No abstract

A putative tumor suppressor locus on the short arm of human chromosome 9 has been localized to a region of less than 40 kilobases by means of homozygous deletions in melanoma cell lines. This region contained a gene, Multiple Tumor Suppressor 1 (MTS1), that encodes a previously identified inhibitor (p16) of cyclin-dependent kinase 4. MTS1 was homozygously deleted at high frequency in cell lines derived from tumors of lung, breast, brain, bone, skin, bladder, kidney, ovary, and lymphocyte. Melanoma cell lines that carried at least one copy of MTS1 frequently carried nonsense, missense, or frameshift mutations in the gene. These findings suggest that MTS1 mutations are involved in tumor formation in a wide range of tissues.

Telomerase, the ribonucleoprotein enzyme that elongates telomeres, is repressed in normal human somatic cells but is reactivated during tumor progression. We report the cloning of a human gene, hEST2, that shares significant sequence similarity with the telomerase catalytic subunit genes of lower eukaryotes. hEST2 is expressed at high levels in primary tumors, cancer cell lines, and telomerase-positive tissues but is undetectable in telomerase-negative cell lines and differentiated telomerase-negative tissues. Moreover, the message is up-regulated concomitant with the activation of telomerase during the immortalization of cultured cells and down-regulated during in vitro cellular differentiation. Taken together, these observations suggest that the induction of hEST2 mRNA expression is required for the telomerase activation that occurs during cellular immortalization and tumor progression.

The cysteinyl leukotrienes-leukotriene C4(LTC4), leukotriene D4(LTD4) and leukotriene E4(LTE4)-are important mediators of human bronchial asthma. Pharmacological studies have determined that cysteinyl leukotrienes activate at least two receptors, designated CysLT1 and CysLT2. The CysLT1-selective antagonists, such as montelukast (Singulair), zafirlukast (Accolate) and pranlukast (Onon), are important in the treatment of asthma. Previous biochemical characterization of CysLT1 antagonists and the CysLT1 receptor has been in membrane preparations from tissues enriched for this receptor. Here we report the molecular and pharmacological characterization of the cloned human CysLT1 receptor. We describe the functional activation (calcium mobilization) of this receptor by LTD4 and LTC4, and competition for radiolabelled LTD4 binding to this receptor by the cysteinyl leukotrienes and three structurally distinct classes of CysLT1-receptor antagonists. We detected CysLT1-receptor messenger RNA in spleen, peripheral blood leukocytes and lung. In normal human lung, expression of the CysLT1-receptor mRNA was confined to smooth muscle cells and tissue macrophages. Finally, we mapped the human CysLT1-receptor gene to the X chromosome.

The Wnt/β-catenin signaling system plays essential roles in embryonic development and in the self-renewal and maintenance of adult stem cells. R-spondins (RSPOs) are a group of secreted proteins that enhance Wnt/β-catenin signaling and have pleiotropic functions in development and stem cell growth.LGR5, an orphan receptor of the G protein-coupled receptor (GPCR) superfamily, is specifically expressed in stem cells of the intestinal crypt and hair follicle. Knockout of LGR5 in the mouse results in neonatal lethality.LGR4, a receptor closely related to LGR5, also has essential roles in development, as its knockout leads to reduced viability and retarded growth. Overexpression of both receptors has been reported in several types of cancer. Here we demonstrate that LGR4 and LGR5 bind the R-spondins with high affinity and mediate the potentiation of Wnt/β-catenin signaling by enhancing Wntinduced LRP6 phosphorylation. Interestingly, neither receptor is coupled to heterotrimeric G proteins or to β-arrestin when stimulated by the R-spondins, indicating a unique mechanism of action. The findings provide a basis for stem cell-specific effects of Wnt/ β-catenin signaling and for the broad range of functions LGR4, LGR5, and the R-spondins have in normal and malignant growth.cell signaling | stem cell control | gastrointestinal growth | colon cancer A dult stem cells are specialized, undifferentiated cells that are capable of self-renewal and of generating all cell types of the tissue in which they reside. They are generally identified and traced by one marker, or a set of markers, that is specifically expressed in these cells. These markers are likely to constitute some of the important processes that ultimately define stem cells, and thus hold key information to the understanding of stem cell biology. Nevertheless, for the majority of these markers, the functions remain unknown. LGR5 (leucine-rich repeat containing G protein-coupled receptor 5) has been identified and validated as a marker of the crypt basal columnar stem cells along the gastrointestinal tract and of the bulge stem cells in the hair follicle (1-2). This receptor, also known as HG38, GPR49, and FEX, was first reported by us as an orphan receptor (HG38) with homology to the glycoprotein hormone receptor subfamily of the class A rhodopsin-like seven transmembrane (7-TM) domain, G proteincoupled receptors (GPCRs) (3-5).LGR5 is closely related to two other receptors, LGR4 and LGR6 (∼50% identity between each other), and together the trio (LGR4-6) forms a structurally distinct group of 7-TM receptors that have a substantially large N-terminal extracellular domain (ECD) composed of 17 leucinerich repeats (6). Knockout of LGR5 in the mouse leads to total neonatal lethality accompanied by ankyloglossia and gastrointestinal distension (7). Loss of LGR4 results in reduced viability with developmental defects in many organs, including the kidney (8, 9), testis (10, 11), eye (12), bone (13), skin (14), and gall bladder (15). LGR4 and LGR5 are also overexpressed in sev...