Ciliogenic RFX transcription factors regulate FGF1 gene promoter

Abstract

Fibroblast growth factor 1 (FGF1) has been shown to regulate cell proliferation, cell division, and neurogenesis. Human FGF1 gene 1B promoter (-540 to +31)-driven green fluorescence (F1BGFP) was shown to recapitulate endogenous FGF1 gene expression. It can also be used to isolate neural stem/progenitor cells (NSPCs) and glioblastoma stem cells (GBM-SCs) from developing mouse brains and human glioblastoma tissues, respectively. However, the regulatory mechanisms of FGF-1B promoter and F1BGFP(+) cells are not clear. In this study, we present several lines of evidence to show the roles of ciliogenic RFX transcription factors in the regulation of FGF-1B gene promoter and F1BGFP(+) cells: (i) RFX1, RFX2, and RFX3 transcription factors could directly bind the 18-bp cis-element (-484 to -467), and contribute to the regulation of FGF1 promoter and neurosphere formation. (ii) We demonstrated RFX2/RFX3 complex could only be detected in the nuclear extract of FGF-1B positive cells, but not in FGF-1B negative cells. (iii) Protein kinase C inhibitors, staurosporine and rottlerin, could decrease the percentage of F1BGFP(+) cells and their neurosphere formation efficiency through reducing the RFX2/3 complex. (iv) RNA interference knockdown of RFX2 could significantly reduce the percentage of F1BGFP(+) cells and their neurosphere formation efficiency whereas overexpression of RFX2 resulted in the opposite effects. Taken together, this study suggests ciliogenic RFX transcription factors regulate FGF-1B promoter activity and the maintenance of F1BGFP(+) NSPCs and GBM-SCs.

Primary cilium and glioblastoma

“… 74 Interestingly, RFX1, RFX2 and RFX3 cooperate to modulate the maintenance of neural progenitors and GSCs through regulating fibroblast growth factor 1 (FGF1) promoter activity, an important mitogen for neurogenesis. 75 , 76 It would be necessary to explore whether RFX1 mediates GBM progression through primary cilia, since this possibility was not addressed in the abovementioned studies. In this sense, although the biological role of RFX1 is not well defined and includes regulation of ciliary and non-ciliary targets, 72 RFX1 and RFX2 were recently demonstrated to regulate the transcription level of ALMS1 gene, which encodes a protein localized to basal bodies and centrosomes that is mutated in Alström syndrome, a ciliopathy.…”

FGF1 signaling regulates self-renewal of glioblastoma stem cells through activation of aurora a kinase

“…We demonstrated that knockdown of FGF1 decreases sphere formation in GBM cells [48] . Recently, in our other report, blocking of FGF1/FGFR by small molecule, SU5402, results in decreased sphere forming capacity in GBM cells [28] .…”

Ciliary transcription factors in cancer - how understanding ciliogenesis can promote the detection and prognosis of cancer types

“…Alterations in RFX1 expression are associated with several cancer types, including glioblastomas, breast cancer and a subset of lymphomas . It has been shown that RFX1 down‐regulates expression of the proto‐oncogene MYC , transforming growth factor‐β2 ( TGFβ2 ) as well as CD44 , a hyaluronic acid cell surface receptor .…”