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Biomedical subjects

D N Louis

Publications and source records attributed to D N Louis.

At least 91 records · Page 5Linked to original sources
PubMed1997

A molecular genetic model of astrocytoma histopathology.

As the molecular events responsible for astrocytoma formation and progression are being clarified, it is becoming possible to correlate these alterations with the specific histopathological and biological features of astrocytoma, anaplastic astrocytoma and glioblastoma multiforme. In WHO grade II astrocytomas, autocrine stimulation by the plateletderived growth factor system coupled with inactivation of the p53 gene may lead to a growth stimulus in the face of decreased cell death with slow net growth ensuing. Such cells would also have defective responses to DNA damage and impaired DNA repair, setting the stage for future malignant change. Such biological scenarios recapitulate many of the clinicopathological features of WHO grade II astrocytomas. Anaplastic astrocytomas further display release of a critical cell cycle brake that involves the CDKN2/p16, RB and CDK4 genes. This results in mitoses seen histologically; clinically, there is more conspicuous, rapid growth. Finally, glioblastomas may emerge from the microenvironmental outgrowth of more malignant clones in a complex vicious cycle that involves necrosis, hypoxia, growth factor release, angiogenesis and clonal selection; growth signals mediated by activation of epidermal growth factor receptors may precipitate glioblastomas. It is clear as well that glioblastoma multiforme can arise via a number of independent genetic pathways, although the clinical significance of these distinctions remains unclear.

Apoptosis↗
PubMed1997

Expression of NF2-encoded merlin and related ERM family proteins in the human central nervous system.

Germline mutations of the neurofibromatosis 2 (NF2) gene are associated with an increased incidence of gliomas and glial harmartomas, suggesting a role for the NF2-encoded protein, merlin, in glial growth control. Using monoclonal and polyclonal anti-merlin antibodies for Western blotting and immunohistochemistry, we evaluated the cellular pattern of merlin expression in the normal human central nervous system (CNS), reactive gliosis; and NF2-associated glial hamartomas. In the normal CNS, merlin is widely expressed in coarse cytoplasmic granules in both glia and neurons, with less pronounced expression in other cells. Merlin is also expressed in reactive astrocytes and in the astrocytes of NF2-associated glial hamartomas. In reactive astrocytes, however, merlin is also present at the cell membrane and in cellular processes, suggesting redistribution of the protein in activated cells. Merlin is structurally related to ezrin, radixin and moesin, which are also expressed in the CNS, as demonstrated by Western blotting. The pattern of merlin expression, however, is distinct from that of ezrin, which has been previously described, and that of moesin, in which immunohistochemistry with an anti-moesin antibody showed expression in endothelial cells, glia and neurons in a membranous or diffuse cytoplasmic pattern. These findings imply that merlin has widespread and specific functions in the human central nervous system.

Adult↗
PubMed1997

A novel splice site associated polymorphism in the tuberous sclerosis 2 (TSC2) gene may predispose to the development of sporadic gangliogliomas.

The tuberous sclerosis 2 (TSC2) gene is thought to function as a growth suppressor in sporadic and TSC-associated hamartomas and tumors. Clusters of dysplastic glial cells are a common feature of cortical tubers and subependymal nodules in tuberous sclerosis patients. In an effort to identify TSC2 gene alterations in sporadic gliomas, we detected a novel polymorphism adjacent to the 3'splice site of intron 4. We evaluated the distribution of this variant allele in a series of 244 patients with glial tumors, including 55 gangliogliomas, 31 pilocytic astrocytomas (WHO grade I), 50 astrocytomas (WHO grades II and III), and 108 glioblastomas (WHO grade IV). The allelic distribution in the general population was estimated by examining 381 healthy blood donors. This rare allele appeared in the control population and in the patients with astrocytic gliomas with a virtually identical frequency (8.14%, and 8.20%, respectively). The frequency of the rare allele in gangliogliomas, however, was significantly higher (15.5%; p = 0.024). The fact that both gangliogliomas and cortical tubers in tuberous sclerosis contain neuronal and astrocytic elements and may resemble each other histologically suggests that the TSC2 gene may be involved in the development of these tumors. The rare allele of the TSC2 gene emerges as a candidate for a predisposing factor for the formation of sporadic gangliogliomas.

Adult↗
PubMed1997

Molecular genetic analysis of giant cell glioblastomas.

Glioblastomas (GBMs) are a heterogeneous group of tumors. Recently, distinct molecular genetic alterations have been linked to subgroups of patients with GBM. Giant cell (gc)GBMs are a rare variant of GBM characterized by a marked preponderance of multinucleated giant cells. Several reports have associated this entity with a more favorable prognosis than the majority of GBMs. To evaluate whether gcGBM may also represent a genetically defined subgroup of GBM, we analyzed a series of 19 gcGBMs for mutations in the TP53 gene for amplification of the EGFR and CDK4 genes and for homozygous deletions in the CDKN2A (p16/MTS1) gene. Seventeen of nineteen gcGBMs carried TP53 mutations whereas EGFR and CDK4 gene amplification was seen in only one tumor each and homozygous deletion of CDKN2A was not observed at all. The strikingly high incidence of TP53 mutations and the relative absence of other genetic alterations groups gcGBM together with a previously recognized molecular genetic variant of GBM (type 1 GBM). It is tempting to speculate that the better prognosis of gcGBM patients may result from the low incidence of EGFR amplification and CDKN2A deletion, changes known for their growth-promoting potential.

Adult↗
PubMed1997

Universal absence of merlin, but not other ERM family members, in schwannomas.

NF2 (neurofibromatosis 2, encoding the merlin protein) gene mutations and chromosome 22q loss have been demonstrated in the majority of sporadic and NF2-associated schwannomas, but many schwannomas fail to demonstrate genetic evidence of biallelic NF2 gene inactivation. In addition, the role of the merlin-related ERM family members (ezrin, radixin, and moesin) remains unclear in these tumors. We therefore studied expression of NF2-encoded merlin as well as ezrin, radixin, and moesin in 22 vestibular and peripheral schwannomas that had been evaluated for NF2 mutations and chromosome 22q loss. Western blotting and immunohistochemistry with antibodies directed against the amino and carboxy termini of merlin demonstrated loss of merlin expression in all studied schwannomas, including 12 tumors lacking genetic evidence of biallelic NF2 gene inactivation. Western blotting with antibodies directed against ezrin, radixin, and moesin, however, showed expression of these proteins in all schwannomas. In addition, immunohistochemistry with an antibody to moesin revealed widespread expression in tumor and endothelial cells. These data indicate that the specific loss of merlin is universal to schwannomas and is not linked to loss of ezrin, radixin, or moesin expression.

Blood Proteins↗
PubMed1996

Refined deletion mapping of the chromosome 19q glioma tumor suppressor gene to the D19S412-STD interval.

Allelic loss of chromsome 19q occurs frequently in malignant gliomas, suggesting the presence of a chromosome 19q glioma tumor suppressor gene. Deletion mapping studies have delineated a 3.5 Mb candidate region between D19S219 and HRC. Cloned sequences from the proximal 425 kb of this interval, however, have not shown tumor-specific alterations. To refine the location of the tumor suppressor gene further, we conducted loss of heterozygosity studies on 191 malignant gliomas using nine PCR-based polymorphisms. These included the previously identified and physically mapped markers D19S219, DM, D19S112, HRC and the recently physically mapped polymorphisms at D19S412, STD, D19S596 and GYS. In addition, we isolated a novel microsatellite polymorphism that maps 400 kb telomeric to D19S112. Oligodendroglial tumors showed frequent loss of heterozygosity in all grades, and typically displayed allelic loss at all studied markers. Astrocytomas, however, showed frequent loss primarily in anaplastic astrocytomas and displayed deletion breakpoints within the candidate region. Deletion mapping revealed a minimal region of overlap between D19S412 and STD, a distance of 900 kb. These data suggest that the D19S412-STD interval represents the most likely location for a chromsome 19q glioma tumor suppressor gene involved in astrocytoma, and perhaps oligodendroglioma, tumorigenesis.

Alleles↗
PubMed1996

CDKN2/p16 or RB alterations occur in the majority of glioblastomas and are inversely correlated.

p16 is involved in a cell cycle regulatory cascade that includes cyclin-dependent kinase 4 (cdk4), cyclin D1, and pRb (retinoblastoma). Alterations of each of these components have been described in primary human glioblastoma multiforme (GBM) or in GBM cell lines. Because perturbation of any component in this pathway may have similar oncogenic effects, we studied the relationship between abnormalities of CDKN2/p16 and RB, the two commonly involved tumor suppressor genes, in 55 astrocytic gliomas (42 GBMs, 8 anaplastic astrocytomas, and 5 astrocytomas). By using comparative multiplex PCR, homozygous deletions of the CDKN2/p16 gene were detected in 24 GBMs (57%) and in 2 anaplastic astrocytomas. Two additional GBMs and one anaplastic astrocytoma had allelic loss of chromosome 9p, as assessed by microsatellite polymorphisms flanking the CDKN2/p16 region. Single-strand conformation polymorphism and DNA sequencing analysis of all three coding exons of CDKN2/p16 revealed a frameshift mutation (four-bp deletion) in one of the three GBMs that had lost the remaining 9p allele. Allelic loss of chromosome 13q at the RB gene, RB gene mutations, or loss of pRb expression was noted in 14 GBMs (33%) and 2 anaplastic astrocytomas. Thirty-six of 42 GBMs (86%) had alterations of either CDKN2/p16 (n = 22), RB (n = 10), or both (n = 4); these two genetic changes, however, were relatively exclusive (P = 0.003). Furthermore, of the six GBMs without either CDKN2/p16 or RB gene abnormalities, one case had CDK4 gene amplification. These data indicate that the vast majority of GBMs probably have inactivation of the p16-cdk4/cyclin D1-pRb pathway. The findings also provide corroborative evidence that CDKN2/p16 and RB are the critical glioma tumor suppressor genes on chromosomes 9p and 13q, respectively.

Base Sequence↗
PubMed1996

Association of loss of heterozygosity on chromosome 17p with high platelet-derived growth factor alpha receptor expression in human malignant gliomas.

The aim of this study was to examine platelet-derived growth factor alpha receptor (PDGFR-alpha) expression in gliomas of various degrees of malignancy and to correlate the findings with genetic alterations present in the same tumor samples. We analyzed 83 tumors by in situ hybridization using a PDGFR-alpha cRNA probe. Increased PDGFR-alpha mRNA expression was observed in astrocytic tumors of all stages of malignancy, although the highest levels were found in glioblastoma multiforme. To evaluate the frequency of PDGFR-alpha gene amplification, differential PCR requiring less DNA than Southern analysis was used with fluorescence-labeled primers corresponding to the kinase insert region of the PDGFR-alpha. Only 7 of 43 glioblastomas and none of the other tumors tested showed amplification of the PDGFR-alpha gene, suggesting that a mechanism other than gene amplification is responsible for the overexpression of PDGFR-alpha in glial brain tumors. Comparison of the in situ hybridization data with genetic alterations in the same tumor material showed a significant correlation of loss of heterozygosity on chromosome 17p (Fisher's exact, P < 0.0002) with high expression levels of PDGFR-alpha. Because that was the case in both low- and high-grade astrocytomas, our data imply that PDGFR-alpha is actively involved in tumor cell proliferation in early and late stages of glioma development. The association of PDGFR-alpha expression with a distinct subset of glioblastomas characterized by loss of heterozygosity 17p further supports the differentiation of these tumors into molecular variants.

Base Sequence↗
PubMed1996

Homozygous deletions of the CDKN2/p16 gene in dural hemangiopericytomas.

While most authors currently classify dural-based hemangiopericytoma (HPC) as a distinct entity rather than as a subtype of meningioma, the histogenesis of HPC has long been debated. We have recently shown that meningiomas contain frequent mutations of the neurofibromatosis 2 gene, while HPCs do not, suggesting that HPC is genetically distinct from meningioma. In the present study, we evaluated a series of 31 dural HPCs (including 3 pairs of primary and recurrent tumor) and 26 meningiomas for alterations in the cell-cycle regulatory genes CDKN2/p16 and p53. Homozygous deletions of the CDKN2/p16 gene were detected using a comparative multiplex polymerase chain reaction assay in 7 of 28 primary HPCs (25%), but in only one of 26 meningiomas (P = 0.03). Among the HPCs with recurrence, 1 pair of 3 had a homozygous CDKN2/p16 deletion. The 1 meningioma with a CDKN2/p16 deletion was a meningothelial meningioma, without atypical or malignant features. Single-strand conformational polymorphism analysis of all three exons of CDKN2/p16 and exons 5-8 of p53 revealed no mutations in either HPCs or meningiomas. These results illustrate that homozygous deletions of CDKN2/p16 occur in HPCs and suggest that alterations of the p16-mediated cell-cycle regulatory pathway may underlie the formation or progression of some HPCs. The data also provide further genetic evidence that HPC is not a subtype of meningioma.

Gene Deletion↗
PubMed1996

Molecular genetic alterations in pleomorphic xanthoastrocytoma.

Pleomorphic xanthoastrocytoma (PXA) is a low-grade glioma that may recur as a malignant diffuse astrocytoma such as glioblastoma (GBM). While the molecular genetic basis of diffuse astrocytomas has been studied extensively, PXAs have not been analyzed in detail. We, therefore analyzed DNA from archival primary and recurrent PXAs from eight patients (three grade II PXAs without recurrence, one grade II PXA with recurrence as grade II PXA, two grade II PXAs with progression to GBM, and two grade III anaplastic PXAs with recurrence as grade III anaplastic PXA or GBM) for genetic changes associated with diffuse astrocytomas. Single-strand conformation polymorphism analysis of p53 exons 5-8 revealed migration shifts in two cases, one primary PXA without recurrence and one recurrent grade II PXA in which the primary tumor did not show a shift. DNA sequencing showed two missense mutations in codons 220 (exon 6) and 292 (exon 8), respectively, mutations which have not been previously noted in astrocytomas. Differential polymerase chain reaction analysis demonstrated epidermal growth factor receptor gene amplification in only one tumor, a GBM without allelic loss of chromosome 10 that was the second GBM recurrence of an initial grade II PXA. Loss of heterozygosity studies on tumors from five patients, using three microsatellite polymorphisms on chromosome 10q and three on chromosome 19q, did not disclose allelic loss in any recurrent tumor. These findings suggest that the genetic events that underlie PXA formation and progression may differ significantly from those involved in diffuse astrocytoma tumorigenesis.

Adolescent↗
PubMed1996

Amplification of the cyclin-dependent kinase 4 (CDK4) gene is associated with high cdk4 protein levels in glioblastoma multiforme.

Genetic alterations on the long arm of chromosome 12, including both gene amplification and allelic loss, are associated with malignant progression of human gliomas. The region of the chromosomal arm 12q that is amplified in malignant gliomas contains the CDK4 gene, a cell cycle regulatory gene which promotes cell division. To evaluate the frequency of CDK4 gene amplification, we analyzed a series of 355 brain tumors using a quantitative non-radioactive polymerase chain reaction assay. CDK4 gene amplification occurred in 9 of 81 glioblastomas (11%), but was rare in other neoplasms, including low-grade and anaplastic gliomas, meningiomas, medulloblastomas and metastatic carcinomas (only 6 of 274 cases). There was no correlation between CDK4 gene amplification and allelic loss of chromosome 12. To assess the significance of CDK4 gene amplification, we analyzed protein extracts from 37 glioblastomas by Western blotting with a commercially available polyclonal antibody to cdk4. All tumors with CDK4 gene amplification showed high cdk4 expression levels, whereas no increased cdk4 expression was seen in glioblastomas without CDK4 gene amplification. These data support the functional activity of CDK4 gene amplification in glioblastoma multiforme and point to an important role of CDK4 gene amplification in a subset of glioblastomas.

Brain Neoplasms↗
PubMed1996

The BAX gene maps to the glioma candidate region at 19q13.3, but is not altered in human gliomas.

The bax protein regulates apoptosis in a cellular pathway that involves both bcl-2 and p53, two molecules associated with human glioma tumorigenesis. We therefore evaluated the possibility that BAX functions as a glioma tumor suppressor gene. Somatic cell hybrid panels, fluorescence in situ hybridization and cosmid mapping localized the BAX gene to 19q13.3, approximately 300 kb centromeric to HRC. Thus BAX maps to the region of chromosome 19 most frequently deleted in gliomas. Routine and pulsed-field gel electrophoresis/Southern blotting studies, however, failed to reveal large-scale deletions or rearrangements of the BAX gene in gliomas. In addition, single strand conformation polymorphism analysis of all six BAX exons and flanking intronic sequences did not disclose mutations in 20 gliomas with allelic loss of the other copy of 19q. A C/T polymorphism was detected in intron 3 and was common in the general population. Therefore, although BAX maps to the glioma candidate region on the long arm of chromosome 19, BAX is probably not the 19q glioma tumor suppressor gene.

Base Sequence↗
PubMed1996

Regional expression and subcellular localization of the tyrosine-specific phosphatase SH-PTP2 in the adult human nervous system.

The protein tyrosine phosphatase SH-PTP2 has been implicated in a variety of cell signaling cascades, including those mediating neuronal survival. We therefore investigated the expression of SH-PTP2 in the adult human nervous system using Western blotting, immunohistochemistry and immunoelectron microscopy. SH-PTP2 immunoreactivity was noted only in neurons, but was not restricted to a specific neuronal type or location. Immunohistochemistry showed perikaryal staining, whereas Western blotting and ultrastructural analysis suggested that SH-PTP2 is present in axons as well. While immunohistochemistry showed a Nissl-like pattern in large motor neurons, immunoelectron microscopy demonstrated a diffuse pattern of cytoplasmic staining, without apparent preferential localization. The presence of the SH2 domain-containing tyrosine-specific phosphatase SH-PTP2 in diverse neurons in the adult nervous system suggests that SH-PTP2 may play a role in a broad spectrum of neuronal responses.

Adult↗
PubMed1996

Sentinel lesions of primary CNS lymphoma.

Some patients ultimately diagnosed with primary CNS lymphoma (PCNSL) have transient symptomatic contrast enhancing lesions. These "sentinel lesions" of PCNSL recede spontaneously or with corticosteroid treatment and present an important diagnostic dilemma because they show variable, but non-diagnostic histopathological features. Four previously healthy, immunocompetent patients aged 49 to 58 years had contrast enhancing intraparenchymal brain lesions. Before biopsy, three of the four were treated with corticosteroids. Initial biopsies showed demyelination with axonal sparing in two, non-specific inflammation in one, and normal brain in one. Infiltrating lymphocytes predominantly expressed T cell markers with rare B cells. All four patients recovered within two to four weeks after the initial biopsy and imaging studies showed resolution of the lesions. The CSF was normal in three of the four patients tested; oligoclonal bands were absent in both of the two tested. After seven to 11 months, each patient developed new symptomatic lesions in a different region of the brain, biopsy of which showed a B cell PCNSL. The mechanism of spontaneous involution of sentinel lesions is not understood, but may represent host immunity against the tumour. Sentinel lesions of PCNSL should be considered in patients with contrast enhancing focal parenchymal lesions that show non-specific or demyelinative histopathological changes. Close clinical and radiographic follow up is essential if PCNSL is to be diagnosed early in such patients.

Adrenal Cortex Hormones↗
PubMed1996

Chronic lymphocytic leukemia and the central nervous system: a clinical and pathological study.

Chronic lymphocytic leukemia is the most common human leukemia but infrequently causes neurologic symptoms. We have reviewed all previously reported cases of chronic lymphocytic leukemia in the CNS along with three new cases; one patient was diagnosed antemortem and treated with immediate improvement and 4-year survival. In addition, we reviewed all autopsy cases since 1972 and available lumbar puncture data on patients with chronic lymphocytic leukemia admitted to the Massachusetts General Hospital. Invasion of the CNS by chronic lymphocytic leukemia often leads to confusional state, meningitis with cranial nerve abnormalities, optic neuropathy, or cerebellar dysfunction. Lumbar puncture shows a lymphocytosis consisting of monoclonal B cells, but CSF cytology studies are of limited value in establishing the diagnosis. Long-term survival may be related to the stage of chronic lymphocytic leukemia at the time of CNS disease and may be associated with intrathecal chemotherapy. A mild, asymptomatic infiltration of the brain, frequently noted in late-stage chronic lymphocytic leukemia in autopsy series, may explain the CSF lymphocytosis in some patients with late-stage chronic lymphocytic leukemia.

Aged↗
PubMed1996

Procarbazine, lomustine, and vincristine (PCV) chemotherapy for grade III and grade IV oligoastrocytomas.

The authors provided procarbazine, lomustine (CCNU), and vincristine (PCV) chemotherapy to 32 patients whose tumors contained varying mixtures of oligodendroglial and astrocytic cells. Twenty-five patients had oligodendroglioma-astrocytoma (oligoastrocytoma) with a histological Grade of III (19 patients) or IV (six patients); seven had anaplastic oligodendroglioma. The PCV therapy was administered every 6 weeks for a total of at least 124 cycles. The median duration of follow-up review from the start of chemotherapy was 19.3 months. Nineteen patients were treated before receiving radiation therapy and 12 after receiving it (one patient received concurrent radiotherapy and chemotherapy). Grade 3 or 4 hematological toxicity was experienced by nine (31%) of 29 patients. Ten patients had delayed treatment due to treatment-related toxicities (34.5%). Ninety-one percent of the 32 patients responded to the therapy. These included 10 patients with a complete response and 19 with a partial response. The median time to progression was 15.4 months for all patients and 23.2 months for those with Grade III tumors. The median time to progression for patients with Grade III oligoastrocytomas was 13.8 months; for those with Grade IV oligoastrocytoma it was 12.4 months and for those with anaplastic oligodendrogliomas it was 63.4 months (p = 0.0348). These patients survived a median of 49.8 months, 16 months, and 76 or more months, respectively, from the start of chemotherapy (p = 0.0154). The PCV therapy provides durable responses in patients with Grade III or IV oligoastrocytomas.

Adult↗
PubMed1996

Up-regulation of specific NF 1 gene transcripts in sporadic pilocytic astrocytomas.

Pilocytic astrocytomas of the optic nerve (optic nerve gliomas) are closely associated with neurofibromatosis 1 (NF1), and allelic losses of the NF1 gene region on chromosome 17q occur in sporadic pilocytic astrocytomas. We therefore hypothesized that the NF1 gene acts as a tumor suppressor gene in pilocytic astrocytomas, and that NF1 gene expression would be reduced or absent in these tumors. To evaluate this possibility, we examined quantitative and qualitative aspects of NF1 gene expression in six sporadic pilocytic astrocytomas. Surprisingly, the NF1 gene was overexpressed up to fourfold in these tumors when compared with normal brain. This up-regulation was accompanied by immunohistochemical positivity using a carboxyl-terminal antibody and by the absence of mutations in one kilobase of the NF1 coding sequence, consistent with the expressed transcript and protein being full length and probably wild type. Pilocytic astrocytomas showed a marked predominance of transcripts containing exon 23a and lacking exon 9br, the same isoforms that are expressed by normal and reactive astrocytes and malignant astrocytomas. These data illustrate that pilocytic astrocytomas overexpress specific NF1 gene transcripts, perhaps as a regulatory response to growth stimuli. The role of the NF1 gene as a tumor suppressor in pilocytic astrocytomas, however, remains to be proven.

Adolescent↗