The prognostic value of six SNPs located in either genes encoding proteins involved in the miRNA biogenesis or in miRNA-binding sites located in myeloma-related genes was evaluated in 137 patients with multiple myeloma who underwent autologous stem cell transplantation [
13]. Association with survival was observed for two SNPs: CC genotype of rs3660 in
KRT81 conferred longer overall survival (OS), while patients with CC/AC genotype of rs11077 in
XPO5 had significantly longer OS and progression-free survival (PFS) (Table
1). KRT81 belongs to a family of hair keratins which are involved in maintaining cell integrity and regulating cell motility and growth in epithelial cells, and have been described as prognostic markers in epithelial tumors [
14]. The C allele of rs3660 in
KRT81 reduced significantly the protein level in luciferase reporter assay in one of two myeloma cell lines (RPMI-8226). Also in healthy lymphocytes a significant reduction of KRT81 protein, but not mRNA, level was observed. Furthermore, a significant decrease of the proliferation rate of RPMI-8226 cells was observed upon silencing of the
KRT81 gene, which indicates the possible mechanism underlying the better prognosis in myeloma patients carrying the CC genotype of
KRT81 _rs3660. However, although the authors indicate that according to bioinformatics prediction the C allele destroys binding sites for several miRNAs, results of their experiments indicate otherwise – that in myeloma cell lines and healthy lymphocytes this SNP enhances binding of some miRNAs, which results in decreased protein levels. Since levels of specific miRNAs were not controlled in the luciferase assay, it is not clear whether the observed effect is a consequence of altered miRNA binding, and if so – of which specific miRNA. rs3660 in
KRT81 was also studied in Hodgkin lymphoma (HL) [
15]. Here, the GG genotype was found more frequently in patients (30.9%) than in the European population (18.3%, data from the HapMap project) but this should be validated in a control group ethnically matched with patients. Further analysis showed that although rs3660 had no influence on survival of HL patients, the GG genotype is an independent risk factor for treatment-related neurological toxicity. In non-Hodgkin lymphoma (NHL), in turn, distribution of rs3660 genotypes did not differ between patients and control group but carriers of CC and CG genotypes had significantly longer OS compared to the GG genotype [
16]. The studies in lymphomas did not attempt to verify whether rs3660 in
KRT81 affects miRNA binding and what are the functional consequences of the polymorphism.
Table 1
Polymorphisms in miRNA-binding sites in hematological malignancies
KRT81
| rs3660 | G > C | miR-17, miR-20a/b, miR-93, miR-106a/b, miR-519d | MM | 137 | | OS | p = 0.037 | Effect on protein expression confirmed in gene reporter assay and in vivo | |
| HL | 139 | | Treatment-related toxicity | 6.65 (1.33-33.26), p = 0.021 | Not examined | |
| NHL | 210 | | OS | p = 0.012 | Not examined | |
XPO5
| rs11077 | A > C | miR-4763-5p | MM | 137 | | OS | p = 0.012 | Effect on protein expression confirmed in gene reporter assay | |
PFS | p = 0.013 |
| HL | 127 | | Treatment-related toxicity | 0.49 (0.006-0.376), p = 0.004 | Not examined | |
DFS | p = 0.039 |
OS | p = 0.033 |
TP53
| 187 novel SNVs | | majority of SNVs located in miRNA-binding sites | DLBCL | 491 | | OS | p = 0.019 | Effect of three SNVs on miR-125b binding and protein expression confirmed in gene reporter assay | |
PFS | p = 0.018 |
in patients with mutated p53 CDS |
C14orf101
| rs4901706 | G > A | | NHL | 359 | | OS | p = 0.015 | Effect on protein expression confirmed in gene reporter assay | |
| NHL | 210 | 233 | Risk | NS | Not examined | |
OS | NS |
NPM1
| rs34351976 | T > - | miR-337-5p, miR-887 | AML | 93 | | OS | p = 0.016 | Effect on miR-337-5p binding and protein expression confirmed in gene reporter assay, effect on mRNA levels confirmed in vivo | |
RFS | p = 0.007 |
ETV6
| rs1576313 | T > C | miR-34c-5p, miR-449b-5p | Childhood ALL | 101 | 471 | Risk | 1.9 (1.16-3.11), p = 0.0107 | Effect on miR-34c-5p and miR-449b-5p binding and protein expression confirmed in gene reporter assay | |
TLX1
| rs2742038 | C > T | miR-492 | Childhood ALL | 101 | 471 | Risk | 3.97 (1.43-11.02), p = 0.0081 | No effect on miR-492 binding and protein expression observed in gene reporter assay | |
PML
| rs9479 | G > A | miR-510-5p, miR-589-3p | Childhood ALL | 101 | 471 | Risk | 0.55 (0.36-0.85), p = 0.0079 | Effect on miR-510-5p binding and protein expression confirmed in gene reporter assay; no effect observed for miR-589-3p | |
AML | 87 | 471 | Risk | 0.6 (0.38-0.97), p = 0.0372 |
ARHGAP26
| rs187729 | T > C | miR-18a-3p | CML | 140 | 471 | Risk | 1.63 (1.07-2.47), p = 0.0213 | Effect on miR-18a-3p binding and protein expression confirmed in gene reporter assay | |
IRF8
| rs10514611 | C > T | miR-330-3p | CML | 140 | 471 | Risk | 2.4 (1.12-5.15), p = 0.0246 | No effect on miR-330-3p binding and protein expression observed in gene reporter assay | |
The second polymorphism found to affect survival of patients with multiple myeloma was rs11077 in
XPO5. This miRSNP, apart from its potential impact on expression of XPO5, can also affect the whole miRNA-ome of the cell as
XPO5 encodes for exportin-5, which is required for the export of precursor miRNAs from nucleus to cytoplasm where they are subject to further steps of maturation [
17]. Bioinformatics analysis indicated that the C allele of
XPO5 _rs11077 creates a new binding site for miR-4763-5p. Indeed, luciferase reporter assay showed a significant reduction in protein levels in two myeloma cell lines. Also, in healthy lymphocytes the CC genotype was associated with slightly decreased XPO5 protein levels, but the difference did not reach statistical significance [
13]. However, it remains to be established whether miR-4763-5p or another miRNA is responsible for the observed effect. Also, the mechanism by which reduced XPO5 levels could contribute to a better prognosis in multiple myeloma needs to be elucidated. rs11077 in
XPO5 was also studied in Hodgkin lymphoma [
15]. Here, the AC genotype was associated with longer overall and disease-free survival (DFS), as well as with lower rate of bleomycin-associated pulmonary toxicity. Better performance of heterozygous patients seems somewhat unusual and probably a replication in a larger cohort of patients could indicate which allele is associated with a better prognosis. This study did not provide any further clues for the functional significance of
XPO5 _rs11077.