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Stk40 deletion elevates c-JUN protein level and impairs mesoderm differentiation

ABSTRACT: Mesoderm development is a finely tuned process initiated by the differentiation of pluripotent epiblast cells. Serine/threonine kinase 40 (STK40) controls the development of several mesoderm-derived cell types, its overexpression induces differentiation of mouse embryonic stem cells (mESCs) towards the extraembryonic endoderm, and Stk40 knockout (KO) results in multiple organ failure and is lethal at the perinatal stage in mice. However, molecular mechanisms underlying the physiological functions of STK40 in the mesoderm differentiation remain elusive. Here, we report that Stk40 ablation impairs mesoderm differentiation both in vitro and in vivo. Mechanistically, STK40 interacts with both the E3 ubiquitin ligase mammalian constitutive photomorphogenesis protein 1 (COP1) and the transcriptional regulator proto-oncogene c-Jun (c-JUN), promoting c-JUN protein degradation. Consequently, Stk40 knockout leads to c-JUN protein accumulation, which, in turn, apparently suppresses the WNT signaling activity and impairs the mesoderm differentiation process. Overall, this study reveals that STK40, together with COP1, represents a previously unknown regulatory axis that modulates the c-JUN protein level within an appropriate range during mesoderm differentiation from mESCs. Our findings provide critical insights into the molecular mechanisms regulating the c-JUN protein level and may have potential implications for managing cellular disorders arising from c-JUN dysfunction.

ORGANISM(S): Mus musculus

PROVIDER: GSE125877 | GEO | 2019/05/10

REPOSITORIES: GEO

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Project description:The proto-oncogenes ETV1, ETV4, and ETV5 encode members of the E26 transformation-specific (ETS) transcription factor family, which includes the most frequently rearranged and overexpressed genes in prostate cancer. Despite being critical regulators of development, little is known about their post-translational regulation. Here we identify the ubiquitin ligase COnstitutive Photomorphogenic-1 (COP1, also called RFWD2) as a tumor suppressor that negatively regulates ETV1, ETV4, and ETV5. ETV1, which is the member mutated more frequently in prostate cancer, was degraded after being ubiquitinated by COP1. Truncated ETV1 encoded by prostate cancer translocation TMPRSS2:ETV1 lacks the critical COP1 binding motifs (degrons) and was 50-fold more stable than wild-type ETV1. Almost all patient translocations eliminate these ETV1 degrons, implying that translocations rendering ETV1 insensitive to COP1 confer a significant selective advantage to prostate epithelial cells. Indeed, COP1 deficiency in mouse prostate elevated ETV1 levels and produced increased cell proliferation, hyperplasia, and early prostate intraepithelial neoplasia. The combined loss of COP1 and PTEN enhanced the invasiveness of mouse prostate adenocarcinomas. Finally, relatively rare human prostate cancer samples showed hemizygous loss of the COP1 gene, loss of COP1 protein expression, and abnormally elevated ETV1 protein while lacking a translocation event. These findings identify COP1 as a bona fide tumor suppressor whose down-regulation promotes prostatic epithelial cell proliferation and tumorigenesis. LNCap prostate cancer cell line were treated with 5 different sets of siRNAs: (1) control siRNA; (2) COP1 (RFWD2) siRNA; (3) COP1 siRNA + ETV1 siRNA; (4) COP1 siRNA + c-JUN siRNA; (5) COP1 siRNA + ETV1 siRNA + c-JUN siRNA. The experiments were conducted in two batches; each batch has its own control siRNA group, so that the batch effect can be properly modelled. Each group has 4-6 replicates; there are 31 samples in total.

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Stk40 deletion elevates c-JUN protein level and impairs mesoderm differentiation

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