NF-κB over-activation portends improved outcomes in HPV-associated head and neck cancer.

Evolving understanding of head and neck squamous cell carcinoma (HNSCC) is leading to more specific diagnostic disease classifications. Among HNSCC caused by the human papilloma virus (HPV), tumors harboring defects in TRAF3 or CYLD are associated with improved clinical outcomes and maintenance of episomal HPV. TRAF3 and CYLD are negative regulators of NF-κB and inactivating mutations of either leads to NF-κB overactivity. Here, we developed and validated a gene expression classifier separating HPV+ HNSCCs based on NF-κB activity. As expected, the novel classifier is strongly enriched in NF-κB targets leading us to name it the NF-κB Activity Classifier (NAC). High NF-κB activity correlated with improved survival in two independent cohorts. Using NAC, tumors with high NF-κB activity but lacking defects in TRAF3 or CYLD were identified; thus, while TRAF3 or CYLD gene defects identify the majority of tumors with NF-κB activation, unknown mechanisms leading to NF-kB activity also exist. The NAC correctly classified the functional consequences of two novel CYLD missense mutations. Using a reporter assay, we tested these CYLD mutations revealing that their activity to inhibit NF-kB was equivalent to the wild-type protein. Future applications of the NF-κB Activity Classifier may be to identify HPV+ HNSCC patients with better or worse survival with implications for treatment strategies.

Long range interactions regulate Igf2 gene transcription during skeletal muscle differentiation.

The differentiation, maintenance, and repair of skeletal muscle is controlled by interactions between genetically determined transcriptional programs regulated by myogenic transcription factors and environmental cues activated by growth factors and hormones. Signaling through the insulin-like growth factor 1 (IGF1) receptor by locally produced IGF2 defines one such pathway that is critical for normal muscle growth and for regeneration after injury. IGF2 gene and protein expression are induced as early events in muscle differentiation, but the responsible molecular mechanisms are unknown. Here we characterize a distal DNA element within the imprinted mouse Igf2-H19 locus with properties of a muscle transcriptional enhancer. We find that this region undergoes a transition to open chromatin during differentiation, whereas adjacent chromatin remains closed, and that it interacts in differentiating muscle nuclei but not in mesenchymal precursor cells with the Igf2 gene found more than 100 kb away, suggesting that chromatin looping or sliding to bring the enhancer in proximity to Igf2 promoters is also an early event in muscle differentiation. Because this element directly stimulates the transcriptional activity of an Igf2 promoter-reporter gene in differentiating myoblasts, our results indicate that we have identified a bona fide distal transcriptional enhancer that supports Igf2 gene activation in skeletal muscle cells. Because this DNA element is conserved in the human IGF2-H19 locus, our results further suggest that its muscle enhancer function also is conserved among different mammalian species.

Cytokinesis is blocked in mammalian cells transfected with Chlamydia trachomatis gene CT223.

BACKGROUND: The chlamydiae alter many aspects of host cell biology, including the division process, but the molecular biology of these alterations remains poorly characterized. Chlamydial inclusion membrane proteins (Incs) are likely candidates for direct interactions with host cell cytosolic proteins, as they are secreted to the inclusion membrane and exposed to the cytosol. The inc gene CT223 is one of a sequential set of orfs that encode or are predicted to encode Inc proteins. CT223p is localized to the inclusion membrane in all tested C. trachomatis serovars. RESULTS: A plasmid transfection approach was used to examine the function of the product of CT223 and other Inc proteins within uninfected mammalian cells. Fluorescence microscopy was used to demonstrate that CT223, and, to a lesser extent, adjacent inc genes, are capable of blocking host cell cytokinesis and facilitating centromere supranumeracy defects seen by others in chlamydiae-infected cells. Both phenotypes were associated with transfection of plasmids encoding the carboxy-terminal tail of CT223p, a region of the protein that is likely exposed to the cytosol in infected cells. CONCLUSION: These studies suggest that certain Inc proteins block cytokinesis in C. trachomatis-infected cells. These results are consistent with the work of others showing chlamydial inhibition of host cell cytokinesis.

Clonal isolation of chlamydia-infected cells using flow cytometry.

This manuscript describes a new technique for the microbiological cloning of chlamydia-infected cells using a fluorescence activated cell sorter (FACS). The approach exploits chlamydial acquisition of the fluorescent, Golgi-specific, stain 6-((N-7-(-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-hexanoyl)sphingosine (C6-NBD-cer). This fluorescent lipid is delivered from the Golgi apparatus to the chlamydial inclusion membrane and then to the developmental forms within the inclusion in living, infected cells. Labeling with C6-NBD-cer results in easily identifiable chlamydial inclusions that can then be analyzed and sorted by FACS. This technique was used successfully to sort individual chlamydia-infected cells into individual wells of a culture dish and, in this experimental system, resulted in the isolation of cloned chlamydial isolates. FACS-based sorting was used to isolate clonal populations of prototype strains from Chlamydia trachomatis, C. caviae and C. suis. Recent clinical isolates were also successfully cloned using FACS. The procedure is simple and rapid, with single cloning cycles being completed 24 h post-culture of a sample. It is anticipated that FACS-based sorting of live chlamydia-infected cells will be a significant technical tool for the isolation of clonal populations of any chlamydial strain.

Biochemical characterization of diverse Stat5b-binding enhancers that mediate growth hormone-activated insulin-like growth factor-I gene transcription.

Many of the biological effects of growth hormone (GH) are mediated by insulin-like growth factor I (IGF-I), a 70-amino acid secreted peptide whose gene expression is rapidly induced by GH via the Stat5b transcription factor. We previously identified multiple evolutionarily conserved GH-activated chromosomal binding domains for Stat5b within the rat Igf1 locus, and proposed that they could regulate IGF-I gene activity. Here we investigate the biochemical and functional characteristics of these putative long-range transcriptional enhancers. Each element contained 2 or 3 individual Stat5b recognition sequences that could bind Stat5b in vitro, but with affinities that varied over a >100-fold range. Full transcriptional responsiveness to GH required that all Stat5b sites be intact within an individual enhancer. Replacement of a single lower-affinity Stat5b sequence with a higher-affinity one increased in vitro binding of Stat5b, and boosted transcriptional potency of the entire element to GH. As enhanced transcriptional activity involved changes in only one or two nucleotides within an enhancer DNA segment, there appears to be remarkable specificity and sensitivity in the ability of Stat5b to transform DNA binding activity into transcriptional function. Stat5b was able to stimulate the transcriptional activity of two enhancers in the absence of GH, indicating that individual Stat5b-regulated elements possess distinct functional features. We conclude that combinatorial interplay among multiple Stat5b-binding response elements with distinguishable biochemical properties is responsible for highly regulated control of IGF-I gene activity by GH.

Development of secondary inclusions in cells infected by Chlamydia trachomatis.

The chlamydiae are obligate intracellular bacteria that occupy a non-acidified vacuole (the inclusion) during their entire developmental cycle. These bacteria produce a set of proteins (Inc proteins) that localize to the surface of the inclusion within infected cells. Chlamydia trachomatis IncA is also commonly found in long fibers that extend away from the inclusion. We used standard and confocal immunofluorescence microscopy to demonstrate that these fibers extend to newly developed inclusions, termed secondary inclusions, within infected cells. Secondary inclusions observed at early time points postinfection were devoid of chlamydial reticulate bodies. Later in the developmental cycle, secondary inclusions containing variable numbers of reticulate bodies were common. Reticulate bodies were also observed within the IncA-laden fibers connecting primary and secondary inclusions. Quantitative differences in secondary inclusion formation were found among clinical isolates, and these differences were associated with serovar. Isolates of serovar G consistently produced secondary inclusions at the highest frequency (P < 0.0001). Similar quantitative studies demonstrated that secondary inclusion formation was associated with segregation of inclusions to daughter cells following cytokinesis. We conclude that the production of secondary inclusions via IncA-laden fibers allows chlamydiae to generate an expanded intracellular niche in which they can grow and may provide a means for continuous infection within progeny cells following cell division.