RACK1 (receptor for activated C-kinase 1) interactions with spectrin repeat elements

Cytoskeleton and Associated Proteins: Pleiotropic JNK Substrates and Regulators

This review extensively reports data from the literature concerning the complex relationships between the stress-induced c-Jun N-terminal kinases (JNKs) and the four main cytoskeleton elements, which are actin filaments, microtubules, intermediate filaments, and septins. To a lesser extent, we also focused on the two membrane-associated cytoskeletons spectrin and ESCRT-III. We gather the mechanisms controlling cytoskeleton-associated JNK activation and the known cytoskeleton-related substrates directly phosphorylated by JNK. We also point out specific locations of the JNK upstream regulators at cytoskeletal components. We finally compile available techniques and tools that could allow a better characterization of the interplay between the different types of cytoskeleton filaments upon JNK-mediated stress and during development. This overview may bring new important information for applied medical research.

High expression of RACK1 is associated with poor prognosis in patients with pancreatic ductal adenocarcinoma

Receptor for activated C kinase 1 (RACK1) is associated with certain aspects of cancer biology and signaling pathways, but its function in pancreatic ductal adenocarcinoma (PDAC) remains unknown. In the present study, 157 patients with PDAC were enrolled. RACK1 mRNA and protein expression levels were analyzed in PDAC tissues and matched adjacent noncancerous tissues by reverse transcription-quantitative polymerase chain reaction and western blotting. RACK1 expression levels in paraffin-embedded PDAC tissues were determined by immunohistochemistry. The associations between RACK1 expression and clinical data were evaluated using χ² analysis. The relationship between RACK1 expression and the survival data of patients was analyzed using Kaplan-Meier and log rank tests. RACK1 mRNA and protein were revealed to be overexpressed in PDAC tumor tissues compared with adjacent noncancerous tissues. RACK1 expression was associated with clinical stage (P=0.001), lymph node invasion (P=0.003) and liver metastasis (P=0.001). Furthermore, patients with PDAC and high RACK1 expression demonstrated shorter overall survival times compared with patients with low RACK1 expression (P=0.002). Multivariate analysis indicated that RACK1 overexpression was an independent prognostic factor for patients with PDAC. Overexpression of RACK1 may contribute to tumor progression, and may be a potential prognostic biomarker for patients with PDAC.

Kale BoRACK1 is involved in the plant response to salt stress and Peronospora brassicae Gaumann

The receptor for activated C kinase 1 (RACK1) belongs to a protein subfamily containing a tryptophan-aspartic acid-domain (WD) repeat structure. Compelling evidence indicates that RACK1 can interact with many signal molecules and affect different signal transduction pathways. In this study, a kale (Brassica oleracea var. acephala f.tricolor) RACK1 gene (BoRACK1) was cloned by RT-PCR. The amino acid sequence of BoRACK1 had seven WD repeats in which there were typical GH (glycine-histidine) and WD dipeptides. Comparison with AtRACK1 from Arabidopsis revealed 87.1% identity at the amino acid level. Expression pattern analysis by RT-PCR showed that BoRACK1 was expressed in all analyzed tissues of kale and that its transcription in leaves was down-regulated by salt, abscisic acid, and H₂O₂ at a high concentration. Overexpression of BoRACK1 in kale led to a reduction in symptoms caused by Peronospora brassicae Gaumann on kale leaves. The expression levels of the pathogenesis-related protein genes, PR-1 and PRB-1, increased 2.5-4-fold in transgenic kale, and reactive oxygen species production was more active than in the wild-type. They also exhibited increased tolerance to salt stress in seed germination. H₂O₂ may also be involved in the regulation of BoRACK1 during seed germination under salt stress. Quantitative real-time PCR analyses showed that the transcript levels of BoRbohs genes were significantly higher in overexpression of BoRACK1 transgenic lines. Yeast two-hybrid assays showed that BoRACK1 could interact with WNK8, eIF6, RAR1, and SGT1. This study and previous work lead us to believe that BoRACK1 may form a complex with regulators of plant salt and disease resistance to coordinate kale reactions to pathogens.