Phosphorylation state of Ser¹⁶⁵ in α-tubulin is a toggle switch that controls proliferating human breast tumors

Area of Science:

• Cell Biology
• Molecular Biology
• Cancer Research

Background:

• Protein kinase Cα (PKCα) phosphorylates α-tubulin at Ser165, stimulating microtubule dynamics, cell motility, and epithelial-mesenchymal transition (EMT).
• Endogenous phosphorylation of α-tubulin at PKC sites is observed in metastatic breast cancer cell lines.

Purpose of the Study:

• To investigate the role of α-tubulin phosphorylation at Ser165 in regulating breast cancer cell behavior, specifically EMT and proliferation.
• To determine if specific phosphorylation states of α-tubulin can act as a molecular switch between EMT and hyper-proliferation.

Main Methods:

• Stable expression of α-tubulin mutants mimicking phosphorylated (S165D) and non-phosphorylated (S165N) states in MDA-MB-231-LM2-4175 cells.
• Analysis of cadherin expression (N-cadherin, E-cadherin) to assess EMT status.
• Cell cycle analysis, spindle fiber measurement, and proliferation assays.
• In vivo studies in nude mice to evaluate tumor formation and growth.

Main Results:

• The S165D mutant promoted N-cadherin expression, indicative of EMT.
• The S165N mutant suppressed N-cadherin, induced E-cadherin (cadherin switch), accelerated cell cycle progression, and increased proliferation.
• In vivo, S165N-expressing cells formed hyper-proliferative lung tumors with increased incidence and Ki67 expression.

Conclusions:

• The phosphorylation state of Ser165 in α-tubulin acts as a PKC-regulated molecular switch.
• This switch dictates whether breast cancer cells exhibit EMT characteristics or hyper-proliferative behavior.
• Findings suggest clinical relevance in human breast tumors, highlighting α-tubulin phosphorylation as a potential therapeutic target.