Lncrna Famlf-2 Inhibits Acute Lymphoblastic Leukemia Apoptosis through the p38 MAPK Signaling Pathway

Background:Acute lymphocytic leukemia (ALL) is a hematologic malignancy caused by the clonal proliferation of immature lymphocytes. Long noncoding RNAs (lncRNAs) are involved in the pathogenesis and progression of ALL. Our previous study identified Familial acute myelogenous leukemia related factor (FAMLF) from a AML pedigree. There are at least three splice variants from FAMLF, referred as FAMLF-1, FAMLF-2 and FAMLF-3. We have shown higher expression of FAMLF-1 was related to a higher complete remission (CR) rate, and shorter relapse free survival (RFS) in AML. Another FAMLF variants, FAMLF-2 is highly expressed in ALL, and the potential mechanism of FAMLF-2 in regulating ALL progression is unclear. This study aims to investigate the functional and mechanistic roles of FAMLF-2 in ALL.

Methods:The expression of FAMLF-2 was detected by real-time PCR (Q-PCR) in peripheral blood of ALL patients (N=85) and healthy controls (N=60). The full length of FAMLF-2 was obtained by 5' and 3' rapid amplification of the cDNA ends (RACE). FAMLF-2 subcellular location in Jurkat cells was detected by lncRNA FISH, nuclear/cytoplasmic RNA fractionation, and qPCR. The proliferation and apoptosis of Jurkat cell were determined by CCK-8 and flow cytometry experiments in vitro. RNA-seq was performed to study the molecular mechanism of FAMLF-2 in regulating ALL cell apoptosis.

Results:The FAMLF-2 mRNA expression and in ALL patients was significantly higher than those in the normal individuals (P=0.000). The expression of FAMLF-2 was positively correlated with percentage of peripheral blood blasts (P=0.032). The ALL patients with higher FAMLF-2 expression had significantly poor overall survival (P=0.036). We defined a 2393-bp full-length transcript of FAMLF-2, and examined the subcellular localization of FAMLF-2, which showed that FAMLF-2 predominately resides in the nucleus of Jurkat cells. The cell proliferation was inhibited, and cell apoptosis was induced when FAMLF-2 were down-regulated in Jurkat and Nalm6 cells, whereas the overexpression of FAMLF-2 showed the opposite results. We analyzed the RNA-seq data of the knockdown and overexpression of FAMLF-2 in Jurkat cells, and the GSEA analysis suggested that FAMLF-2 knockdown was associated with "MYC TARGETS V1", "MYC TARGETS V2" pathways. The knockdown of FAMLF-2 in Jurkat cells upregulated the expression of p-P38 and downregulated the expression of c-Myc, bcl-2.

Conclusion: Taken together, our study indicate that FAMLF-2 inhibits the apoptosis of ALL through the p38 MAPK signaling pathways, which might act as a prospective prognostic biological marker for ALL.

Keywords: Acute lymphocytic leukemia, Long noncoding RNAs, FAMLF-2, apoptosis, p38 MAPK

No relevant conflicts of interest to declare.