Hodivala, Kairbaan Jimmy; (1994) Changes in integrin expression during keratinocyte terminal differentiation and immortalisation. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Integrins are a family of cell-extracellular matrix adhesion molecules that regulate keratinocyte terminal differentiation. In stratified squamous epithelia integrins are normally expressed by the cells in the basal layer and are lost from the cell surface during terminal differentiation. In my thesis I have examined two situations in which this pattern of expression is perturbed: the presence of human papilloma virus and in cultures of keratinocytes grown in low extracellular calcium concentrations. I have compared two HPV-16 immortalised keratinocyte cell lines up and vp with their normal parental strains of normal keratinocytes from which they were derived u and v, and also with upr which was obtained by viral-Harvey-ras transfection of the up cell lines. The HPV-16 immortalised cell lines displayed reduced levels of integrin protein and mRNA and changes in adhesion and motlity. The upr cell line was not tumorigenic in nude mice and had little effect on integrin levels or cell motility when compared to the up; the only difference between the up and upr was that upr showed slight increased adhesion to fibronectin. Eight cervical biopsies with various grades of cervical intraepithelial neoplasia showed evidence of HPV infection. Integrin levels were either reduced or discontinuous in the most severe lesions and integrins were expressed in suprabasal layers in the less severe lesions. Thus, the impaired differentiation that is associated with the presence of HPV genes in vivo and in culture is correlated with abnormal integrin expression. When stratification is inhibited by growing keratinocytes in low calcium medium (0.1mM Ca2+) terminally differentiating cells express functional integrins which are diffusely distributed over the cell surface. When cells were transferred into standard calcium medium (1.8mM Ca2+) the integrins appeared to become concentrated at the lateral and basal surfaces of the cells. After 6 hr in standard calcium medium terminally differentiating cells migrated upwards to from a suprabasal layer and no longer expressed integrin protein or mRNA. A combination of antibodies to P- and E-cadherin which blocked calcium-induced stratification, prevented integrin redistribution and the selective loss of integrin protein and mRNA from the terminally differentiating cells. This suggests that cadherins play a role in the down regulation of integrin expression that is associated with tenninal differentiation. Further study into the mechanism of the interaction between integrins and cadherins using cytoskeleton-disrupting drugs and antibody microinjection have revealed a requirement for polymerised actin and a role for β catenin, plakoglobin and the β1 integrin cytoplasmic domain.

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