Betulinic Acid Decreases Specificity Protein 1 (Sp1) Level via Increasing the Sumoylation of Sp1 to Inhibit Lung Cancer Growth

Abstract

Previous studies have shown that the inhibitory effect of betulinic acid (BA) on specificity protein 1 (Sp1) expression is involved in the prevention of cancer progression, but the mechanism of this effect remains to be delineated. In this study, we determined that BA treatment in HeLa cells increased the sumoylation of Sp1 by inhibiting sentrin-specific protease 1 expression. The subsequent recruitment of E3 ubiquitin-protein ligase RING finger protein 4 resulted in ubiquitin-mediated degradation in a 26S-proteosome-dependent pathway. In addition, both BA treatment and mithramycin A (MMA) treatment inhibited lung tumor growth and down-regulated Sp1 protein expression in Kras G12D -induced lung cancers of bitransgenic mice. In gene expression profiles of Kras G12D -induced lung cancers in bitransgenic mice with and without Sp1 inhibition, 542 genes were affected by MMA treatment. One of the gene products, cyclin A2, which was involved in the S and G 2 /M phase transition during cell cycle progression, was investigated in detail because its expression was regulated by Sp1. The down-regulation of cyclin A2 by BA treatment resulted in decreased retinoblastoma protein phosphorylation and cell cycle G 2 /M arrest. The BA-mediated cellular Sp1 degradation and antitumor effect were also confirmed in a xenograft mouse model by using H1299 cells. The knockdown of Sp1 in lung cancer cells attenuated the tumor-suppressive effect of BA. Taken together, the results of this study clarify the mechanism of BA-mediated Sp1 degradation and identify a pivotal role for Sp1 in the BA-induced repression of lung cancer growth.

Sp1-mediated microRNA-182 expression regulates lung cancer progression

“…Our recent studies showed that Sp1 increased the growth of lung cancer cells, but inhibits metastatic activity [23, 32]. In the present study, we found that Sp1, which accumulated in the early stages of cancer, positively regulated miR-182 gene expression to silence FOXO3 expression and thereby promote cancer cell growth.…”

“…Our previous studies demonstrated that Sp1 is involved in Kras G12D -induced lung tumorigenesis [23, 32]. Using cDNA microarray analysis, we found that Sp1 increased oncogene expression and decreased tumor suppressor gene expression.…”

“…In the late stages, Sp1 could be sumoylated, leading to recruitment of its E3-ligase, RNF4, followed by polyubiquitination and degradation [32]. To clarify the molecular mechanism underlying gene regulation by Sp1, we used microarray analysis to assess gene expression in Kras G12D -induced lung tumor transgenic mice and identified thousands of genes potentially regulated by Sp1 [23]. However, some of the genes do not harbor a conserved Sp1 binding motif within their promoter region, suggesting that another regulatory mechanism is involved in Sp1-mediated gene regulation.…”

“…Sp1 regulates thousands of coding genes, such as those encoding cyclin A2, p21 cip1/waf1 , E-cadherin and Sp1 itself. These genes are involved in a variety of physiological processes including cell cycle progression and cell migration [23-26]. Sp1 also regulates the expression of noncoding genes.…”

MicroRNA-149 targets specificity protein 1 to suppress human tongue squamous cell carcinoma cell proliferation and motility

“…An increasing number of studies suggest that SP1 regulates a variety of biological functions, including cell survival, proliferation, differentiation, migration and invasion (32)(33)(34). Additionally, several compounds with anti-tumor effects, which target SP1 have been developed or are in development, and some of them are currently used clinically for cancer treatment (35)(36)(37)(38). Therefore, SP1 has been suggested to be a novel target for cancer therapy due to the cancer-associated functions of the protein.…”