Structural maintenance of chromosomes (SMC) proteins are chromosomal ATPases, and are highly conserved from bacteria to humans. They play fundamental roles in many aspects of higher-order chromosome organization and dynamics [
22]. SMC proteins act as global organizers and safeguards by directly and indirectly influencing chromosome structure and dynamics. They participate in a vast number of vital cellular processes ranging from cell division to gene regulation and DNA repair [
23]. Individual eukaryotic organisms have at least six SMC family members that form three heterodimers in specific combinations: SMC1 and SMC3, SMC5 and SMC6, SMC2 and SMC4. SMC2 and SMC4 that are central components of condensin complexes [
24]. SMC4 encodes a “structural maintenance of chromosomes” protein, and is a subunit of condensin. It has clear roles in chromosome condensation and mitosis, and is required for normal S phase progression, indicating a previously unrecognized role of Smc4p in the synchronous progression from G1 into S phase [
25,
26]. Research also suggests that SMC4 is a potential biomarker of the sensitivity of breast cancer cells to paclitaxel and the response to SAHA/paclitaxel combination treatment [
27]. Previous studies have shown that the expression of SMC4 mRNA and protein was highly upregulated in HCC tissues and cell lines. Levels of SMC4 protein were significantly associated with tumor size, differentiation, TNM stage, and vascular invasion of primary liver cancer [
17]. From data presented on these 72 cases published previously, the 4 specimens selected in the current study are representative of the others. In the present study, we also found that SMC4 was frequently upregulated in HCC cases and cell lines, consistent with our previous study. Therefore, we assumed that SMC4 played an important role in HCC development and invasion. In the current study, the effects of SMC4 on HCC development and invasion were investigated. One important task was to identify the upstream targets that regulate SMC4. Using five different bioinformatics software to analyze the 3’UTR of SMC4, miR-219 was found to be involved. A previous study also showed that miR-219 was potentially involved in gastric cancer progression and metastasis [
28]. MiR-219 has been found to be significantly downregulated in HCC, and exert tumor-suppressive effects in hepatic carcinogenesis through negative regulation of GPC3 expression [
15], which is consistent with our experimental results in HCC cell lines and tissues. Previous studies have shown that miR-219 inhibited cell proliferation [
29,
30]. There are several known pathways, including the GPC3 pathway by which the proliferation of HCC cells is regulated. GPC3 is a cell surface protein that has been implicated as a possible tumor marker for HCC [
31]. In the current study, we found that SMC4 is also a target of miR-219 in the regulation of the proliferation and invasion of HCC cells. Correlation analysis showed that these two indexes had a trend of negative correlation (r = −0.394, p = 0.000). Quantitative PCR and Western Blotting analysis also demonstrated that miR-219 decreased SMC4 mRNA levels. In addition, inhibiting miR-219 expression increased SMC4 levels. Luciferase assays showed a negative regulatory relationship between miR-219 and SMC4. Furthermore, we identified the downstream target regulated by SMC4. JAK2/Stat3 was identified as the target of SMC4. JAK2, a member of the Janus (JAK) family of non-receptor protein tyrosine kinases, regulates signaling via multiple cytokine receptors [
32,
33]. Stat3, which is associated with oncogenesis, cell proliferation, angiogenesis, immune evasion, and apoptotic resistance, is constitutively activated in human HCC tissues, but not in normal human liver tissues [
34‐
36]. One study showed that celecoxib decreased Stat3 phosphorylation by reducing Janus kinase (JAK2) phosphorylation, and caused apoptosis in HCC cells [
37]. Peak Stat3 phosphorylation occurred within 15–60 min of exposure to cytokine. This constitutive activation of Stat3 is due to deregulation of protein tyrosine kinases or constitutive release of growth factors that activate Stat3 [
38‐
40]. Activation of JAK2/ Stat3 signaling in solid tumors may represent a prognostic biomarker and therapeutic target [
41].