Abstract
It is urgent to identify and validate biomarkers for early diagnosis and efficient treatment of nasopharyngeal carcinoma (NPC). Recent studies have proposed p38 gamma (p38γ) as a cyclin-dependent kinase (CDK)-like kinase that phosphorylates retinoblastoma (Rb) to promote cyclins expression and tumorigenesis. Here the Gene Expression Profiling Interactive Analysis (GEPIA) database and results from the local NPC tissues demonstrate that p38γ is significantly upregulated in NPC tissues, correlating with poor overall survival. Furthermore, p38γ mRNA and protein expression is elevated in established NPC cell lines (CNE-1 HONE-1 and CNE-2) and primary human NPC cells, but low expression detected in human nasal epithelial cells. In established and primary NPC cells, p38γ depletion, using the shRNA strategy or the CRISPR/Cas9 gene-editing method, largely inhibited cell growth, proliferation and migration, and induced significant apoptosis activation. Contrarily, ectopic p38γ overexpression exerted opposite activity and promoted NPC cell proliferation and migration. Retinoblastoma (Rb) phosphorylation and cyclin E1/A expression were decreased in NPC cells with p38γ silencing or knockout, but increased after p38γ overexpression. Moreover, mitochondrial subcellular p38γ localization was detected in NPC cells. Significantly, p38γ depletion disrupted mitochondrial functions, causing mitochondrial depolarization, reactive oxygen species production, oxidative injury and ATP depletion in NPC cells. In vivo, intratumoral injection of adeno-associated virus-packed p38γ shRNA potently inhibited primary human NPC xenograft growth in nude mice. In p38γ shRNA virus-injected NPC xenograft tissues, p38γ expression, Rb phosphorylation, cyclin E1/A expression and ATP levels were dramatically decreased. Taken together, we conclude that p38γ overexpression is required for NPC cell growth, acting as a promising therapeutic target of NPC.
Highlights
Nasopharyngeal carcinoma (NPC) is a common nasopharynx epithelial malignancy with diverse etiopathogy and histopathology, causing ~65,000 cancer-related mortalities each year [1–3]
The cancer-promoting activity by p38γ overexpression in NPC cells The results showed that shRNA-induced p38γsilencing or CRISPR/Cas9-induced p38γ KO exerted significant anti-cancer activity in NPC cells, we tested whether p38γ overexpression could exert opposite activity
We found that p-PFKFB3/PFKFB3/glucose transporter 2 (GLUT2) expression was robustly decreased in p38γ-silenced or p38γ-KO CNE-1 cells (Fig. 6P), where the cellular ATP contents were decreased (Fig. 6Q). These results showed that p38γ depletion disrupted mitochondrial functions and depleted ATP in NPC cells
Summary
Nasopharyngeal carcinoma (NPC) is a common nasopharynx epithelial malignancy with diverse etiopathogy and histopathology, causing ~65,000 cancer-related mortalities each year [1–3]. There are three subtypes of NPC, including squamous cell carcinoma, non-keratinizing carcinoma and undifferentiated carcinoma [4–6]. The current clinical treatments for NPC include surgery, platinum-based chemotherapy and radiotherapy [4–6]. The latter includes 3D conformal radiation therapy, intensity-modulated radiation therapy, particle beam therapy and brachytherapy [4–6]. For the recurrent, metastatic and other advanced NPC patients, the progression-free survival (PFS) and overall survival (OS) are not satisfactory [1]. Treatments for these patients are largely limited to palliative systemic therapies [1, 4, 5]. P38γ phosphorylates retinoblastoma (Rb), the tumor suppressor protein, thereby increasing cyclin E1 and cyclin A expression and tumor cell growth. The isolation of mitochondria through the high-speed centrifugation was through the Pierce kit
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