Nuclear targeting of the beta isoform of type II phosphatidylinositol phosphate kinase (phosphatidylinositol 5-phosphate 4-kinase) by its alpha-helix 7.
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ABSTRACT:
SUBMITTER: Ciruela A
PROVIDER: S-EPMC1220889 | biostudies-other | 2000 Mar
REPOSITORIES: biostudies-other
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Project description:The generation of diacylglycerol (DAG) in response to receptor stimulation is a well-documented signalling mechanism that leads to activation of protein kinase C (PKC). Putative alternative effectors contain sequences that interact with DAGs, but the mechanisms of signal transduction are unknown. We have identified a Dictyostelium gene encoding a novel protein which contains a domain with high identity to the DAG-binding domain of PKC. It does not encode a PKC homologue as the conservation does not extend outside this region. We confirm that the proposed DAG-binding domain is sufficient to mediate interaction of a fusion protein with vesicles containing DAG. The protein also shows significant homology to mammalian phosphatidylinositol phosphate (PIP) kinases and we show that this domain has PIP kinase activity. The protein, PIPkinA, is enriched in the nucleus and abrogation of gene function by homologous recombination inhibits early developmental gene expression, blocking development at an early stage. Thus, we have identified a PIP kinase from Dictyostelium which is required for development, is a candidate effector for DAG and has the potential to synthesize nuclear PIP(2).
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Project description:Rationale: Oxaliplatin is a widely used chemotherapy drug for advanced colorectal cancer (CRC) and its resistance is a major challenge for disease treatment. However, the molecular mechanism underlying oxaliplatin resistance remains largely elusive. Methods: An integrative analysis was performed to determine differentially expressed genes involved in oxaliplatin resistance. Loss- and gain-of-function studies were employed to investigate the roles of type Iγ phosphatidylinositol phosphate kinase (PIPKIγ) on oxaliplatin resistance in CRC cells. Exosomes derived from CRC cell lines were assessed for PD-L1 level and the ability to promote oxaliplatin resistance. Quantitative real-time PCR, immunofluorescence, luciferase reporter assay, Western blotting and other techniques were conducted to decipher the molecular mechanism. Results: PIPKIγ was identified as a critical gene related to oxaliplatin resistance in CRC. Genetic manipulation studies revealed that PIPKIγ profoundly facilitated oxaliplatin resistance and affected the expression of DNA damage repair proteins. Mechanistically, PIPKIγ promoted the expression of the immune checkpoint molecule PD-L1 via activation of NF-κB signaling pathway. Genetic silencing of PD-L1 did not affect CRC cell proliferation but significantly sensitized CRC cells to oxaliplatin. Notably, PD-L1 was revealed to be encapsulated in the exosomes, and the addition of exosomal PD-L1 to sh-PD-L1 CRC cells restored oxaliplatin resistance. Pharmacological hijacking PIPKIγ-exosomal PD-L1 axis largely reduced oxaliplatin resistance in CRC cells. In vivo experiments showed that PD-L1 loss significantly blocked oxaliplatin resistance and the addition of PD-L1-enriched exosomes promoted tumor growth and reduced mouse survival time. Conclusion: Our findings reveal a previous unprecedented role of PIPKIγ in oxaliplatin resistance and provide a key mechanism of exosomal PD-L1 in CRC with potential therapeutics.
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