The transcription factors E2F and Myc participate in the control of cell proliferation and apoptosis, and can act as oncogenes or tumor suppressors depending on their levels of expression. Positive feedback loops in the regulation of these factors are predicted-and recently shown experimentally-to lead to bistability, which is a phenomenon characterized by the existence of low and high protein levels (''off'' and ''on'' levels, respectively), with sharp transitions between levels being inducible by, for example, changes in growth factor concentrations.

The intracellular Gram-negative bacterium Francisella tularensis causes the disease tularemia and is known for its ability to subvert host immune responses. Previous work from our laboratory identified the PI3K/Akt pathway and SHIP as critical modulators of host resistance to Francisella. Here, we show that SHIP expression is strongly down-regulated in monocytes and macrophages following infection with F. tularensis novicida (F.n.). To account for this negative regulation we explored the possibility that microRNAs (miRs) that target SHIP may be induced during infection. There is one miR that is predicted to target SHIP, miR-155. We tested for induction and found that F.n. induced miR-155 both in primary monocytes/macrophages and in vivo. Using luciferase reporter assays we confirmed that miR-155 led to down-regulation of SHIP, showing that it specifically targets the SHIP 3′UTR. Further experiments showed that miR-155 and BIC, the gene that encodes miR-155, were induced as early as four hours post-infection in primary human monocytes. This expression was dependent on TLR2/MyD88 and did not require inflammasome activation. Importantly, miR-155 positively regulated pro-inflammatory cytokine release in human monocytes infected with Francisella. In sharp contrast, we found that the highly virulent type A SCHU S4 strain of Francisella tularensis (F.t.) led to a significantly lower miR-155 response than the less virulent F.n. Hence, F.n. induces miR-155 expression and leads to down-regulation of SHIP, resulting in enhanced pro-inflammatory responses. However, impaired miR-155 induction by SCHU S4 may help explain the lack of both SHIP down-regulation and pro-inflammatory response and may account for the virulence of Type A Francisella.

Lung cancer is the leading cause of cancer related deaths in the United States. It is estimated that in 2008 there were 215,000 new diagnoses of lung cancer and 163, 000 deaths. Despite emerging technologies for potential early diagnosis and discovery of novel targeted therapies, the overall five year survival remains a disappointing 15%. Explanations for the poor survival include late presentation of disease, a lack of markers for early detection and both phenotypic and genotypic heterogeneity within patients of similar histological classification. In order to further understand this heterogeneity and thus complexity of lung cancer, investigators have applied various technologies including high throughput analysis of both the genome and proteome. Such approaches have been successful in identifying signatures that may clarify molecular differences in tumors, identify new targets and improve prognostication. In the last decade, investigators have identified a new mode of gene regulation in the form of non-coding RNAs termed microRNAs (miRNAs or miRs). First determined to be of importance in larval development, microRNAs are ~19–22 nucleotide single stranded RNAs that regulate genes by either inducing mRNA degradation or inhibiting translation. MiRNAs have been implicated in several cellular processes including apoptosis, development, proliferation and differentiation. By regulating hundreds of genes simultaneously, miRNAs have the capacity for regulation of biological networks. Global alterations in miRNA expression in both solid organ and haematological malignancies suggest their importance in the pathogenesis of disease. To date, both in vivo and in vitro studies in lung cancer demonstrate a dysregulation of miRNA expression. Furthermore, investigators are beginning to identify individual targets and pathways of miRNAs relevant to lung tumorigenesis. Thus, miRNAs may identify critical targets and be important in the pathogenesis of lung cancer.

The receptor for advanced glycation end-products (RAGE) is a transmembrane receptor of the immunoglobulin super family or is the soluble portion of extracellular domain of RAGE (sRAGE). sRAGE is a competitive, negative regulator of transmembrane RAGE. RAGE and its ligands are overexpressed in a wide variety of diseases. However, the biological function of RAGE and sRAGE on human mononuclear phagocytes is unclear. Using flow cytometry, we found that sRAGE directly bound to human monocytes to mediate their survival and differentiation into macrophages, events that were dependent on cellular adhesion. In both monocytes and MDM, sRAGE treatment activated Akt, Erk and NFk-B signaling, and decreased caspase-3 activity. Interestingly, while sRAGE bound the surface of suspended pre-monocytic leukemic THP1 cells, it failed to stimulate intracellular signaling or cellular differentiation. Furthermore, we found sRAGE induced monocytes chemotaxis in vitro and recruited monocytes to the lung in vivo. Our data suggest a novel role for sRAGE in mononuclear phagocyte survival, differentiation, and cell recruitment of human monocytes. These observations suggest a potential role for sRAGE to modulate organ-based inflammation.