In yeast, the conserved histone acetyltransferase (HAT) Gcn5 associates with Ada2 and Ada3 to form the catalytic module of the ADA and SAGA transcriptional coactivator complexes. Gcn5 also contains an acetyl-lysine binding bromodomain that has been implicated in regulating nucleosomal acetylation in vitro, as well as at gene promoters in cells. However, the contribution of the Gcn5 bromodomain in regulating site specificity of HAT activity remains unclear. Here, we used a combined acid-urea gel and quantitative mass spectrometry approach to compare the HAT activity of wild-type and Gcn5 bromodomain-mutant ADA subcomplexes (Gcn5-Ada2-Ada3). Wild-type ADA subcomplex acetylated H3 lysines with the following specificity; H3K14 > H3K23 > H3K9 Ϸ H3K18 > H3K27 > H3K36. However, when the Gcn5 bromodomain was defective in acetyl-lysine binding, the ADA subcomplex demonstrated altered site-specific acetylation on free and nucleosomal H3, with H3K18ac being the most severely diminished. H3K18ac was also severely diminished on H3K14R, but not H3K23R, substrates in wildtype HAT reactions, further suggesting that Gcn5-catalyzed acetylation of H3K14 and bromodomain binding to H3K14ac are important steps preceding H3K18ac. In sum, this work details a previously uncharacterized cross-talk between the Gcn5 bromodomain "reader" function and enzymatic HAT activity that might ultimately affect gene expression. Future studies of how mutations in bromodomains or other histone post-translational modification readers can affect chromatin-templated enzymatic activities will yield unprecedented insight into a potential "histone/epigenetic code." MS data are available via ProteomeXchange with identifier PXD001167. Molecular &

Molecular pathways regulating melanoma initiation and progression are potential targets of therapeutic development for this aggressive cancer. Identification and molecular analysis of these pathways in patients has been primarily restricted to targeted studies on individual proteins. Here, we report the most comprehensive analysis of formalin-fixed paraffin-embedded human melanoma tissues using quantitative proteomics. From 61 patient samples, we identified 171 proteins varying in abundance among benign nevi, primary melanoma, and metastatic melanoma. Seventy-three percent of these proteins were validated by immunohistochemistry staining of malignant melanoma tissues from the Human Protein Atlas database. Our results reveal that molecular pathways involved with tumor cell proliferation, motility, and apoptosis are mis-regulated in melanoma. These data provide the most comprehensive proteome resource on patient melanoma and reveal insight into the molecular mechanisms driving melanoma progression.

Merkel Cell Carcinoma (MCC) is an aggressive neuroendocrine cancer of the skin. The incidence has been quadrupled with a 5-year mortality rate of 46%, presently there is no cure for metastatic disease. Despite the contribution of Merkel cell polyomavirus, the molecular events of MCC carcinogenesis are poorly defined. To better understand MCC carcinogensis, we have performed the first quantitative proteomic comparison of formalin-fixed, paraffin-embedded (FFPE) MCC tissues using another neuroendocrine tumor (carcinoid tumor of the lung) as controls. Bioinformatic analysis of the proteomic data has revealed that MCCs carry distinct protein expression patterns. Further analysis of significantly over-expressed proteins suggested the involvement of MAPK, PI3K/Akt/mTOR, wnt, and apoptosis signaling pathways. Our previous study and that from others have shown mTOR activation in MCCs. Therefore, we have focused on two downstream molecules of the mTOR pathway, lactate dehydrogenase B (LDHB) and heterogeneous ribonucleoprotein F (hnRNPF). We confirm over-expression of LDHB and hnRNPF in two primary human MCC cell lines, 16 fresh tumors, and in the majority of 80 tissue microarray samples. Moreover, mTOR inhibition suppresses LDHB and hnRNPF expression in MCC cells. The results of the current study provide insight into MCC carcinogenesis and provide rationale for mTOR inhibition in pre-clinical studies.

Latency-associated nuclear antigen (LANA) is a conserved, multifunctional protein encoded by members of the rhadinovirus subfamily of gammaherpesviruses, including Kaposi sarcoma-associated herpesvirus (KSHV) and murine gammaherpesvirus 68 (MHV68). We previously demonstrated that MHV68 LANA (mLANA) is required for efficient lytic replication. However, mechanisms by which mLANA facilitates viral replication, including interactions with cellular and viral proteins, are not known. Thus, we performed a mass spectrometry-based interaction screen that defined an mLANA protein-protein interaction network for lytic viral replication consisting of 15 viral proteins and 191 cellular proteins, including 19 interactions previously reported in KSHV LANA interaction studies. We also employed a stable-isotope labeling technique to illuminate high-priority mLANA-interacting host proteins. Among the top prioritized mLANA-binding proteins was a cellular chaperone, heat shock cognate protein 70 (Hsc70). We independently validated the mLANA-Hsc70 interaction through coimmunoprecipitation and in vitro glutathione S-transferase (GST) pulldown assays. Immunofluorescence and cellular fractionation analyses comparing wild-type (WT) to mLANA-null MHV68 infections demonstrated mLANA-dependent recruitment of Hsc70 to nuclei of productively infected cells. Pharmacologic inhibition and small hairpin RNA (shRNA)-mediated knockdown of Hsc70 impaired MHV68 lytic replication, which functionally correlated with impaired viral protein expression, reduced viral DNA replication, and failure to form viral replication complexes. Replication of mLANA-null MHV68 was less affected than that of WT virus by Hsc70 inhibition, which strongly suggests that Hsc70 function in MHV68 lytic replication is at least partially mediated by its interaction with mLANA. Together these experiments identify proteins engaged by mLANA during the MHV68 lytic replication cycle and define a previously unknown role for Hsc70 in facilitating MHV68 lytic replication. IMPORTANCELatency-associated nuclear antigen (LANA) is a conserved gamma-2-herpesvirus protein important for latency maintenance and pathogenesis. For MHV68, this includes regulating lytic replication and reactivation. While previous studies of KSHV LANA defined interactions with host cell proteins that impact latency, interactions that facilitate productive viral replication are not known. Thus, we performed a differential proteomics analysis to identify and prioritize cellular and viral proteins that interact with the MHV68 LANA homolog during lytic infection. Among the proteins identified was heat shock cognate protein 70 (Hsc70), which we determined is recruited to host cell nuclei in an mLANA-dependent process. Moreover, Hsc70 facilitates MHV68 protein expression and DNA replication, thus contributing to efficient MHV68 lytic replication. These experiments expand the known LANA-binding proteins to include MHV68 lytic replication and demonstrate a previously unappreciated role for Hsc70 in regulating viral...

The molecular effects of total body gamma-irradiation exposure are of critical importance as large populations of people could be exposed either by terrorists, nuclear blast, or medical therapy. In this study, we aimed to identify changes in the urine proteome using a non-human primate model system, Rhesus macaque, in order to characterize effects of acute radiation syndrome following whole body irradiation (Co-60) at 6.7 Gy and 7.4 Gy with a twelve day observation period. The urine proteome is potentially a valuable and non-invasive diagnostic for radiation exposure. Using high-resolution mass spectrometry, we identified 2346 proteins in the urine proteome. We show proteins involved in disease, cell adhesion, and metabolic pathway were significantly changed upon exposure to differing levels and durations of radiation exposure. Cell damage increased at a faster rate at 7.4 Gy compared with 6.7 Gy exposures. We report sets of proteins that are putative biomarkers of time- and dose-dependent radiation exposure. The proteomic study presented here is a comprehensive analysis of the urine proteome following radiation exposure.