The coordination of cell-cell and cell-substrate adhesion plays a key role in regulating motility and intracellular signaling during epithelial cell remodeling that occurs in processes such as tissue morphogenesis and wound healing. The desmosomal protein plakoglobin (PG) is emerging as an important regulatory molecule in these processes. PG strengthens cell-cell adhesion and suppresses motility not only of keratinocytes in contact, but also, unexpectedly, cells not in contact with their neighbors. Preliminary data in the Green lab indicates that PG-null keratinocytes exhibit alterations in cell-substrate adhesion structures, actin organization and spreading that correlate with increased single cell motility. Based on these observations, we hypothesize that PG inhibits keratinocyte motility by regulating cell-substrate adhesion and cytoskeleton reorganization. Further, as preliminary data suggest that Src or Src family kinases are involved in PG-dependent suppression of motility, we propose to test the idea that PG suppresses motility through sequestration and/or inhibition of Src and associated signaling partners. Towards this end we propose: (1) To determine whether PG regulates integrin-mediated keratinocyte cell-substrate interaction; (2) To establish whether PG regulates cell motility by controlling cell-substrate dependent engagement of the actin cytoskeleton; (3) To elucidate the intracellular signaling mechanism of PG-dependent suppression of single cell motility.
These aims will be accomplished by using murine PG-null and human PG-difficient as well as control keratinocytes, to biochemically and visually assess the role of PG in integrin-dependent cell substrate adhesion and actin cytoskeleton remodeling. Further, we will determine the activity and intracellular distribution of key molecules involved in these processes. We will then use the existing PG mutants to establish whether there is a mechanistic link between the regulation of adhesion and cytoskeleton and motility suppression. Finally, we will determine the potential contribution of PG-mediated inhibition of Src as a part of the intracellular signaling mechanism by which PG controls key molecules regulating cell-substrate adhesion, actin cytoskeleton remodeling and cell motility. Cell-cell and cell substrate adhesion are responsible for maintaining tissue integrity, and breakdown of this mechanism leads to defects in normal processes such as wound healing as well as autoimmune, inherited and infectious skin disease and cutaneous cancer. The proposed studies focused on PG, an emerging regulator of cell-cell and cell-substrate adhesion, will provide a basis for the future diagnostic and therapeutic strategies in epithelial diseases. ? ? ?
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