Infection with cagA-positive Helicobacter pylori is associated with gastric adenocarcinoma and gastric mucosa-associated lymphoid tissue (MALT) lymphoma of B cell origin. The cagA-encoded CagA protein is delivered into gastric epithelial cells via the bacterial type IV secretion system and, upon tyrosine phosphorylation by Src family kinases, specifically binds to and aberrantly activates SHP-2 tyrosine phosphatase, a bona fide oncoprotein in human malignancies. CagA also elicits junctional and polarity defects in epithelial cells by interacting with and inhibiting partitioning-defective 1 (PAR1)/microtubule affinity-regulating kinase (MARK) independently of CagA tyrosine phosphorylation. Despite these CagA activities that contribute to neoplastic transformation, a causal link between CagA and in vivo oncogenesis remains unknown. Here, we generated transgenic mice expressing wild-type or phosphorylation-resistant CagA throughout the body or predominantly in the stomach. Wild-type CagA transgenic mice showed gastric epithelial hyperplasia and some of the mice developed gastric polyps and adenocarcinomas of the stomach and small intestine. Systemic expression of wild-type CagA further induced leukocytosis with IL-3/GM-CSF hypersensitivity and some mice developed myeloid leukemias and B cell lymphomas, the hematological malignancies also caused by gain-of-function SHP-2 mutations. Such pathological abnormalities were not observed in transgenic mice expressing phosphorylation-resistant CagA. These results provide first direct evidence for the role of CagA as a bacterium-derived oncoprotein (bacterial oncoprotein) that acts in mammals and further indicate the importance of CagA tyrosine phosphorylation, which enables CagA to deregulate SHP-2, in the development of H. pyloriassociated neoplasms.bacterial oncoprotein ͉ transgenic mouse

We have examined the effects of a stromal cell-derived cytokine designated interleukin 11 (IL-11) on the proliferation of murine hemopoietic progenitors in methylcellulose culture. COS cell-conditioned medium containing IL-11 supported formation of granulocyte/macrophage colonies and a small number of multilineage colonies including blast cell colonies in cultures of marrow cells from normal mice. When tested with marrow cells harvested 2 days after injection of 5-fluorouracil at 150 mg/kg, IL-11 enhanced interleukin 3-dependent colony formation, whereas IL-11 alone supported only scant colony formation. Serial observations (mapping studies) of cultures of post-5-fluorouracil spleen cells indicated that the mechanism of the synergistic effect of IL-11 is to shorten the dormant period of stem cells, an effect very similar to that of interleukin 6. When pooled blast cells were plated into medium containing IL-11 and erythropoietin, only macrophage colonies were observed. Thus, IL-11 can directly support the proliferation of committed macrophage progenitors and, like interleukin 6 and granulocyte colony-stimulating factor, act synergistically with interleukin 3 to shorten the Go period of early progenitors.

RBM5 (RNA-binding motif protein 5) is a nuclear RNA binding protein containing 2 RNA recognition motifs. The RBM5 gene is located at the tumor suppressor locus 3p21.3. Deletion of this locus is the most frequent genetic alteration in lung cancer, but is also found in other human cancers. RBM5 is known to induce apoptosis and cell cycle arrest but the molecular mechanisms of RBM5 function are poorly understood. Here, we show that RBM5 is important for the activity of the tumor suppressor protein p53. Overexpression of RBM5 enhanced p53-mediated inhibition of cell growth and colony formation. Expression of RBM5 augmented p53 transcriptional activity in reporter gene assays and resulted in increased mRNA and protein levels for endogenous p53 target genes. In contrast, shRNA-mediated knockdown of endogenous RBM5 led to decreased p53 transcriptional activity and reduced levels of mRNA and protein for endogenous p53 target genes. RBM5 affected protein, but not mRNA, levels of endogenous p53 after DNA damage suggest that RBM5 contributes to p53 activity through posttranscriptional mechanisms. Our results show that RBM5 contributes to p53 transcriptional activity after DNA damage and that growth suppression and apoptosis mediated by RBM5 are linked to activity of the tumor suppressor protein p53.RBM5 (also known as LUCA-15 or H37) is a nuclear RNA binding protein widely distributed in mammalian tissues. 1 RBM5 was initially cloned as a putative tumor suppressor gene mapping to the human chromosomal locus 3p21.3 2-4 that is frequently deleted in human cancers, including lung, renal and breast cancer. 5,6 Deletion at chromosome 3p21.3 is the most frequent genetic alteration in lung cancer suggesting that the region contains 1 or more tumor suppressor genes. 6 Accumulating evidence suggests that RBM5 can function as a tumor suppressor protein by inhibiting tumor transformation and progression. 7,8 The expression of the RBM5 transcript and protein is decreased in 70-80% of lung cancers. 9 RBM5 is also downregulated in human schwannomas 10 and in ras-transformed rat embryonic fibroblastic cells. 11 Ectopic expression of the RBM5 gene suppresses growth of human lung cancer, breast cancer, 9 fibrosarcoma 11 and leukemic cells. 12 These observations suggest that RBM5 has antiproliferative properties. Furthermore, decrease of RBM5 expression is part of a 17 gene expression signature predictive of metastasis and poor clinical outcome for various types of human cancers. 13 Most of the functional studies for RBM5 have focused on its ability to induce cell cycle arrest and apoptosis. 7,8 Overexpression of RBM5 inhibits cell proliferation by extending the G1 phase of the cell cycle in leukemic cells. 12 RBM5 also inhibits tumor growth of lung cancer cells both in vitro and in vivo with antitumor mechanisms involving G1 cell cycle arrest and apoptosis. The extended G1 phase correlated with reduced levels of cyclin A and of phosphorylated Rb. 14

To elucidate the mechanisms by which hematopoietic progenitor cells transmigrate via the bone marrow (BM) endothelial cells, we first established endothelial cell lines from BM and lung, and BM fibroblast cell lines; then we established an in vitro model of transendothelial migration of hematopoietic progenitor cells in the presence of chemoattractants secreted by BM fibroblast cells. The BM endothelial cells expressed vascular cell adhesion molecule-1 (VCAM-1), but the lung endothelial cells did not. The BM fibroblast cells secreted chemoattractants including stroma cell–derived factor (SDF)-1, which could attract hematopoietic progenitor cells to BM and activate the adhesion molecules expressed on hematopoietic progenitor cells after rolling along the endothelial cells. Anti–SDF-1 antibody inhibited the transendothelial migration of a hematopoietic progenitor cell line, FDCP-2. FDCP-2 that expressed very late activation antigen-4 (VLA-4) and normal progenitor cells transmigrated through BM endothelial cells but not lung endothelial cells, even if in the presence of chemoattractants produced by BM fibroblasts. Both anti–VLA-4 and anti–VCAM-1 antibodies inhibited the transendothelial migration of FDCP-2 cells and normal hematopoietic progenitor cells. These findings suggest that the transendothelial migration of hematopoietic progenitor cells is characteristic of BM endothelial cells, and that VLA-4/VCAM-1 and SDF-1 play important roles in the transendothelial migration and, consequently, homing of hematopoietic progenitor cells to BM.