Loss of transforming growth factor beta 1 (TGF-beta 1)-induced growth arrest and p34cdc2 regulation in ras-transfected epithelial cells

Abstract

Transforming growth factor beta 1 (TGF-beta 1) is a potent inhibitor of mink lung epithelial (CCL64) cell growth in culture. The fact that many transformed epithelial cells have escaped from negative growth control by TGF-beta 1 suggests that transfected epithelial cells may be an appropriate model for investigating the growth-inhibitory mechanism of TGF-beta 1. We transfected CCL64 cells with a mouse c-myc oncogene (pSVc-myc1), a mutated Harvey-ras (Ha-ras) oncogene, or a combination of both. The results indicate that cells transfected with c-myc alone exhibit normal morphology and maintain sensitivity to TGF-beta 1 growth arrest, but are unable to form colonies in soft agar in the presence or absence of TGF-beta 1. Cells transfected with Ha-ras, or co-transfected with c-myc, display a transformed morphology, grow spontaneously under anchorage-independent conditions and acquire a complete resistance to growth inhibition by TGF-beta 1. Affinity cross-linking of [125I]TGF-beta 1 to cell-surface receptors from these transfectants revealed that all three TGF-beta receptor types were present and no significant differences in [125I]TGF-beta 1 labeling of these receptors was observed. Since we have previously demonstrated that modulation of p34cdc2 kinase is a marker for TGF-beta 1 growth inhibition, we investigated p34cdc2 activity in the CCL64 transfected clones. The results show that in the control CCL64 cells and in the myc-transfected clones TGF-beta 1 regulation of p34cdc2 activity is maintained. In the ras- and ras + myc-transfected cells p34cdc2 phosphorylation and histone H1 kinase activity is significantly increased and regulation by TGF-beta 1 is lost.