Abstract
BackgroundThe tazarotene-induced gene 1 (TIG1) is a putative tumor suppressor gene. We have recently demonstrated both TIG1A and TIG1B isoforms inhibited cell growth and induced the expression of G protein-coupled receptor kinase 5 (GRK5) in colon cancer cells. Because elevated prostaglandin E2 (PGE2) signaling plays a significant role in colorectal carcinogenesis, the objective of this study was to explore the effect of TIG1 on PGE2-induced cellular proliferation and signaling in colon cancer cells.MethodsHCT116 cells as well as TIG1A and TIG1B stable cells established from HCT116 colon cancer cells using the GeneSwitch system were used. TIG1 isoform expression was induced by mifepristone treatment in stable cells. Cell growth was determined using the WST-1 cell proliferation assay. Activation of β-catenin/TCF and cyclic adenosine monophosphate (cAMP)/CREB signaling pathways were determined using luciferase reporter assays. Expression and subcellular distribution of β-catenin were analyzed using Western blot and confocal microscope. Levels of cAMP were measured using an enzyme immunoassay. RNA interference was used to examine the effects of TIG1- and GRK5-mediated changes.ResultsPGE2-stimulated cell growth was reduced in inducible TIG1A- and TIG1B-stable HCT116 cells. GRK5 expression was upregulated by both TIG1A and TIG1B isoforms, and its expression suppressed PGE2-stimulated HCT116 cell growth. GRK5, TIG1A, and TIG1B expression significantly inhibited PGE2-stimulated β-catenin/TCF and cAMP signaling pathway reporters and cAMP. Also, PGE2-stimulated nuclear localization of β-catenin was inhibited by expression of TIG1A and TIG1B, which was ameliorated by both TIG1 and GRK5 siRNAs.ConclusionsTIG1 suppressed PGE2-stimulated Wnt and cAMP signaling pathways in colon cancer cells through GRK5.
Highlights
The tazarotene-induced gene 1 (TIG1) is a putative tumor suppressor gene
TIG1A and TIG1B upregulate G proteincoupled receptor kinase 5 (GRK5) expression and suppress prostaglandin E2 (PGE2)-stimulated HCT116 cell growth In the COX-2-negative HCT116 cells, TIG1A and TIG1B expression was markedly induced after the respective stable cells were incubated with 5 nM MFP for 24 and 48 h (Figure 1A)
This study further demonstrated that PGE2-stimulated TOPFLASH and cyclic adenosine monophosphate (cAMP) response element binding protein (CREB) reporter activities were downregulated by TIG1, and the effects were alleviated by GRK5 small interfering RNAs (siRNA)
Summary
We have recently demonstrated both TIG1A and TIG1B isoforms inhibited cell growth and induced the expression of G proteincoupled receptor kinase 5 (GRK5) in colon cancer cells. Because elevated prostaglandin E2 (PGE2) signaling plays a significant role in colorectal carcinogenesis, the objective of this study was to explore the effect of TIG1 on PGE2induced cellular proliferation and signaling in colon cancer cells. Ectopic expression of the TIG1A and TIG1B isoforms suppress cellular growth and/or invasion of cancer cells [2,3,5,11]. Prostaglandin E2 (PGE2), which is regulated by cyclooxygenase-2 (COX-2), promotes the growth and invasion of colorectal tumors [16]. The Wnt signaling pathway, which is activated in most colorectal cancer cells and some precancerous lesions, is activated by PGE2 [18,19]. PGE2stimulated GPCRs stabilize cytosolic b-catenin, resulting in nuclear b-catenin accumulation and transcription factor 7 (TCF7)-mediated transcription [19,20,21,22]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
