Dysregulation of pre-mRNA alternative splicing (AS) is closely associated with cancers. However, the relationships between the AS and classic oncogenes/tumor suppressors are largely unknown. Here we show that the deletion of tumor suppressor PTEN alters pre-mRNA splicing in a phosphatase-independent manner, and identify 262 PTEN-regulated AS events in 293T cells by RNA sequencing, which are associated with significant worse outcome of cancer patients. Based on these findings, we report that nuclear PTEN interacts with the splicing machinery, spliceosome, to regulate its assembly and pre-mRNA splicing. We also identify a new exon 2b in GOLGA2 transcript and the exon exclusion contributes to PTEN knockdown-induced tumorigenesis by promoting dramatic Golgi extension and secretion, and PTEN depletion significantly sensitizes cancer cells to secretion inhibitors brefeldin A and golgicide A. Our results suggest that Golgi secretion inhibitors alone or in combination with PI3K/Akt kinase inhibitors may be therapeutically useful for PTEN-deficient cancers.

Apoptosis-inducing factor (AIF) exerts dual roles on cell death and survival, but its substrates as a putative oxidoreductase and roles in tumorigenesis remain elusive. Here, we report that AIF physically interacts with and inhibits the oxidation of phosphatase and tensin homolog on chromosome ten (PTEN), a tumor suppressor susceptible for oxidation-mediated inactivation. More intriguingly, we also identify PTEN as a mitochondrial protein and the ectopic expression of mitochondrial targeting sequence-carrying PTEN almost completely inhibits Akt phosphorylation in PTEN-deficient cells. AIF knockdown causes oxidation-mediated inactivation of the lipid phosphatase activity of PTEN, with ensuing activation of Akt kinase, phosphorylation of the Akt substrate GSK-3β, and activation of β-catenin signaling in cancer cells. Through its effect on β-catenin signaling, AIF inhibits epithelial–mesenchymal transition (EMT) and metastasis of cancer cells in vitro and in orthotopically implanted xenografts. Accordingly, the expression of AIF is correlated with the survival of human patients with cancers of multiple origins. These results identify PTEN as the substrate of AIF oxidoreductase and reveal a novel function for AIF in controlling tumor metastasis.

Recently, we have reported that apoptosis-inducing factor (AIF) regulates the epithelial-mesenchymal transition (EMT) process of cancers, but the mechanisms underlying the regulation of AIF expression in cancers remain greatly unknown. Here, we report that hypoxia inversely correlates with the expression of AIF in tumor tissues from a cohort of colon cancer patients and inhibits AIF expression in multiple colon cancer cell lines. This inhibition is mediated by hypoxia-inducible factor-1 (HIF-1), which transcriptionally represses AIF through direct binding to the hypoxia-response element in AIF promoter as revealed by luciferase reporter and chromatin immunoprecipitation assays. We also show that downregulation of AIF contributes to hypoxia-induced EMT as overexpression or silencing of AIF partially reverses or potentiates the EMT program initiated by hypoxic treatment. Mechanistic study reveals that downregulation of AIF by hypoxia causes oxidative inactivation of the lipid phosphatase activity of phosphatase and tensin homolog on chromosome 10 (PTEN), with ensuing activation of Akt kinase, phosphorylation of the Akt substrate GSK-3β and activation of WNT/β-catenin signaling in colon cancer cells. These results identify AIF as a novel target gene of HIF-1 and reveal the role of AIF downregulation in hypoxia-induced EMT.

Objective: Cell division cycle 7 (CDC7), a receptor serine/threonine kinase which features high-affinity with protein DBF4, plays an important role in DNA replication and DNA damage response via MCM2 phosphorylation. CDC7 has been reported to be up-regulated by about 50% in various human cancers and is being investigated as a therapeutic target in clinical trials. The purpose of this study is to investigate the in-vitro and in-vivo antitumor activities of TQB3824, a small molecule of CDC7 kinase inhibitor, in preclinical models with CDC7 overexpression. Method: Kinase inhibition activities of TQB3824 were determined with CDC7/DBF4 kinase assays. Cellular anti-proliferative activities were evaluated in COLO205 cell line and NCI-H226 cell line, which features CDC7 overexpression and no CDC7 expression, respectively. Three CDX models, colorectal cancer COLO205/SW620 and pancreatic cancer CAPAN-1 with KRAS mutation, were used to test the efficacy of TQB-3824 in vivo. Result: TQB3824 showed potent activities in both kinase inhibition and COLO205 cell anti-proliferation, with IC50 of 2.9 nM and 14.5 nM, separately. In contrast, TQB3824 showed much weaker anti-proliferative activity in NCI H226 cells with IC50 of 8154 nM. TQB3824 displayed strong antitumor efficacy in CDC7 highly expressed colorectal cancer CDX model COLO205 (TGI = 77% @5 mpk, BID), SW620 CDX model (TGI = 100% @5 mpk, BID), and pancreatic cancer CAPAN-1 CDX model (TGI = 115% @6 mpk, BID). Conclusion: We have identified a novel potent CDC7 inhibitor TQB3824, which shows high antitumor efficacy in CDC7 overexpressed solid tumor models. TQB3824 represents a promising clinical candidate for treating solid tumors with high CDC7 expression. Citation Format: Gang Li, Xiquan Zhang, Ling Yang, Xin Tian, Zhong xiong, Lihong Hu, Yuanfeng xia, Chi-chung chan, Charles Z. Ding, Shuhui Chen. Preclinical candidate TQB3824, a small molecule inhibitor of CDC7, shows strong antitumor efficacy in colorectal and pancreatic tumor models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1970.