Date of Award

Spring 1-1-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry & Biochemistry

First Advisor

Xuedong Liu

Second Advisor

Robert Kuchta

Third Advisor

Natalie Ahn

Fourth Advisor

Amy Palmer

Fifth Advisor

Kristi Anseth

Abstract

The migration of individual cells and collective groups of cells has been repeatedly shown to be an important cellular behavior throughout normal biology and disease progression. Although a significant amount of research has been conducted to understand how an individual cell achieves migration, relatively little is known about how groups of cells coordinate their efforts to migrate collectively. Several protein cytokines, including Transforming Growth Factor Beta (TGFβ), have been identified that can be globally administered to cells in vitro, but yield highly directional collective cell migration. In this thesis, I detail my efforts in elucidating how TGFβ stimulation of the human keratinocyte cell line, HaCaT, results in directional and collective cell migration.

I developed an in vitro assay and computational analysis program, named Pathfinder, to accurately quantify the angular movements of individual cells in time-lapse microscopy videos. This innovative approach allowed me to measure the degree to which individual cells turn as they migrate and the degree to which neighboring cells adopt the same migration direction. Using my newly developed tools to measure cellular migration, I found that TGFβ stimulation of HaCaT cells

indirectly activates MEK1 kinase activity, which is modulated by ligand induced cellular spreading. The resulting MEK1 kinase activity is required and sufficient to elicit collective cell migration in a group of physically interacting cells. I also showed that such collective cell migration is likely the result of the ability of MEK1 kinase activity to suppress turning behavior in individual cells, which contributes to the spontaneous induction of collective migration behavior in a group of cells. My findings contribute to the TGFβ field by providing an explanation for how MEK1 kinase can be activated by TGFβ receptor activation. In addition, my findings contribute to the collective cell migration field by detailing the important role of MEK1 activity in cellular steering, and providing an improved simple model for how collective migration can arise spontaneously.

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