Smooth muscle myosin heavy chain (SMHC) isoforms, SM1 and SM2, are the products of alternative splicing from a single gene (P. Babij and M. Periasamy. J. Mol. Biol. 210: 673-679, 1989). We have previously shown that this splicing occurs at the 3'-end of the mRNA, resulting in proteins that differ at the carboxyterminal (R. Nagai, M. Kuro-o, P. Babij, and M. Periasamy. J. Biol. Chem. 264: 9734-9737, 1989). In the present study we demonstrate that additional SMHC isoform diversity occurs in the globular head region by isolating and characterizing two distinct rat SMHC cDNA (SMHC-11 = SM1B and SMHC-5 = SM1A). Sequence comparison of the two clones reveals that they are completely identical in their coding regions, except at the region encoding the 25/50 kDa junction of the myosin head, where the SM1B isoform contains an additional seven amino acids. This divergent region is located adjacent to the Mg(2+)-ATPase site, and differences in this region may be of functional importance. Ribonuclease protection analysis demonstrates that the corresponding SM1B and SM1A mRNA messages are coexpressed in all smooth muscle tissues; however, the proportion of the two mRNA present differs significantly between tissues. The SM1A-type mRNA predominates in most smooth muscle tissues, with the exception of intestine and urinary bladder, which contain greater proportions of the SM1B message. The differential distribution of these two isoforms may provide important clues toward understanding differences in smooth muscle contractile properties.

—The smooth muscle myosin heavy chain (SM-MHC) gene encodes a major contractile protein whose expression exclusively marks the smooth muscle cell (SMC) lineage. To better understand smooth muscle differentiation at the transcriptional level, we have initiated studies to identify those DNA sequences critical for expression of the SM-MHC gene. Here we report the identification of an SM-MHC promoter-intronic DNA fragment that directs smooth muscle–specific expression in transgenic mice. Transgenic mice harboring an SM-MHC- lac Z reporter construct containing ≈16 kb of the SM-MHC genomic region from −4.2 to +11.6 kb (within the first intron) expressed the lac Z transgene in all smooth muscle tissue types. The inclusion of the intronic sequence was required for transgene expression, since 4.2 kb of the 5′-flanking region alone was not sufficient for expression. In the adult mouse, transgene expression was observed in both arterial and venous smooth muscle, in airway smooth muscle of the trachea and bronchi, and in the smooth muscle layers of all abdominal organs, including the stomach, intestine, ureters, and bladder. During development, transgene expression was first detected in airway SMCs at embryonic day 12.5 and in vascular and visceral SMC tissues by embryonic day 14.5. Of interest, expression of the SM-MHC transgene was markedly reduced or absent in some SMC tissues, including the pulmonary circulation. Moreover, the transgene exhibited a heterogeneous pattern between individual SMCs within a given tissue, suggesting the possibility of the existence of different SM-MHC gene regulatory programs between SMC subpopulations and/or of episodic rather than continuous expression of the SM-MHC gene. To our knowledge, results of these studies are the first to identify a promoter region that confers complete SMC specificity in vivo, thus providing a system with which to define SMC-specific transcriptional regulatory mechanisms and to design vectors for SMC-specific gene targeting.

This review describes normal and abnormal wound healing, the latter characterized by excessive fibrosis and scarring, which for lung can result in morbidity and sometimes mortality. The cells, the extracellular matrix (ECM) proteins, and the growth factors regulating the synthesis, degradation, and deposition of the ECM proteins will be discussed. Therapeutics with particular emphasis given to gene therapies and their effects on specific signaling pathways are described. Bleomycin (BM), a potent antineoplastic antibiotic increases TGFb1 transcription, TGF-b1 gene expression, and TGF-b protein. Like TGF-b1, BM acts through the same distal promoter cis-element of the COL1A1 gene causing increased COL1 synthesis and lung fibrosis. Lung fibroblasts exist as subpopulations with one subset predominately responding to fibrogenic stimuli which could be a specific cell therapeutic target for the onset and development of pulmonary fibrosis.J TGF-b1 is an important modulator in the acute repair phase of a wound. It is a profibrotic factor that affects many cellular functions, including fibroblast proliferation and chemotaxis, stimulating the synthesis and deposition of connective tissue, and the inhibition of connective tissue breakdown. Type I collagen (COL 1) is the major fibrous collagen synthesized by wound fibroblasts in the repair process. When levels of TGF-b1 are chronically elevated, excessive fibrosis results which is characterized by increased collagen deposition. Fibrosis is the response to a traumatic event which terminates in the deposition of a connective tissue matrix. The composition and volume of that matrix differentiates between normal scar in acute wound repair and excessive fibrosis from chronic inflammation. In general, excess fibrosis contains increased concentrations of collagen, a rich blood supply, and myofibroblasts, identified by a-smooth muscle (SM) actin in cytoplasmic stress fibers. The development of fibrosis follows the sequence of overlapping phases; lag, proliferative, and remodeling. Either prolonging the proliferative phase and/or hindering the remodeling phase causes excess fibrosis. Trauma initiates the repair process that can terminate in a normal flat scar or a raised hypertrophic scar. The acute wound repair process provides a rapid and efficient way to restore mechanical tissue integrity. On the other hand, excess fibrosis is a prolonged process that can terminate into functional morbidity. An early event in repair is the restoration of homeostasis by the deposition of a fibrin clot which forms the highway for the migration of cells into the defect. At the termination of fibrosis, the fibrin matrix is replaced with a collagen matrix. The initial cells to travel the fibrin highway are the inflammatory cells. First, neutrophils enter the wound site followed by macrophages. Inflammatory cells prevent microbial colonization, remove dead tissue, and release factors that promote the proliferative phase. Fibroblasts and endothelial cells migrate into the wound site, where they synthesiz...