Conservation of inter-protein binding sites in RUSH and RFBP, an ATP11B isoform

Prolactin induces Jak2 phosphorylation of RUSHY195

Jak2/RUSH-mediated prolactin signaling culminates in RUSH-1α-DNA-binding. Heretofore, Jak2-specific phosphorylation residues in RUSH were unknown. Genpathway's discovery approaches correlated RUSH-DNA binding (-126/-121) in uteroglobin's proximal promoter with recruitment of the transcriptional machinery. NetPhos 2.0 server found a single tyrosine phosphorylation site in RUSH's minimal DNA-binding domain. Y195 had identical context and prediction scores (0.52) for rabbit and human (HLTF) orthologs. The mouse ortholog (Hltf) had a higher prediction score (0.897). Affinity purified RUSHY195ph antibodies recognized native tyrosine phosphorylated RUSH protein immunoprecipitated from nuclear extracts. When R5020-treated HRE-H9 cells±the Jak2 inhibitor, Tyrene CR4, were stimulated with prolactin, confocal immunofluorescence images provided conclusive evidence that Jak2 mediated the availability of phosphorylated RUSHY195 in nucleus and cytoplasm. Catalytically active Jak2 is ipso facto a RUSH site-specific tyrosine kinase. Immunoprecipitation/Western blotting revealed both phosphorylation at Y195 and the physical interaction between p-Jak2/RUSH/HLTF/Hltf are evolutionarily conserved across three mammalian (rabbit, human, mouse) orthologs.

Prolactin-induced Jak2 phosphorylation of RUSH: a key element in Jak/RUSH signaling

Jak2/Stat-mediated prolactin signaling culminates in Stat5a-DNA-binding. However, not all Jak2-dependent genes have Stat5 sites. Western analysis with inhibitors showed Jak2 is a proximal intermediate in prolactin-induced RUSH phosphorylation. Transfection assays with HRE-H9 cells showed the RUSH-binding site mediated the ability of prolactin to augment progesterone-dependent transcription of the RUSH gene. Jak2 inhibitors or targeted RUSH-site mutation blocked the prolactin effect. RUSH co-immunoprecipitated with phospho-Jak2 from nuclear extracts. Jak2 inhibitors abolished the nuclear pool of phospho-RUSH not the nuclear content of RUSH in HRE-H9 cells. Nucleolar-affiliated partners, e.g. nucleolin, were identified by microLC/MS/MS analysis of nuclear proteins that co-immunoprecipitated with RUSH/GST-RING. RUSH did not exclusively co-localize with fibrillarin to the nucleolus. MG-132 (proteasomal inhibitor) failed to block Tyrene CR4-mediated decrease in phospho-RUSH, and did not promote RUSH accumulation in the nucleolus. These studies authenticate prolactin-dependent Jak2 phosphorylation of RUSH, and provide functional implications on the RUSH network of nuclear interactions.

High resolution analysis of the human transcriptome: detection of extensive alternative splicing independent of transcriptional activity

BACKGROUND

Commercially available microarrays have been used in many settings to generate expression profiles for a variety of applications, including target selection for disease detection, classification, profiling for pharmacogenomic response to therapeutics, and potential disease staging. However, many commercially available microarray platforms fail to capture transcript diversity produced by alternative splicing, a major mechanism for driving proteomic diversity through transcript heterogeneity.

RESULTS

The human Genome-Wide SpliceArray(TM) (GWSA), a novel microarray platform, utilizes an existing probe design concept to monitor such transcript diversity on a genome scale. The human GWSA allows the detection of alternatively spliced events within the human genome through the use of exon body and exon junction probes to provide a direct measure of each transcript, through simple calculations derived from expression data. This report focuses on the performance and validation of the array when measured against standards recently published by the Microarray Quality Control (MAQC) Project. The array was shown to be highly quantitative, and displayed greater than 85% correlation with the HG-U133 Plus 2.0 array at the gene level while providing more extensive coverage of each gene. Almost 60% of splice events among genes demonstrating differential expression of greater than 3 fold also contained extensive splicing alterations. Importantly, almost 10% of splice events within the gene set displaying constant overall expression values had evidence of transcript diversity. Two examples illustrate the types of events identified: LIM domain 7 showed no differential expression at the gene level, but demonstrated deregulation of an exon skip event, while erythrocyte membrane protein band 4.1 -like 3 was differentially expressed and also displayed deregulation of a skipped exon isoform.

CONCLUSION

Significant changes were detected independent of transcriptional activity, indicating that the controls for transcript generation and transcription are distinct, and require novel tools in order to detect changes in specific transcript quantity. Our results demonstrate that the SpliceArray(TM) design will provide researchers with a robust platform to detect and quantify specific changes not only in overall gene expression, but also at the individual transcript level.