Calponin h1 Suppresses Tumor Growth of Src‐induced Transformed 3Y1 Cells in Association with a Decrease in Angiogenesis

Calponin h1 (CNhl) is a basic actin‐binding protein that is abundantly expressed in smooth muscle cells and involved in smooth muscle contraction by inhibiting actomyosin MgATPase. In recent studies, CNhl was noted to suppress cell proliferation and tumorigenicity in leiomyosarcoma and tumor growth in fibrosarcoma cell lines. To further investigate the function of CNhl as a tumor suppressor, we transfected the human CNhl gene into a v‐src‐transformed rat fibroblast cell line SR–3Y1. The volume of the tumors derived from one randomly selected CNh1‐transfectant (C1) in nude mice was reduced to 34.1% of that from a randomly selected vector transfectant (VI). A similar tendency was observed in another independent pair (C2, V2). Pathological analysis showed a significant decrease in the number of mitotic cells in the CNh1‐transfectants. Further, a marked reduction in the number of vessels in the CNhl‐transfectant was observed. DNA synthesis under conditions without serum was significantly reduced in the CNhl‐transfectant (C1) compared with the control transfectant (VI), while no significant difference was seen in the cellular growth in the presence of 10% serum. A slight but significant reduction in in vitro cellular motility in the CNhl‐transfectant was also observed. While the suppression of growth potential and cell motility by CNhl transfer was significant but partial, a marked reduction in vascular endothelial growth factor (VEGF) mRNA and the secretion of VEGF protein was observed in the CNhl‐transfectant. These results suggest that CNhl plays a role as tumor suppressor in SR–3Y1 mainly by decreasing VEGF expression and angiogenesis in vivo and partially through reducing cellular proliferative potential and cell motility.