Abstract
We previously explored the role of BTK in maintaining multiple myeloma stem cells (MMSCs) self-renewal and drug-resistance. Here we investigated the elevation of BTK suppressing MM cellular senescence, a state of irreversible cellular growth arrest. We firstly discovered that an increased expression of BTK in MM samples compared to normal controls by immunohistochemistry (IHC), and significant chromosomal gain in primary samples. In addition, BTK high-expressing MM patients are associated with poor outcome in both Total Therapy 2 (TT2) and TT3 cohorts. Knockdown BTK expression by shRNA induced MM cellular senescence using β-galactosidase (SA-b-gal) staining, cell growth arrest by cell cycle staining and decreased clonogenicity while forcing BTK expression in MM cells abrogated these characteristics. We also validated this feature in mouse embryonic fibroblast cells (MEFs), which showed that elevated BTK expression was resistant to MEF senescence after serial cultivation in vitro. Further mechanism study revealed that BTK activated AKT signaling leading to down-regulation of P27 expression and hindered RB activity while AKT inhibitor, LY294002, overcame BTK-overexpression induced cellular senescence resistance. Eventually we demonstrated that BTK inhibitor, CGI-1746, induced MM cellular senescence, colony reduction and tumorigenecity inhibition in vivo. Summarily, we designate a novel mechanism of BTK in mediating MM growth, and BTK inhibitor is of great potential in vivo and in vitro suggesting BTK is a promising therapeutic target for MM.
Highlights
Multiple myeloma (MM), the second most common blood cancer, is characterized by heterogenetic plasma cells clonal proliferation in the bone marrow microenvironment, monoclonal protein secretion in the blood or urine, anemia, bone lesion, hypercalcemia and renal damage [1, 2]
To evaluate the role of Bruton’s tyrosine kinase (BTK) in MM, We examined the array-based comparative genomic hybridization data obtained from 67 MM patients and the analysis revealed that the BTK locus is frequently amplified in MM patients (Figure 1A) [31]
The distinction between high and low BTK was of prognostic significance, as eventfree survival (EFS) was reduced in MM patients bearing high BTK expression Total Therapy 2 (TT2) cohort (Figure 1C)
Summary
Multiple myeloma (MM), the second most common blood cancer, is characterized by heterogenetic plasma cells clonal proliferation in the bone marrow microenvironment, monoclonal protein secretion in the blood or urine, anemia, bone lesion, hypercalcemia and renal damage [1, 2]. In parallel with cellular apoptosis, cellular senescence which induces irreversible cell arrest through forcing the cells to quit the cell cycle suggests an alternative way to blunt MM growth and disable MM proliferation. Hayflick and Moorhead firstly described cellular senescence (1961), and they found that after serial cultivation in vitro normal human fibroblasts entered a state of irreversible growth arrest [10], which now is discovered to be induced by DNA damage, cytotoxic drugs, intense oncogenic signaling, and telomere loss [11,12,13,14]. Induction of cancer cellular senescence is considered to contribute to effectiveness of anticancer therapy by perturbing tumor growth [19]
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