Chronic lymphocytic leukemia (CLL), a common blood cancer in western world, is characterized by proliferation and accumulation of neoplastic CD^5high B-cells in bone marrow, peripheral blood, and secondary lymphoid organs [1]. It mainly affects the elderly, and the mean age at diagnosis is about 70 years. CLL is more common in male subjects. About 25–30% of all new leukemia cases can be attributed to CLL in the western population. However, CLL is rare in Asia and accounts for only about 5% of all leukemia cases [2]. Several factors have been reported to increase the risk of CLL including occupational exposure to specific substances (ethylene oxide, benzene, 1,3-butadiene, and pesticides), ethnicity, positive family history of lymphoproliferative disorders, and genetic predisposition [3]. CLL has a heterogeneous nature and involves numerous genetic and epigenetic alterations. Some patients need interventions due to progressive disease course, whereas subjects with indolent course require no therapy for years [4].

Studies have revealed that only 2% of the human genome sequences are protein-coding genes, whereas the majority of transcriptome does not encode proteins. Non-coding RNAs (ncRNAs) are divided into regulatory and housekeeping classes. Regulatory ncRNAs are subcategorized, depending on the nucleotide length, into long (>200 nt) and short (<200 nt) ncRNAs. Long ncRNAs (lncRNAs) play important roles in multiple biological processes such as DNA repair, regulation of gene expression, transcription, and translation [5]. Some lncRNAs, including MEG3, BANCR, and PANDAR, serve as tumor suppressor and inhibit tumor cell growth. Oncogenic lncRNAs, such as ALAT1 and HOTAIR, are upregulated in a variety of malignancies and lead to tumorigenesis, metastasis, and progression of cancers [6]. MALAT1 (metastasis-associated lung adenocarcinoma transcription 1), also named NEAT2 (nuclear enriched abundant transcripts), is an 8.7 kb oncogenic lncRNA located on chromosome 11. It has a key role in alternative splicing and gene expression regulation. In vitro studies have shown that deregulation of TP53 by oncoviruses leads to increased expression of MALAT1 and upregulation of TP53 is associated with MALAT1 depletion [7]. A recent study demonstrated that KG1 myeloid cell line have a higher expression level of MALAT1 than normal bone marrow cells [8]. In multiple myeloma patients, progression-free survival was associated with decreased expression of MALAT1 [9].

Although the precise molecular mechanisms by which MALAT1 may contribute to CLL pathogenesis have not been fully elucidated yet, several observations support the involvement of this lncRNA in CLL. These include its role in cell cycle regulation and p53-mediated response to DNA damage, as well as in mRNA processing. The emerging role of MALAT1 in hematologic malignancies prompted us to quantify its expression in patients with CLL to establish whether its deregulation may be associated with disease progression.

Demographic and clinical information on study participants is listed in Table 1. White blood cells and lymphocyte count were higher in CLL patients. Platelet count and hemoglobin levels were significantly higher in healthy controls. There were no gender-related differences in the groups. According to FISH findings, 20% of patients showed a normal chromosomal pattern. Del13q14 was the most common cytogenetic abnormality as it was found in 53.3% of patients, followed by del 11q22 (16.6%), del 17p13.1 (10%), trisomy 12 (10%), and c-MYC amplification (3.3%).

Malignancies are a global health issue and are the 3rd cause of mortality in Iran. In this context, the increase in the recorded incidence of blood cancers in Iran can be attributed to several causes including improvement in cancer diagnosis setting and registry and increase in cancer-related risk factors or unknown etiologies [10].

With the advancement of biotechnological tools, studies have devoted much attention to genetic alterations as an inseparable part of cancer. In this respect, non-protein-coding transcripts such as lncRNAs play a critical role in regulating cellular functions and may be related to both tumor suppressive and oncogenic characteristics. According to recent evidences, lncRNAs are involved in many principal cellular mechanisms such as transcriptional and post-transcriptional regulation, chromatin rearrangement, and nuclear-cytoplasm trafficking [11]. Deregulation of lncRNA expression has been reported in a variety of human diseases, from neurologic disorders (multiple sclerosis and Alzheimer's disease) to several solid (breast, lung, bladder) and hematologic cancers (lymphoma and leukemia) [12,13].

Initially described as a metastasis biomarker of lung cancer, MALAT1 lncRNA is a pivotal player in the molecular events behind neoplastic transformations In this regard, we examined MALAT1 expression in PBMCs of pre-treatment CLL patients compared to healthy controls, by real-time PCR. Cytogenetic analysis was also performed in patients to determine any possible association between MALAT1. Significantly higher expression of MALAT1 was found in patients, compared to controls. However, MALAT1 expression was not related to the prognostic classification based on cytogenetic alterations in patients. Significantly higher expression of MALAT1 was found in patients, compared to controls. However, MALAT1 expression was not related to the prognostic classification based on cytogenetic alterations in patients. Several genetic and epigenetic events take part in CLL such as chromosomal abnormalities, deregulation of microRNAs, immunoglobulin VH mutations and, more recently, changes in lncRNA expression profiles [14,15,16,17]. Given that in-vitro studies have paid limited attention to the expression and functional characteristics of MALAT1 in CLL cell lines, some explanations are provided with impressions of studies. It was shown that MALAT1 knock-down in multiple myeloma (MM) cell lines results in caspase-dependent cell death. This finding is relevant in view of the fact that proteasome inhibitors are useful therapeutic agents for both MM and CLL [18,19,20]. Dysfunction of TP53 and retinoblastoma (Rb) tumor suppressors, which are associated with a wide range of cancers including CLL [21,22] could be mediated by MALAT1, as depletion of this lncRNA leads to activation of TP53 and its target genes [22].

Previously, the overexpression of MALAT1 observed in patients with the M5 subtype of AML was found associated with lower overall survival. Furthermore, MALAT1 knock-down by Lentiviral vectors was shown to increase apoptosis and inhibit proliferation of leukemic cells [23]. In mononuclear bone marrow cells of multiple myeloma (MM) patients, MALAT1 was overexpressed, whereas a decrease in MALAT1 resulted in improved progression-free survival [9]. Isin et al. [24] performed a study to determine cell-free lncRNA profile in MM and CLL patients. MALAT1 was downregulated in MM patients, whereas no significant differences were observed between CLL patients and healthy controls which is discordant with our findings. Similar in-vitro and in-vivo investigations have been carried out focusing on MALAT1 expression in different types of lymphoma, including lymphomas of mantle cell [25], diffuse large B-cell [26], and T and NK cell lymphomas [27]. All these studies reported that MALAT1 upregulation was associated with poor prognosis.

There are several factors related to CLL prognosis including VH mutation status, zeta-associated protein (ZAP-70) and CD38 expression, and chromosomal aberrations [14,28]. We determined chromosomal abnormalities in patients using the FISH method and 80% of them presented cytogenetic abnormalities. On the contrary, findings from the northeast of Iran (Mashhad) revealed a lower frequency of chromosomal abnormalities in CLL patients (45.5%); however, in line with our data, del13q14 was the most frequent alteration. In Korean patients, a lower overall frequency of abnormalities was observed, compared to western populations and the present report, and also a different frequency distribution, as trisomy 12 represented the most common chromosomal alteration found [29]. Despite the high incidence of chromosomal anomalies in this study, no significant relationships were found between the level of MALAT1 expression and the prognostic classification based on cytogenetic results. Failure to determine other prognostic factors and a relatively small sample size may be responsible for this result. As it is also possible that MALAT1 acts as an independent prognostic factor, additional studies should be designed to investigate its impact on patient survival. As it is also possible that MALAT1 acts as an independent prognostic factor, additional studies should be designed to investigate its impact on patient survival.

In conclusion, a high expression of oncogenic MALAT1 lncRNA in CLL patients may reflect its involvement in tumorigenic processes. Further studies are required to establish the suitability of MALAT1 determination for diagnostic and therapeutic applications in CLL.

Relative expression of MALAT1 (2^−Δct) in CLL and control group using β2m as internal control gene. Increased expression of MALAT1 was observed in CLL patients (P=0.008).