CONTROL OF PROTEINASE EXPRESSION BY PHORBOL-ESTER-DEPENDENT AND FOS-DEPENDENT PATHWAYS IN HUMAN NON-SMALL-CELL LUNG-CANCER CELLS

Activation of protein kinase C- (PKC) and Fos/Jun-dependent signal tra nsduction pathways are thought to be major effects of oncogene action in different tumor systems including human non-small-cell lung carcino ma (NSCLC). We have previously shown that the phorbol ester analogue p horbol-myristate-acetate (PMA), which is a potent activator of PKC, ca n induce squamous-type cellular differentiation and the expression of proteinases, such as plasminogen activators and pro-cathepsin L, in se veral NSCLC cell lines, To investigate the PMA dependent effect on pro teinase secretion in more detail, we have now analysed the role of a d ownstream transmitter of PKC activity in this process, namely Fos, whi ch is part of the AP-I transcription factor in the nucleus. We transfe cted a cell line derived from an undifferentiated squamous-cell lung c arcinoma with different chimeric fos-estrogen receptor constructs (fos -ER) which makes selective activation of this transcription factor pos sible, The resulting clones were treated either with PMA as activator of PKC, or with diethylstilbestrol (DES), an estrogen analogue binding to and thereby activating preformed Fos-ER molecules, We show that ce lls treated with either substance undergo similar phenotypic changes ( change from cuboidal to spindle-cell type) and decrease their doubling rates and cloning efficiencies. This is paralleled by the induction o f several proteinase genes such as t-PA, urokinase, and pro-cathepsins B and L. Contrary to activated PKC, Fos in this system seems to be un able to initiate terminal squamous-cell differentiation, as assessed b y the production of cornified envelopes. It is, however, efficient in the stimulation of neutral or lysosomal proteinase secretion as determ ined by Western-blot analysis and zymography, This Fos-ER expressing s ystem thus seems to be a valuable tool in the molecular dissection of pathways that lead to the activation and secretion of proteinases in N SCLC cells. (C) 1997 Wiley-Liss, Inc.