Igor V. Korobko

Genome-wide association studies of autoimmune vitiligo identify 23 new risk loci and highlight key pathways and regulatory variants

Vitiligo is an autoimmune disease in which depigmented skin results from the destruction of melanocytes, with epidemiological association with other autoimmune diseases. In previous linkage and genome-wide association studies (GWAS1 and GWAS2), we identified 27 vitiligo susceptibility loci in patients of European ancestry. We carried out a third GWAS (GWAS3) in European-ancestry subjects, with augmented GWAS1 and GWAS2 controls, genome-wide imputation, and meta-analysis of all three GWAS, followed by an independent replication. The combined analyses, with 4,680 cases and 39,586 controls, identified 23 new significantly associated loci and 7 suggestive loci. Most encode immune and apoptotic regulators, with some also associated with other autoimmune diseases, as well as several melanocyte regulators. Bioinformatic analyses indicate a predominance of causal regulatory variation, some of which corresponds to expression quantitative trait loci (eQTLs) at these loci. Together, the identified genes provide a framework for the genetic architecture and pathobiology of vitiligo, highlight relationships with other autoimmune diseases and melanoma, and offer potential targets for treatment.

Pdcd4 protein and mRNA level alterations do not correlate in human lung tumors

Pdcd4 (programmed cell death 4) gene is tumor suppressor which expression is frequently down-regulated in tumors, which is considered as a diagnostic and prognostic marker as well as promising target for anti-cancer therapy. Pdcd4 protein is a target for post-translational regulation by phosphorylation marking Pdcd4 for degradation. We questioned if Pdcd4 mRNA decline in human lung tumors is accompanied by proportional depletion of Pdcd4 protein. We found that Pdcd4 protein-to-mRNA ratio varies greatly in human lung cancer cell lines. In squamous cell carcinoma samples where Pdcd4 mRNA suppression was found to be a typical event, Pdcd4 protein level frequently remained unchanged or even up-regulated. Our studies demonstrate that at least in squamous cell carcinoma, alterations in Pdcd4 mRNA and protein levels are not directly linked, and this fact should be taken into consideration when developing Pdcd4-based anti-cancer therapeutic approaches.

Review of current clinical studies of vitiligo treatments.

There is a limited number of options in vitiligo treatment, with the disease frequently refractory to all existing treatment modalities. This warrants development of novel and improving existing vitiligo treatments as well as finding predicting factors to improve treatment outcome through appropriate selection and the most efficient application of a treatment. These issues are addressed in clinical studies aiming to evaluate safety and efficiency of novel treatments, improvements and modifications introduced to existing treatments, and to define predictors of treatment efficiency and their limitations. Here, results of recent (since year 2009) clinical studies in vitiligo field are overviewed, with the emphasis on their contribution to improved vitiligo management.

The Rab5 effector Rabaptin‐5 and its isoform Rabaptin‐5δ differ in their ability to interact with the small GTPase Rab4

Rabaptin‐5 is an effector for the small GTPase Rab5, a regulator of the early steps in endocytosis. In addition, Rabaptin‐5 interacts with the small GTPase Rab4 that has been implicated in recycling from early endosomes to the cell surface. Recently we have identified a ubiquitous transcript encoding the Rabaptin‐5 isoform, Rabaptin‐5δ. To evaluate the interaction properties of Rabaptin‐5δ with the small GTPases Rab4 and Rab5, we have applied protein interaction assays using the yeast two‐hybrid system and a glutathione S‐transferase pull‐down assay. We found that unlike Rabaptin‐5, that interacts with both GTPases in GTP‐bound conformations, Rabaptin‐5δ interacts only with GTP‐bound Rab5, and does not interact with Rab4, presumably due to a disrupted Rab4 binding site. Immunofluorescence microscopy analysis carried out to address the localization of Rabaptin‐5δ relative to GTP‐bound Rab4 and Rab5 in BHK‐21 cells supported these data. Our data suggests that while Rabaptin‐5 was proposed to act as a molecular linker between Rab5 and Rab4, to coordinate endocytic and recycling traffic, Rabaptin‐5δ is involved only in the Rab5‐driven events.

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.

Pdcd4 tumor suppressor: Properties, functions, and possible applications in oncology

The 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 the increased interest in Pdcd4 as a potential diagnostic and prognostic marker and a target for anti-neoplastic therapy. The review summarizes the well-known properties and functions of Pdcd4 tumor suppressor and the mechanisms of its regulation in tumor tissues, the role of Pdcd4 in cellular transformation and tumor progression, and its potential practical application in oncology.

mTOR-dependent transcriptional repression of Pdcd4 tumor suppressor in lung cancer cells

Programmed cell death 4 (Pdcd4) tumor suppressor is frequently lost in tumors of various origins including lung cancer, and its loss contributes to tumor progression. However molecular mechanisms underlying Pdcd4 suppression in lung cancer cells remain largely unexplored. Here we investigated molecular mechanisms of Pdcd4 suppression in lung cancer cells. Besides enhanced mTOR-dependent proteasomal degradation of Pdcd4 protein, we found that Pdcd4 transcription is negatively regulated by mTOR signaling, and localized cis-acting element in Pdcd4 promoter responsible for this effect. In conclusion, we described a novel molecular mechanism of Pdcd4 suppression in cancer cells consisting from mTOR signaling-dependent transcriptional repression of Pdcd4.

Treatments of vitiligo: what's new at the horizon

Vitiligo is a manageable disease. However, current vitiligo treatments can be considered suboptimal as they do not guarantee high efficacy and cannot be standardized for most patients. Recently, combination therapies have been introduced in order to obtain better results and reduce risks in the management of the disease. Novel efficacious products are hereunder discussed to improve the therapeutic options for vitiligo patients.

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.

Rho family GTPase Chp/RhoV induces PC12 apoptotic cell death via JNK activation.

Rho GTPases regulate numerous cellular processes including apoptosis. Chp/RhoV is an atypical Rho GTPase which functions are poorly understood. Here we investigated the role of Chp in regulation of cell viability using PC12 cells with inducible expression of Chp as a model. We found that expression of Chp results in apoptosis in PC12 cells. Chp-induced apoptosis was accompanied by activation of JNK signaling and both death receptor-mediated and mitochondrial apoptotic pathways as justified by caspase-8 and caspase-9 activation, respectively. Moreover, inhibition of JNK by SP600125 rescued PC12 cells from Chp-triggered cell death and attenuated activation of caspases-9 and -3/7 suggesting that activation of JNK mediates pro-apoptotic effect of Chp. Expression of Chp resulted in increased phosphorylation of c-Jun in PC12 cells, and Chp expression in HEK293 cells up-regulated AP-1-dependent transcription in a JNK-dependent manner. Together results of our study reveal the role of Chp GTPase as a putative regulator of JNK-dependent apoptotic death in PC12 cells, similarly to previously described pro-apoptotic activity of the related Cdc42 and Rac1 GTPases.