Comprehensive copy number and gene expression profiling of the 17q23 amplicon in human breast cancer

The biological significance of DNA amplification in cancer is thought to be due to the selection of increased expression of a single or few important genes. However, systematic surveys of the copy number and expression of all genes within an amplified region of the genome have not been performed. Here we have used a combination of molecular, genomic, and microarray technologies to identify target genes for 17q23, a common region of amplification in breast cancers with poor prognosis. Construction of a 4-Mb genomic contig made it possible to define two common regions of amplification in breast cancer cell lines. Analysis of 184 primary breast tumors by fluorescence in situ hybridization on tissue microarrays validated these results with the highest amplification frequency (12.5%) observed for the distal region. Based on GeneMap'99 information, 17 known genes and 26 expressed sequence tags were localized to the contig. Analysis of genomic sequence identified 77 additional transcripts. A comprehensive analysis of expression levels of these transcripts in six breast cancer cell lines was carried out by using complementary DNA microarrays. The expression patterns varied from one cell line to another, and several overexpressed genes were identified. Of these, RPS6KB1, MUL, APPBP2, and TRAP240 as well as one uncharacterized expressed sequence tag were located in the two common amplified regions. In summary, comprehensive analysis of the 17q23 amplicon revealed a limited number of highly expressed genes that may contribute to the more aggressive clinical course observed in breast cancer patients with 17q23-amplified tumors.

The control of hematopoiesis and leukemia: from basic biology to the clinic.

Hematopoiesis gives rise to blood cells of different lineages throughout normal life. Abnormalities in this developmental program lead to blood cell diseases including leukemia. The establishment of a cell culture system for the clonal development of hematopoietic cells made it possible to discover proteins that regulate cell viability, multiplication and differentiation of different hematopoietic cell lineages, and the molecular basis of normal and abnormal blood cell development. These regulators include cytokines now called colony-stimulating factors (CSFs) and interleukins (ILs). There is a network of cytokine interactions, which has positive regulators such as CSFs and ILs and negative regulators such as transforming growth factor beta and tumor necrosis factor (TNF). This multigene cytokine network provides flexibility depending on which part of the network is activated and allows amplification of response to a particular stimulus. Malignancy can be suppressed in certain types of leukemic cells by inducing differentiation with cytokines that regulate normal hematopoiesis or with other compounds that use alternative differentiation pathways. This created the basis for the clinical use of differentiation therapy. The suppression of malignancy by inducing differentiation can bypass genetic abnormalities that give rise to malignancy. Different CSFs and ILs suppress programmed cell death (apoptosis) and induce cell multiplication and differentiation, and these processes of development are separately regulated. The same cytokines suppress apoptosis in normal and leukemic cells, including apoptosis induced by irradiation and cytotoxic cancer chemotherapeutic compounds. An excess of cytokines can increase leukemic cell resistance to cytotoxic therapy. The tumor suppressor gene wild-type p53 induces apoptosis that can also be suppressed by cytokines. The oncogene mutant p53 suppresses apoptosis. Hematopoietic cytokines such as granulocyte CSF are now used clinically to correct defects in hematopoiesis, including repair of chemotherapy-associated suppression of normal hematopoiesis in cancer patients, stimulation of normal granulocyte development in patients with infantile congenital agranulocytosis, and increase of hematopoietic precursors for blood cell transplantation. Treatments that decrease the level of apoptosis-suppressing cytokines and downregulate expression of mutant p53 and other apoptosis suppressing genes in cancer cells could improve cytotoxic cancer therapy. The basic studies on hematopoiesis and leukemia have thus provided new approaches to therapy.

Single neuron control over a complex motor program.

While there are many instances of single neurons that can drive rhythmic stimulus-elicited motor programs, such neurons have seldom been found to be necessary for motor program function. In the isolated central nervous system of the marine mollusc Tritonia diomedea, brief stimulation (1 sec) of a peripheral nerve activates an interneuronal central pattern generator that produces the long-lasting (approximately 30-60 sec) motor program underlying the animal's rhythmic escape swim. Here, we identify a single interneuron, DRI (for dorsal ramp interneuron), that (i) conveys the sensory information from this stimulus to the swim central pattern generator, (ii) elicits the swim motor program when driven with intracellular stimulation, and (iii) blocks the depolarizing "ramp" input to the central pattern generator, and consequently the motor program itself, when hyperpolarized during the nerve stimulus. Because most of the sensory information appears to be funneled through this one neuron as it enters the pattern generator, DRI presents a striking example of single neuron control over a complex motor circuit.