Microfilament organization and total actin content are decreased in hybrids derived from the fusion of HeLa cells with human fibroblasts.

The organization of the microfilaments and the actin content of matched pairs of tumorigenic and non-tumorigenic HeLa/fibroblast hybrid cells was compared. Each pair consisted of a hybrid cell line with suppressed tumorigenicity and a segregant tumorigenic cell line derived from it. The tumorigenic HeLa parent cell line and a non-tumorigenic human fibroblast line were also included in the comparison. Microfilament organization of the cell lines was assessed by fluorescence microscopy using NBD-phallacidin, a probe that specifically binds to actin filaments. The re-expression of tumorigenicity is associated with a loss of microfilament organization. The actin content, as measured by the DNase I inhibition assay, was significantly lower in the tumorigenic hybrids and the HeLa parent than in the non-tumorigenic cells. The comparison was significant when the actin concentration was expressed either per cell or per protein. Despite this reduced level of total actin in tumorigenic cells, the ratio of monomeric to total actin remained constant in all cell lines tested.