Increased activity of MAP, p70S6 and p90rs kinases is associated with AP-1 activation in spontaneous liver tumours, but not in adjacent tissue in mice.

Growth factor-responsive protein kinases regulate expression of genes involved in cell cycle control, cell proliferation and differentiation. To better understand the role of these kinases in the abnormal proliferation of malignant cells, we examined basal and epidermal growth factor (EGF)-inducible mitogen-activated protein kinase (MAPK), p70S6k and p90rsk activities in spontaneous hepatocellular neoplasms (adenomas and carcinomas) from CBA-T6 mice and in L1 sarcoma tumours implanted in livers of BALB/c mice. In spontaneous and implanted hepatic tumours, basal cytoplasmic and nuclear MAPK, p70S6k and p90rsk activities were significantly higher compared to the activities found in the part of the liver uninvolved by the tumour. Interestingly, the activities of these enzymes in the uninvolved tissue of the livers harbouring the tumour were higher compared to the livers from control mice. Basal kinase activities correlated with tumour morphology; they were lower in adenomas than in carcinomas and sarcomas. In contrast to basal activities, EGF-triggered kinase responses in normal livers and hepatic tumours were indistinguishable. Activating protein-1 (AP-1) DNA-binding activity was detected in tumours but not in the adjacent tissues. Constitutively activated kinases and AP-1 transcription factor found in hepatic malignancies are reminiscent of cells activated by EGF, suggesting that EGF and its intracellular effectors play a role in these malignancies.