Cks1 proteasomal turnover is a predominant mode of regulation in breast cancer cells: Role of key tyrosines and lysines

The acetylation of MDH1 and IDH1 is associated with energy metabolism in acute liver failure

The liver is the main organ associated with metabolism. In our previous studies, we identified that the metabolic enzymes malate dehydrogenase 1 (MDH1) and isocitrate dehydrogenase 1 (IDH1) were differentially expressed in ALF. The aim of this study was to explore the changes in the acetylation of MDH1 and IDH1 and the therapeutic effect of histone deacetylase (HDAC) inhibitor in acute liver failure (ALF). Decreased levels of many metabolites were observed in ALF patients. MDH1 and IDH1 were decreased in the livers of ALF patients. The HDAC inhibitor ACY1215 improved the expression of MDH1 and IDH1 after treatment with MDH1-siRNA and IDH1-siRNA. Transfection with mutant plasmids and adeno-associated viruses, identified MDH1 K118 acetylation and IDH1 K93 acetylation as two important sites that regulate metabolism in vitro and in vivo.

Structural determinants and genetic modifications enhance BMP2 stability and extracellular secretion

The short half-life and use of recombinant bone morphogenetic protein (BMP)-2 in large doses poses major limitations in the clinic. Events regulating post-translational processing and degradation of BMP2 in situ, linked to its secretion, have not been understood. Towards identifying mechanisms regulating intracellular BMP2 stability, we first discovered that inhibiting proteasomal degradation enhances both intracellular BMP2 level and its extracellular secretion. Next, we identified BMP2 degradation occurs through an ubiquitin-mediated mechanism. Since ubiquitination precedes proteasomal turnover and mainly occurs on lysine residues of nascent proteins, we systematically mutated individual lysine residues within BMP2 and tested them for enhanced stability. Results revealed that substitutions on four lysine residues within the pro-BMP2 region and three in the mature region increased both BMP2 turnover and extracellular secretion. Structural modeling revealed key lysine residues involved in proteasomal degradation occupy a lysine cluster near proprotein convertase cleavage site. Interestingly, mutations within these residues did not affect biological activity of BMP2. These data suggest preventing intracellular proteasomal loss of BMP2 through genetic modifications can overcome limitations related to its short half-life.

Structural determinants and genetic modifications enhance BMP2 stability and extracellular secretion

The short half-life and use of recombinant bone morphogenetic protein (BMP)-2 in large doses poses major limitations in the clinic. Events regulating post-translational processing and degradation of BMP2 in situ, linked to its secretion, have not been understood. Towards identifying mechanisms regulating intracellular BMP2 stability, we first discovered that inhibiting proteasomal degradation enhances both intracellular BMP2 level and its extracellular secretion. Next, we identified BMP2 degradation occurs through an ubiquitin-mediated mechanism. Since ubiquitination precedes proteasomal turnover and mainly occurs on lysine residues of nascent proteins, we systematically mutated individual lysine residues within BMP2 and tested them for enhanced stability. Results revealed that substitutions on four lysine residues within the pro-BMP2 region and three in the mature region increased both BMP2 turnover and extracellular secretion. Structural modeling revealed key lysine residues involved in proteasomal degradation occupy a lysine cluster near proprotein convertase cleavage site. Interestingly, mutations within these residues did not affect biological activity of BMP2. These data suggest preventing intracellular proteasomal loss of BMP2 through genetic modifications can overcome limitations related to its short half-life.

CKS1 expression in melanocytic nevi and melanoma

Cyclin-dependent kinase subunit 1 (Cks1) regulates the degradation of p27, an important G1-S inhibitor, which is up regulated by MAPK pathway activation. In this study, we sought to determine whether Cks1 expression is increased in melanocytic tumors and correlates with outcome and/or other clinicopathologic prognostic markers. Cks1 expression was assessed by immunohistochemistry in 298 melanocytic lesions. The frequency and intensity of cytoplasmic and nuclear expression was scored as a labeling index and correlated with clinico-pathological data. Nuclear Cks1 protein was found in 63% of melanocytic nevi, 89% primary and 90% metastatic melanomas with mean labeling index of 7 ± 16, 19 ± 20, and 30 ± 29, respectively. While cytoplasmic Cks1 was found in 41% of melanocytic nevi, 84% primary and 95% metastatic melanomas with mean labeling index of 18 ± 34, 35 ± 34, and 52 ± 34, accordingly. Histologic stepwise model of tumor progression, defined as progression from benign nevi to primary melanomas, to melanoma metastases, revealed a significant increase in nuclear and cytoplasmic Cks1 expression with tumor progression. Nuclear and cytoplasmic Cks1 expression correlated with the presence of ulceration, increased mitotic rate, Breslow depth, Clark level, tumor infiltrating lymphocytes and gender. However, other well-known prognostic factors (age, anatomic site, and regression) did not correlate with any type of Cks1 expression. Similarly, increasing nuclear expression of Cks1 significantly correlated with worse overall survival. Thus, Cks1 expression appears to play a role in the progression of melanoma, where high levels of expression are associated with poor outcome. Cytoplasmic expression of Cks1 might represent high turnover of protein via the ubiquination/proteosome pathway.

Effects of ε-Polylysine on Pseudomonas Aeruginosa and Aspergillus Fumigatus Biofilm In Vitro

Background

The antimicrobial mechanisms of ɛ-polylysine (EPL) against Pseudomonas aeruginosa and Aspergillus fumigatus biofilm were investigated.

Material/Methods

We assessed the changes in electric conductivity of broth and total sugar concentration, as well as changes in phosphorous metabolism and protein expression, of the 2 organisms before and after treatment with EPL.

Results

The experimental results showed that EPL has antimicrobial activity against Pseudomonas aeruginosa and Aspergillus fumigatus, but the activity was much stronger for the former. After treatment with EPL, the electric conductivity and total sugar concentration of microbial broth increased, suggesting that EPL damages the cell membrane structure, which increases permeability of the cell membrane and release of cell components.

Conclusions

The consumption of phosphorous decreased in the EPL-treated organisms, which seriously affected the synthesis of important cell components such as nucleic acid and phospholipid, as well as energy metabolism.

Cks1 proteasomal degradation is induced by inhibiting Hsp90-mediated chaperoning in cancer cells

PURPOSE

Cks1, a conformationally heterogenous 9 kDa protein, is markedly overexpressed in cancer cells and contributes to tumor development. Cks1 is an essential component of the SCF-Skp2 ubiquitin ligase complex that targets the Cdk inhibitors p27(Kip1) and p21(Cip1). Cks1 is known to interact with the Hsp90-Cdc37 chaperone machinery, although whether this facilitates its conformational maturation and stability is not known. To test whether abrogating the chaperone function of Hsp90 could destabilize Cks1, we examined the effects of treating different cancer cell lines with the benzoquinone ansamycin 17-allylamino geldanamycin (17-AAG), a compound that selectively binds Hsp90 and potently inhibits its ATP-dependent chaperone activity.

METHODS

The effect of Hsp90 inhibition using 17-AAG on Cks1 protein and associated cell cycle proteins including Skp2, p27(Kip1), p21(Cip1), and Cdk1 in cancer cells was determined by Western blotting. Ubiquitination analysis was carried out by transfecting cells with an HA-ubiquitin plasmid and specifically immunoprecipitating Cks1 to examine polyubiquitinated species. Flow cytometry was utilized to examine the effects of Hsp90 inhibition on cell cycle profiles.

RESULTS

Here, we demonstrate for the first time that inhibition of Hsp90 utilizing 17-AAG destabilizes Cks1 in cancer cells by promoting its ubiquitination and proteasomal degradation. 17-AAG-induced Cks1 depletion was accompanied by concomitant decreases in Skp2 and Cdk1. 17-AAG treatment also induced G2/M accumulation in MCF-7 breast carcinoma cells, and G1 accumulation in the colon carcinoma lines HCT116 and SW620.

CONCLUSIONS

We conclude that perturbing the Hsp90 pathway could provide a useful therapeutic strategy in tumors driven by Cks1 overexpression.