Smooth muscle proliferation is an important feature of diseases such as atherosclerosis and hypertension, and is generally held responsible for restenosis after angioplasty and the failure of coronary bypass grafts. Associated with this process is an increased expression of nonmuscle myosin isoforms. The significance of this observation is presently unclear but our hypothesis is that this protein is required for cell division and that its deregulated expression is key to the abberrant proliferation seen in restenotic lesions. The long-term aim of this project is to understand the role of nonmuscle myosin in proliferating cells both in normal and disease states. We intend to determine the factors which regulate the expression of nonmuscle myosin heavy chain (NMMHC) at the levels of transcription and translation. Human surgical specimens including those obtained by endarterectomy and atherectomy will be analyzed by in situ hybridization and immunocytochemistry to localize transcription and translation of nonmuscle myosin isoforms. Northern blots and Dot blots will be used to determine relative abundance of mRNAs. Regulatory elements in the NMMHC-A gene will be identified by transfection experiments and these will be used to characterize nuclear proteins which interact with them. Translational regulation will be explored by isolating cytosolic factors which specifically bind to the large stem-loop structure at the 5 prime end of the NMMHC-A mRNA, and investigating their activity in an in vitro model system. Ultimately, we wish to understand in detail how transcriptional and translational controls together may alter the pattern of nonmuscle myosin expression to produce the proliferative phenotype in smooth muscle.
