The Integrated Duality Of Nur77 And TGFβ Signaling In Regulating ID1 Expression In Colon Cancer

Colon cancer is the third most common cancer globally.The risk of developing colon cancer is influenced by a number of factors that include age and diet,but is primarily a genetic disease,resulting from oncogene over expression and tumor suppressor gene inactivation.The process of colon cancer development is sequentially controlled by different signaling pathways,of which transforming growth factor-β(TGFβ)signaling plays a unique role by imposing opposite influence at different stages of cancer developments.In early-stage cancer,TGFβ exerts tumor-suppressor functions including cell-cycle arrest and apoptotic induction.However,it promotes tumorigenesis including metastasis and chemoresistance in late-stage cancer.Aberrantly high expression of inhibitor of differentiation 1(ID1)contributes to the growth,self-renewal,and metastasis of a variety of tumors including colon cancer while ID1 transcription is upregulated by TGFβ/Smad3 signaling in cancer cells.Nur77,an orphan member of the nuclear receptor superfamily,plays a critical role in numerous biological processes.Nur77 was reported to exert both tumor-suppressing and tumor-promoting effects in colon cancers.It has been identified as a positive regulator of TGFβ signaling involved in breast cancer progression.The paradoxical roles of TGFβ signaling and nuclear receptor Nur77 in colon cancer development are known but with obscure mechanisms.Here,we reveal an unanticipated crosstalk between Nur77 and TGFβ signaling in regulating ID1 expression at both transcriptional and post-translational levels,which is pathologically relevant to colon cancer development.Here,we show that Nur77 has dual activity in regulating ID1 expression in colon cancers,a finding which likely reflects a combination of genomic and non-genomic mechanisms of Nur77.When TGFβ signal is low or absent,Nur77 acts as a negative regulator of ID1 by enhancing Smurf2-mediated ID1 ubiquitylation and degradation,which embodied a non-genomic activity of Nur77.However,TGFβ can convert Nur77 from a negative to a positive regulator.This likely occurs in cancers when high TGFβsignal disrupts Nur77-mediated ID1 interaction with and ubiquitylation by Smurf2.Meanwhile,TGFβ induces Nur77 interacting with Smad3 to enhance ID1 gene transcription,exhibiting Nur77 genomic action.TGFβ also up-regulates ID1 expression post-translationally through inhibiting its ubiquitin-mediated degradation,presenting an unidentified acting mode of TGFβ in upregulating ID1.This finding signifies the role of TGFβ in cancer promotion in two aspects.First,TGFβ can efficiently increase ID1 expression in cancer cells through both mRNA induction and protein stabilization.Secondly,TGFβ can actively exert its oncogenic effect in Smad4-null cancers through stabilizing ID1 protein.Thus,Smad4/-colon cancer cells not only evade TGFβ-induced growth inhibition through Smad4 deletion but also actively respond to TGFβ-induced progression at least through ID1 stabilization,reflecting their high malignancy.Thus,our results invoke a model according to which TGFβ signaling exerts dual regulation of specific protein expression,a principle that may apply to other signal pathways as well.Moreover,it is Nur77 that mediates the dual modes of TGFβ on ID1 expression while it is TGFβ that converts Nur77 role and mode in regulating ID1 expression.These findings define the integrated duality of Nur77 and TGFβ signaling in regulating ID1 expression during colon cancer progression and provide new therapeutic strategies for colon cancers.Indeed,we show that Nur77 ligand Celastrol potently inhibits colon cancer cell growth,metastasis and resistance to oxaliplatin through inducing ID1 degradation in a Nur77-dependent manner.Notably,Celastrol inhibits TGFβ-induced both ID1 mRNA expression and ID1 protein stability in a Nur77dependent manner,suggesting its therapeutic effects in tumors harboring high TGFβsignaling.In conclusion,the mechanistic principles emerging from our study highlight the tightly integrated duality of Nur77 and TGFβ signaling in regulating ID1 expression as well as its implications in colon cancer development and applications in treating colon cancer and overcoming oxaliplatin resistance.