Protein Kinase C Delta Is a Novel Biomarker for Hepatocellular Carcinoma

Proposal for Prognosis-Oriented Definition of Borderline Resectable Hepatocellular Carcinoma

BACKGROUND

Owing to advances in the multidisciplinary treatment of hepatocellular carcinoma (HCC), a conceptualization and definition for borderline resectable (BR) HCC, which carries a high risk of recurrence, is warranted. In this study, we aimed to define BR-HCC using a prognosis-oriented approach.

STUDY DESIGN

The study included an original cohort of 221 patients and an independent validation cohort of 181 patients who had undergone primary hepatic resection for HCC. To define biological BR-HCC, we evaluated the risk factors for early recurrence beyond the Milan criteria within 1 year after hepatic resection using multivariable logistic regression models. Subsequently, we developed high-risk scores using the identified risk factors and defined BR-HCC. The utility of high-risk score was validated in the validation cohort.

RESULTS

In the original cohort (hepatitis B virus:hepatitis C virus = 20%:29%), recurrence beyond the Milan criteria within 1 year was observed in 28 patients (13%), with a 5-year survival rate of 25%. Multivariable analysis identified risk factors for recurrence beyond the Milan criteria within 1 year, including serum alpha-fetoprotein levels of 12 ng/mL or more (p = 0.02), tumor diameters less than 5 cm (p = 0.02), tumor number 3 or more (p = 0.001), and macrovascular invasion (p = 0.04). BR-HCC was defined as a tumor with 2 or more identified risk factors, and 42 patients (19%) were diagnosed with BR-HCC, with a 5-year survival rate of 51%. In the validation cohort, 45 (25%) patients had BR-HCC, with a 5-year survival rate of 42%.

CONCLUSIONS

The prognosis-oriented definition of BR-HCC enabled us to identify patients who are susceptible to early unresectable recurrence and have poor survival after hepatic resection for HCC. For patients with BR-HCC, preoperative systemic therapy may be a viable option to improve postresection outcomes.

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.

Cancer-Related Unconventional Protein Secretion: A New Role of the Endoplasmic Reticulum

Unconventional protein secretion (UPS) is a crucial mechanism controlling the localization of cytosolic proteins lacking signal peptides and is implicated in inflammation, neurodegenerative diseases, and cancer. Several previous studies on immune cells have demonstrated the mechanisms of UPS. In cancer, the active secretion of several cytosolic proteins, including PKCδ and nucleolin, has been described. Moreover, we have recently demonstrated that extended synaptotagmin 1, one of the membrane proteins of the endoplasmic reticulum, plays a critical role in UPS in liver cancer cells. Importantly, UPS in cancer cells shows characteristics that are markedly different from those of the previously known UPS, and therefore, we categorize them as cancer-related UPS (CUPS). In this article, we provide an overview of UPS mechanisms and discuss the process that leads to the naming of cancer-specific UPS as CUPS.