Hyperplasia in multiple smooth muscle tissues in transgenic mice expressing a temperature-sensitive SV40 T-antigen under the control of smooth musclealpha-actin regulatory sequences

Control of smooth muscle cell (SMC) proliferation is of fundamental importa nce in the development and pathology of the vasculature. To derive vascular SMC with conditional inactivation of negative cell cycle regulatory protei ns in the context of smooth muscle protein expression, a 3.4 kb fragment of the mouse SMC alpha-actin promoter was used to target a temperature-sensit ive mutant SV40 T antigen (tsA58) to smooth in transgenic mice. Mice with t his genotype display heritable phenotype of abnormal SMC proliferation in t he central tail artery, vasa deferentia, seminal vesicles, prostate, and ut erus, with the latter resembling uterine leiomyomatosis and prostatic hyper trophy. Neither the aorta nor other viscera manifested abnormal proliferati on, Cultures from aorta, vas deferens, seminal vesicle, and kidney tissue w ere characterized with regard to protein expression, stability, and matrix remodelling capacity. The a-actin content/cell was up to 3-4-fold higher, a s well as more stable than in primary SMC cultures, suggesting successful s election for propagation of cells expressing this differentiation marker, A ll cells displayed enhanced growth at the permissive temperature, As an ini tial functional assessment, the cells were compared to non-transformed mous e aortic SMC with respect to the ability to remodel collagen gel matrices, and demonstrated conservation of this physiologic function. This in vivo an alysis of the SMC alpha-actin promoter supports a broader range of smooth m uscle-directed expression activity than previously recognized, and establis hes the feasibility of its use to direct transgene expression to vascular a s well as genito-urinary smooth muscle. The targeted expression of the tsA5 8 T antigen has yielded transgenic animals with several manifestations of s mooth muscle hyperplasia; these animals have in turn permitted the derivati on of several murine SMC lines with phenotypic stability and conditionally- modulated proliferation. These cells will allow expansion of derivative tra nsfected smooth muscle cell lines under permissive conditions, as well as o ncogene inactivation at the restrictive temperature when desired for functi onal studies.