STAM-binding protein regulates melanoma metastasis through SLUG stabilization.

STAM-binding protein, STAMBP, is a JAMM-family deubiquitinating enzyme containing the microtubule-interacting/transport domain and STAM-binding domain. Although the biological importance of STAMBP in development has been recognized because the microcephaly-capillary malformation syndrome in human is caused by its somatic mutations, the role of STAMBP in cancer has not yet been determined. In this study, we demonstrate that STAMBP is a key molecule for regulating melanoma migration and invasion, but not survival, by knocking down STAMBP in vitro. STAMBP regulates SLUG expression through a post-transcriptional mechanism to control protein stability and further contributes to the in vivo metastatic potential of melanoma. Collectively, these results indicate the importance of STAMBP in melanoma metastasis by regulating SLUG. It is therefore a potential therapeutic target.

P38 pathway as a key downstream signal of connective tissue growth factor to regulate metastatic potential in non-small-cell lung cancer.

Although the secretory matricellular protein connective tissue growth factor (CTGF) has been reported to be related to lung cancer metastasis, the precise mechanism by which CTGF regulates lung cancer metastasis has not been elucidated. In the present study, we show the molecular link between CTGF secretion and the p38 pathway in the invasive and metastatic potential of non-small-cell lung cancer (NSCLC). Among three different human NSCLC cell lines (PC-14, A549, and PC-9), their in vitro invasiveness was inversely correlated with the level of CTGF secretion. By supplementing or reducing CTGF secretion in NSCLC culture, dysregulation of the invasive and metastatic potential of NSCLC cell lines was largely compensated. By focusing on the protein kinases that are known to be regulated by CTGF, we found that the p38 pathway is a key downstream signal of CTGF to regulate the metastatic potential of NSCLC. Importantly, a negative correlation between CTGF and phosphorylation status of p38 was identified in The Cancer Genome Atlas lung adenocarcinoma dataset. In the context of the clinical importance of our findings, we showed that p38 inhibitor, SB203580, reduced the metastatic potential of NSCLC secreting low levels of CTGF. Collectively, our present findings indicate that the CTGF/p38 axis is a novel therapeutic target of NSCLC metastasis, particularly NSCLC secreting low levels of CTGF.

Terminal bridging of siRNA duplex at the ribose 2' position controls strand bias and target sequence preference.

Small interfering RNA (siRNA) and short hairpin RNA (shRNA) are widely used as RNA interference (RNAi) reagents. Recently, truncated shRNAs that trigger RNAi in a Dicer-independent manner have been developed. We generated a novel class of RNAi reagent, designated enforced strand bias (ESB) RNA, in which an siRNA duplex was chemically bridged between the 3' terminal overhang region of the guide strand and the 5' terminal nucleotide of the passenger strand. ESB RNA, which is chemically bridged at the 2' positions of ribose (2'-2' ESB RNA), functions in a Dicer-independent manner and was highly effective at triggering RNAi without the passenger strand-derived off-target effect. In addition, the 2'-2' ESB RNA exhibited a unique target sequence preference that differs from siRNA and silenced target sequences that could not be effectively suppressed by siRNA. Our results indicate that ESB RNA has the potential to be an effective RNAi reagent even when the target sequence is not suitable for siRNA.

Targeting PSMD14 inhibits melanoma growth through SMAD3 stabilization.

Although melanoma therapy is improved by novel molecular targeted reagents, including vemurafenib, aberrant proliferation and early metastasis remain obstacles for melanoma; therefore, novel target molecules for melanoma need to be identified. In this study, we focused on deubiquitinating enzymes, which regulate protein stability through ubiquitin-proteasome systems, and identified 26S proteasome non-ATPase regulatory subunit 14 (PSMD14) as a molecule related to melanoma growth using siRNA library screening. Similar to a previous report, PSMD14 knockdown strongly induced p21 expression and inhibited RB phosphorylation in melanoma. After in silico analysis, TGF-ß signaling was identified as a negatively correlated gene set with PSMD14 expression. Although TGF-ß signaling is also related to the invasive phenotype of melanoma, PSMD14 knockdown suppressed melanoma migration and reduced SLUG expression, suggesting that targeting PSMD14 suppresses both growth and migration. Furthermore, SMAD3 expression increased in nucleus and SMAD3 degradation was delayed after PSMD14 knockdown. Thus, our present study suggests that targeting PSMD14 can inhibit melanoma growth and migration through either SMAD3 accumulation or SLUG reduction, respectively.

COP9 signalosome subunit 5 regulates cancer metastasis by deubiquitinating SNAIL.

Cancer metastasis is a major cause of mortality in cancer patients. The transcription factor SNAIL plays an important role in cancer metastasis and progression, and its expression is tightly regulated by the ubiquitin-proteasome system through the balance between ubiquitin ligases and deubiquitinating enzymes. While several ubiquitin ligases of SNAIL have been identified, it is not yet clear regarding deubiquitinating enzyme. In this study, we identified COP9 signalosome subunit 5 (COPS5) as a deubiquitinating enzyme of SNAIL by using siRNA library screening. COPS5 downregulation significantly reduced the expression of SNAIL and impaired the metastatic potential of lung cancer cells both in vitro and in vivo. Importantly, we demonstrated that COPS5 binds to SNAIL and stabilizes its expression by deubiquitination. Furthermore, we observed the positive correlation between COPS5 and SNAIL expression in the clinical tissue samples of lung adenocarcinomas by using tissue microarray analysis. These findings provide strong evidence that COPS5 can be a new therapeutic target for cancer metastasis as a deubiquitinating enzyme of SNAIL.