeneity underlying G6PD variation in the country. The Wosera G6PD- enzyme was found in a male from the East Sepik Province; it had unique biochemical characteristics compared with other previously described G6PD variants from PNG. The Wosera mutation occurred in exon 12 and led to an Arg463-->His substitution. The Kalo mutation, which led to G6PD deficiency in a male from the Central Province along the south coast of PNG, was found in exon 11 and resulted in an Arg454-->Cys substitution. Although screening for the two molecular mutations using sequence-specific oligonucleotide (SSO) hybridization revealed a wide distribution for the Kalo variant along the coastal belt, no additional copy of the Wosera variant was found in a range of samples. Moreover, 28 G6PD- genes from various parts of PNG failed to hybridize with oligonucleotides encoding either the Kalo or Wosera variants. This suggests that more than the two G6PD mutations exist in PNG, confirming the previously noted biochemical heterogeneity of G6PD deficiency in the Melanesian populations of this region.

Base Sequence↗
PubMed1995

Regulation of JAK3 expression and activation in human B cells and B cell malignancies.

Members of the Janus family (JAK) of protein tyrosine kinases are critical enzymes in signaling pathways via hematopoietin receptors. We have cloned JAK3, which unlike other known family members (JAK1, JAK2, and TYK2) is preferentially expressed in hematopoietic cells but not in a variety of other cells. Functionally, JAK3 and JAK1 are coupled to the receptors for IL-2, IL-4, IL-7, IL-9, and IL-15 in T cells and NK cells. Because of the importance of IL-2, IL-4, and IL-7 in B cell physiology, we sought to determine whether JAK3 was also present in B lymphocytes and whether it was involved in signaling via cytokines that are important for B cell development and function. In this report, we demonstrate that JAK3 is expressed in normal human peripheral blood B cells at levels that are comparable to those in T cells. In addition, the levels were found to be markedly up-regulated following stimulation with staphylococcal protein A Cowan and anti-CD40 Abs. In addition, IL-4 and IL-7 induced the rapid tyrosine phosphorylation of JAK3 and JAK1, and IL-4 activated both JAK3 and JAK1 phosphotransferase activity. JAK3 protein was also detected in immature B cell lines, but not in more well differentiated cell lines. Additionally, JAK3 was detected in lysates from bone marrow lymphoblasts of patients with B cell precursor acute lymphocytic leukemia and cell lines derived from human B cell lymphomas. Together, these data suggest that the regulation of JAK3 expression and activity is likely to be important in B cell development and function.

B-Lymphocytes↗
PubMed1995

Infection of human endothelial cells with Epstein-Barr virus.

Interleukin-6 (IL-6) promotes growth and tumorigenicity of Epstein-Barr virus (EBV)-immortalized B cells, and is abnormally elevated in the serum of solid organ transplant recipients who develop EBV-positive posttransplant lymphoproliferative disease (PTLD), but not in control transplant recipients. Endothelial cells derived from PTLD lesions were found to secrete spontaneously high levels of IL-6 in vitro for up to 4 mo. We examined possible mechanisms for sustained IL-6 production by endothelial cells. Here, we show that EBV can infect endothelial cells in vitro. After 3-4 wk incubation with lethally irradiated EBV-positive, but not EBV-negative cell lines, a proportion of human umbilical cord-derived endothelial cells (HUVECs) expressed in situ the EBV-encoded small RNAs (EBER). Southern blot analysis after polymerase chain reaction showed EBV DNA in HUVEC that had been incubated with lethally irradiated EBV-positive cells, but not in the controls. Exposure of HUVECs to lethally irradiated EBV-positive but not EBV-negative cell lines induced IL-6 production that was sustained for up to 120 d of culture. These studies identify endothelial cells as targets for EBV infection and raise the possibility that this infection may be important in the life cycle and pathology of EBV.

Base Sequence↗
PubMed1995

Relationships between G1 arrest and stability of the p53 and p21Cip1/Waf1 proteins following gamma-irradiation of human lymphoma cells.

We investigated temporal relationships between ionizing radiation-induced G1 arrest and induction of the p53-regulated genes GADD45, CIP1/WAF1, and MDM2 in a series of Burkitt's lymphoma and lymphoblastoid cell lines that differed in p53 gene status. Emphasis was placed on characterization of the EW36 cell line, which despite expressing wild-type p53 genes, is defective in G1 arrest following gamma-irradiation (P. M. O'Connor et al., Cancer Res., 53: 4776-4780, 1993). Induction of CIP1/WAF1, GADD45, and to a lesser extent MDM2 mRNA was observed in all wild-type p53 lines that arrested in G1. Cell lines that contained only mutant p53 genes or were heterozygous for p53 mutations failed to induce appreciable levels of these p53-regulated transcripts and did not arrest in G1. G1 arrest in the wild-type p53 cell line WMN was more prolonged than elevation of CIP1/WAF1, GADD45, or MDM2 transcripts, suggesting that G1 arrest duration must be dependent upon stability of these newly synthesized proteins. In agreement, we found that p21Cip1/Waf1, a potent inhibitor of G1-S phase cyclin-dependent kinases, was maintained at elevated levels throughout the period that WMN cells remained arrested in G1. EW36 cells exhibited normal induction of CIP1/WAF1, GADD45, and MDM2 mRNA following gamma-irradiation, suggesting that the defect in G1 arrest must reside downstream of p53 transactivation. Investigations into the stability of p53 and p21Cip1/Waf1 revealed that EW36 cells failed to maintain elevated levels of these proteins following irradiation. p53 levels decreased within 4 h of irradiation, and p21Cip1/Waf1 levels decreased shortly after the normal decline of CIP1/WAF1 mRNA levels. Degradation of p21Cip1/Waf1 coincided with the escape of EW36 cells from G1 arrest. Our studies suggest that p21Cip1/Waf1 stability may determine G1 arrest duration and that premature degradation of this protein could provide an alternative route to subversion of the G1 checkpoint in cancer cells.

Burkitt Lymphoma↗
PubMed1995

A mutant p21 cyclin-dependent kinase inhibitor isolated from a Burkitt's lymphoma.

The growth arrest mediated by p53 is caused at least in part by the p53 mediated expression of p21 (p21waf1/Cip1). Since only one-third of primary Burkitt's lymphomas (BL) demonstrate mutations in the p53 gene, we examined the structural integrity of the p21 coding region by single-strand conformational polymorphism and DNA sequence analysis to determine the extent to which this gene is mutated in BL. Of 34 BLs analyzed, a frequent change (38%) at codon 31 that replaced Ser with Arg was found in 13 samples, 10 of which were from Africa. This change at codon 31 is also detected in peripheral blood DNA from normal subjects and may thus represent a polymorphism. One BL cell line, DH978, carried a change at codon 63: Phe to Leu. This mutation was heterozygous, and both the wild-type and the mutated p21 mRNA were expressed in the tumor cell line. By transfection experiments, the mutant p21 was less efficient in suppressing clonogenicity than wild-type p21. To our knowledge, this is the only mutation described in p21. The availability of this mutant p21 should further help in functional studies of p21.

Base Sequence↗
PubMed1995

Mutations in the coding region of c-myc occur independently of mutations in the regulatory regions and are predominantly associated with myc/Ig translocation.

Constitutive expression of c-myc resulting from a chromosomal translocation, which juxtaposes c-myc to an immunoglobulin gene, is a pivotal lesion in Burkitt's lymphomas. This deregulated expression of c-myc is associated with mutations in the regulatory regions, i.e. the first exon and the first intron of c-myc in tumors where the chromosomal breakpoint is not itself within the regulatory region. Until recently it was widely believed that the c-myc protein in these tumors is wild type. We have demonstrated that in a fraction of Burkitt's lymphomas from Africa and from the continental USA, and in mouse plasmacytomas, the c-myc gene carries mutations in the coding region. We now show that, occasionally, such mutations are also present in multiple myelomas--tumors which do not carry translocations or amplifications of c-myc. We also show that the frequency of the c-myc coding region mutations in BL is independent of the frequency of mutations in the regulatory region. These results suggest that the mechanisms that induce missense mutations involving the coding region of c-myc may be different from those that lead to mutations in the regulatory regions.

Burkitt Lymphoma↗
PubMed1995

Molecular epidemiology of acute lymphoblastic leukemia in Egypt.

We have characterized immunophenotypically defined acute lymphoblastic leukemia (ALL) in Egypt for rearrangements of the antigen receptor genes, and correlated this with rearrangements of ALL-1 and the presence of p53 mutations. Thirty-nine cases were analyzed for rearrangements of the immunoglobulin (Ig) and T-cell receptor (TCR) genes. All precursor B-cell ALLs (12 cases) contained rearranged Ig heavy-chain (JH) region which was biallelic in 92% of these tumors. In addition to JH rearrangements, TCR delta, beta and gamma rearrangements were observed in 80, 40 and 30% of these cases, respectively. TCR genes were invariably rearranged in T-cell ALLs (11 cases). A small fraction (2/11) of T-cell ALL showed concurrent IgJH rearrangement which was monoallelic. Simultaneous rearrangement of IgJH and TCR genes was also observed in both cases of biphenotypic ALL (coexpressing B and T markers). We observed marked heterogeneity in the pattern of rearrangement of antigen receptor genes in mixed-lineage leukemias (ALL coexpressing myeloid-associated markers), including the retention of germline configuration in two cases. Rearrangements of the ALL-1 gene were confined to the leukemias that demonstrated lineage infidelity. Mutations in p53 were infrequent and were present in only three of 47 ALL cases (6%) analyzed; two of these were mixed-lineage leukemias. These results suggest that mixed-lineage and biphenotypic leukemias accumulate pathogenetic lesions that are distinct from B- and T-cell ALL, and that ALL in developing countries includes molecular entities similar to those in developed countries.

Adolescent↗
PubMed1994

A role for deregulated c-Myc expression in apoptosis of Epstein-Barr virus-immortalized B cells.

When deprived of autocrine growth factors, Epstein-Barr virus (EBV)-immortalized B cells stop growing and die. In this study, we show that death of EBV-immortalized cells deprived of autocrine growth factors occurred by apoptosis. Cycloheximide, a protein synthesis inhibitor, inhibited apoptosis, suggesting that de novo protein synthesis is required. Because p53, Bcl-2, and c-Myc were previously implicated in the induction or prevention of apoptosis in other systems, we assessed their possible involvement here. Unlike normal cells that respond to growth factor deprivation by down-regulating c-Myc expression, EBV-immortalized cells continued to express c-Myc, p53, and Bcl-2 at levels comparable to those measured prior to starvation. Consistent with data demonstrating that c-Myc expression is sufficient to drive quiescent cells into the cell cycle, autocrine growth factor-deprived EBV-immortalized cells did not undergo growth arrest but rather continued to proliferate until death, which occurred randomly throughout the cell cycle. In contrast to EBV-immortalized B cells, normal peripheral blood B cells activated in vitro with anti-CD40 monoclonal antibody and interleukin 4 rapidly down-regulated c-Myc expression and underwent growth arrest in response to growth factors and serum deprivation. These findings demonstrated that c-Myc expression is deregulated in EBV-immortalized cells. Addition of antisense oligonucleotides to c-Myc specifically promoted the survival of starved EBV-immortalized cells and suppressed growth of nonstarved EBV-immortalized cells. Thus, deregulated expression of c-Myc in EBV-immortalized cells promotes proliferation and apoptosis following autocrine growth factor deprivation.

Apoptosis↗
PubMed1994

p53 gene mutations are associated with decreased sensitivity of human lymphoma cells to DNA damaging agents.

The present study assessed the role of the p53 tumor suppressor gene in cell cycle arrest and apoptosis following treatment of Burkitt's lymphoma and lymphoblastoid cell lines with gamma-rays, etoposide, nitrogen mustard, and cisplatin. Cell cycle arrest was measured by flow cytometry; p53 and p21Waf1/Cip1 protein levels were measured by Western blotting; cell survival was measured in 72-96-h growth inhibition assays and by trypan blue staining, and apoptotic DNA fragmentation was assessed by either agarose gel electrophoresis or a modified filter elution method. We found that gamma-rays and etoposide induced a strong G1 arrest in the wild-type p53 lines while nitrogen mustard and cisplatin induced relatively little G1 arrest. All agents failed to induce G1 arrest in cells containing mutant p53 genes. The degree of G1 arrest observed with these agents correlated with the rate of p53 and p21Waf1/Cip1 protein accumulation: gamma-rays and etoposide induced rapid accumulation of both p53 and p21Waf1/Cip1; nitrogen mustard and cisplatin induced slow accumulation of p53 and no major accumulation of the p21Waf1/Cip1 protein. Despite differences in G1 arrest and kinetics of p53 or p21Waf1/Cip1 protein accumulation, all agents tended to decrease survival to a greater extent in the wild-type p53 lines compared to the mutant p53 lines. Cell death in the wild-type p53 lines was associated with intracellular DNA degradation into oligonucleosomal sized DNA fragments, indicative of apoptosis. We also observed an inverse sensitivity relationship between nitrogen mustard/cisplatin and etoposide in the mutant p53 lines and this was found to correlate with topoisomerase II mRNA levels in the cells. Our results suggest that p53 gene status is an important determinant of both radio- and chemosensitivity in lymphoid cell lines and that p53 mutations are often associated with decreased sensitivity to DNA damaging agents.

Apoptosis↗
PubMed1994

Mutations in the coding region of c-myc occur frequently in acquired immunodeficiency syndrome-associated lymphomas.

We have analyzed 30 cases of high- and intermediate-grade acquired immunodeficiency syndrome-associated non-Hodgkin's lymphoma (AIDS-NHL) for mutations in the c-myc coding region. In addition, in these same tumors, we have sought the presence of mutations in a regulatory region within the first c-myc intron defined by the binding to a factor that inhibits c-myc transcription (MYC intron factor, or mif). Mutations in the c-myc coding region were present in 10 of 16 small noncleaved cell lymphoma (SNCL), but in only 3 of 14 other histologic subtypes tested (0/3 large non-cleaved cell, 2/8 immunoblastic, and 1/3 anaplastic large cell lymphomas). Nineteen of the AIDS-NHLs analyzed contained a c-myc rearrangement and in 10 of these the c-myc gene was mutated in its coding region. In contrast, we could detect a mutation in the coding region in only 2 of 8 AIDS-NHL without a c-myc rearrangement. Mutations in the mif region were detected in 5 of 16 SNCL. Among AIDS-NHL carrying mutations in the c-myc coding region, only 4 carried mutations in the regulatory region. These results suggest that the mutations in the coding region of the c-myc protein may either be a consequence of the translocations involving c-myc, or may be necessary only in tumors where c-myc is deregulated as a result of a c-myc/lg translocation.

Base Sequence↗
PubMed1994

Binding and suppression of the Myc transcriptional activation domain by p107.

An amino-terminal transactivation domain is required for Myc to function as a transcription factor controlling cell proliferation, differentiation, and apoptosis. A complementary DNA expression library was screened with a Myc fusion protein to identify proteins interacting with this domain, and a clone encoding the Rb-related p107 protein was isolated. The p107 protein was shown to associate with Myc in vivo and to suppress the activity of the Myc transactivation domain. However, mutant forms of Myc from Burkitt lymphoma cells, which contain sequence alterations in the transactivation domain, were resistant to p107-mediated suppression. Thus, disruption of a regulatory interaction between Myc and p107 may be important in tumorigenesis.

3T3 Cells↗
PubMed1994

Regression of experimental Burkitt's lymphoma induced by Epstein-Barr virus-immortalized human B cells.

Epstein-Barr virus (EBV)-immortalized human B cells survive only transiently when injected subcutaneously into athymic mice, whereas Burkitt's lymphoma cells give rise to progressively growing subcutaneous tumors. In this study, we tested whether these Burkitt's tumors could be induced to regress via a bystander effect induced by EBV-immortalized B cells. Simultaneous inoculation of EBV-immortalized B cells and Burkitt's lymphoma cells in the same subcutaneous site resulted in tumors that regressed with necrosis and scarring. Similarly, simultaneous inoculation of EBV-immortalized B cells and Burkitt's lymphoma cells in separate subcutaneous sites resulted in regression of a proportion of the Burkitt's tumors. Furthermore, most of the established human Burkitt's tumors regressed with necrosis and scarring after intratumor inoculations with EBV-immortalized B cells. The EBV-immortalized B cells continued to exert this antitumor effect even when killed with irradiation. The experimental approach to Burkitt's lymphoma treatment described here exploits the ability of athymic mice to reject EBV-immortalized B cells to target an effective antitumor response to malignant cells normally incapable of eliciting it.

Animals↗
PubMed1994

Altitude, language, and class I HLA allele frequencies in Papua New Guinea.

Class I HLA gene frequencies show considerable variation over short geographical distances in Papua New Guinea. Hypothesis to account for this invoke natural selection, population structure, the pattern of population movement, or past demographic changes. To determine the role of the various factors in shaping this distribution, we have studied correlations between HLA-based genetic distances, geographical distances, altitude, and linguistic differences in Papua New Guinea. Linguistic differences at the family or stock level within the Trans-New Guinea Phylum generally correspond to genetic differences. However, on the basis of their HLA gene frequencies, speakers of Austronesian (AN) languages do not form a distinct group of populations. Linguistic variation and spatial autocorrelation do not fully account for the altitudinal cline differences noted in gene frequencies, particularly at the HLA-A locus. We propose that the distribution of HLA gene frequencies in Papua New Guinea is partially under the control of selection operating differentially along the altitude gradient.

Alleles↗
PubMed1994

Dystonia as the major manifestation of Leigh's syndrome.

We report eight patients who had a progressive illness dominated by generalised dystonia and who had clinical and imaging features suggestive of Leigh's syndrome (LS). Six of the eight cases were male. Early development was usually normal but three cases exhibited impaired mental and/or motor development, and three others had a history of an earlier unexplained encephalopathy or febrile illness. The onset of the dystonia occurred at a mean age of 3 years (range 2 months-7 years). All had abnormalities in the basal ganglia on brain imaging; symmetrical bilateral lucencies or calcification were seen in the basal ganglia on computed tomography scan in five cases, and high signal lesions were evident in these regions on T2-weighted magnetic resonance imaging sequences in seven cases. Other causes of such changes in the basal ganglia were excluded by appropriate investigations. Raised blood lactate levels were found in four of the eight patients. Muscle biopsies were done in seven patients but histology and histochemistry were normal. The common mitochondrial DNA mutations associated with LS in mitochondrial encephalopathies were not found in the six cases examined. LS presenting as a pure dystonic syndrome is uncommon, but should be considered in the differential diagnosis of symptomatic dystonia presenting in childhood.

Adolescent↗
PubMed1994

A 3.5 kb deletion in the glycophorin C gene accounts for the Gerbich-negative blood group in Melanesians.

The Gerbich-negative blood group types are rare in most populations, but reach appreciable frequencies in certain Melanesian groups in Papua New Guinea. The recent cloning of the human glycophorin C (GPC) gene, that encodes Gerbich (Ge) blood group antigens, has facilitated study of its genetic variants. We have obtained partial genomic clones of a normal GPC gene, for molecular analysis of Ge: -1, -2, -3 types in Melanesians, and have shown that a 3.5 kb deletion in the GPC gene that removes all of exon 3 accounts for at least one Gerbich-negative phenotype in Melanesians. Population distributions of GPC RFLP have shown that the deletion-type GPC is not confined to mainland Papua New Guinea as previously thought, but occurs sporadically in Melanesians from Fiji as well as in Micronesians.

Anion Exchange Protein 1, Erythrocyte↗