Date of Award

12-2007

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Program

Interdisciplinary Program

Research Advisor

Xin Zhang, Ph.D.

Committee

Lisa K. Jennings, Ph.D. Ken Nishimoto, Ph.D. Rennolds S. Ostrom, Ph.D. Radhakrishna Rao, Ph.D.

Keywords

KAI1/CD82, tetraspanins, actin, lamellipodia, Rac, and Rho

Abstract

To determine how tetraspanin KAI1/CD82, a tumor metastasis suppressor, inhibits cell migration, we assessed which motility-related cellular events are altered by KAI1/CD82 and how KAI1/CD82 regulates these events. We found that KAI1/CD82-overexpressing cancer cells exhibit various morphologies but typically display elongated cellular extensions and a lack of lamellipodia. Live imaging demonstrated that the formation of lamellipodia and retraction of extensions were deficient upon KAI1/CD82 overexpression.

The deficiency in developing motility-related cellular events was accompanied by defects in actin cortical network and stress fiber formations. Notably, actin polymerization was attenuated by KAI1/CD82. Although Rac1 activity was diminished upon KAI1/CD82 expression, Rac1 could not rescue lamellipodia formation because Rac1 activity is not required for this process in Du145 prostate cancer cells. Surprisingly, RhoA activity was upregulated upon KAI1/CD82 overexpression despite the loss of stress fiber and lack of cellular retraction, suggesting that enhanced RhoA activity is a compensatory effect resulting form impaired actin polymerization. Cofilin, an effector of both Rac and Rho, cannot translocate to the cell periphery in KAI1/CD82-overexpressing cells to facilitate lamellipodia formation, though the total and active cofilin proteins remain unchanged.

In summary, we demonstrate that KAI1/CD82 inhibits protrusion and retraction events crucial for cell movement by disrupting actin cortical network and stress fiber formations. At the molecular level, KAI1/CD82 impairs actin polymerization by unbalancing Rac1 and RhoA activities. KAI1/CD82-induced disruption of actin organization likely results from the suppression of common signaling steps of multiple pathways but is alleviated by cell-cell adhesion.

DOI

10.21007/etd.cghs.2007.0187

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