CK2-mediated phosphorylation of Che-1/AATF is required for its pro-proliferative activity

Protein kinase CK2 – diverse roles in cancer cell biology and therapeutic promise

The association of protein kinase CK2 (formerly casein kinase II or 2) with cell growth and proliferation in cells was apparent at early stages of its investigation. A cancer-specific role for CK2 remained unclear until it was determined that CK2 was also a potent suppressor of cell death (apoptosis); the latter characteristic differentiated its function in normal versus malignant cells because dysregulation of both cell growth and cell death is a universal feature of cancer cells. Over time, it became evident that CK2 exerts its influence on a diverse range of cell functions in normal as well as in transformed cells. As such, CK2 and its substrates are localized in various compartments of the cell. The dysregulation of CK2 is documented in a wide range of malignancies; notably, by increased CK2 protein and activity levels with relatively moderate change in its RNA abundance. High levels of CK2 are associated with poor prognosis in multiple cancer types, and CK2 is a target for active research and testing for cancer therapy. Aspects of CK2 cellular roles and targeting in cancer are discussed in the present review, with focus on nuclear and mitochondrial functions and prostate, breast and head and neck malignancies.

CK2 and the Hallmarks of Cancer

Cancer is a leading cause of death worldwide. Casein kinase 2 (CK2) is commonly dysregulated in cancer, impacting diverse molecular pathways. CK2 is a highly conserved serine/threonine kinase, constitutively active and ubiquitously expressed in eukaryotes. With over 500 known substrates and being estimated to be responsible for up to 10% of the human phosphoproteome, it is of significant importance. A broad spectrum of diverse types of cancer cells has been already shown to rely on disturbed CK2 levels for their survival. The hallmarks of cancer provide a rationale for understanding cancer’s common traits. They constitute the maintenance of proliferative signaling, evasion of growth suppressors, resisting cell death, enabling of replicative immortality, induction of angiogenesis, the activation of invasion and metastasis, as well as avoidance of immune destruction and dysregulation of cellular energetics. In this work, we have compiled evidence from the literature suggesting that CK2 modulates all hallmarks of cancer, thereby promoting oncogenesis and operating as a cancer driver by creating a cellular environment favorable to neoplasia.

AATF is Overexpressed in Human Head and Neck Squamous Cell Carcinoma and Regulates STAT3/Survivin Signaling

Objective

Dysregulation of apoptosis antagonizing transcription factor (AATF) has been implicated in several cancers. However, its involvement in human head and neck squamous cell carcinoma (HNSCC) remains unclear. This study aimed to explore the expression pattern and biological roles of AATF in head and neck squamous cell carcinoma tissues and cell lines.

Methods

Immunohistochemistry was used to detect the level of AATF protein in 119 cases of HNSCC samples. CCK-8, colony formation, Annexin V/PI staining, Western blotting and RNA-sequencing were carried out to examine the change of proliferation, apoptosis and potential underlying mechanisms.

Results

Immunohistochemical staining showed that AATF was elevated in HNSCC, and high AATF level correlated with higher stage. The Cancer Genome Atlas (TCGA) and Oncomine data showed upregulated AATF expression in HNSCC compared with normal tissues. TCGA data also suggested that high AATF expression correlated with poor patient survival. Ectopic AATF expression upregulated the cell growth and colony formation ability in both FaDu and Detroit 562 cell lines, while AATF siRNA decreased the cell proliferation rate and colony numbers. AATF overexpression also decreased cisplatin sensitivity, downregulated cisplatin-induced apoptosis. Mechanistically, AATF overexpression upregulated survivin, while AATF knockdown downregulated survivin. RNA-sequencing (RNA-seq) and Gene Set Enrichment Analysis (GSEA) suggested that AATF knockdown decreased STAT3 signaling. Western blotting showed that AATF overexpression upregulated while AATF knockdown downregulated STAT3 phosphorylation. There was a positive correlation between AATF and survivin mRNA based on TCGA data analysis. Blockage of STAT3 signaling using inhibitor downregulated survivin expression and largely abolished the effects of AATF on survivin.

Conclusion

Our results showed that AATF was overexpressed in human HNSCC. AATF promoted cisplatin resistance and reduced apoptosis possibly through regulation of STAT3/survivin signaling. AATF could serve as a potential therapeutic target in HNSCC.