In this study we established the simultaneous status of TP53, p16, p14ARF and PTEN tumor suppressor genes in 34 randomly chosen human glioma cell lines. Nine cell lines (26.4%) harbored mutations or deletions in all four tumor suppressor genes and 22 cell lines (64%) had alterations in at least three. Mutations/deletions were found at the following frequencies: TP53 (76.5%), p14ARF (64.7%), p16 (64.7%), PTEN (73.5%). Thus, there was a high incidence of alterations in the cellular pathways involving the p53 transcription factor (94.1%), the retinoblastoma protein (64.7%) and the PTEN phosphatase (73.5%) and 91% of cell lines carried mutations in two or more pathways. This provides the first clear genetic evidence that these tumor suppressors participate in biological pathways which are functioning separately/independently in glioma cells. The status of the gene alterations did not correlate with tumorigenicity in immunocompromized mice or any clinical parameters. Although the mutation rate was higher in glioma cell lines than that reported for glioma tissues, the alterations were molecularly representative of those found in adult de novo glioblastoma. This study highlights the importance of developing therapeutic approaches applicable to tumors with a broad range of genetic alterations and also provides an invaluable panel of glioma cell lines to make this possible.

The axonal projection mutations irregular chiasm C of Drosophila melanogaster comap and genetically interact with the roughest locus, which is required for programmed cell death in the developing retina. We cloned the genomic region in 3C5 by transposon tagging and identified a single transcription unit that produces a major, spatially and temporally regulated mRNA species of -5.0 kb. Postembryonic expression is strong in the developing optic lobe and in the eye imaginal disc. The gene encodes a transmembrane protein of 764 amino acids with five extracellular immunoglobulin-like domains and similarity to the chicken axonal surface glycoprotein DM-GRASP/SC1/BEN. Both known irreC alleles reduce the level of transcription, whereas the roughest cT mutation disrupts the intracellular domain of the protein.[Key Words: Cell adhesion; Immunoglobulin superfamily; DM-GRASP; optic chiasms; structural brain mutant; verticals]Received August 19, 1993; revised version accepted September 27, 1993.The assembly of a functional nervous system requires the numerical matching and precise connection of neuronal populations, which are often spatially distant. This is achieved through the remarkable ability of developing axons specifically to find and follow the pathways leading to their synaptic targets (for review, see Bixby and Harris 1991;Doherty and Walsh 1992;Hynes and Lander 1992) and through the degeneration of surplus cells (Hollyday and Hamburger 1976;Katz and Lasek 1978). The elucidation of the molecular mechanisms responsible for axonal guidance, neural recognition, and the triggering of cell death is therefore essential to an understanding of the basic developmental strategies generating the intricate pattern of neural organization seen in the adult.In the past few years several studies have provided new insights into the cellular and molecular cues required for correct axonal pathfinding. These include the molecular cloning and characterization of a number of cell surface Present addresses: tlnstituto

P16 and P14ARF are two tumor suppressors encoded by the locus ink4a-arf which is frequently deleted in human tumors. Recent experiments performed with mouse embryonic ®broblasts have shown that P14ARF is an upstream regulator of the P53 pathway. This raises the question as to whether in human tumors the loss of p14arf and mutation of p53 are mutually exclusive events which segregate with genetic alterations at other loci. To examine this question we performed a multigenic analysis on 29 gliomas. We analysed p53 and p14arf in relation with ®ve other genetic loci encoding the most frequently mutated genes in human gliomas: cdkn2a, mdm2, egfr, pten and the chromosomal regions 10q23.3 and 10q25-26. Our study shows for the ®rst time that p53 mutations and p14arf deletions appear mutually exclusive in human glioblastoma, suggesting that they may be functionally redundant in glioma tumorigenesis. The P53 pathway is, therefore, disrupted in 81.8% of malignant gliomas (WHO grades III and IV), either by mutation of the p53 gene (31.8%) or by p14arf deletion (54.5%). These tumors further showed MDM2 overexpression (9.1%), egfr oncogene ampli®cation/egfr overexpression (50%), pten mutations (27.3%) and loss of heterozygosity (LOH) at the chromosomal regions 10q23.3 (86.4%) and 10q25-26 (100%). These alterations did not segregate with p53 mutations or p14arf deletions, while p14arf and cdkn2a were always deleted. Oncogene (2000) 19, 3816 ± 3822.

Antigen receptors of B lymphocytes transmit their activation signal to the cell interior by associating with and activation of specific non-receptor tyrosine kinases. Most of these kinases as well as other cytoplasmic effectors contain at least one Src homology 2 (SH2) domain, known to bind tyrosine-phosphorylated proteins. We examined the binding specificity of SH2 domains from different signaling molecules in B cells and found that each of the SH2 domains tested bound distinct subsets of stimulation-dependent phosphoproteins in vitro. SH2 domains from Src-like tyrosine kinases bound predominantly to the HS1 phosphoprotein. The tandem SH2 domains of the ZAP-70 tyrosine kinase bound to phosphorylated Ig-beta but only weakly to Ig-alpha. Also the SHC-derived SH2 domain formed complexes with the tyrosine-phosphorylated Ig-alpha/beta heterodimer, while the C- and N-terminal SH2 domains of GTPase-activating protein displayed completely different binding preferences. These results suggest that cytoplasmic effector molecules can be recruited to the activated B cell receptor in an SH2-phosphotyrosine-mediated manner. The data also provide a possible explanation for the notion that Ig-alpha and Ig-beta might couple to different biochemical pathways.

The 10q25-26 region between the dinucleotide markers D10S587 and D10S216 is deleted in glioblastomas and, as we have recently shown, in low-grade oligodendrogliomas. We further re®ned somatic mapping on 10q23-tel and simultaneously assessed the role of the candidate tumor suppressor gene PTEN/MMAC1 in glial neoplasms by sequence analysis of eight low-grade and 24 high-grade gliomas. These tumors were selected for partial or complete loss of chromosome 10 based on deletion mapping with increased microsatellite marker density at 10q23-tel. Three out of eight (38%) low-grade and 3/24 (13%) high-grade gliomas exclusively target 10q25-26. We did not ®nd a tumor only targeting 10q23.3, and most tumors (23/32, 72%) showed large deletions on 10q including both regions. The sequence analysis of PTEN/MMAC1 revealed nucleotide alterations in 1/8 (12.5%) low-grade gliomas in a tumor with LOH at 10q21-qtel and in 5/21 (24%) high-grade gliomas displaying LOH that always included 10q23-26. Our re®ned mapping data point to the 10q25-26 region as the primary target on 10q, an area that also harbors the DMBT1 candidate tumor suppressor gene. The fact that we ®nd hemizygous deletions at 10q25-qtel in low-grade astrocytomas and oligodendrogliomas ± two histologically distinct entities of gliomas ± suggests the existence of a putative suppressor gene involved early in glial tumorigenesis.