Nontransfected HEK293 cells were examined as control.C, CAT-ELISA results determined repressions of transcriptional activity of the 2 2.12- (down by 40.9 4.1%,n= 3) and 1.57-kb (down by 53.5 5.8%,n= 6)Cnn2promoter constructs in cells cultured on soft gel as compared with that in cells cultured on hard gels. 5 truncations was studied. Transcriptional activity of theCnn2promoter-reporter constructs was examined in transfected NIH/3T3, HEK293, and C2C12 cells for their responses to the stiffness of culture substrate. The results showed significant transcriptional activities of the 1.00- and 1.24-kb promoter constructs, whereas the 0.61-kb construct was inactive. The 1.38-, 1.57-, and 2.12-kb constructs showed higher transcriptional activity, whereas only the 1.57- and 2.12-kb constructs exhibited repression of expression when the host cells were cultured on low stiffness substrate. Internal deletion of the segment between 1.57 and 1.38 kb in the 2 2.12-kb promoter construct abolished the low substrate stiffness-induced repression. Site-specific deletion or mutation of an HES-1 transcription factor binding site in this region also abolished this repression effect. The level of HES-1 increased in cells cultured under a low tension condition, corresponding to the down-regulation of h2-calponin. h2-Calponin gene expression is further affected by the treatment of cells with Notch inhibitor and activator, Cyclosporin B suggesting an upstream signaling mechanism. == Introduction == Mechanical forces have significant effects on various biochemical and genetic processes in living organisms and contribute to multiple physiological regulations and pathological conditions (1). It is well established that chemical energy can be converted into mechanical forces in living cells by the activity of motor proteins, such as myosin and kinesin/dynein ATPases (2,3). However, it is much less well understood how mechanical force signals are transduced and converted into chemical signals in cells to regulate biochemical processes and gene expression. The actin cytoskeleton is a dynamic network in eukaryotic cells capable of bearing forces and undergoing rearrangements in adaptation to mechanical changes in the Cyclosporin B environment, playing essential functions in cellular mechanical properties and responses Rabbit Polyclonal to BEGIN to mechanical signals (4). For the dual function of actin cytoskeleton in generating as well as sensing mechanical forces, regulation of actin cytoskeleton is essential for mechanoregulation in eukaryotic cells. Calponin is an actin filament-associated regulatory protein (5). First found in smooth muscle (6), Cyclosporin B three isoforms of calponin (h1, h2, and h3) encoded by homologous genes (CNN1, CNN2, andCNN3) have been identified in vertebrates (711). h1-Calponin is expressed specifically in differentiated smooth muscle cells (12). h3-Calponin, also called acidic calponin, is found in smooth muscle cells (10) and neuronal tissues (11). In contrast, h2-calponin is present in multiple tissue and cell types, including smooth muscle, lung alveolar cells, endothelial cells, epidermal keratinocytes, fibroblasts, and myeloid leukocytes (9,1316). Calponin binds F-actin with high affinity and inhibits the actin-activated myosin ATPase (1720) and motor (12,21,22) activities. Extensive biochemical and biophysical studies have demonstrated that calponin regulates the function of actin filaments to modify smooth muscle contractility and non-muscle cell motility. For its expression in multiple tissue and cell types, the function and regulation of h2-calponin is of broad biological and medical significances. h2-Calponin stabilizes actin filaments and inhibits actin cytoskeleton-related cellular functions, such as cytokinesis, migration, and phagocytosis (13,14,16). The expression of h2-calponin gene and the degradation of h2-calponin protein are both regulated by mechanical tension in the cytoskeleton (13,14). In response to tension changes, proteolysis of h2-calponin provides rapid structural and functional modifications in the actin cytoskeleton, whereas its gene regulation conveys chronic and sustained alterations. The regulation of h2-calponin gene expression may be studied as a representative for understanding the mechanisms of mechanoregulation in living cells. In a previous study, we demonstrated that h2-calponin protein and mRNA was significantly decreased in NIH/3T3 cells when cytoskeleton tension was reduced after blebbstatin inhibition of myosin II motor function (14). In contrast to the endogenous h2-calponin gene, transfective expression of h2-calponin cDNA under the control of CMV promoter was not regulated by mechanical tension (13). This observation suggests that transcriptional control is a primary regulation for the mechanoregulation of h2-calponin gene expression. The promoter ofCNN2gene therefore provides a novel experimental system to investigate how mechanical force signal is transduced in the regulation of gene transcription (23). In the present study, we characterized the transcriptional activity of h2-calponin gene.