Different propensity for spontaneous differentiation of cell clones isolated from the human ovarian surface epithelial cell line HOC-7.

Limiting dilution culture of cell fractions obtained by discontinuous density gradient centrifugation was used to establish six different cell clones from HOC-7 ovarian adenocarcinoma cells (D1-D3, N1-N3). Clones D1-D3 revealed a phenotype similar to that seen in parental cells exposed to differentiation inducers such as dimethyl sulfoxide (DMSO, 0.8% [v/v]). They were flattened, slowly growing cells (doubling times: 42-46 h). The cells developed long cytoplasmic extensions and adopted a complicated growth pattern. Fixed-cell enzyme-linked immunosorbent assay (ELISA) and Western blotting demonstrated that these cells contained high levels of epidermal growth factor-receptor (EGF-R), carbohydrate antigen 125 (CA 125), fibronectin and desmoplakin, but low levels of myc oncoproteins. However, untreated parental cells and clones N1-N3 were fast-growing (doubling times: 23-28 h), regularly shaped, polygonal cells ("cobblestone" monolayer) with low levels of EGF-R, CA 125, fibronectin and desmoplakin, but relatively higher amounts of myc oncoproteins. The similarity of the sublines to either untreated or inducer-treated parental cells indicated that clones D1-D3 represented spontaneously differentiated HOC-7 cells, whereas clones N1-N3 originated from less-differentiated cells. The features examined in this model cell system proved to be closely related to ovarian cancer cell proliferation and differentiation. The observation of a tumor-inherent propensity for spontaneous differentiation suggests that exogenous stimulation of existing differentiation pathways may represent an alternative approach for tackling the problem of growth control and differentiation in malignant tissues.