SUMO modification modulates the activity of calpain-2

Proteostasis and SUMO in the heart

Heart proteostasis relies on a complex and integrated network of molecular processes surveilling organ performance under physiological and pathological conditions. For this purpose, cardiac cells depend on the correct function of their proteolytic systems, such as the ubiquitin-proteasome system (UPS), autophagy and the calpain system. Recently, the role of protein SUMOylation (an ubiquitin-like modification), has emerged as important modulator of cardiac proteostasis, which will be the focus of this review.

Involvement of activated SUMO-2 conjugation in cardiomyopathy

Sumoylation is a posttranslational modification that regulates a wide spectrum of cellular activities. Cardiomyopathy is the leading cause of heart failure. Whether sumoylation, particularly SUMO-2/3 conjugation, is involved in cardiomyopathy has not been investigated. We report here that SUMO-2/3 conjugation was elevated in the human failing hearts, and we investigated the impact of increased SUMO-2 conjugation on heart function by using the gain-of-function approach in mice, in which cardiac specific expression of constitutively active SUMO-2 was governed by alpha myosin heavy chain promoter (MHC-SUMO-2 transgenic, SUMO-2-Tg). Four of five independent SUMO-2-Tg mouse lines exhibited cardiomyopathy with various severities, ranging from acute heart failure leading to early death to the development of chronic cardiomyopathy with aging. We further revealed that SUMO-2 directly regulated apoptotic process by at least partially targeting calpain 2 and its natural inhibitor calpastatin. SUMO conjugation to calpain 2 promoted its enzymatic activity, and SUMO attachment to calpastatin mainly promoted its turnover and altered its subcellular distribution. Thus, enhanced SUMO-2 conjugation led to increased apoptosis and played a pathogenic role in the development of cardiomyopathy and heart failure.

Src-homology 2 domain-containing tyrosine phosphatase 2 promotes oral cancer invasion and metastasis

Background

Tumor invasion and metastasis represent a major unsolved problem in cancer pathogenesis. Recent studies have indicated the involvement of Src-homology 2 domain-containing tyrosine phosphatase 2 (SHP2) in multiple malignancies; however, the role of SHP2 in oral cancer progression has yet to be elucidated. We propose that SHP2 is involved in the progression of oral cancer toward metastasis.

Methods

SHP2 expression was evaluated in paired oral cancer tissues by using immunohistochemical staining and real-time reverse transcription polymerase chain reaction. Isogenic highly invasive oral cancer cell lines from their respective low invasive parental lines were established using a Boyden chamber assay, and changes in the hallmarks of the epithelial-mesenchymal transition (EMT) were assessed to evaluate SHP2 function. SHP2 activity in oral cancer cells was reduced using si-RNA knockdown or enforced expression of a catalytically deficient mutant to analyze migratory and invasive ability in vitro and metastasis toward the lung in mice in vivo.

Results

We observed the significant upregulation of SHP2 in oral cancer tissues and cell lines. Following SHP2 knockdown, the oral cancer cells markedly attenuated migratory and invasion ability. We observed similar results in phosphatase-dead SHP2 C459S mutant expressing cells. Enhanced invasiveness was associated with significant upregulation of E-cadherin, vimentin, Snail/Twist1, and matrix metalloproteinase-2 in the highly invasive clones. In addition, we determined that SHP2 activity is required for the downregulation of phosphorylated ERK1/2, which modulates the downstream effectors, Snail and Twist1 at a transcript level. In lung tissue sections of mice, we observed that HSC3 tumors with SHP2 deletion exhibited significantly reduced metastatic capacity, compared with tumors administered control si-RNA.

Conclusions

Our data suggest that SHP2 promotes the invasion and metastasis of oral cancer cells. These results provide a rationale for further investigating the effects of small-molecule SHP2 inhibitors on the progression of oral cancer, and indicate a previously unrecognized SHP2-ERK1/2-Snail/Twist1 pathway that is likely to play a crucial role in oral cancer invasion and metastasis.

SUMOylation pathway in Trypanosoma cruzi: functional characterization and proteomic analysis of target proteins

SUMOylation is a relevant protein post-translational modification in eukaryotes. The C terminus of proteolytically activated small ubiquitin-like modifier (SUMO) is covalently linked to a lysine residue of the target protein by an isopeptide bond, through a mechanism that includes an E1-activating enzyme, an E2-conjugating enzyme, and transfer to the target, sometimes with the assistance of a ligase. The modification is reversed by a protease, also responsible for SUMO maturation. A number of proteins have been identified as SUMO targets, participating in the regulation of cell cycle progression, transcription, translation, ubiquitination, and DNA repair. In this study, we report that orthologous genes corresponding to the SUMOylation pathway are present in the etiological agent of Chagas disease, Trypanosoma cruzi. Furthermore, the SUMOylation system is functionally active in this protozoan parasite, having the requirements for SUMO maturation and conjugation. Immunofluorescence analysis showed that T. cruzi SUMO (TcSUMO) is predominantly found in the nucleus. To identify SUMOylation targets and get an insight into their physiological roles we generated transfectant T. cruzi epimastigote lines expressing a double-tagged T. cruzi SUMO, and SUMOylated proteins were enriched by tandem affinity chromatography. By two-dimensional liquid chromatography-mass spectrometry a total of 236 proteins with diverse biological functions were identified as potential T. cruzi SUMO targets. Of these, metacaspase-3 was biochemically validated as a bona fide SUMOylation substrate. Proteomic studies in other organisms have reported that orthologs of putative T. cruzi SUMOylated proteins are similarly modified, indicating conserved functions for protein SUMOylation in this early divergent eukaryote.