Role of the TIS7/SKMc15 genes in regeneration processes

The regulation of gene expression plays an important role during the muscle and neuronal regeneration processes. Tightly regulated gene expression in particular cell types requires a sophisticated interplay between the basic transcriptional machinery and specific transcriptional regulators - activators, repressors, co-activators and co- repressors. TPA Induced Sequence 7 (TIS7) was originally identified as a regulator of neuronal differentiation [1, 2]. It was shown previously that TIS7 may have a regulatory function in the process of myogenesis [3]. We have identified the biochemical mechanism of TIS7 action [4] and proposed a mechanism by which TIS7 in a specific situation represses expression of key genes necessary for the maintenance of the cell morphology affecting thereby the organ function. We have proved in vivo, using a newly generated mouse knock out model, that the TIS7 gene is not crucial for the development but plays a vital role during regeneration processes [5]. We have also cloned SKMc15, a second mouse gene with very high homology to TIS7 [6, 7] which, according to our preliminary studies, may replace the biochemical function of TIS7. In order to analyze the SKMc15 functional role in vivo we generated the SKMc15 knock out and TIS7 / SKMc15 double knock out mice. These unique models will allow us in the future to study the biological function of the novel gene family in vivo. The goal of this proposal is to study the role of both genes, TIS7 and SKMc15 during the regeneration processes. In our laboratory and in collaboration with two outside specialists we will study the function of TIS7 and SKMc15 proteins during the regeneration post muscular injury and in response to the partial small intestine resection / gut regeneration. The response to the injury will be characterized using biochemical and electrophysiological techniques. Using unique cell systems we will analyze the regulation of expression of genes in the two new mouse models and cell lines derived from these mice. Taken together, our effort to characterize the role and mechanism of action of the novel TIS7 and SKMc15 gene family should provide insight into the mechanisms of regulation of gene expression during regeneration. Together with other ongoing studies in our lab characterizing the expression of TIS7 gene and protein in human specimen we expect to gain crucial knowledge clarifying the mechanism of regeneration which will be beneficial also in the treatment of debilitating diseases as e.g. muscular dystrophies. 1. Tirone, F. and E.M. Shooter, Early gene regulation by nerve growth factor in PC12 cells: induction of an interferon-related gene. Proc.Natl.Acad.Sci.U.S.A.Proc.Natl.Acad.Sci.U.S.A., 1989. 86: p. 2088-2092. 2. Guardavaccaro, D., et al., Nerve growth factor regulates the subcellular localization of the nerve growth factor- inducible protein PC4 in PC12 cells. J.Neurosci.Res., 1994. 37: p. 660-674. 3. Guardavaccaro, D., et al., Inhibition of differentiation in myoblasts deprived of the interferon-related protein PC4. Cell Growth.Differ., 1995. 6: p. 159-169. 4. Vietor, I., et al., TIS7 interacts with the mammalian SIN3 histone deacetylase complex in epithelial cells. Embo J, 2002. 21(17): p. 4621-4631. 5. Vadivelu, S.K., et al., Muscle regeneration and myogenic differentiation defects in mice lacking TIS7. Mol Cell Biol, 2004. 24(8): p. 3514-25. 6. Buanne, P., et al., Cloning of the human interferon-related developmental regulator (IFRD1) gene coding for the PC4 protein, a member of a novel family of developmentally regulated genes [In Process Citation]. Genomics., 1998. 51: p. 233-242. 7. Latif, F., et al., The human homolog of the rodent immediate early response genes, PC4 and TIS7, resides in the lung cancer tumor suppressor gene region on chromosome 3p21. Hum Genet, 1997. 99(3): p. 334-41.

The regulation of gene expression plays an important role during the muscle and neuronal regeneration processes. TPA Induced Sequence 7 (TIS7) was originally identified as a regulator of neuronal differentiation and we showed previously that TIS7 has a regulatory function in the process of muscle regeneration. We have also identified TIS7 as a transcriptional co-repressor. We have proved in vivo, using a newly generated mouse knockout model, that the TIS7 gene is not essential for the development but plays a crucial role during regeneration processes. We have also cloned SKMc15, a second mouse gene with very high homology to TIS7. In order to analyze the SKMc15 functional role in vivo we generated the SKMc15 knockout and TIS7 / SKMc15 double knockout mice. These unique models allowed us to study the biological function of this novel gene family in vivo. We studied in our laboratory and in collaboration with outside specialists the phenotype of TIS7 single and TIS7 / SKMc15 double knockout mice. We have identified that TIS7 may play an important role in the process of neuronal regeneration since the axon outgrowth of adult sensory neurons in culture was clearly modified by the absence of TIS7. We have further demonstrated that lack of functional TIS7 enhanced the effects of nerve growth factor on axon branching. Secondly, we have identified that SKMc15 fulfills in muscle regeneration a very similar role as TIS7, since all physiological parameters were significantly stronger affected than in the TIS7 single knockout. Last but not least, the TIS7 / SKMc15 double knockout mice have a prominent phenotype, namely a significant decrease in the overall body size. Furthermore, when these mice were fed with high fat diet they gained less weight and had significantly less fat tissue deposits than the wild type controls. Taken together, analyzing the phenotype of TIS7 single and TIS7 / SKMc15 double knockout mice we confirmed a regulatory function of TIS7 and SKMc15 genes in the muscle and neuronal regeneration and in addition identified a novel role in the regulation of lipid metabolism. Analysis of gene expression in neuronal cells showed changes in expression levels of a protein (CRABP II) affecting the retinoic acid signaling pathway. Similarly, gene expression analysis in the small intestines showed changes in expression levels of genes regulating the lipid metabolism.