Non-contrast magnetic resonance imaging for monitoring patients with acoustic neuroma.

OBJECTIVE: To assess the feasibility of non-contrast T2-weighted magnetic resonance imaging as compared to T1-weighted post-contrast magnetic resonance imaging for detecting acoustic neuroma growth. METHODS: Adult patients with acoustic neuroma who underwent at least three magnetic resonance imaging scans of the internal auditory canals with and without contrast in the past nine years were identified. T1- and T2-weighted images were reviewed by three neuroradiologists, and tumour size was measured. Accuracy of the measurements on T2-weighted images was defined as a difference of less than or equal to 2 mm from the measurement on T1-weighted images. RESULTS: A total of 107 magnetic resonance imaging scans of 26 patients were reviewed. Measurements on T2-weighted magnetic resonance imaging scans were 88 per cent accurate. Measurements on T2-weighted images differed from measurements on T1-weighted images by an average of 1.27 mm, or 10.4 per cent of the total size. The specificity of T2-weighted images was 88.2 per cent and the sensitivity was 77.8 per cent. CONCLUSION: The T2-weighted sequences are fairly accurate in measuring acoustic neuroma size and identifying growth if one keeps in mind the caveats associated with the tumour characteristics or location.

An osteopontin fragment is essential for tumor cell invasion in hepatocellular carcinoma.

Tumor cell invasion is a primary event in the metastatic progression of hepatocellular carcinoma (HCC). Our recent results indicate a concordant elevated expression of osteopontin (OPN) and matrix metalloproteinase-9 (MMP-9) in primary metastatic HCC. This study hypothesizes an MMP-9-directed cleavage of OPN that biologically contributes to HCC metastasis. We found that MMP-9 cleaved OPN into specific fragments in vitro, of which three could be identified by Edman degradation amino-acid sequencing. One of these fragments (OPN-5 kDa, residues 167-210) induced low-metastatic HCC cellular invasion via CD44 receptors, which was effectively blocked by the addition of small peptides within the region of OPN-5 kDa. Increased expression of an OPN splice variant (OPN-c) was associated with clinical metastatic HCC. Overexpression of OPN-c with physiological levels of MMP-9 enhanced cellular invasion and coincided with elevated OPN-5 kDa levels. Our data suggest that an alternative splicing event (OPN-c) promotes extracellular cleavage of OPN by MMP-9, thus releasing a distinct region of OPN (OPN-5 kDa) that is essential for HCC cellular invasion and appears to correlate with metastatic potential. The findings of this study may help to improve advanced-stage HCC prognosis and suggest the utility of small peptides for novel therapies.

Induction of a unique gene expression profile in primary human hepatocytes by hepatitis C virus core, NS3 and NS5A proteins.

Hepatocellular carcinoma (HCC) is a fatal disease and hepatitis B and C viruses (HBV and HCV) are considered as major causative factors for the development of HCC. We have conducted gene expression profiling studies to search for potential target genes responsible for HCV-mediated HCC. Adenoviruses encoding core (HCV structural protein), NS3 and NS5A [HCV non-structural (NS) proteins] were generated and infected individually or together in freshly isolated primary human hepatocytes. An adenovirus harboring the oncogenic HBV protein, HBx, was included for comparison. A microarray platform of over 22,000 human oligos was analyzed to seek out significant differentially expressed genes among these viral proteins. We also compared these gene expression profiles with those obtained from HCV-infected liver samples from chronic liver disease (CLD) patients and HCV-related HCC. We found that HCV-related proteins largely induce unique genes when compared with HBx. In particular, interferon-inducible gene 27 (IFI27) was highly expressed in HCV or core-infected hepatocytes and HCV-related CLD or HCC, but was not significantly expressed in HBx-infected hepatocytes or HBV-related CLD or HCC, indicating that IFI27 may play a role in HCV-mediated HCC. In conclusion, our results suggest that HBV and HCV promote HCC development mainly through different mechanisms.

Hepatitis B virus X mutants derived from human hepatocellular carcinoma retain the ability to abrogate p53-induced apoptosis.

Chronic hepatitis B virus (HBV) infection and the integration of its X gene (HBx) are closely associated with the development of hepatocellular carcinoma (HCC). The integrated HBx frequently is truncated or contains point mutations. Previous studies indicated that these HBx mutants have a diminished co-transactivational activity. We have compared the effects of wild-type (wt) HBx and its naturally occurring mutants derived from human HCCs on transcriptional co-transactivation, apoptosis and interactive effects with p53. We demonstrated that overexpression of mutant, but not wt HBx, is defective in transcriptional co-transactivation of the NF-kappaB-driven luciferase reporter. By using a microinjection technique, the HBx mutants were shown to have an attenuated pro-apoptotic activity. This deficiency may be attributed to multiple mutations in the co-transactivation domain of HBx, that leads to decreased stability of the translated product. However, wt or mutant HBx bind to p53 in vitro and retain their ability to block p53-mediated apoptosis in vivo, which has been implicated as its major tumor suppressor function. The abrogation of p53-mediated apoptosis by integrated HBx mutants may provide a selective clonal advantage for preneoplastic or neoplastic hepatocytes and contribute to hepatocellular carcinogenesis.

Distinctive gene expression profiles associated with Hepatitis B virus x protein.

Hepatitis B virus (HBV) is a major risk factor for the development of hepatocellular carcinoma (HCC). HBV encodes the potentially oncogenic HBx protein, which mainly functions as a transcriptional co-activator involving in multiple gene deregulations. However, mechanisms underlying HBx-mediated oncogenicity remain unclear. To determine the role(s) of HBx in the early genesis of HCC, we utilized the NCI Oncochip microarray that contains 2208 human cDNA clones to examine the gene expression profiles in either freshly isolated normal primary adult human hepatocytes (Hhep) or an HCC cell line (SK-Hep-1) ecotopically expressing HBx via an adenoviral system. The gene expression profiles also were determined in liver samples from HBV-infected chronic active hepatitis patients when compared with normal liver samples. The microarray results were validated through Northern blot analysis of the expression of selected genes. Using reciprocally labeling hybridizations, scatterplot analysis of gene expression ratios in human primary hepatocytes expressing HBx demonstrates that microarrays are highly reproducible. The comparison of gene expression profiles between HBx-expressing primary hepatocytes and HBV-infected liver samples shows a consistent alteration of many cellular genes including a subset of oncogenes (such as c-myc and c-myb) and tumor suppressor genes (such as APC, p53, WAF1 and WT1). Furthermore, clustering algorithm analysis showed distinctive gene expression profiles in Hhep and SK-Hep-1 cells. Our findings are consistent with the hypothesis that the deregulation of cellular genes by oncogenic HBx may be an early event that favors hepatocyte proliferation during liver carcinogenesis.

Interaction of the hepatitis B virus X protein with the Crm1-dependent nuclear export pathway.

The leucine-rich nuclear export signal (NES) is used to shuttle large cellular proteins from the nucleus to the cytoplasm. The nuclear export receptor Crm1 is essential in this process by recognizing the NES motif. Here, we show that the oncogenic hepatitis B virus (HBV) X protein (HBx) contains a functional NES motif. We found that the predominant cytoplasmic localization of HBx is sensitive to the drug leptomycin B (LMB), which specifically inactivates Crm1. Mutations at the two conserved leucine residues to alanine at the NES motif (L98A,L100A) resulted in a nuclear redistribution of HBx. A recombinant HBx protein binds to Crm1 in vitro. In addition, ectopic expression of HBx sequesters Crm1 in the cytoplasm. Furthermore, HBx activates NFkappaB by inducing its nuclear translocation in a NES-dependent manner. Abnormal cytoplasmic sequestration of Crm1, accompanied by a nuclear localization of NFkappaB, was also observed in hepatocytes from HBV-positive liver samples with chronic active hepatitis. We suggest that Crm1 may play a role in HBx-mediated liver carcinogenesis.

Identification of a functional domain in a GADD45-mediated G2/M checkpoint.

Cell cycle checkpoints are essential for the maintenance of genomic stability in response to DNA damage. We demonstrated recently that GADD45, a DNA damage-inducible protein, activates a G(2)/M checkpoint induced by either UV radiation or alkylating agents. GADD45 can interact in vivo with the G(2) cell cycle-specific kinase, Cdc2, proliferating cell nuclear antigen (PCNA), and the cell cycle kinase inhibitor p21(waf1). The ability of GADD45 to induce a G(2)/M arrest may be caused in part by the inhibition of Cdc2 kinase activity. Here, we report the identification of a region of GADD45 that is involved in this G(2)/M checkpoint. Mutants of GADD45 that lacked either the first 35 or the last 80 residues still retained an ability to induce G(2)/M arrest. A mutant with a deletion of the central region (residues 50-76), which is conserved in the family members GADD45beta and GADD45gamma, lacked such activity. This mutant also lacked an ability to bind to Cdc2, PCNA, and p21(waf1) in vivo. Consistently, either GADD45beta or GADD45gamma bind to Cdc2 in vivo. However, unlike GADD45, neither GADD45beta nor GADD45gamma inhibited the Cdc2 kinase or induced G(2)/M arrest. The unique effect of GADD45 may be caused by the presence of a region containing DEDDDR residues. Alanine substitutions in the region abolished GADD45 induction of a G(2)/M arrest and its inactivation of the Cdc2 kinase but not its binding to Cdc2, PCNA, or p21(waf1). Therefore, the binding of GADD45 to Cdc2 was insufficient to induce a G(2)/M arrest, and additional activity contributed by the DEDDDR residues may be necessary to regulate the G(2)/M checkpoint.

Curriculum evaluation, education financing, and career plans of 1983 medical school graduates.

The Association of American Medical Colleges annually gathers data on curriculum evaluation, financing, and career plans from senior medical students through a graduation questionnaire. According to the 1983 survey, a majority of the seniors perceived that an appropriate amount of time was devoted to the various areas of instruction at their institutions. The average indebtedness of the graduates was reported to be increasing, and 84.4 percent reported having medical school debts. Only 13.2 percent of the graduates indicated plans to enter a career in research, although over one-third had some research involvement while in medical school. Those who participated in research activities during medical school were somewhat more likely to plan significant research involvement after graduation than those who were not involved in research in medical school.

Validity of the MCAT in predicting performance in the first two years of medical school.

In this paper, the authors present the first systematic summary of predictive validity research on the new Medical College Admission Test (MCAT) since its introduction in 1977. Data are drawn primarily from the MCAT Interpretive Studies Program, a cooperative effort between the Association of American Medical Colleges and 30 of its member schools to conduct research that will both facilitate local use of the test scores and contribute to a national perspective on their value in medical school admissions. The results show that MCAT scores by themselves have significant predictive validity with respect to first- and second-year medical school course grades and National Board of Medical Examiners Part I examination scores and that they complement the predictive validity of undergraduate college grades. The MCAT Science Knowledge areas of assessment, particularly Biology and Chemistry, and the Science Problems subtest tend to have higher correlations than the Skills Analysis subtests with initial performance in medical school; however, the Skills Analysis: Reading subtest may retain its predictive value best over time. Correlation values are discussed in terms of methodological factors which constrain their size. They are also compared with those found for other professional and graduate school admission tests. Further directions for MCAT validity research are described.

A factor comparison of old and new MCAT scales.

The old Medical College Admission Test (MCAT) and the New MCAT were compared by factor-analyzing the scores of a sample of 1,484 examinees who had taken both test batteries during 1976-77. Three common factors were extracted and interpreted. The first, a general science-quantitative factor, linked scales from both test batteries. A second factor, labeled verbal ability, characterized primarily two scales from the old test, Verbal Ability and General Information. A third factor, interpretation skills, was common to the two skills analysis scales of a new test. Specific variance for each subtest was also estimated by comparing the variance accounted for by these factors with the systematic variance indicated by the reliability. It appears that the old Quantitative Ability subtest measured unique skills which have not been incorporated into the new battery. Also the new Biology and Physics scores seem to provide specific information on knowledge in a particular discipline in addition to general science knowledge. Discussion centers on the implications of these data for the use of New MCAT scores in admissions.