Description: Acute myelogenous leukemia stem cells (AML–LSC) give rise to the leukemic bulk population and maintain disease. Relapse can arise from residual LSCs that have distinct sensitivity and dependencies when compared with the AML bulk. AML–LSCs are driven by genetic and epigenomic changes, and these alterations influence prognosis and clonal selection. Therapies targeting these molecular aberrations have been developed and show promising responses in advanced clinical trials; however, so far success with LSCs has been limited. Besides the genetic diversity, AML–LSCs are critically influenced by the microenvironment, and a third crucial aspect has recently come to the fore: A group of evolutionarily conserved signaling pathways such as canonical Wnt signaling, Notch signaling, or the Hedgehog pathway can be essential for maintenance of AML–LSC but may be redundant for normal hematopoietic stem cells. In addition, early reports suggest also regulators of cell polarity may also influence hematopoietic stem cells and AML biology. Interactions between these pathways have been investigated recently and suggest a network of signaling pathways involved in regulation of self-renewal and response to oncogenic stress. Here, we review how recent discoveries on regulation of AML–LSC-relevant evolutionarily conserved pathways may open opportunities for novel treatment approaches eradicating residual disease. Clin Cancer Res; 21(2); 240–8. ©2015 AACR .

Description: Shiga toxin-producing Escherichia coli (STEC) belonging to certain serogroups (e.g., O157 and O26) can cause serious conditions like hemolytic-uremic syndrome (HUS), but other strains might be equally pathogenic. While virulence factors, like stx and eae , have been well studied, little is known about the prevalence of the E. coli hemolysin genes ( hlyA , ehxA , e-hlyA , and sheA ) in association with these factors. Hemolysins are potential virulence factors, and ehxA and hlyA have been associated with human illness, but the significance of sheA is unknown. Hence, 435 E. coli strains belonging to 62 different O serogroups were characterized to investigate gene presence and phenotypic expression of hemolysis. We further investigated ehxA subtype patterns in E. coli isolates from clinical, animal, and food sources. While sheA and ehxA were widely distributed, e-hlyA and hlyA were rarely found. Most strains (86.7%) were hemolytic, and significantly more hemolytic (95%) than nonhemolytic strains (49%) carried stx and/or eae ( P 〈 0.0001). ehxA subtyping, as performed by using PCR in combination with restriction fragment length polymorphism analysis, resulted in six closely related subtypes (〉94.2%), with subtypes A/D being eae -negative STECs and subtypes B, C, E, and F eae positive. Unexpectedly, ehxA subtype patterns differed significantly between isolates collected from different sources ( P 〈 0.0001), suggesting that simple linear models of exposure and transmission need modification; animal isolates carried mostly subtypes A/C (39.3%/42.9%), food isolates carried mainly subtype A (81.9%), and clinical isolates carried mainly subtype C (66.4%). Certain O serogroups correlated with particular ehxA subtypes: subtype A with O104, O113, and O8; B exclusively with O157; C with O26, O111, and O121.

Description: Interference with tumor suppressor pathways by polyomavirus-encoded tumor antigens (T-Ags) can result in transformation. Consequently, it is thought that T-Ags encoded by Merkel cell polyomavirus (MCPyV), a virus integrated in ~90% of all Merkel cell carcinoma (MCC) cases, are major contributors to tumorigenesis. The MCPyV large T-Ag (LT-Ag) has preserved the key functional domains present in all family members but has also acquired unique regions that flank the LxCxE motif. As these regions may mediate unique functions, or may modulate those shared with T-Ags of other polyomaviruses, functional studies of MCPyV T-Ags are required. Here, we have performed a comparative study of full-length or MCC-derived truncated LT-Ags with regard to their biochemical characteristics, their ability to bind to retinoblastoma (Rb) and p53 proteins, and their transforming potential. We provide evidence that full-length MCPyV LT-Ag may not directly bind to p53 but nevertheless can significantly reduce p53-dependent transcription in reporter assays. Although early region expression constructs harboring either full-length or MCC-derived truncated LT-Ag genes can transform primary baby rat kidney cells, truncated LT-Ags do not bind to p53 or reduce p53-dependent transcription. Interestingly, shortened LT-Ags exhibit a very high binding affinity for Rb, as shown by coimmunoprecipitation and in vitro binding studies. Additionally, we show that truncated MCPyV LT-Ag proteins are expressed at higher levels than those for the wild-type protein and are able to partially relocalize Rb to the cytoplasm, indicating that truncated LT proteins may have gained additional features that distinguish them from the full-length protein. IMPORTANCE MCPyV is one of the 12 known polyomaviruses that naturally infect humans. Among these, it is of particular interest since it is the only human polyomavirus known to be involved in tumorigenesis. MCPyV is thought to be causally linked to MCC, a rare skin tumor. In these tumors, viral DNA is monoclonally integrated into the genome of the tumor cells in up to 90% of all MCC cases, and the integrated MCV genomes, furthermore, harbor signature mutations in the so-called early region that selectively abrogate viral replication while preserving cell cycle deregulating functions of the virus. This study describes comparative studies of early region T-Ag protein characteristics, their ability to bind to Rb and p53, and their transforming potential.

Description: Purpose: The phosphoinositide 3-kinase (PI3K) pathway is fundamental for cell proliferation and survival and is frequently altered and activated in neoplasia, including carcinomas of the lung. In this study, we investigated the potential of targeting the catalytic class I A PI3K isoforms in small cell lung cancer (SCLC), which is the most aggressive of all lung cancer types. Experimental Design: The expression of PI3K isoforms in patient specimens was analyzed. The effects on SCLC cell survival and downstream signaling were determined following PI3K isoform inhibition by selective inhibitors or downregulation by siRNA. Results: Overexpression of the PI3K isoforms p110-α and p110-β and the antiapoptotic protein Bcl-2 was shown by immunohistochemistry in primary SCLC tissue samples. Targeting the PI3K p110-α with RNA interference or selective pharmacologic inhibitors resulted in strongly affected cell proliferation of SCLC cells in vitro and in vivo , whereas targeting p110-β was less effective. Inhibition of p110-α also resulted in increased apoptosis and autophagy, which was accompanied by decreased phosphorylation of Akt and components of the mTOR pathway, such as the ribosomal S6 protein, and the eukaryotic translation initiation factor 4E-binding protein 1. A DNA microarray analysis revealed that p110-α inhibition profoundly affected the balance of pro- and antiapoptotic Bcl-2 family proteins. Finally, p110-α inhibition led to impaired SCLC tumor formation and vascularization in vivo . Conclusion: Together our data show the key involvement of the PI3K isoform p110-α in the regulation of multiple tumor-promoting processes in SCLC. Clin Cancer Res; 19(1); 96–105. ©2012 AACR .

Description: The transcription factor GATA2 is required for expansion and differentiation of hematopoietic stem cells (HSCs). In mesenchymal stem cells (MSCs), GATA2 blocks adipogenesis, but its biological relevance and underlying genomic events are unknown. We report a dual function of GATA2 in bone homeostasis. GATA2 in MSCs binds near genes involved in skeletal system development and colocalizes with motifs for FOX and HOX transcription factors, known regulators of skeletal development. Ectopic GATA2 blocks osteoblastogenesis by interfering with SMAD1/5/8 activation. MSC-specific deletion of GATA2 in mice increases the numbers and differentiation capacity of bone-derived precursors, resulting in elevated bone formation. Surprisingly, MSC-specific GATA2 deficiency impairs the trabecularization and mechanical strength of bone, involving reduced MSC expression of the osteoclast inhibitor osteoprotegerin and increased osteoclast numbers. Thus, GATA2 affects bone turnover via MSC-autonomous and indirect effects. By regulating bone trabecularization, GATA2 expression in the osteogenic lineage may contribute to the anatomical and cellular microenvironment of the HSC niche required for hematopoiesis.