Different propensity for spontaneous differentiation of cell clones isolated from the human ovarian surface...

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.