Isoforms of Wilms’ tumor suppressor gene (WT1) have distinct effects on mammary epithelial cells

Abstract

The role of WT1 (Wilm's tumor suppressor gene) in breast cancer is controversial, with evidence for both tumorpromoting and tumor-suppressing activities. In order to address this question, we expressed different WT1 isoforms in the mammary epithelial cell line H16N-2, which does not express endogenous WT1. Cells were stably transfected with either WT1 (ÀEx5/ÀKTS) or WT1 ( þ Ex5/ þ KTS) under the control of the inducible metallothionein promoter. Induction of WT1 (ÀEx5/ ÀKTS) upregulated p21, causing a slowing of proliferation and a G2-phase cell cycle arrest. In artificial basement membrane, the WT1 (ÀEx5/ÀKTS) isoform promoted the appearance of highly organized acinar cellular aggregates. In contrast, WT1 ( þ Ex5/ þ KTS) had no effect on p21 or proliferation, but rather caused an epithelial-mesenchymal transition and a redistribution of E-cadherin from the cell membrane to the cytoplasm. This isoform also causes the cellular aggregates growing in artificial basement membrane to appear significantly less organized than control cells. Thus, different WT1 isoforms have distinct effects in this cell line, suggesting that depending on the ratio of WT1 isoform expression in mammary epithelial cells, WT1 could function to either promote or suppress a transformed phenotype.

Wilms' tumor protein 1: an early target of progestin regulation in T-47D breast cancer cells that modulates proliferation and differentiation

“…This does not, however, exclude a role for the other isoforms, as indicated by the recent observation that overexpression of the Wt1 (À/À) isoform may increase motility and invasion in ZR-75 and SKBr3 breast cancer cells (Jomgeow et al, 2006). More commonly however, overexpression of the Wt1 (À/À) isoform has been observed to have tumor suppressor effects in mammary epithelial cells (Reizner et al, 2005;Burwell et al, 2007).…”

“…In this context, it is of significance that the transcript distribution of Wt1 varies considerably between tissues: only 7% of Wt1 transcripts are KTS negative in breast cancer cell lines (Figure 1), whereas in human kidney development, where Wt1 can act as a tumor suppressor in Wilms' tumor, 22% of the transcripts are KTS negative (Haber et al, 1991). In mammary epithelial cells, the Wt1 ( þ / þ ) isoform promoted a transformed phenotype, whereas overexpression of the Wt1 (À/À) isoform decreased proliferation (Burwell et al, 2007). Thus, it is likely that the high relative levels of Wt1 ( þ KTS) isoforms in breast cancer cell lines contribute to the pro-proliferative effects of Wt1 in breast cancer cells, and consequently to a role as a potential breast oncogene.…”

Prolactin and oestrogen synergistically regulate gene expression and proliferation of breast cancer cells

“…Several isoforms of WT1 with distinct effects have been reported. One of the isoforms was shown to cause oncogenic transformation of breast cancer cells, whereas another caused breast cancer cell cycle arrest (Burwell et al 2007). Down-regulation of all WT1 isoforms using siRNA in T47D breast cancer cells resulted in reduced levels of cyclin D1, phosphorylated Rb and S-phase content, implying a role of WT1 in breast cancer cell growth (Caldon et al 2008).…”

Real-time PCR quantification of major Wilms’ tumor gene 1 (WT1) isoforms in acute myeloid leukemia, their characteristic expression patterns and possible functional consequences

“…Disturbed WT1 regulatory function may alter the mesenchymal-epithelial balance, resulting in malignant proliferation as well as non-malignant diseases associated with the WT1 gene (for example, glomerulosclerosis). 8,9 WT1 is located on chromosome 11p13 and encodes a zincfinger transcription factor. It activates or more often represses the transcription of many target genes involved in the cell cycle, proliferation, differentiation and apoptosis control, and is also involved in post-transcriptional mRNA processing.…”

“…15,34 Functional studies suggest that many of WT1 effects are related to particular WT1 isoforms. 8,20,[35][36][37][38][39][40] The available data on WT1 isoform expression patterns in normal and malignant hematopoiesis are scarce and the methods so far used for the detection of WT1 major isoforms (reverse transcriptase PCR, GeneScan, quantitative PCR of EX5[ þ ] and KTS[ þ ] variants) have only yielded an approximate estimation of WT1 isoform levels.…”