FANCL ubiquitinates β-catenin and enhances its nuclear function

Abstract

Bone marrow failure is a nearly universal complication of Fanconi anemia. The proteins encoded by FANC genes are involved in DNA damage responses through the formation of a multisubunit nuclear complex that facilitates the E3 ubiquitin ligase activity of FANCL. However, it is not known whether loss of E3 ubiquitin ligase activity accounts for the hematopoietic stem cell defects characteristic of Fanconi anemia. Here we provide evidence that FANCL increases the activity and expression of ␤-catenin, a key pluripotency factor in hematopoietic stem cells. We show that FANCL ubiquitinates ␤-catenin with atypical ubiquitin chain extension known to have nonproteolytic functions. Specifically, ␤-catenin modified with lysine-11 ubiquitin chain extension efficiently activates a lymphocyte enhancer-binding factor-T cell factor reporter. We also show that FANCL-deficient cells display diminished capacity to activate ␤-catenin leading to reduced tran- IntroductionFanconi anemia (FA) is the most common inherited bone marrow failure syndrome. The majority of patients develop bone marrow failure within the first decade of life. Patients are also at high risk for the development of acute myeloid leukemia and solid tumors of the head and neck and gastrointestinal tract. The disease is caused by loss-of-function of any 1 of 15 FANC genes. [1][2][3][4][5][6] The nuclear core complex includes FANCA, B, C, E, F, G, L, and M. 1 FANCL is a ring type E3 ubiquitin ligase that monoubiquitinates FANCD2 and FANCI, which enhances their function at sites of DNA damage. [7][8][9][10] The core complex scaffold is essential for facilitating the activity of FANCL because loss of any one of the core proteins results in loss of FANCL E3 ubiquitin ligase function. 1 Although FANC proteins are known to execute a normal DNA damage response to crosslinking agents, emerging evidence points to alternative functions for these proteins in hematopoietic stem cells (HSCs), and the loss of these alternative functions may represent a driving force behind the common FA complications of myelodysplasia and acute myeloid leukemia. [11][12][13][14][15][16] Functional defects in FA HSCs exist, including decreased repopulating ability, reduced numbers of HSCs, defective homing capacity, tumor necrosis factor (TNF)-␣ hypersensitivity, and limited replicative and survival potential compared with normal HSCs. [17][18][19][20][21][22][23][24][25][26] Collectively these studies support the argument that the FA pathway has a role in maintaining the HSC pool and regulating stem cell fitness. 15 However, the molecular mechanisms underlying such HSC defects have not been well characterized.In light of the well established role of TNF-␣ in the pathogenesis of marrow failure and leukemia in Fancc-deficient mice, [24][25][26] we first sought mechanistic insights by comparing the transcriptomal response to TNF-␣ of Fancc-deficient Kit ϩ /Sca1 ϩ /Lin Ϫ (KSL) marrow cells to the transcriptomal response of wild-type (WT) KSL cells. Ontological analysis of gene expression changes in...

Fanconi anemia proteins interact with CtBP1 and modulate the expression of the Wnt antagonist Dickkopf-1

“…Because CtBP1 and FA proteins interact and seem to be implicated in the regulation of the Wnt signal molecule DKK1, and because DKK1 is implicated in biological processes linked to FA pathogenesis, we argue that CtBP1 and FA proteins (or pathway) might share a common function. Recent work by Dao et al 52 showing that FANCL ubiquitinates the Wnt transcription factor b-catenin supports our finding of interplay between the FA and Wnt pathways. We argue that an altered FA/CtBP1/DKK1 pathway would lead to the reduced capacity for self-renewal exhibited by FA mutant HSCs, which facilitates the progressive loss of bone marrow cells and subsequent bone marrow failure.…”

The Fanconi anemia pathway has a dual function in Dickkopf-1 transcriptional repression

“…Taken together, those studies and our results imply that FA core complex activity may modulate β-catenin function. Indeed, this is supported by a study by Dao et al (23), which showed that β-catenin activity is facilitated by FA core complex ubiquitin ligase activity. Our findings support a role of the FA pathway in β-catenin nuclear accumulation and subsequent activity.…”

“…1 target genes, along with a previous study showing immunoprecipitation (IP) of β-catenin with FANCC (7,23), we sought to determine whether FANCC with CtBP1 forms a complex with β-catenin. We performed IP experiments in human HEK293T cells expressing FANCC with β-catenin and other components of the FA core complex.…”

The fate of granulosa cells following premature oocyte loss and the development of ovarian cancers

“…The fifteen known FA proteins are clearly involved in DNA repair but there is increasing evidence that at least some of them have additional functions, including the support of stem cell pluripotency (Dao et al, 2012). FANCD2 is clearly an important component of repair complex formation.…”