Regulation of transformed state by calpastatin via PKCepsilon in NIH3T3 mouse fibroblasts

MiR-34a regulates blood-tumor barrier function by targeting protein kinase Cε

It is shown for the first time that overexpression of miR-34a increases blood–tumor barrier permeability by targeting PKCε, which is activated by p-PKCε and directly regulates the expression of tight junction–related proteins.

MicroRNA-34a (miR-34a) functions to regulate protein expression at the posttranscriptional level by binding the 3′ UTR of target genes and regulates functions of vascular endothelial cells. However, the role of miR-34a in regulating blood–tumor barrier (BTB) permeability remains unknown. In this study, we show that miR-34a overexpression leads to significantly increased permeability of BTB, whereas miR-34a silencing reduces the permeability of the BTB. In addition, miR-34a overexpression significantly down-regulates the expression and distribution of tight junction–related proteins in glioma endothelial cells (GECs), paralleled by protein kinase Cε (PKCε) reduction. Moreover, luciferase reporter gene analysis shows that PKCε is the target gene of miR-34a. We also show that cotransfection of miR-34a and PKCε inversely coregulates BTB permeability and protein expression levels of tight junction–related proteins. Pretreatment of ψεRACK, a PKCε-specific activator, decreases BTB permeability in miR-34a–overexpressed GECs and up-regulates expression levels of tight junction proteins. In contrast, pretreatment of εV1-2, a specific PKCε inhibitor, gives opposite results. Collectively, our findings indicate that miR-34a regulates BTB function by targeting PKCε; after phosphorylation, PKCε is activated and contributes to regulation of the expression of tight junction–related proteins, ultimately altering BTB permeability.

Analogues of Y27632 increase gap junction communication and suppress the formation of transformed NIH3T3 colonies

BACKGROUND

Constitutive activation of RhoA-dependent RhoA kinase (ROCK) signalling is known to promote cellular transformation and the ROCK inhibitor Y-27632 has the ability to suppress focus formation of RhoA transformed NIH3T3 cells.

METHODS

Sixty-four novel structural analogues of Y27632 were synthesised and tested for their ability to persistently inhibit the transformation of NIH3T3 cells by Rho guanidine exchange factor 16 (ARHGEF16) or Ras. In vitro kinase inhibitor profiling, co-culture of transformed cells with non-transformed cells and a novel Lucifer yellow/PKH67 dye transfer method were used to investigate their mode of action.

RESULTS

Four Y27632 analogues inhibited transformed focus formation that persisted when the compound was withdrawn. No toxicity was observed against either transformed or non-transformed cells and the effect was dependent on co-culture of these two cell types. In vitro kinase inhibitor profiling indicated that these compounds had reduced activity against ROCK compared with Y27632, targeting instead Aurora A (AURKA), p38 (MAPK14) and Hgk (MAP4K4). Dye transfer analysis showed they increased gap junction intercellular communication (GJIC) between transformed and non-transformed cells.

CONCLUSIONS

These data are the first to suggest that transient blockade of specific kinases can induce a persistent inhibition of non-contact inhibited transformed colony formation and can also remove pre-formed colonies. These effects could potentially be mediated by the observed increase in GJIC between transformed and non-transformed cells. Selection of kinase inhibitors with this property may thus provide a novel strategy for cancer chemoprevention.

Identification of Makorin 1 as a novel SEREX antigen of esophageal squamous cell carcinoma

Background

Esophageal squamous cell carcinoma (SCC) represents one of the most malignant tumors. To improve the poor prognosis, it is necessary to diagnose esophageal SCC at early stages using new tumor markers. SEREX (serological identification of antigens by recombinant cDNA expression cloning) is suitable for large-scale screening of tumor antigens and has been applied for various types of human tumors.

Methods

Tumor markers of esophageal squamous cell carcinoma (SCC) were screened by SEREX method. The presence of serum anti-makorin 1 (MKRN1) antibodies (s-MKRN1-Abs) was examined by Western blotting using bacterially expressed MKRN1 protein. The expression levels of MKRN1 mRNA in tissues were examined by RT-PCR. The biological activity of MKRN1 was examined by transfection of ras-NIH3T3 mouse fibroblasts with MKRN1 cDNA. Major ubiquitinated proteins in MKRN1-transfected cells were identified by immunoprecipitation with anti-ubiquitin antibody followed by mass spectrometry.

Results

MKRN1 was identified as a novel SEREX antigen of esophageal SCC. Although a total of 18 (25%) of 73 patients with esophageal SCC had s-MKRN1-Abs, none of the 43 healthy donors had a detectable level of s-MKRN1-Abs. There was no correlation between the presence of s-MKRN1-Abs and clinicopathological variables other than histological grading. Well-differentiated tumors were associated significantly with the presence of s-MKRN1-Abs in the patients. The mRNA levels of MKRN1 were frequently higher in esophageal SCC tissues than in the peripheral normal esophageal mucosa. Stable transfection of ras-NIH3T3 cells with MKRN1 cDNA induced prominent morphological changes such as enlargement of the cell body and spreading. Ubiquitination of 80- and 82-kDa proteins were clearly observed in MKRN1-transfected cells but not in the parental cells, which were identified as L-FILIP (filamin A interacting protein 1).

Conclusion

MKRN1 is a novel SEREX antigen of esophageal SCC, and s-NKRN1-Abs can be a candidate of diagnostic markers of esophageal SCC with high specificity. It is plausible that MKRN1 is involved in carcinogenesis of the well-differentiated type of tumors possibly via ubiquitination of L-FILIP.

The growth and tumor suppressors NORE1A and RASSF1A are targets for calpain-mediated proteolysis

Background

NORE1A and RASSF1A are growth and tumour suppressors inactivated in a variety of cancers. Methylation of NORE1A and RASSF1A promoters is the predominant mechanism for downregulation of these proteins; however, other mechanisms are likely to exist.

Methodology/Principal Findings

Here we describe a proteolysis of NORE1A and RASSF1A by calpains as alternative mechanism of their downregulation. Extracts of H358 cell line, a human bronchoalveolar carcinoma, and H460, a large cell carcinoma, were capable of proteolysis of NORE1A protein in the calpain-dependent manner. Likewise, RASSF1A tumor suppressor was proteolyzed by the H358 cell extract. Addition of calpain inhibitor to H358 and H460 cells growing in tissue culture resulted in re-expression of endogenous NORE1A. A survey of 10 human lung tumours revealed that three of them contain an activity capable of inducing NORE1A degradation.

Conclusions/Significance

Thus, degradation by calpains is a novel mechanism for downregulation of NORE1A and RASSF1A proteins and might be the mechanism allowing cancer cells to escape growth suppression.

Calpastatin overexpression attenuates amyloid-beta-peptide toxicity in differentiated PC12 cells

Amyloid beta peptide (Abeta) plays a major role in the pathogenesis of Alzheimer's disease (AD). Abeta is toxic to neurons, possibly through causing initial synaptic dysfunction and neuronal membrane dystrophy, promoted by increased cellular Ca(2+). Calpain (Ca(2+)-dependent protease) and caspase have been implicated in AD. Previously, we used calpain and caspase pharmacological inhibitors to study effects of Abeta25-35 (sAbeta) on neuronal-like differentiated PC12 cells. We reported that sAbeta-treated cells exhibited calpain activation and protein degradation (due to both calpain and caspase-8). We have now found that overexpression of the calpain specific inhibitor calpastatin in differentiated PC12 cells significantly inhibited the sAbeta-induced calpain activation and decreased the protease activity. Calpastatin overexpression inhibited the sAbeta-promoted degradation of fodrin, protein kinase Cepsilon, beta-catenin (membrane structural proteins and proteins involved in signal transduction pathways), and prevented the sAbeta-induced alteration of neurite structure (manifested by varicosities). Overexpression of calpastatin also inhibited Ca(2+)-promoted calpain activation and protein degradation; this is consistent with the notion that the Abeta-induced increase in calpain activity results from a rise in cellular Ca(2+), provided the calpastatin level is not so high as to strongly inhibit calpain. Carrying out transfection without selection allowed the comparison in the same culture of calpastatin-overexpressing with non-overexpressing cells. In cultures transfected with green fluorescent protein (GFP)-calpastatin plasmid, calpastatin overexpression (indicated by GFP-labeling) led to inhibition in sAbeta-induced membrane propidium iodide (PI) permeability, whereas non-transfected, GFP-unlabeled cells exhibited PI permeability. Overall, the results demonstrate that the effects of Abeta-toxicity studied here were attenuated to a large extent by calpastatin overexpression, indicating that the protease calpain is involved in Abeta-toxicity (obviating a primary, direct role for caspases). Increased expression of calpastatin and/or decrease in calpain may serve as one of the means for ameliorating some of the early symptoms of AD.

Enhancement of chemosensitivity toward peplomycin by calpastatin-stabilized NF-kappaB p65 in esophageal carcinoma cells: possible involvement of Fas/Fas-L synergism

Chemosensitivity to anticancer drugs was compared between two human esophageal carcinoma cell lines, T.Tn and YES-6 cells. T.Tn cells were more resistant than YES-6 cells to peplomycin (PEP) but not to the other anticancer drugs such as camptothecin, mitomycin C and cytosine arabinoside. Western blot analysis showed higher expression levels of m-calpain and activated mu-calpain in T.Tn cells than in YES-6 cells. On the other hand, YES-6 cells showed a high expression level of calpastatin, which is a calpain-specific endogenous inhibitor. To investigate whether calpain activity was involved in the chemosensitivity, T.Tn cells were transfected with calpastatin cDNA in an inducible expression vector. The induction of calpastatin was accompanied by increased chemosensitivity to PEP. The increases in calpastatin levels were followed by serial increases in the expression levels of NF-kappaB p65 and Fas. Since purified m- or mu-calpain degraded NF-kappaB p65 in vitro, it is possible that calpastatin suppressed calpain-mediated degradation of NF-kappaB p65. Fas ligand (Fas-L) protein levels increased after treatment of the parental T.Tn and calpastatin-transfected cells with PEP, suggesting the synergism between calpastatin-induced Fas and PEP-induced Fas-L. These results suggest that calpain/calpastatin expression levels are effective markers for predicting the sensitivity of human esophageal carcinoma cells to PEP.

Calpain activity is generally elevated during transformation but has oncogene-specific biological functions

Several oncogene and tumor-suppressor gene products are known substrates for the calpain family of cysteine proteases, and calpain is required for transformation by v-src and tumor invasion. Thus, we have now addressed whether calpain is generally associated with transformation and how calpain contributes to oncogene function. Our results demonstrate that calpain activity is enhanced upon transformation induced by the v-Src, v-Jun, v-Myc, k-Ras, and v-Fos oncoproteins. Furthermore, elevated calpain activity commonly promotes focal adhesion remodelling, disruption of actin cytoskeleton, morphological transformation, and cell migration, although proteolysis of target substrates (such as focal adhesion kinase, talin, and spectrin) is differently specified by individual oncoproteins. Interestingly, v-Fos differs from other common oncoproteins in not requiring calpain activity for actin/adhesion remodelling or migration of v-Fos transformed cells. However, anchorage-independent growth of all transformed cells is sensitive to calpain inhibition. In addition, elevated calpain activity contributes to oncogene-induced apoptosis associated with transformation by v-Myc. Taken together, these studies demonstrate that calpain activity is necessary for full cellular transformation induced by common oncoproteins, but has distinct roles in oncogenic events induced by individual transforming proteins. Thus, targeting calpain activity may represent a useful general strategy for interfering with activated proto-oncogenes in cancer cells.

Drug-sensitivity pattern analysis for study of functional relationship between gene products

We have developed a method that we call 'drug-sensitivity pattern analysis', or DSPA, for analysis of protein function. Cells are transfected with cDNA of the test molecule, followed by analysis of the sensitivity of the transfected cells to multiple growth-inhibitory drugs. If two cDNA products have similar functions, their transfected cells should show similar drug-sensitivity patterns. The cDNAs of some signaling molecules were transfected into NIH3T3 or Ha-ras-transformed NIH3T3 (ras-NIH) cells and stable transfectants, which expressed high amounts of the gene product, were isolated. Chemosensitivity of the transfected clone was compared with the parental cells by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide method using more than 40 drugs. The chemosensitivity changes caused by the transfected gene were calculated and expressed numerically as 'drug chemosensitivity index' (DCI). When the DCI values were analyzed by regression analysis, a significant positive relationship between IkappaBalpha superrepressor and dominant-negative IKKbeta and an inverse relationship between p53 and Mdm2 were consistent with previous reports. Thus, the DSPA method is useful for identifying functional similarities between gene products.

Calpastatin exon 1B-derived peptide, a selective inhibitor of calpain: enhancing cell permeability by conjugation with penetratin

The ubiquitous calpains, mu- and m-calpain, have been implicated in essential physiological processes and various pathologies. Cell-permeable specific inhibitors are important tools to elucidate the roles of calpains in cultivated cells and animal models. The synthetic N-acetylated 27-mer peptide derived from exon B of the inhibitory domain 1 of human calpastatin (CP1B) is unique as a potent and highly selective reversible calpain inhibitor, but is poorly cell-permeant. By addition of N-terminal cysteine residues we have generated a disulfide-conjugated CP1B with the cell-penetrating 16-mer peptide penetratin derived from the third helix of the Antennapedia homeodomain protein. The inhibitory potency and selectivity of CP1B for calpain versus cathepsin B and L, caspase 3 and the proteasome was not affected by the conjugation with penetratin. The conjugate was shown to efficiently penetrate into living LCLC 103H cells, since it prevents ionomycin-induced calpain activation at 200-fold lower concentration than the non-conjugated inhibitor and is able to reduce calpain-triggered apoptosis of these cells. Penetratin-conjugated CP1B seems to be a promising alternative to the widely used cell-permeable peptide aldehydes (e.g. calpain inhibitor 1) which inhibit the lysosomal cathepsins and partially the proteasome as well or even better than the calpains.

Calpain: a role in cell transformation and migration

Calpains represent a well conserved family of calcium-dependent proteolytic enzymes. Recent progress in determining the three-dimensional crystal structure of calpains and generation of calpain knock out animals have significantly advanced our understanding of both the activation mechanism and physiological role of this protease family. Studies applying molecular intervention strategies and genetic ablation of calpain now provide indisputable evidence that calpain activity contributes to remodelling of the actin cytoskeleton, cell migration and oncogenic transformation. Src and epidermal growth factor receptor (EGFR) stimulated cell motility is dependent upon calpain activation. In addition, calpain promotes accelerated cell-cycle progression and anchorage-independent growth of Src transformed cells. In vivo studies demonstrate a link between calpain expression levels and activity with tumour development and invasion. Thus, recent investigations suggest that the role of calpain in promoting cell transformation and cell migration may have important in vivo consequences in the context of cancer pathobiology.

Identification of a potent and selective pharmacophore for Cdc25 dual specificity phosphatase inhibitors

Small molecules provide powerful tools to interrogate biological pathways but many important pathway participants remain refractory to inhibitors. For example, Cdc25 dual-specificity phosphatases regulate mammalian cell cycle progression and are implicated in oncogenesis, but potent and selective inhibitors are lacking for this enzyme class. Thus, we evaluated 10,070 compounds in a publicly available chemical repository of the National Cancer Institute for in vitro inhibitory activity against oncogenic, full-length, recombinant human Cdc25B. Twenty-one compounds had mean inhibitory concentrations of <1 microM; >75% were quinones and >40% were of the para-naphthoquinone structural type. Most notable was NSC 95397 (2,3-bis-[2-hydroxyethylsulfanyl]-[1,4]naphthoquinone), which displayed mixed inhibition kinetics with in vitro K(i) values for Cdc25A, -B, and -C of 32, 96, and 40 nM, respectively. NSC 95397 was more potent than any inhibitor of dual specificity phosphatases described previously and 125- to 180-fold more selective for Cdc25A than VH1-related dual-specificity phosphatase or protein tyrosine phosphatase 1b, respectively. Modification of the bis-thioethanol moiety markedly decreased enzyme inhibitory activity, indicating its importance for bioactivity. NSC 95397 showed significant growth inhibition against human and murine carcinoma cells and blocked G(2)/M phase transition. A potential Cdc25 site of interaction was postulated based on molecular modeling with these quinones. We propose that inhibitors based on this chemical structure could serve as useful tools to probe the biological function of Cdc25.