ABSTRACT
PTENα and PTENß (PTENα/ß), two long translational variants of phosphatase and tensin homolog on chromosome 10 (PTEN), exert distinct roles from canonical PTEN, including promoting carcinogenesis and accelerating immune-resistant cancer progression. However, their roles in carcinogenesis remain greatly unknown. Herein, we report that, after secreting into the extracellular space, PTENα/ß proteins are efficiently cleaved into a short N-terminal and a long C-terminal fragment by the proprotein convertase Furin at a polyarginine stretch in their N-terminal extensions. Although secreted PTENα/ß and their cleaved fragment cannot enter cells, treatment of the purified C-terminal fragment but not cleavage-resistant mutants of PTENα exerts a tumor-suppressive role in vivo. As a result, overexpression of cleavage-resistant PTENα mutants manifest a tumor-promoting role more profound than that of wild-type PTENα. In line with these, the C-terminal fragment is significantly downregulated in liver cancer tissues compared to paired normal tissues, which is consistent with the downregulated expression of Furin. Collectively, we show that extracellular PTENα/ß present opposite effects on carcinogenesis from intracellular PTENα/ß, and propose that the tumor-suppressive C-terminal fragment of PTENα/ß might be used as exogenous agent to treat cancer.
Subject(s)
Furin , Liver Neoplasms , Carcinogenesis , Furin/genetics , Humans , Proprotein ConvertasesABSTRACT
Nuclear localization of PTEN is essential for its tumor suppressive role, and loss of nuclear PTEN is more prominent than cytoplasmic PTEN in many kinds of cancers. However, nuclear PTEN-specific regulatory mechanisms were rarely reported. Based on the finding that nuclear PTEN is more unstable than cytoplasmic PTEN, here we identify that F-box only protein 22 (FBXO22) induces ubiquitylation of nuclear but not cytoplasmic PTEN at lysine 221, which is responsible for the degradation of nuclear PTEN. FBXO22 plays a tumor-promoting role by ubiquitylating and degrading nuclear PTEN. In accordance, FBXO22 is overexpressed in various cancer types, and contributes to nuclear PTEN downregulation in colorectal cancer tissues. Cumulatively, our study reports the mechanism to specifically regulate the stability of nuclear PTEN, which would provide the opportunity for developing therapeutic strategies aiming to achieve complete reactivation of PTEN as a tumor suppressor.
Subject(s)
Carcinogenesis/genetics , Cell Nucleus/metabolism , Cell Transformation, Neoplastic/genetics , Colorectal Neoplasms/metabolism , F-Box Proteins/metabolism , PTEN Phosphohydrolase/metabolism , Receptors, Cytoplasmic and Nuclear/metabolism , Animals , Cell Line, Tumor , Chromatography, Liquid , Colorectal Neoplasms/genetics , Cytoplasm/metabolism , F-Box Proteins/genetics , Female , Humans , Mice , Mice, Inbred NOD , Mice, Nude , Mice, SCID , PTEN Phosphohydrolase/chemistry , PTEN Phosphohydrolase/genetics , RNA, Small Interfering , Receptors, Cytoplasmic and Nuclear/genetics , Signal Transduction/genetics , Tandem Mass Spectrometry , Tissue Array Analysis , Transplantation, Heterologous , UbiquitinationABSTRACT
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
ABSTRACT
PTENα and PTENß are two longer translational variants of phosphatase and tensin homolog (PTEN) messenger RNA. Their expressional regulations and functions in carcinogenesis remain largely unknown. Here, we demonstrate that, in contrast with the well-established tumour-suppressive role of canonical PTEN, PTENα and PTENß promote tumourigenesis by directly interacting with the histone H3 lysine 4 (H3K4) presenter WDR5 to promote H3K4 trimethylation and maintain a tumour-promoting signature. We also show that USP9X and FBXW11 bind to the amino-terminal extensions of PTENα/ß, and respectively deubiquitinate and ubiquitinate lysines 235 and 239 in PTENα to regulate PTENα/ß stability. In accordance, USP9X promotes tumourigenesis and FBXW11 suppresses tumourigenesis through PTENα/ß. Taken together, our results indicate that the Pten gene is a double-edged sword for carcinogenesis, and reinterpretation of the importance of the Pten gene in carcinogenesis is warranted.
Subject(s)
Carcinogenesis/genetics , Carcinoma, Hepatocellular/genetics , Gene Expression Regulation, Neoplastic , Histones/genetics , Intracellular Signaling Peptides and Proteins/genetics , Liver Neoplasms/genetics , PTEN Phosphohydrolase/genetics , Animals , Carcinogenesis/metabolism , Carcinogenesis/pathology , Carcinoma, Hepatocellular/metabolism , Carcinoma, Hepatocellular/mortality , Carcinoma, Hepatocellular/pathology , Cell Line, Tumor , Cell Movement , Cell Proliferation , Female , Histones/metabolism , Humans , Intracellular Signaling Peptides and Proteins/metabolism , Isoenzymes/genetics , Isoenzymes/metabolism , Liver/metabolism , Liver/pathology , Liver Neoplasms/metabolism , Liver Neoplasms/mortality , Liver Neoplasms/pathology , Male , Mice , Mice, Nude , PTEN Phosphohydrolase/metabolism , Proteolysis , Signal Transduction , Survival Analysis , Ubiquitin Thiolesterase/genetics , Ubiquitin Thiolesterase/metabolism , Ubiquitin-Protein Ligases/genetics , Ubiquitin-Protein Ligases/metabolism , Xenograft Model Antitumor Assays , beta-Transducin Repeat-Containing Proteins/genetics , beta-Transducin Repeat-Containing Proteins/metabolismABSTRACT
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.
