Biomedical subjects

N Waseem

Publications and source records attributed to N Waseem.

4 recordsLinked to original sources

PubMed1999

Diagnostic importance of the two-stage factor VIII:C assay demonstrated by a case of mild haemophilia associated with His1954-->Leu substitution in the factor VIII A3 domain.

In some families with mild haemophilia higher results are obtained for factor VIII activity (FVII:C) determined by one-stage assay than by two-stage or chromogenic assays. Amino-acid substitutions in the A1, A2 and A3 domains of factor VIII have been described in affected individuals with this phenotype. We describe a case of mild haemophilia A in which FVIII:C measured by one-stage assay was normal at 106%. However, FVIII:C levels measured by two-stage and chromogenic assays were 18% and 35% respectively. DNA analysis revealed a novel mutation in the A3 domain of factor VIII, His1954-->Leu. In a molecular model of the FVIII A domains, His1954 is placed in close proximity to two other mutations that have previously been shown also to be associated with one-stage/two-stage discrepancies. In this patient the diagnosis of haemophilia A would be missed if only the one-stage assay was used.

Amino Acid Substitution↗

PubMed1996

A keratin antibody recognizing a heterotypic complex: epitope mapping to complementary locations on both components of the complex.

Keratin filaments in simple epithelial cells are heteropolymers of keratin 8 (K8) and keratin 18 (K18), which can be stained by the monoclonal antibody (MAb) LE61. This antibody has been widely used to study keratin expression in normal and neoplastic tissues. In this study we have found that MAb LE61 does not react with individual keratin polypeptides either derived from natural sources or expressed as recombinant proteins in Escherichia coli. However, when K8 or K18 bound to nitrocellulose were incubated with complementary keratin they became reactive with this antibody. A mixture of K8 and K18 in solution also reacted strongly with the MAb LE61 in ELISA. These observations suggest that the antibody recognizes a discontinuous epitope on the keratin complex. The antibody also reacted with complexes of K8 and K18 with other keratins. To locate the epitope of this antibody we have expressed K8 and K18 fragments, deleted from the amino- and carboxyl-termini, as fusion proteins with glutathione S-transferase. These fragments were able to form a heterotypic complex with the complementary keratin. Binding of the MAb LE61 to these complexes mapped the two halves of the epitope on K8, between residues 353 and 367, and on K18, between residues 357 and 385. The two halves of the epitope appear to be in close association in the heterotypic complex since deletions from the amino-terminus did not influence the antibody binding. The highly conserved nature of this epitope in both type I and type II keratins could explain the MAb LE61 reactivity with complexes of K8 or K18 with other keratins.

Amino Acid Sequence↗

PubMed1995

Mutant p53 but not hepatitis B virus X protein is present in hepatitis B virus-related human hepatocellular carcinoma.

Hepatitis B virus (HBV) X protein is thought to play an important role in the development of hepatocellular carcinoma. Recent studies on a transgenic mouse tumor model suggest that HBV X protein may contribute to transformation by binding to and inactivating the cellular growth suppressor protein p53. We have studied 31 hepatocellular carcinoma tissues from Chinese patients for the possible occurrence of such interactions. Although most of the samples contained markers of HBV infection, including free and/or integrated HBV DNA, there was no detectable expression of HBV X protein by Western blot, immunoprecipitation, or histochemical staining. There was also no evidence of HBV X protein associated with p53 immunoprecipitated from the tumors. These observations suggest that, in naturally occurring human hepatocellular carcinoma, such interactions are uncommon and, therefore, unlikely to be of relevance in the latter stages of tumor development. On the other hand, 29 of 31 (93%) samples contained mutated forms of p53, as determined by various antibodies that detect wild-type or mutant p53 or both, and by the association of heat shock protein 70 with immunoprecipitated p53. These results show that conformationally altered p53 protein is present in tumors at a much higher frequency than is suggested by the presence of known mutations in the gene. This mutant p53 is functionally inactive, as suggested by the lack of expression of the p53-induced M(r) 21,000 Cip1/Waf1 protein in the tumors. Because this inactivation of p53 was not correlated with the expression of HBV X protein, any interaction of HBV X protein with p53 may be relevant only during acute infection. Such an interaction could serve to relax cell growth control at a time when virus replication requires hepatocyte destruction to be balanced by regeneration.

Antibodies, Monoclonal↗

PubMed1991

Prognostic value of proliferating cell nuclear antigen in gastric carcinoma.

A new monoclonal antibody to proliferating cell nuclear antigen (PCNA), PC10, which can be used on routinely processed tissue, was applied to 93 cases of gastric carcinoma. Significant intra-tumoural variation in staining occurred. In addition to a PCNA index (percentage of positive cells per 1000 tumour cells), a semiquantitative PCNA grading system was devised, based on estimates of less than or more than 50% of positive tumour cells in whole sections. Neither PCNA index nor PCNA grade showed any correlation with established histological variables, tumour stage, or the presence of lymph node metastases. No significant correlation was observed between PCNA index and S + G2M phase fraction measured by flow cytometric analysis. To analyse survival tumours with PCNA indices above and below the median level (41%) were compared. Those with a higher index tended to have a worse prognosis, but when PCNA grade was considered, it was found to have definite independent prognostic value, tumours of low grade surviving better than those of high grade. The ability of semiquantitative PCNA grading to allow for intra-tumoural variation suggests it may have advantages over absolute counting, which is prone to sampling error when tumour heterogeneity is a major factor. The prognostic value of PC10 staining in gastric carcinoma is therefore promising.

Adult↗