p53 modulates the activity of the GLI1 oncogene through interactions with the shared coactivator TAF9

Abstract

The GLI1 oncogene and p53 tumor suppressor gene function in an inhibitory loop that controls stem cell and tumor cell numbers. Since GLI1 and p53 both interact with the coactivator TATA Binding Protein Associated Factor 9 (TAF9), we hypothesized that competition between these transcription factors for TAF9 in cancer cells may contribute to the inhibitory loop and directly affect GLI1 function and cellular phenotype. We showed that TAF9 interacts with the oncogenic GLI family members GLI1 and GLI2 but not GLI3 in cell-free pull-down assays and with GLI1 in rhabdomyosarcoma and osteosarcoma cell lines. Removal of the TAF9-binding acidic alpha helical transactivation domain of GLI1 produced a significant reduction in the ability of GLI1 to transform cells. We then introduced a point mutation into GLI1 (L1052I) that eliminates TAF9 binding and a point mutation into GLI3 (I1510L) that establishes binding. Wild-type and mutant GLI proteins that bind TAF9 showed enhanced transactivating and cell transforming activity compared with those that did not. Therefore, GLI-TAF9 binding appears important for oncogenic activity. We then determined whether wild-type p53 down-regulates GLI function by sequestering TAF9. We showed that p53 binds TAF9 with greater affinity than does GLI1 and that co-expression of p53 with GLI1 or GLI2 down-regulated GLI-induced transactivation, which could be abrogated using mutant forms of GLI1 or p53. This suggests that p53 sequesters TAF9 from GLI1, which may contribute to inhibition of GLI1 activity by p53 and potentially impact therapeutic success of agents targeting GLI-TAF9 interactions in cancer.

Immunohistochemical visualization of the signature of activated Hedgehog signaling pathway in cutaneous epithelial tumors

“…Another possible explanation for the nuclear GLI1 localization could rest on the role of non‐canonical pathways of HH signaling. GLI transcription factors have been shown to be positively regulated by K‐Ras and PI3K‐AKT, and negatively regulated by p53 . As dysfunctions of these molecules are reported to promote the development of cutaneous SCC, it is plausible that some cutaneous SCC, including in situ lesions, have nuclear localization of GLI1.…”

Targeting the Sonic Hedgehog Signaling Pathway: Review of Smoothened and GLI Inhibitors

“…K-Ras, in particular, seems to be a pathway capable of activating GLI1 independent of the Shh pathway as knockdown of SUFU does not affect K-Ras-induced GLI1 [ 38 , 40 ]. Additionally, the GLI proteins have been shown to be negatively regulated by p53, PKA, and PKC-δ [ 42 , 43 , 44 , 45 ]. GLI1 transcriptional activity has also been shown to be reduced with p53 overexpression and enhanced with p53 knockdown [ 44 ].…”

“…GLI1 transcriptional activity has also been shown to be reduced with p53 overexpression and enhanced with p53 knockdown [ 44 ]. Furthermore, p53 has been shown to interact with TAF9 leading to suppression of GLI1 activity [ 45 ]. PKA regulation of GLI1 is very specific as PKA directly phosphorylates Thr374 of GLI1, which promotes cytoplasmic localization and reduced activity of GLI1 [ 43 ].…”

Pharmacogenomic Characterization and Isobologram Analysis of the Combination of Ascorbic Acid and Curcumin—Two Main Metabolites of Curcuma longa—in Cancer Cells

“…Furthermore, its knockdown decreased cyclin D1 (Faria et al, 2013 ). The TATA-binding protein associated factor 9 (TAF9) interacts with oncogenic GLI family members to form GLI-TAF9 binding, which is important for carcinogenesis activity and malignant growth (Yoon et al, 2015 ). PNN is a nuclear and cell adhesion-related protein participating in the regulation of gene expression and thereby, positively promoting cell-cell adhesion, and negatively affecting cell migration and cell proliferation (Shi et al, 2001 ).…”