LLC-PK1 CELL-GROWTH IS REPRESSED BY WT1 INHIBITION OF G-PROTEIN ALPHA(I-2) PROTOONCOGENE TRANSCRIPTION

The temporal expression of the early growth response gene (EGR-1) is o ne molecular mechanism for both maximal activation of the G alpha(i-2) gene and accelerated growth in mitotically active predifferentiated L LC-PK1 renal cells. These events are dependent on an enhancer area in the 5'-flanking region of the G alpha(i-2) gene that contains an EGR-1 motif (5'-CGCCCCCGC-3'). However, acquisition of the polarized phenot ype in LLC-PK1 cells is accompanied by loss of EGR-1 expression and oc cupancy of the EGR-1 site by nuclear binding proteins other than EGR-1 . We now demonstrate that one of these binding proteins is the Wilms' tumor suppressor (WT1). Furthermore, the temporal expression of WT1 in LLC-PK1 cells acquiring the polarized phenotype represses both G alph a(i-2) gene activation and growth in these cells. These findings sugge st the existence of differentiation-induced pathways in LLC-PK1 cells that alternatively abrogrates EGR-1 and promotes WT1 gene expression, thereby modulating a target protooncogene G alpha(i-2) that is partici patory for growth and differentiation in renal cells. These studies em phasize the usefulness of the LLC-PK1 renal cell as a model to elucida te normal programs of genetic differentiation in which WT1 participate s.