Phosphorylation of alpha-tubulin by protein kinase C engenders dramatic changes in microtubules.

What is it about?

When induced to express high levels of PKCα, non-transformed cells ⎯¬¬ normally non-motile and rounded in shape ⎯¬¬ acquired strong motility, a flat morphology and proliferated much more slowly. All of these attributes were indicative of a transition to a more cancerous state. Furthermore, a pivotal observation was that breast cells that were moving were not proliferating and vice versa. To determine how this might occur, we had to identify the next link in the chain of events. We discovered two protein substrates whose phosphorylation by PKCα resulted in cell motility of non-motile MCF-10A cells. One of these substrates, α-tubulin, was subsequently shown to undergo phosphorylation at a single site, Ser165. α-Tubulin and β-tubulin form a dimer that is the building block of microtubules, components of the cytoskeleton important for cell movement, cell division, and cell shape. Using genetic tools or pharmacological agents that respectively simulate or activate phosphorylation of α-tubulin at Ser165, we showed that the phosphorylated state dramatically activates microtubule dynamics of non-metastatic MCF-10A cells, but not metastatic breast cells. Conversely, when Ser165 phosphorylation was blocked in a site-specific mutant of α-tubulin, movement of metastatic breast cells was decreased substantially. This study preceded a subsequent work that showed that phosphorylation of this site results in slowed proliferation of metastatic cells and that when the phosphorylation site is blocked, these cells undergo rapid proliferation.

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Why is it important?

This work documents the significance of Ser165 phosphorylation as a possible biomarker for metastatic cancers, and as a target for PKC inhibitors as anti-metastasis drugs.

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