Glucose homeostasis is regulated by insulin, which is produced in the β-cells of the pancreas. The synthesis of insulin is controlled by several transcription factors including PDX-1, USF1 and USF2. Both, PDX-1 and USF1 were identified as substrates for protein kinase CK2. Here, we have analysed the interplay of PDX-1, USF1 and CK2 in the regulation of PDX-1 gene transcription. We found that the PDX-1 promoter is dose-dependently transactivated by PDX-1 and transrepressed by USF1. With increasing glucose concentrations the transrepression of the PDX-1 promoter by USF1 is successively abrogated. PDX-1 binding to its own promoter was not influenced by glucose, whereas USF1 binding to the PDX-1 promoter was reduced. The same effect was observed after inhibition of the protein kinase activity by three different inhibitors or by using a phospho-mutant of USF1. Moreover, phosphorylation of USF1 by CK2 seems to strengthen the interaction between USF1 and PDX-1. Thus, CK2 is a negative regulator of the USF1-dependent PDX-1 transcription. Moreover, upon inhibition of CK2 in primary islets, insulin expression as well as insulin secretion were enhanced without affecting the viability of the cells. Therefore, inhibition of CK2 activity may be a promising approach to stimulate insulin production in pancreatic β-cells.

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CK2 is a serine/threonine protein kinase, which is so important for many aspects of cellular regulation that life without CK2 is impossible. Here, we analysed CK2 during adipogenic differentiation of human mesenchymal stem cells (hMSCs). With progress of the differentiation CK2 protein level and the kinase activity decreased. Whereas CK2α remained in the nucleus during differentiation, the localization of CK2β showed a dynamic shuttling in the course of differentiation. Over the last years a large number of inhibitors of CK2 kinase activity were generated with the idea to use them in cancer therapy. Our results show that two highly specific inhibitors of CK2, CX-4945 and quinalizarin, reduced its kinase activity in proliferating hMSC with a similar efficiency. CK2 inhibition by quinalizarin resulted in nearly complete inhibition of differentiation whereas, in the presence of CX-4945, differentiation proceeded similar to the controls. In this case, differentiation was accompanied by the loss of CX-4945 inhibitory function. By analysing the subcellular localization of PPARγ2, we found a shift from a nuclear localization at the beginning of differentiation to a more cytoplasmic localization in the presence of quinalizarin. Our data further show for the first time that a certain level of CK2 kinase activity is required for adipogenic stem cell differentiation and that inhibition of CK2 resulted in an altered localization of PPARγ2, an early regulator of differentiation.

Diallyl sulfanes derived from edible plants are highly potent compounds which at sub-millimolar concentrations are able to induce the formation of reactive oxygen species (ROS) in a variety of different cells, where they often cause an altered redox status. The loss of cellular thiols and/or formation of ROS subsequently triggers a range of cellular responses, including the induction of apoptosis. A great disadvantage of natural diallyl mono- and polysulfanes, however, is their inherent insolubility in water and the extremely bad odour which limits their practical use in humans. Here, we present the synthesis and biological evaluation of two new, especially designed polysulfanes, namely the trisulfide 1-Allyl-3-(2-ethoxyethyl)trisulfide (ATSEE) and the tetrasulfide Allyl-4-benzyltetrasulfide (ATTSB), which are nearly odourless. Both compounds produce O2•- radicals in HCT116 cells and both induce an oxidative defence signalling. Cell viability is especially reduced by the tetrasulfane ATTSB, with an arrest of the cell cycle in the G2-phase. In contrast, the trisulfane ATSEE does not inhibit the cell cycle. In agreement with these findings, treatment of HCT116 cells with ATTSB ultimately results in apoptosis whereas only limited induction of apoptosis has been detected for cells treated with ATSEE. We further show that antioxidative defence mechanisms and death response signalling run in parallel and the dominant pathway decides the fate of the cell. Thus, our results not only illuminate the intricate mode of action of certain polysulfanes; they also demonstrate that the new odourless tri- and tetrasulfanes exhibit a similar activity compared to their natural counterparts, yet are easier to handle and also deprived of the offensive odour which so far has prevented most practical applications of such polysulfanes, at least in the context of medicine.

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