Localization of the human phosphatidylinositol-specific phospholipase c beta 3 gene (PLCB3) within chromosome band 11q13

The molecular genetics of gastroenteropancreatic neuroendocrine tumors

The pathobiology of neuroendocrine tumors (NETs) is hampered by the lack of scientific tools that define their mechanisms of secretion, proliferation, and metastasis; and, currently, there are no accurate means to assess tumor behavior and disease prognosis. Molecular biologic techniques and genetic analysis may facilitate the delineation of the molecular pathology of NETs and provide novel insights into their cellular mechanisms. The current status and recent advances in assessment of the molecular basis of tumorigenesis of gastroenteropancreatic neuroendocrine tumors (GEP-NETs) were reviewed (1981-2004). The objectives of this retrospective study were to provide a cohesive overview of the current state of knowledge and to develop a molecular understanding of these rare tumor entities to facilitate the establishment of therapeutic targets and rational management strategies. Multiple differences in chromosomal aberration patterns were noted between gastrointestinal (GI) neuroendocrine and pancreatic endocrine tumors (PETs). Divergence in gene expression patterns in the development of GI carcinoids and PETs was identified, whereas examination of the PET and GI carcinoid data demonstrated only few areas of overlap in the accumulation of genetic aberrations. These data suggest that the recent World Health Organization classification of GEP-NETs may require updating. In addition, previous assumptions of tumor similarity (pancreatic vs. GI) may be unfounded when they are examined at a molecular level. On the basis of the evolution of genetic information, enteric neuroendocrine lesions (carcinoids) and PETs may need to be classified as two distinct entities rather than grouped together as the single entity "GEP-NETs."

Specificity and structural requirements of phospholipase C-beta stimulation by Rho GTPases versus G protein beta gamma dimers

Phospholipase C-beta(2) (PLC beta(2)) is activated both by heterotrimeric G protein alpha- and beta gamma- subunits and by Rho GTPases. In this study, activated Rho GTPases are shown to stimulate PLC beta isozymes with the rank order of PLC beta(2) > PLC beta(3) > or = PLC beta(1). The sensitivity of PLC beta isozymes to Rho GTPases was clearly different from that observed for G protein beta gamma dimers, which decreased in the following order: PLC beta(3) > PLC beta(2) > PLC beta(1) for beta(1)gamma(1/2) and PLC beta(2) > PLC beta(1) >>> PLC beta(3) for beta(5)gamma(2). Rac1 and Rac2 were found to be more potent and efficacious activators of PLC beta(2) than was Cdc42Hs. The stimulation of PLC beta(2) by Rho GTPases and G protein beta gamma dimers was additive, suggesting that PLC beta(2) activation can be augmented by independent regulation of the enzyme by the two stimuli. Using chimeric PLC beta(1)-PLC beta(2) enzymes, beta gamma dimers, and Rho GTPases are shown to require different regions of PLC beta(2) to mediate efficient stimulation of the enzyme. Although the catalytic subdomains X and Y of PLC beta(2) were sufficient for efficient stimulation by beta gamma, the presence of the putative pleckstrin homology domain of PLC beta(2) was absolutely required for the stimulation of the enzyme by Rho GTPases. Taken together, these results identify Rho GTPases as novel PLC beta regulators, which mediate PLC beta isozyme-specific stimulation and are potentially involved in coordinating the activation of PLC beta(2) by extracellular mediators in intact cells.

Construction of a 350-kb sequence-ready 11q13 cosmid contig encompassing the markers D11S4933 and D11S546: mapping of 11 genes and 3 tumor-associated translocation breakpoints

Previously, we located three novel human tumor-associated translocation breakpoints in the chromosome 11q13 region between the markers D11S4933 and D11S546. To facilitate the molecular analysis of these breakpoints, we have constructed a continuous sequence-ready cosmid and PAC contig of approximately 350 kb, including the markers D11S4933 and D11S546. In addition, a detailed transcript map was generated. This resulted in the precise positioning of 11 genes and ESTs within the contig, including 4 genes already known to map in the 11q13 region. Three other genes that we positioned within the contig showed homologies to unmapped genes from human and/or other species. Three ESTs were novel. Partial cosmid sequencing resulted in the establishment of the direction of transcription of several of the reported genes. This contig will be instrumental for the detailed characterization of the tumor-associated chromosomal breakpoints and the identification of other 11q13-associated disease genes.

Gbeta 5gamma 2 is a highly selective activator of phospholipid-dependent enzymes

In this study, Gbeta specificity in the regulation of Gbetagamma-sensitive phosphoinositide 3-kinases (PI3Ks) and phospholipase Cbeta (PLCbeta) isozymes was examined. Recombinant mammalian Gbeta(1-3)gamma(2) complexes purified from Sf9 membranes stimulated PI3Kgamma lipid kinase activity with similar potency (10-30 nm) and efficacy, whereas transducin Gbetagamma was less potent. Functionally active Gbeta(5)gamma(2) dimers were purified from Sf9 cell membranes following coexpression of Gbeta(5) and Ggamma(2-His). This preparation as well as Gbeta(1)gamma(2-His) supported pertussis toxin-mediated ADP-ribosylation of Galpha(i1). Gbeta(1)gamma(2-His) stimulated PI3Kgamma lipid and protein kinase activities at nanomolar concentrations, whereas Gbeta(5)gamma(2-His) had no effect. Accordingly, Gbeta(1)gamma(2-His), but not Gbeta(5)gamma(2-His), significantly stimulated the lipid kinase activity of PI3Kbeta in the presence or absence of tyrosine-phosphorylated peptides derived from the p85-binding domain of the platelet derived-growth factor receptor. Conversely, both preparations were able to stimulate PLCbeta(2) and PLCbeta(1). However, Gbeta(1)gamma(2-His), but not Gbeta(5)gamma(2-His), activated PLCbeta(3). Experimental evidence suggests that the mechanism of Gbeta(5)-dependent effector selectivity may differ between PI3K and PLCbeta. In conclusion, these data indicate that Gbeta subunits are able to discriminate among effectors independently of Galpha due to selective protein-protein interaction.

Towards the isolation of a human malignant extragonadal germ cell tumour-associated breakpoint in chromosome 11q13

In a previous study we have defined a subgroup of human malignant extragonadal germ cell tumours that is characterized by complex translocations involving chromosomes 6 and 11 (Echten et al. 1995). Here we report (i) the use of fluorescent in situ hybridization, pulsed field gel electrophoresis and direct visual hybridization techniques to localize the tumour-associated breakpoint within band 11q13, and (ii) the construction of a phage library enriched for this region to facilitate genomic walks towards the breakpoint. Extensive breakpoint-flanking contigs were generated and within these contigs six candidate genes could be identified.

Fine mapping of the human renal oncocytoma-associated translocation (5;11)(q35;q13) breakpoint

Recent cytogenetic analysis of a series of human renal oncocytomas revealed the presence of a recurring chromosomal translocation (5;11)(q35;q13) as sole anomaly in a subset of the tumors. The molecular characterization of this translocation was initiated using two primary t(5;11)-positive renal oncocytomas and a panel of somatic cell hybrids derived from one of these tumors, in conjunction with fluorescence in situ hybridization (FISH) and Southern blot analysis. The breakpoint in chromosome band 11q13 could be located within a genomic interval of at maximum 400 Kb immediately centromeric to the BCL1 locus.