LLC-PK1 cell growth is repressed by WT1 inhibition of G-protein alpha i-2 protooncogene transcription.
ABSTRACT The temporal expression of the early growth response gene (EGR-1) is one molecular mechanism for both maximal activation of the G alpha i-2 gene and accelerated growth in mitotically active predifferentiated LLC-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 phenotype in LLC-PK1 cells is accompanied by loss of EGR-1 expression and occupancy 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 alpha i-2 gene activation and growth in these cells. These findings suggest the existence of differentiation-induced pathways in LLC-PK1 cells that alternatively abrogates EGR-1 and promotes WT1 gene expression, thereby modulating a target protooncogene G alpha i-2 that is participatory for growth and differentiation in renal cells. These studies emphasize the usefulness of the LLC-PK1 renal cell as a model to elucidate normal programs of genetic differentiation in which WT1 participates.
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ABSTRACT: The Wilms' tumor 1 (wt1) gene is one of at least three genes that are involved in the development of Wilms' tumor, a pediatric kidney cancer. The expression pattern of the gene indicates that wt1 not only plays a role during kidney development but is also involved in the development and homeostasis of several other tissues. The physiological function of the gene, however, remains to be elucidated. The gene products have been implicated in many processes like proliferation, differentiation, and programmed cell death (apoptosis). The WT1 proteins function as transcription factors but may additionally be involved in splicing. Disruption of these activities may lead to aberrant development. In this paper we will discuss the role of the wt1 gene during normal development and homeostasis of several tissues. In addition, we will address the involvement of the gene products in processes like apoptosis and tumorigenesis.International Review of Cytology 01/1998; 181:151-212. DOI:10.1016/S0074-7696(08)60418-0 · 9.00 Impact Factor
- Kidney International 01/1998; 53:1512. · 8.52 Impact Factor
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ABSTRACT: The product of the Wilm's tumor suppressor gene, WT1, is a zinc-finger DNA-binding protein, which is thought to be a transcription factor. Two genes, those encoding epidermal growth factor receptor and syndecan-1, are known to be endogenous targets of WT1. Previous studies had identified binding sites for WT1 in the promoter of the ornithine decarboxylase (ODC) gene. In this paper, we tested whether the endogenous ODC gene might be a target of WT1 by establishing lines of baby hamster kidney (BHK) cells that expressed WT1 isoform A under control of a tetracycline-regulated expression system. When expression of WT1 was activated in BHK cells, the cellular level of ODC mRNA declined, with kinetics that correlated with the increase in WT1 level, demonstrating that the endogenous ODC gene was indeed responsive to cellular level of WT1. WT1 isoforms A and B inhibited the activity of the ODC promoter by approximately fivefold in transiently transfected BHK cells, while isoforms C and D, which have altered DNA binding domains, had no significant effect. The sequence CTCCCCCGC, located at nucleotides -106 to -98 relative to the site of transcriptional initiation in the ODC gene, interacted with the zinc-finger domain of isoforms A and B of WT1 with high affinity and specificity. A mutation in the binding site that disrupted this interaction partially removed the inhibition of ODC promoter activity by WT1, as did mutation of the two E-box sequences in intron I of the ODC gene. Simultaneous mutation of the WT1-binding motif and the two E-boxes completely abolished inhibition by WT1 of ODC promoter activity. These results, taken together, implicate the ODC gene as a downstream target of the tumor suppressor WT1.Experimental Cell Research 03/1999; 247(1):257-66. DOI:10.1006/excr.1998.4361 · 3.37 Impact Factor