Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Physiology and Pharmacology

Supervisor

Dr Lina Dagnino

Abstract

Integrin-linked kinase (ILK) is a β integrin adaptor protein that translates extracellular stimuli to intracellular signaling events. ILK plays a role in actin cytoskeleton dynamics and cell adhesion. The structure and function of the epidermis is highly dependent on cell-cell adhesion and cell-basement membrane interactions. The mechanisms whereby ILK contributes to epidermal integrity are poorly understood. Using a mouse model of epidermis-restricted Ilk gene inactivation, I observed that ILK loss causes abnormal morphology and presence of intra-epidermal and epidermal-dermal microblisters in embryos as early as E17.5. ILK-deficient epidermis is also characterized by abnormal localization or/and absence of adherens junctions, tight junctions and desmosomes. These are structures that maintain the barrier properties of the epidermis. Ca2+ is an important inducer of cell-cell junctions and differentiation in epidermal keratinocytes. In the absence of ILK, cultured keratinocytes are unable to properly respond to Ca2+, due to an impaired activation of the RhoA GTPase.

I further investigated the barrier function of the epidermis against Staphylococcus aureus, a major component of the skin microbiota. Using cultured keratinocytes, I investigated the role of integrin-linked kinase (ILK) in epidermal S. aureus invasion. ILK-deficient mouse keratinocytes internalized bacteria 2- to 4-fold less efficiently than normal cells. The reduced invasion by live S. aureus of ILK-deficient cells was restored in the presence of exogenous, constitutively active Rac1. Thus, Rac1 functions downstream from ILK during invasion.

Another function of the epidermis is protection against UV radiation. Phagocytic melanosome uptake by epidermal keratinocytes is a central protective mechanism against damage induced by ultraviolet radiation. I have examined the role of ILK in regulation of phagocytosis, and shown that ILK-deficient cells exhibit severely impaired capacity to engulf fluorescent microspheres in response to stimulation of the keratinocyte growth factor (KGF) receptor or the protease-activated receptor-2. KGF promoted activation of Rac1 and formation of pseudopodia in ILK-expressing, but not in ILK-deficient cells. Rac1-deficient keratinocytes also showed substantially impaired phagocytic ability, underlining the importance of ILK-dependent Rac1 function for particle engulfment. In summary, my data suggest a key role for ILK in activation of small GTPases and regulation of actin dynamics during phagocytosis by keratinocytes.


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