| Summary: | The loss of E-cadherin, a critical component of the adherence junctions, is implicated in the metastasis of carcinomas and correlates with tumour grade. Here we show that in PC3 cells loss of Integrin-Linked Kinase (ILK), AKT/PKB or Snail-1, results in the re-expression of E-cadherin at both the mRNA and protein level. We have previously shown that ILK is capable of transcriptionally regulating the E-cadherin repressor Snail-1, via a 65-bp ILK responsive element in the 5' promoter termed the Snail-1 ILK Responsive Element (SIRE). Using a SIRE oligonucleotide we identified three candidate SIRE binding proteins that demonstrate differential binding due to loss of ILK: Poly(ADP-ribose) polymerase-1 (PARP-1), Methyl-CpG domain binding protein 5 (MBD-5) and a fragment of Chromodomain-helicase-DNA-binding protein 8/Helicase with SNF2 domain 1 (CHD-8/HELSNF1). PARP-1, which bound the SIRE in the presence, but not the absence of ILK was further characterized in this study. Like ILK, AKT and Snail-1, PARP-1 siRNA treatment results in the upregulation of E-cadherin. Inhibition of the ADP-ribose polymerase activity of PARP-1 partially blocks the upregulation of E-cadherin in ILK siRNA treated cells. This suggests a mechanism in which ILK has a role in maintaining PARP-1 in an inactive state, repressing expression of E-cadherin. We demonstrate that in Scp2 cells ILK overexpression results in the induction of Snail-1 expression. We suggest a model in which ILK regulates E-cadherin by regulating PARP-1 enzymatic activity. The regulation of PARP-1 activity modulates its ability to bind to the Snail-1 promoter.
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