Biomedical subjects

Kamel Khalili

Publications and source records attributed to Kamel Khalili.

101 records · Page 6Linked to original sources

PubMed2002

Cerebral hypoperfusion generates cortical watershed microinfarcts in Alzheimer disease.

BACKGROUND AND PURPOSE: The watershed cortical areas are the first to be deprived of sufficient blood flow in the event of cerebral hypoperfusion and will be the sites of watershed microinfarcts. Cerebral hypoperfusion is associated with Alzheimer disease (AD), but information regarding the occurrence of watershed cortical infarcts in AD is lacking. METHODS: Brains of 184 autopsy cases (105 definite AD cases and 79 age-matched controls) were selected and analyzed by histochemical and immunohistochemical techniques. The 3-dimensional reconstruction of the whole cerebrum, with 3-mm spaced serial sections, was performed in 6 AD cases to study the intrahemispheric and interhemispheric distribution of the cortical microinfarcts. RESULTS: A significant association (P=0.001) was found between the occurrence of watershed cortical infarcts and AD (32.4% versus 2.5% in controls). The microinfarcts were restricted to the watershed cortical zones. Congophilic angiopathy was revealed to be an important risk factor. Perturbed hemodynamic factors (eg, decreased blood pressure) may play a role in the genesis of cortical watershed microinfarcts. CONCLUSIONS: In AD, cerebral hypoperfusion induces not only white matter changes but cortical watershed microinfarcts as well, further aggravating the degenerative process and worsening dementia. To prevent the formation of watershed cortical microinfarcts in AD, monitoring blood pressure and treating arterial hypotension are essential.

Aged↗

PubMed2002

Insulin-like growth factor I receptor activity in human medulloblastomas.

Medulloblastomas represent about 25% of all pediatric intracranial neoplasms. These highly malignant tumors arise from the cerebellum affecting mainly children between ages 5 and 15. Although the etiology of medulloblastomas has not yet been elucidated, several reports suggest that insulin-like growth factor I (IGF-I) may contribute to the development of these tumors. Results of this study show that the majority of cases examined were characterized by the abundant presence of the receptor for IGF-I (IGF-IR) protein (16 of 20 cases), and its major signaling molecule, insulin receptor substrate 1 (IRS-1; 15 of 20). Protein levels for IGF-IR and IRS-1, determined by Western blot and immunohistochemistry, were significantly higher in medulloblastoma biopsies than in control cerebellar tissue. By immunohistochemistry, 10 of 17 biopsies examined were also positive for the anti-pY1316 antibody staining that specifically recognizes the phosphorylated (active) form of the IGF-IR. These findings correlate with the fact that phosphorylated forms of the downstream-signaling molecules Erk-1, Erk-2, and Akt/protein kinase B were found in medulloblastoma biopsies but not in control cerebellar tissue. Importantly, there is a strong inverse correlation between biopsies that are positive for anti-pY1316 and for anti-Trk-C immunoreactivity. These observations direct our attention to the IGF-IR system as a potential therapeutic target in medulloblastomas and suggest a possibility of using the anti-pY1316 antibody as a potential prognostic marker for medulloblastomas.

Adolescent↗

PubMed2002

Detection of JC polyomavirus DNA sequences and cellular localization of T-antigen and agnoprotein in oligodendrogliomas.

PURPOSE: Productive infection of the human neurotropic polyomavirus JCPyV in oligodendrocytes leads to the development of progressive multifocal leukoencephalopathy, a fatal demyelinating disorder of the central nervous system. In addition to its role in viral infection, JCPyV T-antigen can transform cells in vitro and induce tumors in experimental animals in the absence of viral DNA replication and late gene expression. The goal of this study is to examine the presence of JCPyV DNA sequences and viral antigens in a series of human oligodendrogliomas. EXPERIMENTAL DESIGN: A total of 20 well-characterized oligodendrogliomas were examined for detection of the JCPyV genome by PCR and immunohistochemistry for expression of viral proteins. RESULTS: Gene amplification has revealed the presence of JCPyV DNA sequences corresponding to the NH2-terminal of T-antigen in 15 of 20 samples. DNA sequences corresponding to late regions, which are responsible for production of the capsid protein, VP1, were detected in 14 of 20 samples. Sequencing of the viral control region determined the presence of JCPyV Mad-4 or JCPyV(CY) in these tumors. By immunohistochemistry, T-antigen expression was detected in the nuclei of tumor cells from 10 samples that also contained corresponding DNA sequences by PCR. Eleven of 20 tumors exhibited immunoreactivity for the late auxiliary gene product, agnoprotein. None of the samples showed immunoreactivity for the capsid proteins, ruling out productive infection of neoplastic cells by JCPyV. CONCLUSIONS: Collectively, these observations provide new evidence in support of the association of the oncogenic human neurotropic JCPyV and oligodendrogliomas.

Adult↗

PubMed2001

Coordinate effects of human immunodeficiency virus type 1 protein Tat and cellular protein Puralpha on DNA replication initiated at the JC virus origin.

JC virus (JCV) causes progressive multifocal leukoencephalopathy, a demyelinating disease in brains of individuals with AIDS. Previous work has shown that the Tat protein, encoded by human immunodeficiency virus type 1 (HIV-1), can interact with cellular protein Puralpha to enhance both TAR-dependent HIV-1 transcription and JCV late gene transcription. Tat has been shown to activate JCV transcription through interaction with Puralpha, which binds to promoter sequence elements near the JCV origin of replication. DNA footprinting has shown that Puralpha and large T-antigen cooperatively interact at several binding sites in the origin and transcriptional control region. Overexpression of Puralpha inhibits replication initiated at the JCV origin by T-antigen. In transfected glial cells Tat reversed this inhibition and enhanced DNA replication. In an in vitro replication system maximal activation by Tat, more than sixfold the levels achieved with T-antigen alone, was achieved in the presence of Puralpha. Effects of mutant Tat proteins on both activation of replication and binding to Puralpha have revealed that Cys22 exerts a conformational effect that affects both activities. The origin of an archetypal strain of JCV was less susceptible to activation of replication by Tat relative to the rearranged Mad-1 strain. These results have revealed a previously undocumented role for Tat in DNA replication and have indicated a regulatory role for JCV origin auxiliary sequences in replication and activation by Tat.

Antigens, Viral, Tumor↗

PubMed1999

Interaction of YB-1 with human immunodeficiency virus type 1 Tat and TAR RNA modulates viral promoter activity.

Transcriptional regulation of the human immunodeficiency virus type 1 (HIV-1) genome is mediated by viral and cellular factors. TAR, an unusual RNA regulatory element with a stem-bulge-loop structure at the 5' ends of all nascent viral transcripts is critical for HIV-1 transcription. TAR is the target for Tat, a viral transcription factor encoded early in the HIV-1 life-cycle and essential for gene expression. Evidence demonstrating the interaction of a cellular ssDNA/RNA binding protein, YB-1, with TAR through a region which is important for Tat interaction is presented. Interestingly, results from protein-protein interaction studies revealed that YB-1 can also form a complex with Tat. Results from mapping experiments suggest that while the region spanning aa 125-203 within YB-1 is essential for its association with TAR, a truncated YB-1 spanning aa 1-125 can weakly bind to Tat. Functionally, overexpression of full-length YB-1 enhanced Tat-induced activation of the HIV-1 minimal promoter containing TAR sequences, whereas mutant YB- 1 with no ability to bind to Tat and TAR failed to affect Tat-mediated activation. Expression of mutant YB-1(1-125), which binds to Tat but not RNA, decreased Tat-mediated enhancement of virus transcription. These observations suggest that while full-length YB-1 may function as a facilitator and, by interaction with both Tat and TAR, increase the level of Tat:TAR association, mutant YB-1 with no TAR binding activity, by complexing with Tat, may prevent Tat interaction with TAR. The importance of these findings in light of the proposed mechanism of Tat function is discussed.

CCAAT-Enhancer-Binding Proteins↗

PubMedDate not supplied

T-cell and neuronal apoptosis in HIV infection: implications for therapeutic intervention.

The pathogenesis of HIV infection involves the selective loss of CD4+ T cells contributing to immune deficiency. Although loss of T cells leading to immune dysfunction in HIV infection is mediated in part by viral infection, there is a much larger effect on noninfected T cells undergoing apoptosis in response to activation stimuli. In the subset of patients with HIV dementia complex, neuronal injury, loss, and apoptosis are observed. Viral proteins, gp120 and Tat, exhibit proapoptotic activities when applied to T cell and neuronal cultures by direct and indirect mechanisms. The pathways leading to cell death involve the activation of one or more death receptor pathways (i.e., TNF-alpha, Fas, and TRAIL receptors), chemokine receptor signaling, cytokine dysregulation, caspase activation, calcium mobilization, and loss of mitochondrial membrane potential. In this review, the mechanisms involved in T-cell and neuronal apoptosis, as well as antiapoptotic pathways potentially amenable to therapeutic application, are discussed.

Apoptosis↗

PubMedDate not supplied

Developmental expression of Wnt signaling factors in mouse brain.

The Wnt signaling pathway has been implicated in a variety of biological events inducing neurogenesis. In this study, we aim to investigate the expression pattern of various components of the Wnt pathway including b-catenin and its partners LEF-1/TCF-4, GSK-3beta and their nuclear target genes such as c-myc and cyclin D1 during mouse brain development. We performed a series of Western blot and immunohistochemistry of brain cortex, brainstem, and cerebellum which revealed differential accumulation of these proteins in different types of brain cells including neurons, astrocytes, and oligodendrocytes at different developmental stages. Intense cytoplasmic immunolabeling of beta-catenin in 5 day old neurons throughout the cortex and brainstem significantly decreased as the brain developed, whereas the level of GSK-3beta, the protein that phosphorylates beta-catenin and causes its destabilization, increased during brain maturation. On the other hand, high level accumulation of LEF-1 and TCF-4 in neurons and astrocytes at the early stage of brain development diminished at the later stages. Interestingly, while the majority of LEF-1 and TCF-4 immunoreactivity was detected in the cytoplasm of neurons, it was evident that both proteins accumulated in the nuclei of astrocytes. Examination of cyclin D1, a protein that controls the cell cycle and proliferation, exhibited an intense staining in the nuclei of astrocytes throughout brain parenchyma during development. Interestingly, cyclin D was found in the cytoplasm of neurons from cortex, brainstem, and cerebellum during brain development. These data provide compelling evidence for the differential expression of the Wnt signaling pathway during brain development, and suggest that these signaling pathways may function differently in various brain regions and cell types.

Animals↗

PubMedDate not supplied

T-antigen of human polyomavirus JC cooperates withIGF-IR signaling system in cerebellar tumors of the childhood-medulloblastomas.

Polyomaviruses are implicated in a number of cancers, and the transforming activity of their early protein, large T-antigen, has been documented in a variety of cell types and in experimental animals (1). Although the pathways by which T-antigen induces uncontrolled cell growth are not fully defined, T-antigen mediated inactivation of tumor suppressors, p53 and pRB, is well-documented in some malignancies (2). Here we postulate that functional interaction between the insulin-like growth factor (IGF-IR) and the T-antigen of human polyomavirus JC (JCV T-antigen) may contribute to the process of malignant transformation in medulloblastomas: (i) the IGF-IR signaling system is strongly activated in medulloblastoma cell lines and medulloblastoma biopsies; (ii) the cytoplasmic protein, insulin receptor substrate 1 (IRS-1), is translocated to the nucleus in the presence of JCV T-antigen; (iii) molecular characterization of the interaction between IRS-1 and JCV T-antigen indicates that the binding involves the N-terminal portion of IRS-1 (PH/PTB domain) and the C-terminal region of JCV T-antigen (aa 411-628); and finally (iv) competition for the IRS-1-JCV T-antigen binding attenuates anchorage-independent growth of T-antigen positive medulloblastoma cells in culture. Based on these findings, we propose a novel role for IRS-1 in JCV T-antigen-mediated deregulation of cellular equilibrium, which may involve uncoupling of IRS-1 from the surface receptor and translocation of its function to the nuclear compartment of the cell.

Animals↗

PubMedDate not supplied

Interaction between the pura and E2F-1 transcription factors.

BACKGROUND: Cell proliferation is regulated by E2F-1 which facilitates expression of genes involved in entry into S-phase. Release of E2F-1 from binding partners, e.g. pRb, is critical for G1/S progression. However ectopic E2F-1 overexpression activates p53 and inhibits growth. Previously, the multifunctional Pura protein was found to bind to E2F-1 and inhibit E2F-1 transcriptional activity. MATERIALS AND METHODS: Pura deletion mutants were assayed for: in vitro binding to E2F-1, inhibition of E2F-1-induced promoter activation and effects on cell proliferation. Two RNA species with specific binding to E2F-1 and Pura were analyzed for their effects on E2F-1/Pura binding and cell growth. RESULTS: The N-terminal 72 amino acids of Pura were involved in E2F-1 binding, inhibition of promoter activation by E2F-1 and reversal of E2F-mediated growth inhibition. The RNA species disrupted Pura/E2F-1 interaction and affected cell growth. CONCLUSION: E2F-1/Pura interaction has a role in the control of cell proliferation.

Binding Sites↗

PubMedDate not supplied

Regulation of human neurotropic JCV in colon cancer cells.

BACKGROUND: Recently, the genome of the human polyomavirus, JC (JCV), and expression of its early and late regulatory proteins (T-antigen and agnoprotein) have been demonstrated in neoplastic cells of colonic cancer cases. MATERIALS AND METHODS: Regulation of JCV was investigated in a human colon cancer cell line (SW480) and compared to a human glioblastoma cell line (U87-MG) that is permissive for JCV replication. RESULTS: SW480 cells supported basal transcription of both early and late JCV promoters. The expression of TCF-4, a component of Wnt signaling, modulated JCV transcription in a cell type-specific manner. Both TCF-4 and T-antigen bound to the JCV promoter region and bound to each other. In addition, the expression of TCF-4 caused a decrease in the ability of the T-antigen to stimulate viral DNA replication in U87-MG cells. CONCLUSION: Wnt pathway signaling proteins and T-antigen interact to regulate JCV in colonic epithelial cells.

Antigens, Viral, Tumor↗

PubMedDate not supplied

Analysis of a mutant p53 protein arising in a medulloblastoma from a mouse transgenic for the JC virus early region.

BACKGROUND: JC virus (JCV) is a polyomavirus that causes progressive multifocal leukoencephalopathy (PML) in humans and is highly oncogenic in experimental animals. Transgenic mice with JCV T-antigen develop cerebellar tumors, which resemble human medulloblastomas, containing two distinct cell subpopulations, T-antigen positive and negative. In T-negative clones, a novel mutant p53 was detected (p53(mt)). MATERIALS AND METHODS: We have compared p53(mt) to wild-type p53 (p53wt) in p53-null cells. RESULTS: p53(mt) had lost the transcriptional transactivation activity of p53(wt), and unlike p53(wt), partially localized to the cytoplasm. Unlike mutant p53 from many human cancers, p53(mt) did not show a gain of function or a dominant negative phenotype. Adenovirus expressing p53(wt) but not p53(mt) inhibited cell growth and induced apoptosis of p53-null cells. CONCLUSION: During the course of tumor evolution of the JCV T-antigen mouse medulloblastoma, a mutation occurred that inactivated p53 allowing tumor progression even in the absence of continued T-antigen expression.

Animals↗