Could a Possible Crosstalk between AMPK and TGF-β Signaling Pathways Be a Key Player in Benign and Malignant Salivary Gland Tumors?

Abstract

Background: Salivary gland tumors (SGTs) are known for their specific heterogeneity and ambiguous outcome for the affected patients. The LKB1 and SMAD4 genes are pivotal components of important signaling pathways, including AMPK and TGF-β. To our knowledge, no study has reported an association between the expression levels of these genes in SGTs. The expression levels of LKB1 and SMAD4 were evaluated to clarify their possible crosstalk in SGTs. Materials and Methods: A total of 50 fresh tissue specimens were obtained from patients with SGTs, including pleomorphic adenoma (PA), Warthin’s tumor (WT), intermediate grade mucoepidermoid carcinoma (MEC), salivary duct carcinoma (SDC), and carcinoma ex pleomorphic adenoma (CexPA), as well as 8 normal samples. Quantitative real-time polymerase chain reaction was performed for all samples with specific primers. Results: Data were analyzed using statistical methods. PA, WT, MEC, and SDC showed a significant decrease in LKB1 levels, but the gene was up-regulated in CexPA. SMAD4 was overexpressed in all samples. Conclusion: The results suggest a possible link between downregulation of LKB1 and overexpression of SMAD4 in SGTs. LKB1 depletion leads to upregulation of SMAD4, promoting epithelial-mesenchymal transition in tumor cells. Therefore, LKB1 and SMAD4 could be key players in inducing tumor heterogeneity in SGTs.

Role of Smad signaling in kidney disease

“…The tumor suppressor kinase LKB1 (liver kinase B1), can phosphorylate Thr-77 in Smad4 MH1 domain to form a protein complex between Smad4 and the LKB1-interacting protein 1 (LIP1), which negatively regulates TGF-β gene responses and epithelial-mesenchymal transition [47][48][49]. In addition, p38 MAP kinase acts as an agonist to phosphorylate Smad4 and bind to TGF-β receptors to facilitate Smad binding and activation [50].…”