Acute lymphoblastic leukemia is a disease of malignant hematopoietic stem cells in the bone marrow. It is a malignant proliferation of lymphoid cells blocked at an early stage of differentiation. Clinical manifestation of ALL arises with signs and symptoms reflective of bone marrow failure. Without treatment, most patients with ALL would survive only a few months. ALL is the most common type of cancer in children. The peak incidence of ALL occurs between age 2 and 5 years (Inaba, et al.,2013). In Thailand, the age-standardized incidence rates (ASR) of ALL is 5.2 per 100,000 in males and 4.0 per 100,000 in females. The ASR of ALL is the sixth in males and the tenth in females (Imsamran, et al.,2015). The improvement of ALL therapy is one of the great successes with long-term survival achieved in over 80% of patients (Pui , and Evans, 2006; Vrooman, and Silverman, 2009). However, the remaining cases cannot be cured and has poor prognosis. ALL is a heterogenous leukemia based on the type and stage of lymphoblast. The molecular biology of ALL is not completely understood. Genome-wide association studies show that genetic polymorphisms of some susceptibility genes are associated with the development of childhood ALL. (Treviño, et al., 2009)
Recently, it has been shown that small non coding miRNAs are important components of complex gene regulatory. MiRNAs, small non coding RNAs about 17- 22 nucleotide in length with single strand structure, regulate gene expression by translational repression or mRNA degradation (Bartel, 2004). MiRNAs play roles in development and cellular processes such as cell proliferation, differentiation, apoptosis and tumorigenesis (Hwang, and Mendell, 2006; Wang, et al.,2012). MiRNAs can be classified as oncogenes and tumor suppressor genes. It has been reported that the
expression levels of oncogenic miRNAs are increased in cancer patients, whereas tumor suppressor miRNAs are decreased. (Garcon, et al, 2010)
The most common variation in gene is single nucleotide polymorphism (SNPs). It is occurred when nucleotide change at least 1% of normal population. SNPs can affect the human such as susceptibility to cancer, estimates of prognosis and response to treatment. Recently, the most common pre-miRNA SNPs, that have been studied, includes SNPs of miRNA146, miRNA196, miRNA149 and miRNA499. In this study will be focused at miRNA146a. The function of miRNA146a is the controlling of innate and adaptive immune response including normal and malignant hematopoiesis.
MiRNA146a is a NF-kappaB dependent gene. MiRNA146a was predicted to base-pair with sequences in the 3’ UTR of the TNF receptor-associated factor 6 (TRAF6) and IL-1 receptor associated kinase 1 (IRAK1) genes. (Labbaye, and Testa, 2012)
Jazdaewski, et al.,2008, firstly reported that the miRNA146a (rs2910164) G>C was associated with increased susceptibility to thyroid papillary carcinoma. They found that C allele of mature miRNA146a would cause decrease inhibition target genes including TRAF6, IRAK1 (Jazdaewski, et al.,2008). Moreover, miRNA146a acts as a mediator of the pro-apoptotic transcription factor nuclear-kappaB(NF-kB) (Tagnov, et al.,2006).
MiRNA146a (rs2910164) G>C polymorphism was associated with increased risk of cancer including breast cancer (Qi, et al, 2015), hepatocellular carcinoma (Wang, et al., 2014). On the contrary, it was reported that the rs2910164 CG or GG genotype was associated with a significantly decreased risk for lung cancer compared to that of the CC genotype (Jeon, 2014). Moreover, it was found that MiR146a rs2910164 GG genotype was significantly gastric cancer susceptibility. (Xu, et al., 2014). The conflict of these findings may depend on sample size, ethnic groups and the type of cancer.
Min et al., evaluate the role of four miRNA polymorphisms in patients with colorectal cancer include miRNA 146a, miRNA 149, miRNA 196a and miRNA
499 polymorphisms. They found a significantly increased colorectal cancer risk with the miR-196a CC genotype compared with the TT/CT genotype. In miRNA 146a, miRNA 149 and miRNA 499 polymorphism show no significantly association with colorectal cancer. (Min, et al.,2011)
Yin-Hung Chu et al., study the impacts of miRNA gene polymorphisms on the susceptibility of environmental factors leading to carcinogenesis in oral cancer. They found that miRNA499 CC genotype exhibited significantly associated with risks of oral cancer and miRNA146 polymorphism no significantly associated with oral cancer susceptibility. (Hung, et al.,2012)
Recently, Hasani et al., evaluated the possible relationship between two miRNA polymorphisms, included hsa-miRNA146a and hsa-miRNA499 with the risk of childhood ALL in Iranian population. They found that the G>C variant of hsa- miRNA146a significantly increased the risk of ALL. With respect to hsa-miRNA499, no significant difference in allele and genotype frequencies between ALL patients and controls was reported (Hasani, et al.,2014). In Thailand, there is no report of miRNA146a polymorphism and acute lymphoblastic leukemia.
In this study, miRNA146a G>C polymorphism was not significantly associated with susceptibility to childhood ALL. The different results from the previous study of miR146a G>C polymorphisms in ALL, may be due to different ethnic groups. In control subjects, the allele frequency of miR146a G allele was 0.395 and miR146a C allele was 0.605. The data of these gene frequencies were similar to SNP database in Asian population but different from European groups. It was noted that the frequency of C allele is high in control group. Moreover, allele frequency in miR146a G allele and miR146a C allele in ALL was very similar to control group.
There were no statistically significant differences between miRNA146a (rs2910164) G>C polymorphism in terms of gender, age at diagnosis, initial WBC count, risk classification and immunophenotype. This may be due to the small sample size. However, it is interesting that polymorphism of miR146a (GC/CC) was found in
26 of 27 cases (96.3%) in more than 10 years old ALL patients, and miR146a (GC/CC) was found in 11 of 12 cases (91.67%) of high risk ALL. These two data is in accordance because the age of more than 10 years old is the criteria of high risk ALL.
The age of patients was significantly correlated with prognosis. Thus, under 1-year-old infants and patients older than nine presented poorer prognoses. Over nine year old children and adolescents have higher relapse rates and shorter survival than children aged one to nine years (Lustosa de Sousa, et al., 2015). It is indicated that miRNA146a (rs2910164) G>C polymorphism can be used as a prognostic biomarker for childhood ALL.
Moreover, miRNA146a (rs2910164) G>C polymorphism was found in all of 10 cases (100%) in T cell ALL patients. There was some evidence about the role of miR-146a and T cell response. Expression of miR146a is increased from naïve T cell up to memory T cell. MiR146a is involved in differentiation of various T cell types by modulating some specific genes effective in T cell differentiation (Yang, et al., 2012).
Saki et al., 2014 used Jakrat T cells as a model for in vitro study of T-ALL to investigate the role of miR146a on gene expression involved in T cell differentiation.
They established the ectopic expression of miR146a by transfection of a lentivector that expressed GFP hsa-mir-146a to Jakrat cell which is undifferentiated T lymphoblasts cell line. It was found that miR146a upregulate RUNX1 and down regulate NOTCH 1. RUNX1 is the tumor suppressor gene in T-ALL, thus this finding may indicate that MiR146a is tumor suppressor gene. (Saki, et al., 2014)
In this study all cases of T-cell ALL has a genotype of miR146a G>C. It is possible that the mature miR146a cannot produce because of the polymorphic form of miR146a. Therefore, RUNX1 cannot be upregulated by miR146a in all cases of T cell ALL which is a genotype of miR146a G>C. This pathogenesis of T cell ALL is in accordance that RUNX1 mutation can be found in T-cell ALL. (Grossmann, et al., 2011)
NOTCH1 is another target gene of miR146a. As shown that in this study, mature miR146a cannot occurred because all cases of T cell ALL have genotype of miR146a G>C. Therefore, NOTCH1 cannot be down regulated in T cell ALL.
Accordingly, it was found that NOTCH1 mutation can be found in most cases of T cell ALL. (Ma, et al.,2012)
As already known that T cell ALL is a poor prognostic ALL. Therefore, it should be confirmed that miR146a G>C, which is found in all cases of T cell ALL, can be used as prognostic biomarker for ALL.
However, this study was not found the significant association between miR146a G>C and T cell ALL, because the low incidence of T cell ALL contributed to small sample size. This study is only the preliminary report of clinical outcome.
The larger sample size should be done in the future for the clinical outcome study.
In conclusion, miRNA146a polymorphism was not significantly associated with susceptibility in Thai childhood ALL and was not significantly associated with clinico-pathological variables.
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