Pak6 protein kinase is a novel effector of an atypical Rho family GTPase Chp/RhoV

Chp/RhoV is an atypical Rho GTPase whose functions are far from being fully understood. To date several effector proteins of Chp have been identified, including p21-activated kinases Pak1, Pak2, and Pak4. Using a yeast two-hybrid system and co-immunoprecipitation, here we show that another p21-activated kinase, Pak6, is a novel Chp-binding protein. Interaction between Chp and Pak6 depends on the activation state of the GTPase, suggesting that Pak6 is an effector protein for Chp. Point mutations in the effector domain of Chp or in the CRIB motif of Pak6 significantly impair the interaction between Chp and Pak6 upon co-immunoprecipitation, suggesting that the binding interface involves the effector domain of Chp and the CRIB motif in Pak6. We found that Chp does not affect the phosphorylation status of the S560 residue in the catalytic domain of Pak6 when Chp and Pak6 are co-expressed in HEK293 cells. Therefore, similarly to Cdc42, Chp is not likely to activate Pak6. In NCI-H1299 cells, Chp co-localizes with Pak6 on vesicular structures in activation state-dependent manner. Taking the data together, we report here the identification of p21-activated kinase Pak6 as a novel effector of the atypical Rho GTPase Chp. Our data suggest further directions in elucidating biological functions of these proteins.

[Study of testicular cancer gene expression in samples of oral leukoplakia and squamous cell carcinoma of the mouth]

Cancer-testis (CT) antigens are normally expressed mostly in human germ cells, there is also an aberrant expression in some tumor cells. This expression profile makes them potential tumor growth biomarkers and a promising target for tumor immunotherapy. Specificity of CT genes expression in oral malignant and potentially malignant diseases, e.g. oral leukoplakia, is not yet studied. Data on CT genes expression profile in leukoplakia would allow developing new diagnostic methods with potential value for immunotherapy and prophylaxis of leukoplakia malignization. In our study we compared CT genes expression in normal oral mucosa, oral leukoplakia and oral squamous cell carcinoma. We are the first to describe CT genes expression in oral leukoplakia without dysplasia. This findings make impossible differential diagnosis of oral leukoplakia and squamous cell carcinoma on the basis of CT genes expression. The prognostic value of CT genes expression is still unclear, therefore the longitudinal studies are necessary.

Interaction between MAK-V protein kinase and synaptopodin

MAK-V protein kinase (also known as HUNK) was discovered more than decade ago but its functions and molecular mechanisms of action still remain mostly unknown. In an attempt to associate MAK-V with particular chains of molecular events, we searched for proteins interacting with the C-terminal domain of MAK-V protein kinase. We identified synaptopodin as a protein interaction partner for MAK-V and confirmed this interaction in various ways. Because synaptopodin is important for dendritic spine formation and plays a role in synaptic plasticity, our results might have significant impact on future studies for understanding the role of MAK-V in cells of the nervous system.

Application of mRNA regulatory regions to improve tumor specificity of transgene expression

Efficiency and specificity are two key attributes of anti-cancer drugs including genetic therapeutic agents. We suggest a way to improve specificity of gene therapy drugs based on the ability of 3'-untranslated regions (UTR) of some mRNAs selectively stabilize transcripts only during cell division. The mRNAs of genes encoding DNA methyltransferase I (DNMT1) and topoisomerase IIα (TOP2A) are among such transcripts. When inserted into genetic constructs designed to produce therapeutic protein in tumor cells, such 3'-UTR would lead to diminished effect of therapeutic protein on normal cells, which are characterized by low or absent proliferative activity. However, when included in gene expression cassette, these 3'-UTR might result in decreased transgene expression, thus, overweighting the advantage of increased specificity of expression. We showed that DNMT1 and to the lesser extent TOP2A 3'-UTR do not alter significantly therapeutic transgene expression level in tumor cells, thus, confirming the functionality of the proposed approach.

[Pdcd4 tumor suppressor: properties, functions, and their application to oncology]

Inactivation of tumor suppressors and activation of protooncogenes are critical events in malignant cell transformation and tumor progression. Pdcd4 encodes a protein with tumor suppressor functions, which accounts for an increased interest to Pdcd4 as a potential diagnostic and prognostic marker, as well as a target for antineoplastic therapy. This review summarizes well-known properties and functions of Pdcd4 tumor suppressor and mechanisms of its regulation in tumor cells. It is also focused to the role of Pdcd4 in cellular transformation and tumor progression, as well as on its potential practical application in oncology.

Membrane localization of the MAK-V protein kinase

Activities of many proteins including protein kinases are often regulated by their dynamic association with specific intracellular compartments. MAK-V is an AMPK-like protein kinase with poorly characterized functions and mechanisms of action. Similarly to many other protein kinases, association of MAK-V with specific intracellular compartments could be essential for its proper functions. In this work, we studied subcellular distribution of exogenously produced and endogenous MAK-V proteins in mammalian cells using biochemical cell fractioning aiming to supplement data on MAK-V intracellular localization studied by immunocytochemical methods. We found that a significant portion of MAK-V protein in mammalian cells is associated with membranes. Moreover, MAK-V expressed in yeast was also targeted to membrane, thus suggesting an evolutionarily conservative mechanism of MAK-V membrane association. Based on the ability of various MAK-V deletion mutants to localize to membrane and comparison of MAK-V amino acid sequences from different species, we suggest a possible mechanism governing MAK-V association with intracellular membranes.

[Multiadaptor 4.1 and RanBP9 protein family members as putative interaction partners for VARP, a Rab21 GTPase guanine nucleotide exchange factor]

VARP is a novel VPS9 domain-containing protein which acts as a guanine nucleotide exchange factor for small GTPases Rab21 and Rab5, regulators of early endocytosis. However, the molecular mechanisms underlying VARP activity regulation and intracellular localization remain unknown. Using protein interaction cloning in yeast we isolated multiadaptor proteins of 4.1 protein family and RanBP9 as putative VARP interaction partners. The interactions revealed might be important for proper intracellular localization of VARP and its functions in early endocytosis.

[c-Met and HGF expression in non-small-cell lung carcinomas]

Alterations in the c-Met/HGF system are frequently observed in various types of tumors and can directly influence tumor progression. In particular, the c-Met/HGF system can influence progression of lung tumors. The altered c-Met and HGF expression occurs in non-small-cell lung carcinomas. In this work we analyzed changes in c-Met and HGF expression in non-small-cell lung carcinomas by comparing expression levels with those in adjacent non-malignant tissues using semi-quantitative PCR. The c-Met transcript was detected in 50% of squamous cell carcinoma samples with an elevated level observed in 2 out of 25 cases (8%). HGF expression was detected only in two squamous cell carcinomas. At the same time, the c-Met transcript was observed in all 5 studied adenocarcinoma samples with an increased level compared to adjacent non- malignant tissue in 3 cases. HGF transcript was found in 2 adenocarcinoma samples. Therefore, c-Met rather than HGF transcript is frequently observed in non-small-cell lung carcinomas, especially in adenocarcinomas. According to the results of other studies, the c-Met transcript can serve as an indicator of the aggressive behavior and progression of non-small-cell lung carcinomas.

[Suppression of WIFI transcript and protein in non-small cell lung carcinomas]

Changes in WIFI expression, an extracellular inhibitor of Wnt pathway, in non-small cell lung carcinomas were analyzed. Frequent (67% cases) suppression of WIFI transcript in non-small cell lung carcinomas were found. Our results, together with previously published data, suggest that inhibition of WIFI expression often occurs in squamous cell carcinomas and is less typical of adenocarcinomas. It was also found that a decrease in the WIFI transcript in tumors is parallel to concomitant suppression of the WIFI protein level. Our results provide further evidence that the WIFI suppression is a frequent event in the lung carcinogenesis, which might lead to disregulation of Wnt signaling pathway and contribute to tumor progression.

Dimerization properties of Rabaptin-5 and its isoforms

Rabaptin-5 plays an important role in intracellular membrane traffic acting as an effector molecule of small GTPases Rab5 and Rab4. It was previously demonstrated that Rabaptin-5 exists as a part of a large protein complex in vivo and is able to form dimers in vitro. Data of X-ray structural analysis suggest that dimerization of Rabaptin-5 is an important feature required for its interaction with Rab5 GTPase. Recently several isoforms of Rabaptin-5 characterized by various deletions in the polypeptide chains have been identified. These isoforms might exhibit functional properties that differ from those of Rabaptin-5. In this study, we have investigated dimerization properties of delta and gamma isoforms of Rabaptin-5. In addition, we have provided the first direct evidence for Rabaptin-5 dimerization in cells.

[WIF1: perspectives of application in oncology]

Changes in the intracellular signaling cascades underlay many human pathologies including oncological diseases. Modification of the Wnt-signaling pathway are often associated with development of tumor and may play a significant role in carcinogenesis. This gives rise to a significant interest to studies of regulators and components of the Wnt-signaling pathway and search for approaches to practical implementation of the properties of the regulators. The goal of this work was to review the properties of WIF1 (Wnt inhibitor factor-1), a regulator of Wnt-signaling pathway, as a possible diagnostic and prognostic marker of human tumors, as well as basis for development of novel antitumoral preparations.

[Molecular cloning and characterization of the mouse mak-v/Hunk gene promoter]

MAK-V/Hunk is a recently isolated MARK/Par-1-related mammalian protein kinase with yet unknown function. To investigate transcriptional regulation of the mouse mak-v/Hunk gene, we isolated genomic fragment of the mouse mak-v/Hunk promoter region. The mak-v/Hunk promoter has no typical TATA box or CAAT box, is GC-rich and contains CpG-island. Amplification of cDNA ends suggested that transcription initiation site is 156 nt upstream translation initiation site. The 5'-flanking region of the mak-v/Hunk gene was ligated to luciferase reporter gene and possessed functional promoter activity. Luciferase assay with a series of truncated 5'-flanking regions demonstrated the region between nt -508 and -347 has a pronounced stimulating effect on transcription activity. In addition, our data suggest that mak-v/Hunk promoter region might be a target for CpG methylation.

[Proteinkinase MAK-V/Hunk as a possible dianostic and prognostic marker of human breast carcinoma]

We propose a system for detection of overproduction of protein kinase MAK-V/Hunk in tumours. MAK-V/ Hunk overproduction is observed in about 50% breast carcinomas. Positive staining is obseved in tumour cells only and has mainly cytoplasmic characteristics. Increased production of MAK-V/Hunk does not correlate with histological type of carcinoma, metastasizing, steroid receptor status (estrogen and progesterone), proliferative activity. Tumours positive for MAK-V/ Hunk were more frequently observed in c-erbB2-positive (3+) tumours than in c-erbB2-negative ones. Overproduction of MAK-V/Hunk in human breast cancer may be used fore more precise molecular typing of this tumour, in particular in case of c-erbB2-positive tumors, however, diagnostic-prognostic value of this new molecular marker needs further studies.

[The use of the two-hybrid cloning in yeast for functional characterization of protein kinase MAK-V]

Identification of interaction partners opens a way to direct functional characterization of proteins. Several cDNAs coding for potential partners of protein kinase MAK-V/Hunk were isolated using two-hybrid cloning in yeast. Based on the partner properties, MAK-V/Hunk was assumed to play a role in tumorigenesis and tumor progression. With the previous results of two-hybrid cloning, MAK-V/Hunk was shown to participate in vesicular transport.

The MAK-V protein kinase regulates endocytosis in mouse

We report the cloning of a mouse cDNA encoding the MAK-V protein kinase, with a putative specificity for serine/threonine residues. The mak-v gene is transcribed in adult brain and in the mouse embryo from at least 7.5 dpc. Using the yeast two-hybrid system, we showed that MAK-V interacts with Rabaptin-5, a protein which plays an important role in endocytosis. Functional studies of the MAK-V protein suggest that it regulates endocytosis. We also constructed a human mak-v cDNA and localized the human mak-v gene at 21q22.11. Its chromosomal location suggests that mak-v could be involved in disorders of the nervous system, development or in malignancies.

Resistance to tumor necrosis factor induced apoptosis in vitro correlates with high metastatic capacity of cells in vivo

TNF is one of the cytokines secreted by the cells of the immune system. Our data demonstrate that those cell lines lacking capability to form metastatic tumors in vivo are susceptible to TNF induced apoptosis in vitro. However, cell lines with high metastatic potential are resistant to TNF in vitro. Furthermore, the same cell lines were resistant to cytolytic action of other cytotoxic proteins secreted by LAK cells. Our data showed that TNF resistance in vitro correlates with the increased level of transcription factor NF-kappaB. This finding may provide a tool to improve current protocols of immunotherapy and insights to how tumor cells are or are not killed by LAK cells.