Protein kinase D1 induced epithelial-mesenchymal transition and invasion in salivary adenoid cystic carcinoma via E-cadherin/Snail regulation.

Salivary adenoid cystic carcinoma (SACC) is a malignant tumor, which is characterized by a higher incidence of distant metastasis. The aim of this study was to investigate the role and mechanism of protein kinase D1 (PKD1) in regulating the epithelial-mesenchymal transition (EMT) and promotes the metastasis in SACC. We analyzed the expression of PKD1 in 40 SACC patients and different metastatic potential cell lines. Then, we investigated whether the migration and growth of SACC were regulated by PKD1 using shRNA interference or inhibition of kinase active in vitro cell. Moreover, the mechanism by which PKD1 regulates the stability of Snail protein was determined. Finally, nude mice were used to testify the function of PKD1 via tail vein injection. PKD1 was correlated with metastasis and poor prognosis of SACC patients. PKD1 inhibition attenuated proliferation, migration, invasion, and EMT of SACC cells. Conversely, kinase active PKD1 could induce EMT and promoted cell migration in human HSG cell. Furthermore, downregulation of PKD1 regulated Snail via phosphorylation at Ser-11 on Snail protein and promotion of proteasome-mediated degradation, and reduced lung metastasis in vivo. Our results suggest that PKD1 induces the EMT and promotes the metastasis, which illustrate that PKD1 may be a potential prognostic biomarker and serve as a potential therapeutic target for SACC patients.

Protein Kinase D3 Promotes the Reconstruction of OSCC Immune Escape Niche Via Regulating MHC-I and Immune Inhibit Molecules Expression.

Protein kinase D3 (PKD3) has been involved in various aspects of tumorigenesis and progression in many kinds of cancer types. However, whether PKD3 regulates immune escape in tumor microenvironment is rarely reported. Here, we explored the function and mechanism of PKD3 in reconstructing the immune escape niche of oral squamous cell carcinoma (OSCC). Both the Western blotting analysis in OSCC cells and the gene expression correlation analysis from The Cancer Genome Atlas shows that the expression of Fas and programmed cell death-ligand 1 (PD-L1) was positively correlated with PKD3, while major histocompatibility complex-I (MHC-I) was negatively correlated with PKD3. Knockdown of PKD3 significantly decreased the expression of Fas and PD-L1 and increased the expression of MHC-I. Furthermore, when PKD3 was overexpressed in oral precancerous cells, Fas, PD-L1, and MHC-I showed an opposite trend to that observed when PKD3 was knocked down. In addition, PKD3 knockdown decreased the secretion of transforming growth factor ß, CC-chemokine ligand 21, interleukin-10 by OSCC cells. Finally, the tumor cell antigen, which was extracted from PKD3 knockdown OSCC cells, significantly induced the growth and activation of T lymphocytes. These results demonstrate that PKD3 promotes the immune escape of OSCC cells by regulating the expression of Fas, PD-L1, MHC-I, transforming growth factor ß, CC-chemokine ligand 21, interleukin-10, and plays a key role in reconstructing the tumor immune escape niche.

Small-Molecule Inhibitor Targeting Protein Kinase D: A Potential Therapeutic Strategy.

The protein kinase D (PKD) family is a family of serine-threonine kinases that are members of the calcium/calmodulin-dependent kinase (CaMK) superfamily. PKDs have been increasingly implicated in multiple pivotal cellular processes and pathological conditions. PKD dysregulation is associated with several diseases, including cancer, inflammation, and obesity. Over the past few years, small-molecule inhibitors have emerged as alternative targeted therapy with fewer adverse side effects than currently available chemotherapy, and these specifically targeted inhibitors limit non-specific toxicities. The successful development of PKD inhibitors would significantly suppress the growth and proliferation of various cancers and inhibit the progression of other diseases. Various PKD inhibitors have been studied in the preclinical setting. In this context, we summarize the PKD inhibitors under investigation and their application for different kinds of diseases.

Salivary KLK5 and uPA are potential biomarkers for malignant transformation of OLK and OLP.

BACKGROUND: Oral squamous cell carcinoma (OSCC) usually originates from oral potentially malignant disorders (OPMD), such as oral leukoplakia (OLK) and oral lichen planus (OLP). Identifying biomarkers for the early diagnosis and evaluation of malignant transformation in OPMD could improve the survival rate of OSCC patients. OBJECTIVE: The present study aimed to screen for potential salivary biomarkers for evaluating the malignant transformation of OPMD. METHODS: Salivary proteases from OLK and OSCC patients or healthy donors and proteases in cultural medium from DOK and Cal-27 cells were detected with a human protease array kit. The concentrations of the salivary Kallikrein 5 (KLK5) and urokinase-type plasminogen activator (uPA) proteases were measured by ELISA. Receiver operating characteristics (ROC) to determine the potential value of these proteases in clinical diagnosis were calculated using SPSS software. Immunohistochemistry was used to detect the KLK5 and uPA expression in the oral organizations. RESULTS: The salivary protease spectrum was different among patients with OLK and OSCC and healthy donors. KLK5 and uPA levels in saliva tended to increase as the disease progressed (healthy < OPMD [OLK and OLP] < OSCC). ROC curves showed the optimum diagnostic cutoffs for KLK5 as a biomarker for OLK, OLP, and OSCC were 5.97, 6.03, and 9.45 pg/mL, respectively, while the cutoffs for uPA were 17.19, 17.26, and 20.96 pg/mL. Their combined analysis showed a higher sensitivity for the differential diagnosis of disease. Furthermore, higher levels of KLK5 and uPA were observed in OSCC tissues than in OLK and OLP. CONCLUSIONS: Salivary KLK5 and uPA are potential biomarkers for evaluating OLK and OLP malignant transformation and early diagnosis of OSCC.

PKD3 promotes metastasis and growth of oral squamous cell carcinoma through positive feedback regulation with PD-L1 and activation of ERK-STAT1/3-EMT signalling.

Oral squamous cell carcinoma (OSCC) has a high incidence of metastasis. Tumour immunotherapy targeting PD-L1 or PD-1 has been revolutionary; however, only a few patients with OSCC respond to this treatment. Therefore, it is essential to gain insights into the molecular mechanisms underlying the growth and metastasis of OSCC. In this study, we analysed the expression levels of protein kinase D3 (PKD3) and PD-L1 and their correlation with the expression of mesenchymal and epithelial markers. We found that the expression of PKD3 and PD-L1 in OSCC cells and tissues was significantly increased, which correlated positively with that of mesenchymal markers but negatively with that of epithelial markers. Silencing PKD3 significantly inhibited the growth, metastasis and invasion of OSCC cells, while its overexpression promoted these processes. Our further analyses revealed that there was positive feedback regulation between PKD3 and PD-L1, which could drive EMT of OSCC cells via the ERK/STAT1/3 pathway, thereby promoting tumour growth and metastasis. Furthermore, silencing PKD3 significantly inhibited the expression of PD-L1, and lymph node metastasis of OSCC was investigated with a mouse footpad xenograft model. Thus, our findings provide a theoretical basis for targeting PKD3 as an alternative method to block EMT for regulating PD-L1 expression and inhibiting OSCC growth and metastasis.

[Expression Level of Protein Kinase D in Oral Squamous Cell Carcinoma with Diverse Differentiation].

OBJECTIVE: This study aimed to investigate the expression level of protein kinase D (PKD) in oral squamous cell carcinoma (OSCC) and its relationship with differentiation of OSCC. METHODS: Sample was collected from 10 healthy control subjects and 40 OSCC confirmed by histopathological diagnosis, and the immunohistochemical staining was adopted to detect the expression of PKDs in OSCC tissues. The proportion of stained cell and staining intensity were evaluated to get a score, which used to analyze the difference among PKD1, PKD2 and PKD3 in various differentiation OSCC tissues. The correlations between the staining score of PKDs and differentiation of OSCC were further analyzed. RESULTS: PKD1 and PKD3 were high expression in OSCC tissues. There were statistical significance among the staining score of PKD1, PKD2 and PKD3 in various differentiation OSCC tissues ( P<0.001). In addition, there was a significantly negative correlation between the staining score of PKD1 and PKD2 with the differentiation of OSCC ( r=-0.574, -0.341, P<0.001). CONCLUSION: In OSCC tissues with different degree of differentiation, there might be some differences among PKDs which play a major role. The expression of PKD1 and PKD2 was correlated with the differentiation of OSCC, the poor differentiation of OSCC, the higher expression of PKD1 and PKD2.

Protein kinase D3 regulates the expression of the immunosuppressive protein, PD­L1, through STAT1/STAT3 signaling.

Oral squamous cell carcinoma (OSCC) is capable of constructing a favorable immune escape environment through interactions of cells with cells and of cells with the environment. Programmed death ligand­1 (PD­L1) is a well­recognized inhibitor of anti­tumor immunity that plays an important role in tumor immune escape. However, the molecular mechanisms regulating PD­L1 expression are not yet fully understood. In this study, to investigate the role of protein kinase D3 (PKD3) in the regulation of PD­L1 expression, the expression and correlation of PKD3 and PD­L1 were first analyzed by the immunostaining of human OSCC tissue sections, cell experiments and TCGA gene expression databases. The expression levels of PKD3 and PD­L1 were found to be significantly higher in OSCC cells than in normal tissues or cells. In addition, the expression levels of PKD3 and PD­L1 were found to be significantly positively correlated. Subsequently, it was found that the levsel of PD­L1 expression decreased following the silencing of PKD3 and that the ability of interferon (IFN)­Î³ to induce PD­L1 expression was also decreased in OSCC. The opposite phenomenon occurred following the overexpression of PKD3. It was also found that the phosphorylation of signal transducer and activator of transcription (STAT)1/STAT3 was reduced by the knockdown of PKD3 in OSCC. Moreover, the expression level of PD­L1 was decreased after the use of siRNA to knockdown STAT1 or STAT3. On the whole, the findings of this study confirm that PKD3 regulates the expression of PD­L1 induced by IFN­Î³ by regulating the phosphorylation of STAT1/STAT3. These findings broaden the understanding of the biological function of PKD3, suggesting that PKD is a potential therapeutic target for OSCC.