Endogenous AP-1 levels necessary for oncogenic activity are higher than those sufficient to support normal growth

We investigated the role of endogenous AP-1 in human tumor cell lines by in troducing SupJunD-1, a dominant-negative mutant of AP-1, using vesicular st omatitis virus G protein (VSV-G)-pseudotylped retrovirus vectors. Single in oculation of six human tumor cell lines, originating from osteosarcomas, no nsmall cell lung carcinomas or cervical carcinomas, with recombinant SupJun D-1 virus at a high multiplicity of infection readily inhibited colony form ation in soft agar. We detected no significant changes in expression levels of AP-1 components c-Jun or Fra-1, adhesion molecules CD44 or E-cadherin, or cell cycle regulator p53, which are encoded by genes previously reported to be under the control of API-1 in some mouse or human cell lines. By var ying the dosage of VSV-G-pseudotyped retrovirus, we were able to change the proviral copy number of supjunD-1 from 1 to approximately 10 and monitor s uppression of endogenous AP-1 function as assessed by growth characteristic s of the tumor cell lines, we found a SupJunD-1 dosage which significantly suppressed anchorage-independent growth without affecting the cellular grow th in monolayer cultures at all. We conclude that endogenous AP-1 levels ne cessary for oncogenic activity are much higher than those sufficient to sup port normal growth. (C) 2000 Academic Press.