Influence of extracellular matrix macromolecules on normal human keratinocyte phenotype and parathyroid hormone-related protein secretion and expression in vitro

Parathyroid hormone-related protein (PTHrP) is produced by a wide range of neoplastic and normal cells, including keratinocytes where it may be involved in the regulation of cellular growth and differentiation. There is evidence that the nature of the extracellular matrix (ECM) influences gene expression and cell phenotype. The objective of this study was to investigate the phenotype of normal human keratinocytes grown on different types of ECM (basement membrane components or collagen type I), as well as the expression and secretion of PTHrP. Normal keratinocytes grown on basement membrane extract (Matrigel) actively reorganized the matrix and formed networks of cells with traction of the matrix. This was associated with linear arrays of intracellular microtubules and formation of prominent actin stress fibers and was suppressed by treatment with colchicine or cytochalasin B, confirming the role of the cytoskeleton in this process. In addition, growth on Matrigel was associated with increased PTHrP nuclear translocation, secretion, and mRNA expression compared to growth on collagen where keratinocytes exhibited decreased proliferation and increased differentiation. PTHrP, as a paracrine keratinocyte factor, did not appear to mediate the morphologic changes, since they were not altered by treatment with neutralizing anti-PTHrP antibodies. It was concluded that different types of ECM influenced the morphologic, functional, and proliferative characteristics of keratinocytes, as well as the level of PTHrP expression and secretion in vitro.