RESUMO
The yeast SPT10 gene encodes a putative histone acetyltransferase (HAT) implicated as a global transcription regulator acting through basal promoters. Here we address the mechanism of this global regulation. Although microarray analysis confirmed that Spt10p is a global regulator, Spt10p was not detected at any of the most strongly affected genes in vivo. In contrast, the presence of Spt10p at the core histone gene promoters in vivo was confirmed. Since Spt10p activates the core histone genes, a shortage of histones could occur in spt10Delta cells, resulting in defective chromatin structure and a consequent activation of basal promoters. Consistent with this hypothesis, the spt10Delta phenotype can be rescued by extra copies of the histone genes and chromatin is poorly assembled in spt10Delta cells, as shown by irregular nucleosome spacing and reduced negative supercoiling of the endogenous 2mum plasmid. Furthermore, Spt10p binds specifically and highly cooperatively to pairs of upstream activating sequence elements in the core histone promoters [consensus sequence, (G/A)TTCCN(6)TTCNC], consistent with a direct role in histone gene regulation. No other high-affinity sites are predicted in the yeast genome. Thus, Spt10p is a sequence-specific activator of the histone genes, possessing a DNA-binding domain fused to a likely HAT domain.
Assuntos
Proteínas de Saccharomyces cerevisiae/metabolismo , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Fatores de Transcrição/metabolismo , Sequência de Bases , Sítios de Ligação/genética , Cromatina/genética , DNA Fúngico/genética , DNA Fúngico/metabolismo , Proteínas de Ligação a DNA/química , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Regulação Fúngica da Expressão Gênica , Genes Fúngicos , Histona Acetiltransferases , Histonas/genética , Dados de Sequência Molecular , Fenótipo , Regiões Promotoras Genéticas , Ligação Proteica , Estrutura Terciária de Proteína , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Saccharomyces cerevisiae/crescimento & desenvolvimento , Proteínas de Saccharomyces cerevisiae/química , Proteínas de Saccharomyces cerevisiae/genética , Fatores de Transcrição/química , Fatores de Transcrição/genéticaRESUMO
Surgery is the only chance for cure in pancreatic ductal adenocarcinoma. In unresectable, locally advanced pancreatic cancer (LAPC), the National Comprehensive Cancer Network (NCCN) suggests chemotherapy and consideration for radiation in cases of unresectable LAPC. Here we present a rare case of unresectable LAPC with a complete histopathological response after chemoradiation followed by surgical resection. A 54-year-old female presented to our clinic in December 2013 with complaints of abdominal pain and 30-pound weight loss. An MRI demonstrated a mass in the pancreatic body measuring 6.2 × 3.2 cm; biopsy revealed proven ductal adenocarcinoma. Due to splenic vein/artery and contiguous celiac artery encasement, she was deemed surgically unresectable. She was started on FOLFIRINOX therapy (three cycles), intensity modulated radiation to a dose of 54 Gy in 30 fractions concurrent with capecitabine, followed by FOLFIRI, and finally XELIRI. After 8 cycles of ongoing XELIRI completed in March 2015, restaging showed a remarkable decrease in tumor size, along with PET-CT revealing no FDG-avid uptake. She was reevaluated by surgery and taken for definitive resection. Histopathological evaluation demonstrated a complete R0 resection and no residual tumor. Based on this patient and literature review, this strategy demonstrates potential efficacy of neoadjuvant chemoradiation with prolonged chemotherapy, followed by surgery, which may improve outcomes in patients deemed previously unresectable.