Possible prognostic impact of PKCι genetic variants in prostate cancer

BACKGROUND

Single nucleotide polymorphisms (SNPs) have been linked with prostate cancer (PCa) and have shown potential as prognostic markers for advanced stages. Loss of function mutations in PKCι have been linked with increased risk of malignancy by enhancing tumor cell motility and invasion. We have evaluated the impact of two coding region SNPs on the PKCι gene (PRKCI) and their prognostic potential.

METHODS

Genotypic association of non-synonymous PKCι SNPs rs1197750201 and rs1199520604 with PCa was determined through tetra-ARMS PCR. PKCι was docked with interacting partner Par-6 to determine the effect of these variants on PKCι binding capabilities. Molecular dynamic simulations of PKCι docked with Par-6 were performed to determine variant effects on PKCι protein interactions. The possible impact of changes in PKCι protein interactions on epithelial cell polarity was hypothesized.

RESULTS

PKCι rs1199520604 mutant genotype TT showed association with PCa (p = 0.0055), while rs1197750201 mutant genotype AA also showed significant association with PCa (P = 0.0006). The binding interaction of PKCι with Par-6 was altered for both variants, with changes in Van der Waals energy and electrostatic energy of docked structures.

CONCLUSION

Genotypic analysis of two non-synonymous PKCι variants in association with PCa prognosis was performed. Both variants in the PB1 domain showed potential as a prognostic marker for PCa. In silico analysis of the effect of the variants on PKCι protein interactions indicated they may be involved in PCa progression through aberration of epithelial cell polarity pathways.

PKCι induces differential phosphorylation of STAT3 to modify STAT3-related signaling pathways in pancreatic cancer cells

An increasing number of studies have documented atypical protein kinase C isoform ι (PKCι) as an oncoprotein playing multifaceted roles in pancreatic carcinogenesis, including sustaining the transformed growth, prohibiting apoptosis, strengthening invasiveness, facilitating autophagy, as well as promoting the immunosuppressive tumor microenvironment of pancreatic tumors. In this study, we present novel evidence that PKCι overexpression increases STAT3 phosphorylation at the Y705 residue while decreasing STAT3 phosphorylation at the S727 residue in pancreatic cancer cells. We further demonstrate that STAT3 phosphorylation at Y705 and S727 residues is mutually antagonistic, and that STAT3 Y705 phosphorylation is positively related to the transcriptional activity of STAT3 in pancreatic cancer cells. Furthermore, we discover that PKCι inhibition attenuates STAT3 transcriptional activity via Y705 dephosphorylation, which appears to be resulted from enhanced phosphorylation of S727 in pancreatic cancer cells. Finally, we investigate and prove that by modulating the STAT3 activity, the PKCι inhibitor can synergistically enhance the antitumor effects of pharmacological STAT3 inhibitors or reverse the anti-apoptotic side effects incited by the MEK inhibitor, thereby posing as a prospective sensitizer in the treatment of pancreatic cancer cells.

PKCι Is a Promising Prognosis Biomarker and Therapeutic Target for Pancreatic Cancer

BACKGROUND

As the highest prevalent pancreatic cancer, pancreatic ductal adenocarcinoma (PDAC) ranks the 7th lethal malignancy worldwide. The late diagnosis, chemotherapeutic resistance, and high associated mortality make PDAC a dilemma facing the oncologists. Protein kinase C (PKC) enzymes have been shown to be important in different cancer progression.

METHODS

To understand the pattern of PKC enzymes in PDAC, we examined all PKC family member genes expression in PDAC and matched normal tissues. The critical role of PKCι was further investigated in different PDAC cells using cellular and molecular technology.

RESULTS

We found that PRKCI (PKCι) was the most significantly overexpressed PKCs in pancreatic cancer. However, little is known about its role and regulation of oncogenic signaling pathways in pancreatic cancer. In this study, we confirmed the overexpression of PKCι in PDAC, and this high expression was associated with poor prognosis of patients. We proved that knockdown of PKCι by small interfering RNA or shRNA significantly inhibited pancreatic cancer cell growth and migration or invasion. Conversely, PKCι overexpression promoted pancreatic cancer cell growth and migration. Moreover, bioinformatical and technical studies informed the participation of PKCι in regression of apoptosis in PDAC cells, which may be related to the regulation of both PI3K/AKT and Wnt/β-catenin pathways.

CONCLUSIONS

Therefore, our results are adding more insight into the importance of PKCι in pancreatic cancer. PKCι induces pancreatic cancer progression through activation of PI3K/AKT and Wnt/β-catenin signaling pathways, which may provide a promising therapeutic target for pancreatic cancer.

PKCι regulates the expression of PDL1 through multiple pathways to modulate immune suppression of pancreatic cancer cells

To investigate the impact of oncogenic protein kinase C isoform ι (PKCι) on the microenvironment and the immunogenic properties of pancreatic tumors, we prohibit PKCι activity in various pancreatic ductal adenocarcinoma (PDAC) cell lines and co-culture them with human natural killer NK92 cells. The results demonstrate that PKCι suppression enhances the susceptibility of PDAC to NK cytotoxicity and promotes the degranulation and cytolytic activity of co-cultured NK92 cells. Mechanistic studies pinpoint that downstream of KRAS, both YAP1 and STAT3 are recruited by oncogenic PKCι to elevate the expression of PDL1, contributing to constitute an immune suppressive microenvironment in PDAC. Co-culture with NK92 further induces PDL1 upregulation via STAT3 to stimulate immune escape of PDAC cells. Subsequently, inhibition of PKCι in PDAC alleviates the immune suppression and enhances the cytotoxicity of NK92 towards PDAC through restraining PDL1 overexpression. Combined with PD1/PDL1 blocker, PKCι inhibitor remarkably elevates the cytotoxicity of NK92 against PDAC cells in vitro, establishing PKCι inhibitor as a promising candidate for boosting the immunotherapy of PDAC.

PKCλ/ι Loss Induces Autophagy, Oxidative Phosphorylation, and NRF2 to Promote Liver Cancer Progression

Oxidative stress plays a critical role in liver tissue damage and in hepatocellular carcinoma (HCC) initiation and progression. However, the mechanisms that regulate autophagy and metabolic reprogramming during reactive oxygen species (ROS) generation, and how ROS promote tumorigenesis, still need to be fully understood. We show that protein kinase C (PKC) λ/ι loss in hepatocytes promotes autophagy and oxidative phosphorylation. This results in ROS generation, which through NRF2 drives HCC through cell-autonomous and non-autonomous mechanisms. Although PKCλ/ι promotes tumorigenesis in oncogene-driven cancer models, emerging evidence demonstrate that it is a tumor suppressor in more complex carcinogenic processes. Consistently, PKCλ/ι levels negatively correlate with HCC histological tumor grade, establishing this kinase as a tumor suppressor in liver cancer.

[The Effects of PKCι on Anti-tumor Activity of Cytokine-induced Killer Cells Against Pancreatic Cancer Cells and the Possible Underlying Mechanisms]

OBJECTIVE

To study the impact of atypical protein kinase Cι (PKCι) isoform PKC on the pancreatic cancer cells towards the tumoricidal effect of cytokine-induced killer (CIK) cells and explore its mechanisms.

METHODS

CIK cells were prepared by inducing mononuclear cells isolated from the peripheral blood of healthy people with interleukin-2 (IL-2), interferon (IFN) and CD3 mAb and subsequently co-cultured with pancreatic epithelial cell HPDE6-C7, pancreatic cancer cells MiaPaCa and PANC-1 with or without PKC inhibitor named sodium thiomalate (ATM). All cells were divided into control group, ATM group, co-culture group with CIK and co-culture group with CIK+ATM. Cell count was used to detect the growth of each group from 1 to 8 d. Flow cytometry was used to detect the death rate of the cell lines after 48 h cell culture in each group. The small hairpin RNA (shRNA) was used for PKCι knockdown and the recombinant plasmid transfection was for PKCι overexpression in pancreatic cancer cells. Western blot and real-time fluorescent quantitative PCR (qRT-PCR) were utilized to determine the expression of PKCι protein and the impact on gene expression of transforming growth factor-β (TGF-β), a downstream effector modulated by PKC. Different mass concentrations of TGF-β (1, 10, 20 ng/mL) were added into the co-culture of MiaPaCa and PANC-1 with CIK. The cell death rate was detected by flow cytometry 48 h later, so as to explore the possible mechanisms of the impact of PKCι on the tumoricidal effects of CIK cells.

RESULTS

ATM and CIK were shown to suppress the growth and induce apoptosis or death of pancreatic cancer cells, meanwhile, ATM can enhance the tumoricidal effect of CIK on pancreatic cancer cells. Moreover, we found that PKCι knockdown in pancreatic cancer cells can down-regulate the gene expression of TGF-β. In return, PKCι overexpression in pancreatic cancer cells can increase the gene expression of TGF-β. The death rate of cancer cells with 10, 20 ng/mL TGF-β was lower compared with the control group (P < 0.05).

CONCLUSIONS

PKCι knockdown in pancreatic cancer cells can not only inhibit the growth of pancreatic cancer cells, but also enhance the tumoricidal effects of CIK on cancer cells. The possible mechanism of PKCι is to affect the immune escape of tumor cells by regulating the expression of TGF-β.

PKCι and YAP1 are crucial in promoting pancreatic tumorigenesis

Pancreatic ductal adenocarcinoma (PDAC) is a fatal malignant disease with 5-year survival rate of less than 6%. Activating mutations of Kras (mu-Kras) are often detected in most of PDAC patients. Although it has been known that oncogenic Kras is the driver of pancreatic cancer initiation and development, the underlying mechanisms by which mu-Kras promotes PDAC remain poorly understood. Here, we identify that PKCι is one of the crucial factors for supporting the survival of pancreatic cancer cells expressing mu-Kras. Our study demonstrates that after the knockdown of PKCι, the expression of the transcriptional co-activator YAP1 is decreased, which hinders the expression of the downstream target gene Mcl-1, and subsequently sensitizes pancreatic cancer MiaPaCa and PANC-1 cells experssing mu-Kras to apoptosis. In comparison, the suppression of PKCι has little impact on the viability of non-neoplastic pancreatic HPDE6-C7 cells. Moreover, the transient overexpression of oncogenic Kras in HPDE6-C7 elevates the expression of PKCι and YAP1 concomitantly. The upregulated YAP1 in HPDE6-C7/ mu-Kras cells is abolished once PKCι is suppressed, suggesting the linear relationship among mu-Kras, PKCι and YAP1. This phenomenon is further proven by the co-upregulation of PKCι and YAP1 in HPDE6-C7 cells stably transfected with mu-Kras. Taken together, our findings suggest that PKCι acts through promoting YAP1 function to promote the survival of pancreatic cancer cells expressing mu-Kras. It appears that targeting PKCι-YAP1 signaling is a feasible strategy for developing new therapeutics for treating pancreatic cancer patients.

PKCι depletion initiates mitotic slippage-induced senescence in glioblastoma

Cellular senescence is a tumor suppressor mechanism where cells enter a permanent growth arrest following cellular stress. Oncogene-induced senescence (OIS) is induced in non-malignant cells following the expression of an oncogene or inactivation of a tumor suppressor. Previously, we have shown that protein kinase C iota (PKCι) depletion induces cellular senescence in glioblastoma cells in the absence of a detectable DNA damage response. Here we demonstrate that senescent glioblastoma cells exhibit an aberrant centrosome morphology. This was observed in basal levels of senescence, in p21-induced senescence, and in PKCι depletion-induced senescence. In addition, senescent glioblastoma cells are polyploid, Ki-67 negative and arrest at the G1/S checkpoint, as determined by expression of cell cycle regulatory proteins. These markers are all consistent with cells that have undergone mitotic slippage. Failure of the spindle assembly checkpoint to function properly can lead to mitotic slippage, resulting in the premature exit of mitotic cells into the G1 phase of the cell cycle. Although in G1, these cells have the replicated DNA and centrosomal phenotype of a cell that has entered mitosis and failed to divide. Overall, we demonstrate that PKCι depletion initiates mitotic slippage-induced senescence in glioblastoma cells. To our knowledge, this is the first evidence of markers of mitotic slippage directly in senescent cells by co-staining for senescence-associated β-galactosidase and immunofluorescence markers in the same cell population. We suggest that markers of mitotic slippage be assessed in future studies of senescence to determine the extent of mitotic slippage in the induction of cellular senescence.

PKC iota promotes cellular proliferation by accelerated G1/S transition via interaction with CDK7 in esophageal squamous cell carcinoma

Protein kinase C iota (PKCι) has been shown to play an important role in tumorigenesis of many cancers. It was reported that frequent amplification and overexpression of PKCi were correlated with resistance to anoikis in primary esophageal squamous cell carcinomas (ESCC). In this study, we clarified a novel role of PKCι on the cell cycle progression and proliferation in ESCC. Western blot and immunohistochemistry (IHC) analysis showed that the expression of PKCι was higher in ESCC tumor tissues and cell lines. Meanwhile, IHC stain revealed that PKCι was positively correlated with clinical pathologic variables such as tumor size, tumor grade, and tumor invasion, as well as ki67. Immunoprecipitation and immunofluorescence assay revealed that PKCι/CDK7 has the physical interaction and were co-located in the cell nucleus. And this direct interaction could increase the phosphorylation level of CDK7. In vitro studies such as starvation and refeeding assay along with PKCι-shRNA transfection assay demonstrated that PKCι expression promoted proliferation of ESCC cells. And knocking PKCi down by silencing RNA (siRNA) significantly caused cell cycle arrest at G0/G1 phase, decreased rate of colony formation, and alleviated cellular apoptosis. This research provide new insights into PKCi signaling to more deeply understand its cancer-promoting function in ESCC.