Introduction
Long non-coding RNAs (lncRNAs) are non-protein coding RNAs that are longer than 200 nucleotides. Comparing to other classes of ncRNAs, lncRNAs exhibit a wide range of structures and functions [
1]. Recently, lncRNAs have emerged as important regulators for gene expression via remodeling nuclear architecture, modulating mRNA stability and translation, and post-translational modifications [
1‐
4]. Besides, some lncRNAs are dysregulated and harbor prognostic relevance in several types of cancers [
5‐
8]. However, the roles of lncRNAs in tumorigenesis are still largely unknown.
In recent years, research on lncRNAs has increased drastically, and the results are robust. Although the functions of lncRNAs have not been elusive, recent studies suggested the expressions of lncRNAs could be used as prognostic factors, predictors of response, and potential therapeutic targets in acute leukemia [
9‐
18]. Moreover, several gene expression-based prognostic scores have been developed for better risk stratification of acute myeloid leukemia (AML) patients [
19‐
24]. Among those high-risk genes, lncRNA gene
KIAA0125 (also named as
FAM30A), a hematopoietic stem cell gene localized on chromosome 14, is unique because it is the only non-coding gene and is expressed in humans but not in mice (From the UniProt database,
https://www.uniprot.org/uniprot/Q9NZY2). Additionally,
KIAA0125 expression was integrated into a recently proposed 17-gene stemness score, which could predict outcomes in AML patients [
19].
This study aimed to investigate the association of KIAA0125 expression with clinical and biological characteristics in AML patients. We first profiled the expression levels of KIAA0125 in bone marrow (BM) cells from AML patients and normal controls and demonstrated that AML patients had higher KIAA0125 expression than normal controls. Higher expression of KIAA0125 was associated with distinct clinical and biological characteristics and served as an independent poor prognostic biomarker for AML patients in ours and two other publicly annotated cohorts. Further bioinformatics analyses showed that higher expression of KIAA0125 in AML was closely associated with hematopoietic stem cell (HSC) and leukemic stem cell (LSC) signatures and several important ATP-binding cassette transporters (ABC transporters); these factors are regarded responsible for chemoresistance in AML. Further functional studies are needed to unravel its underlying mechanism and pathogenetic role in AML.
Discussion
AML cells have abnormal genetic background, either mutations or aberrant expression of specific genes. In recent years, several gene expression scores have been proposed for prognostic prediction of AML patients. We previously developed a 11-gene mRNA expression signature, including
AIF1L,
CXCR7,
DNTT,
GPR56,
H1F0,
IFITM3,
KIAA0125,
MX1,
STAB1,
TM4SF1, and
TNS3, for prognostication in AML patients [
21]. Another group built a six-gene leukemia stem cell (LSC) score with the incorporation of
DNMT3B,
GPR56,
CD34,
SOCS2,
SPINK2, and
KIAA0125 expressions for pediatric AML [
40]. Recently, Ng et al. proposed a 17-gene LSC score that incorporated expressions of 17 stemness-related genes, including
KIAA0125, and showed the scoring system was powerful to predict prognosis in AML patients [
19]. Among these prognostic-relevant genes,
KIAA0125 is the only non-coding gene and expressed only in the
Homo sapiens, but not in mice.
KIAA0125 is located on chromosome 14 of the human genome. It was reported to be upregulated in ameloblastoma but shown as a tumor suppressor gene in colorectal cancer [
59,
60]. Nonetheless, the clinical relevancy and biological role of
KIAA0125 in tumorigenesis were still largely unclear.
In this study, we found that the expression level of
KIAA0125 in BM was significantly higher in AML patients than normal HSC transplant donors. The expression of
KIAA0125 was lower in patients with t(8;21) and t(15;17) which are associated with more differentiated AML subtypes, but higher in patients with
RUNX1,
ASXL1 mutations,
NPM1-/
FLT3-ITD+ or poor-risk karyotypes. It is interesting that the expression of
KIAA0125 was high in patients with
RUNX1 mutation but modest in those with
RUNX1/
RUNX1T1 fusion consisting with the fact that AML patients with a
RUNX1 mutation usually had poor outcomes while those with
RUNX1/
RUNX1T1 fusion had favorable prognosis. Recently, Hornung et al. identified that expression of
CD109,
HOPX, and
KIAA0125 genes might be responsible for inferior survival in AML patients with
RUNX1 mutations but, on the other hand, better outcome in
RUNX1/RUNX1T1 fusion through a newly proposed statistical tool “mediation analysis.” The three genes’ expression levels were significantly higher in patients with
RUNX1 mutant but lower in those with
RUNX1/
RUNX1T1 fusion [
61]. Intriguingly, though there has been no study showing direct evidence that
RUNX1 binds to
KIAA0125 till now in the literature,
RUNX1 has been reported to bind to TGTGG core sequences as a heterodimer of
RUNX1 and CBFβ [
62]. We downloaded and retrieved the DNA sequence of
KIAA0125 from the UCSC Genome Browser (
https://genome.ucsc.edu/) and found several sequences of TGTGG (Supplement Table
8) within the 3000 bp upstream sequence, which might be the potential binding sites of
RUNX1. Further studies are needed to explore the effect of the possible interaction between RUNX1 domain and
KIAA0125.
Bioinformatics of the present study showed highly significant association of
KIAA0125 expression with stem cell signatures, either HSC or LSC. We found that expressions of
SPINK2,
MAP7,
HOPX,
MMRN1,
DNMT3B,
TCF4,
SLC38A1,
DOCK1,
ARHGAP22,
MN1, and 4 genes in the ATP-binding cassette (ABC) superfamily (
ABCG1,
ABCA2,
ABCB1, and
ABCC1), which have been reported to be associated with poor prognosis or chemoresistance in AML, were positively correlated to higher expression of
KIAA0125 (Fig.
3b and Table
3).
HOPX,
DOCK1,
DNMT3B,
MMRN1, and
ARHGAP22 genes were reported as important leukemia stem cell markers [
19,
42,
43,
45,
50,
63]. Higher
SPINK2 expression was associated with poor prognosis in adult and pediatric AML [
39,
40].
TCF4 expression could predict outcome in
RUNX1-mutated and translocated AML [
47,
48].
MN1 overexpression could induce AML in mice and predict ATRA resistance in human AML patients [
51,
52]. Current knowledge about the association between theses
KIAA0125-correlated genes and AML is summarized in Table
3.
Interestingly, the expression levels of several ABC transporter genes, including
ABCA2,
ABCB1,
ABCC1, and
ABCG1, were also significantly higher in AML patients with higher
KIAA0125 expression. The ABC transporter family consists of 48 proteins in subfamilies designated A to G and some of them are known to be associated with multidrug resistance via ATP-dependent drug efflux [
53,
54,
57].
ABCB1,
ABCC1, and
ABCG1 were reported to be responsible for chemoresistance in AML [
53,
56]. The translational expression of
ABCA2 was shown to be a prognostic marker for drug resistance in pediatric acute lymphoblastic leukemia [
55,
58]. The underlying mechanistic basis of the high correlation of these 4 genes to the expression of
KIAA0125 warrants further studies.
This study’s limitations lie in its retrospective nature and, crucially, the unsorted BM sample, as many cells in BM may be differentiated cells of myeloid and erythroid lineages. The study could have been more informative if we could profile
KIAA0125 expression of healthy CD34 + CD38- HSCs and more mature progenitors (CD34 + CD38- and CD34-CD117+, respectively) and compare those with leukemia blasts. Moreover, the putative oncogenic role of
KIAA0125 could be more strengthened were the expressions of
KIAA0125 investigated in AML stem cells and bulk. Despite the limitations mentioned, to the best of our knowledge, this is by far the first study specifically addressing the expression of lncRNA
KIAA0125 and its clinical and biological associations in AML patients. We found that higher
KIAA0125 expression was closely associated with
RUNX1 and
DNMT3A1 mutations in both the NTUH and TCGA cohorts. Patients with higher
KIAA0125 expression were more refractory to chemotherapy with a lower CR rate and higher refractory rate (Table
1). They had shorter OS and DFS among the total cohort and subgroups of patients with non-APL and those with normal karyotype. Based on its crucial clinical significance, further experimental studies are necessary to delineate how
KIAA0125 participates in the stem cell biology of hematopoietic lineages and its role in the pathogenesis in AML.
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