Kruppel-like factor 5 incorporates into the β-catenin/TCF complex in response to LPA in colon cancer cells

Lysophosphatidic acid (LPA) is a simple phospholipid with potent mitogenic effects on various cells including colon cancer cells. LPA stimulates proliferation of colon cancer cells by activation of S-catenin or Kruppel-like factor 5 (KLF5), but the functional relationship between these two transcription factors is not clear. Hence, we sought to investigate the mechanism of p-catenin activation by LPA and the role of KLF5 in the regulation of beta-catenin by LPA. We found that LPA and Wnt3 additively activated the beta-catenin/TCF (T cell factor) reporter activity in HCT116 cells. In addition to phosphorylating glycogen synthase kinase 33 (GSK-3 beta) at Ser9, LPA resulted in phosphorylation of p-catenin at Ser552 and Ser675. Mutation of Ser552 and Ser675 ablated PA-induced beta-catenin/TCF transcriptional activity. Knockdown of KLF5 significantly attenuated activation of beta-catenin/TCF reporter activity by LPA but not by Wnt3. However, nuclear accumulation of beta-catenin by LPA was not altered by knockdown of KLF5. beta-catenin, TCF, and KLF5 were present in a 250-300 kDa macro-complex, and their presence was enhanced by LPA. LPA simulated the interaction of beta-catenin with TCF4, and depletion of KLF5 decreased beta-catenin-TCF4 association and the transcriptional activity. In summary, LPA activates beta-catenin by multiple pathways involving phosphorylation of GSK-3 and beta-catenin, and enhancing beta-catenin interaction with TCF4. KLF5 plays a critical role in p-catenin activation by increasing the beta-catenin-TCF4 interaction. (C) 2015 Elsevier Inc All rights reserved.