Gene expression of the lysophosphatidic acid receptor 1 is a target of transforming growth factor beta

Abstract

The lysophosphatidic acid (LPA) receptor LPA 1 /Edg2 is the first identified LPA receptor. Although its wide tissue distribution and biological functions have been well studied, little is known about how LPA 1 is transcriptionally regulated. In the current study, we showed that LPA 1 is a physiological target of transforming growth factor beta (TGFβ)-mediated repression. In both normal and neoplastic cells, TGFβ inhibits LPA 1 promoter activity, LPA 1 mRNA expression and LPA 1 -dependent chemotaxis and tumor cell invasion. Knockdown of the TGFβ intracellular effector Smad3 or Smad4 with lentivirally transduced short hairpin RNA relieved these inhibitory effects of TGFβ. Interestingly, the LPA 1 promoter contains two potential TGFβ inhibitory elements (TIEs), each consisting of a Smad-binding site and an adjacent E2F4/5 element, structurally similar to the TIE found on the promoter of the well-defined TGFβ target gene c-myc. Deletion and point mutation analyses indicate that the distal TIE located at 401 bp from the transcription initiation site, is required for TGFβ repression of the LPA 1 promoter. A DNA pull-down assay showed that the -401 TIE was capable of binding Samd3 and E2F4 in TGFβ-treated cells. TGFβ-induced binding of the Smad complex to the native -401 TIE sequence of the LPA 1 gene promoter was further verified by chromatin immunoprecipitation assays. We therefore identified a novel role of TGFβ in the control of LPA 1 expression and LPA 1 -coupled biological functions, adding LPA 1 to the list of TGFβ-repressed target genes. © 2013 Macmillan Publishers Limited All rights reserved.