Possible role of calponin h1 as a tumor suppressor in human uterine leiomyosarcoma

Background: Calponin h1, a basic actin-binding protein capable of inhibitin g smooth muscle contraction, is a constitutive element of smooth muscle cel ls. However, in leiomyosarcoma (a type of smooth muscle neoplasm of the ute rus), reduced expression of calponin h1 is observed, as we have reported pr eviously. In this study, we sought to assess the effects (in vitro and in v ivo) of increasing calponin hi expression in leiomyosarcoma cells. Methods: A plasmid containing a human calponin hi complementary DNA and a bacterial neomycin-resistance gene was transfected into the human leiomyosarcoma cel l lines SKN and SK-LMS-1 by electroporation, Southern blotting, reverse tra nscription-polymerase chain reaction analysis, western blotting, and immuno histochemistry were used to confirm DNA transfer and expression of the calp onin hi protein in neomycin-resistant clones. We characterized the morpholo gy of calponin hl-transfected cells, and we evaluated their proliferative a ctivity and tumorigenicity by use of a 3-(4,5-dimethylthiazol-2-yl)-2,5-dip henyl-2H-tetrazolium bromide assay, an anchorage-independent growth assay, and a nude mouse tumorigenicity assay. Results: The morphology of calponin h1-transfected cells in culture resembled that of cultured normal myometria l smooth muscle cells. With SK-LMS-1 cells, proliferation of calponin hl-tr ansfection cells was reduced to 69% of control; with SKN cells, calponin hi transfection reduced proliferation to 70% of control. In assays of anchora ge-independent growth and in vivo tumorigenicity, both growth and tumorigen icity were statistically significantly reduced in calponin h1-transfected l eiomyosarcoma cells. Conclusions: Calponin hi may function as a tumor suppr essor in leiomyosarcoma, Clinically, transfer of a calponin h1 complementar y DNA into poorly differentiated leiomyosarcoma cells may be of potential t herapeutic value through induction of a normal, differentiated cellular phe notype.