Induction of High Mobility Group I Architectural Transcription Factors in Proliferating Vascular Smooth Muscle in vivo and in vitro

M. T. Chin, A. Pellacani, C.-M. Hsieh, S. S. J. Lin, M. K. Jain, A. Patel, G. S. Huggins, R. Reeves, M. A. Perrella and M.-E. Lee. Induction of High Mobility Group I Architectural Transcription Factors in Proliferating Vascular Smooth Muscle in vivo and in vitro. Journal of Molecular and Cellular Cardiology (1999) 31, 2199–2205. Proliferation of vascular smooth muscle cells (VSMCs) is a hallmark of arteriosclerosis. Architectural transcription factors of the high mobility group (HMG)-I family have been implicated in the control of cell proliferation and gene expression. We studied the pattern of HMG-I mRNA and protein expression in proliferating VSMCs. HMG-I(Y) and HMGI-C mRNAs were barely detectable by Northern analysis in samples prepared from uninjured rat carotid arteries. In contrast, these mRNAs were induced dramatically in carotid arteries 2 and 5–6 days after balloon injury. By in situ hybridization at 6 days after injury, the induced mRNAs localized to smooth muscle cells of the developing neointima, and immunocytochemical analysis showed that HMG-I(Y) protein was expressed in the nuclei of these cells. To confirm this association between HMG-I protein induction and cell growth, we assessed HMG-I(Y) and HMGI-C mRNA expression in rat aortic smooth muscle cells (RASMCs) in primary culture. The HMG-I mRNAs were barely detectable in quiescent RASMCs but were induced markedly by serum stimulation. This induction of mRNA by serum was time dependent and peaked at 9 h. Western blot analysis confirmed that HMG-I(Y) protein induction also occurred in vitro. To our knowledge, this is the first demonstration of induction of HMG-I protein expression in proliferating RASMCs in vivo and in vitro. This demonstration suggests that the HMG-I proteins may play an important role in smooth muscle cell proliferation.