Progressive abrogation of TGF‐β‐1 and EGF growth control is associated with tumour progression in ras‐transfected human keratinocytes

This study examined the response of human keratinocytes in different stages of transformation to exogenous TGF‐β 1 and EGF as well as their receptor and growth‐factor expression. Cells of the spontaneously immortalized HaCaT cell line and c‐Ha‐ras transfected clones (1–6, 1–7, 11–3, 11–4) exhibited different tumorigenic potentials when transplanted to athymic mice. HaCaT‐ and 1–6 cells were non‐tumorigenic, 1–7 cells formed persisting epidermal cysts (benign tumours) and 11‐3 and 11‐4 cells developed into invasive squamous‐cell carcinomas. TGF‐β 1 inhibited thymidine uptake in a dose‐dependent manner, a progressive decrease in response being associated with an increasing malignant potential (HaCaT > 1–6 > 1–7 = 11‐4). HaCaT‐cells and ras‐clones expressed TGF‐β I mRNA at similar levels, but cells of increasing malignant potential secreted markedly less receptor‐binding TGF‐P (HaCaT > 1–6 = 1–7 > 11‐3 > 11‐4) into the culture medium. Whilst ras‐transfected cells expressed fewer TGF‐P receptors than HaCaT cells, there was little difference between TGF‐p receptor number or affinity between the 4 transfected cell clones. The same was true for the TGF‐p receptor types, but Type‐11 receptors were expressed at lower levels by the malignant clones 11‐3 and 11‐4. When HaCaT and ras‐transfected cells were investigated for their response to exogenous EGF, cells were refractory (1–7, 11‐4), partially stimulated (1–6) or fully stimulated (HaCaT). Cells with increasing malignant potential produced increasing amounts of endogenous TGF‐α (11‐4 = 11‐3 > 1–7 = 1–6 > HaCaT). All tumorigenic ras clones expressed higher mRNA levels than HaCaT‐cells. Ras‐transfected clones expressed fewer high‐ and low‐affinity EGF receptors than HaCaT cells with a tendency toward increased numbers of high‐affinity EGF receptors associated with increasing malignant potential (11‐4 = 11‐3 > 1–7 > 1–6) but these changes were associated with a progressive decrease in receptor affinity. The results indicate that tumour progression in human epidermal keratinocytes transfected with c‐Ha‐ras is associated with a progressive abrogation of TGF‐β 1 and EGF growth control. They suggest that the increased autonomous growth potential associated with advanced stages of epithelial tumour progression can be defined more closely using a cellular profile of TGF‐β and EGF. © 1992 Wiley‐Liss, Inc.