Preservation of the myofibroblastic phenotype of human papilloma virus 16 E6/E7 immortalized human bone marrow cells using the lineage limited alpha-smooth muscle actin promoter.

The in vitro study of mammalian hematopoiesis is hindered by the lack of immortalized human stromal cell lines that support hematopoiesis. We have immortalized human stromal vascular smooth muscle cells characterized by the expression of the alpha-smooth muscle (alpha-SM) actin. This marker is usually down-regulated as a result of oncogenic transformation. To correct this dedifferentiation, we placed the expression of human papilloma virus 16 E6/E7 oncogenes under the control of the tissue-specific alpha-SM actin promoter. The immortalization event is rare and requires polyclonal culture, but the corresponding established line retains alpha-SM actin expression. Moreover, when compared with other lines derived from the same cells from vectors made with the same oncogenes but driven by either an internal SV40 promoter or the viral long terminal repeat, this line is less transformed as shown by anchorage-independent growth assay. We show therefore that the use of a physiological promoter allows the production of human cell lines with a conserved phenotype.