Background
Acute myeloid leukemia (AML) is a heterogeneous disease in terms of genetic basis, clinical, biological and prognostic, and is a malignant clonal disease of leukemia stem cells (LSCs). According to the prognosis, AML patients can be classified based on favorable-risk, intermediate-risk and adverse-risk [
1,
2]. AML can achieve 60% to 70% complete response (CR) post-chemotherapy regimens with supportive care, and with long-term survival reaches 25% to 35% [
3]. After active treatment in young AML patients, the 5-year survival rate is between 40 and 50%, and there are still treatment challenges in elderly AML patients [
3]. However, recurrence is a major obstacle to cure after AML patients achieve CR [
4]. The high recurrence rate of AML is considered to be the persistence of LSC [
5]. Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the best treatment for many AML patients [
6,
7]. Especially for high-risk AML patients, allo-HSCT can achieve the first complete remission (CR1) and become an effective treatment [
8]. As for intermediate-risk acute myeloid leukemia (IR-AML), allo-HSCT is an independent favorable factor for EFS and OS [
9].
Nearly half of adult AML patients exhibit a cytogenetic normal acute myeloid leukemia (CN-AML) [
10]. CN-AML was classified as IR-AML. Next-generation sequencing detected mutations in CN-AML for 19 AML-related genes, and each patient detected at least one mutation: DNMT3A, IDH2, IDH1, NRAS, NPM1, TET2, ASXL1, PTPN11, and RUNX1 [
11]. The prognosis can be further stratified according to different gene mutation combinations in CN-AML patients. For example, mutations in NPM1 and CEBPA are associated with a good prognosis in CN-AML [
12,
13], whereas DNMT3, TET2, and RUNX1 mutations are associated with poor prognosis in CN-AML [
14‐
16]. Besides, high expression of genes including ITPR2, MAPKBP1, CPNE3, RUNX1 and ATP1B1 are associated with poor prognosis of CN-AML, while high expression of LEF1 is considered as a favorable prognostic factor for CN-AML [
17‐
22]. Therefore, the identification of new biomarkers can help to predict the prognosis risk of CN-AML.
NCALD (Neurocalcin Delta) is a member of the Neuronal Calcium Sensor family of calcium binding proteins. The expression of NCALD gene is more abundant in the brain, testis, ovary and small intestine [
23]. Experiments have shown that NCALD is a potential hippocampal memory-related factor related to obesity [
24]. NCALD expression is down-regulated in lung cancer tissues, while low NCALD expression levels are associated with poor prognosis in non-small cell lung cancer (NSCLC) patients [
25]. NCALD gene expression was significantly different in survival analysis, indicating that low expression of NCALD gene predicts poor prognosis in patients with ovarian cancer [
26]. However, the expression level of NCALD gene in CN-AML patients has never been reported. Thus, we analyzed the relationship between the expression of NCALD and the prognosis of CN-AML.
Discussion
The NCALD gene is a regulator of G-protein coupled receptor signaling, and there are several alternatively spliced gene variants that all encode the same protein. So far, little has been reported known about the relationship between NCALD and cancer, and the prognostic relationship between this gene and CN-AML has not been reported. We analyzed the gene expression of NCALD from AML patients in 5 independent datasets. Our study reports that the expression of NCALD is associated with the prognosis of CN-AML and is an independent risk factor of CN-AML.
Previous studies have reported that low expression of the NCALD gene is associated with the prognosis of some kinds of cancer. NCALD expression is down-regulated in the poor prognosis group of advanced ovarian cancer which suggests that NCALD is a prognostic biomarker for these ovarian cancer patients [
32]. Low NCALD expression levels predict poor prognosis in patients with non-small cell lung cancer (NSCLC) [
25]. However, in our survival analysis study, we found that the high expression of NCALD of CN-AML patients has a lower prognosis than patients with low NCALD expression. These results suggest that NCALD can predict different prognosis in different cancers and may play a different role in each type of human cancers.
Predicting the prognosis of AML after allo-HSCT treatment is particularly clinically important. Recent studies have shown that high expression of GAS6-mRNA is associated with poor prognosis of allo-HSCT in AML patients [
33]. Previous studies of TMEM18, TP53, IDH and DNMT3A are potential biomarkers for AML [
34‐
36]. However, there are still challenges to the prediction of the prognosis of AML, especially the prediction of the prognosis of AML after allo-HSCT. Our results suggest that high NCALD expression in AML patients after allo-HSCT can still predict poor prognosis. High NCALD expression also predicts poor prognosis in AML patients after chemotherapy. Therefore, NCALD may be a biomarker for predicting the prognosis of AML with or without allo-HSCT.
In univariate and multivariate analyses, we found that the DNMT3A mutations are associated with EFS and OS in CN-AML, and that the FLT3 mutations are associated with EFS in CN-AML. This is consistent with previous findings that DNMT3A mutations are associated with shorter EFS and OS [
37‐
39]. Multivariate analysis showed that high expression of NCALD in CN-AML patients was confirmed to be associated with worse EFS and OS. Furthermore, in the ROC curve survival analysis, we found that the relation between NCALD gene expression levels and the prognosis of CN-AML patients was superior to other variables. These results suggest that NCALD should be an independent predictor of prognosis in patients with CN-AML.
The LSC immunophenotypic analysis of all subtypes of AML is CD34+ CD38− [
40,
41]. Most of CD34+ and a few of CD34- fractions contain LSC, and LSC was detected in all CD34/CD38 phenotype fractions [
31,
42]. AML is initiated by a small fraction of LSCs that maintain extensive proliferation and unrestricted self-renewal of leukemia mother cells, leading to chemoresistance and relapse [
43,
44]. High expression of LSC gene is independently associated with poor prognosis in patients with AML [
45]. In our study, more LSC+ was present in AML patients with high NCALD gene expression, suggesting that the NCALD gene is enriched in stem cell expression. This result suggests that the NCALD gene may affect LSC.
However, we did not further study the specific function of NCALD in the AML pathogenic signaling pathway. This study only explored the expression of individual genes, and future studies combining different types of potential biomarkers can be conducted to further predict the prognosis of patients with AML.
Acknowledgements
The data is derived from an open datasets and are available in the TCGA dataset and GEO dataset (GSE12417, GSE22778, GSE71014, GSE76004).
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