STAT3-induced SMYD3 transcription enhances chronic lymphocytic leukemia cell growth in vitro and in vivo

Objective and design: The purpose of this study was to investigate the roles of SMYD3 and STAT3 in chronic lymphocytic leukemia (CLL) and the possible underlying mechanisms.

Materials: Blood samples were collected from 20 patients with CLL and 20 hematologically normal donors. Human cell lines K562, HL-60, MEG-1, and BALL-1 were performed in vitro and BALB/c nude mouse was used in subcutaneous tumor experiments.

Treatment: WP1066 (30 mg/kg) was also injected intratumorally two days after the first lentivirus treatment and then every four days for a total of four injections and 3 µM WP1066 was carried out for 48 h to downregulate STAT3 phosphorylation.

Methods: We performed studies using the human CLL cell line MEG-1 in vitro and nude mouse subcutaneous tumor experiments in vivo. Differential expression of RNAs was determined using qRT-PCR. The CCK-8 assay and colony formation assay were conducted to evaluate cell proliferation. Flow cytometry was performed to assess cell Apoptosis. The relative protein levels were detected using western blotting. Chromatin immunoprecipitation (ChIP) assays, luciferase reporter assays and WP1066, a STAT3 Inhibitor, were used to explore the regulatory mechanisms of proteases and transcription factors. A subcutaneous tumor model was constructed to verify the results in vivo.

Results: SMYD3 and STAT3 expressions positively correlated with the progression of CLL. Upregulation of SMYD3 significantly promoted the proliferation and inhibited the expression of apoptosis-related genes. The results of the ChIP assays and luciferase reporter assays suggested that STAT3 targeted the promoter region of SMYD3 and, thus, promoted SMYD3 transcription. Downregulation of the phosphorylation of STAT3 by WP1066 notably inhibited the binding of STAT3 to the SMYD3 promoter, and subsequently downregulated SMYD3 transcription. The STAT3 Inhibitor inhibited CLL cell growth in vivo, and overexpression of SMYD3 promoted CLL cell growth. Furthermore, overexpression of SMYD3 reversed the inhibitory effects of the STAT3 Inhibitor on CLL cell growth.

Conclusions: The STAT3-mediated transcription of SMYD3 plays a role in promoting the progression of chronic lymphocytic leukemia.