Protein kinase C delta enhances the diagnostic performance of hepatocellular carcinoma.

BACKGROUND: The conventional markers for hepatocellular carcinoma (HCC), α-fetoprotein (AFP) and des-γ-carboxy prothrombin (DCP), have several limitations; both have low sensitivity in patients with early-stage HCC; low sensitivity for AFP with HCC after eliminating hepatitis C virus (HCV); low specificity for DCP in patients with non-viral HCC, which is increasing worldwide; low specificity for AFP in patients with liver injury; and low specificity for DCP in patients treated with warfarin. To overcome these issues, the identification of novel biomarkers is an unmet need. OBJECTIVE: This study aimed to assess the usefulness of serum protein kinase C delta (PKCδ) for detecting these HCCs. METHODS: PKCδ levels were measured using a sandwich enzyme-linked immunosorbent assay in 363 chronic liver disease (CLD) patients with and without HCC. RESULTS: In both viral and non-viral CLD, PKCδ can detect HCCs with high sensitivity and specificity, particularly in the very early stages. Notably, the value and sensitivity of PKCδ were not modified by HCV elimination status. Liver injury and warfarin administration, which are known to cause false-positive results for conventional markers, did not modify PKCδ levels. CONCLUSIONS: PKCδ is an enhanced biomarker for the diagnosis of HCC that compensates for the drawbacks of conventional markers.

Extended-Synaptotagmin 1 Enhances Liver Cancer Progression Mediated by the Unconventional Secretion of Cytosolic Proteins.

Extended-synaptotagmin 1 (E-Syt1) is an endoplasmic reticulum membrane protein that is involved in cellular lipid transport. Our previous study identified E-Syt1 as a key factor for the unconventional protein secretion of cytoplasmic proteins in liver cancer, such as protein kinase C delta (PKCδ); however, it is unclear whether E-Syt1 is involved in tumorigenesis. Here, we showed that E-Syt1 contributes to the tumorigenic potential of liver cancer cells. E-Syt1 depletion significantly suppressed the proliferation of liver cancer cell lines. Database analysis revealed that E-Syt1 expression is a prognostic factor for hepatocellular carcinoma (HCC). Immunoblot analysis and cell-based extracellular HiBiT assays showed that E-Syt1 was required for the unconventional secretion of PKCδ in liver cancer cells. Furthermore, deficiency of E-Syt1 suppressed the activation of insulin-like growth factor 1 receptor (IGF1R) and extracellular-signal-related kinase 1/2 (Erk1/2), both of which are signaling pathways mediated by extracellular PKCδ. Three-dimensional sphere formation and xenograft model analysis revealed that E-Syt1 knockout significantly decreased tumorigenesis in liver cancer cells. These results provide evidence that E-Syt1 is critical for oncogenesis and is a therapeutic target for liver cancer.

Extended-synaptotagmin 1 engages in unconventional protein secretion mediated via SEC22B+ vesicle pathway in liver cancer.

Protein secretion in cancer cells defines tumor survival and progression by orchestrating the microenvironment. Studies suggest the occurrence of active secretion of cytosolic proteins in liver cancer and their involvement in tumorigenesis. Here, we investigated the identification of extended-synaptotagmin 1 (E-Syt1), an endoplasmic reticulum (ER)-bound protein, as a key mediator for cytosolic protein secretion at the ER-plasma membrane (PM) contact sites. Cytosolic proteins interacted with E-Syt1 on the ER, and then localized spatially inside SEC22B+ vesicles of liver cancer cells. Consequently, SEC22B on the vesicle tethered to the PM via Q-SNAREs (SNAP23, SNX3, and SNX4) for their secretion. Furthermore, inhibiting the interaction of protein kinase Cδ (PKCδ), a liver cancer-specific secretory cytosolic protein, with E-Syt1 by a PKCδ antibody, decreased in both PKCδ secretion and tumorigenicity. Results reveal the role of ER-PM contact sites in cytosolic protein secretion and provide a basis for ER-targeting therapy for liver cancer.

Acquisition of G0 state by CD34-positive cord blood cells after bone marrow transplantation.

OBJECTIVE: Hematopoietic stem cells are kept in a quiescent state in the hypoxic area of the bone marrow, which is essential for hematopoietic stem cell maintenance. However, when and how hematopoietic stem cells acquire their hypoxic state and maintain quiescence has not been fully elucidated. The aim of this study was to understand this process in human hematopoietic stem cells after bone marrow transplantation. MATERIALS AND METHODS: Human CD34-positive cord blood cells were transplanted into nonobese diabetic/severe combined immunodeficient interleukin-2 receptor γ chain knockout mice. Cell cycle and hypoxia assay analyses were performed, to identify changes in the characteristics of human hematopoietic stem cells following transplantation. Quantitative real-time reverse transcription polymerase chain reaction analysis was used to analyze the transcriptional changes accompanying this transition. RESULTS: Engrafted primitive lineage-negative CD34-positive CD38-negative cells acquired hypoxic state and quiescence in the recipient bone marrow between 4 and 8 weeks, and between 8 and 12 weeks after transplantation, respectively. During 4 and 8 weeks after transplantation, changes in the transcription levels of G0 regulatory factors, such as CCNC and RBL1, and stem cell regulators, such as Flt3, were also seen, which may be related to the characteristic changes in the cell cycle or oxygenation state. CONCLUSIONS: Behavioral changes of hematopoietic stem cells in their cell cycle and oxygenation state during and after bone marrow engraftment may provide insights into hematopoietic stem cell regulation, mediating the improvement of clinical hematopoietic stem cell transplantation protocols and the eradication of leukemia stem cells.