Cellular signaling by tyrosine phosphorylation in keloid and normal human dermal fibroblasts

Keloids represent a dysregulated response to cutaneous wounding that result s in disfiguring scars. Unique to humans, keloids are characterized by an a ccumulation of extracellular matrix components. The underlying molecular me chanisms of keloid pathogenesis, however, remain largely uncharacterized. S imilarly, cellular signaling mechanisms, which may indicate inherent differ ences in the way keloid fibroblasts and normal human dermal fibroblasts int eract with extracellular matrix or other cells, have not been investigated. As part of a fundamental assessment of cellular response to injury in kelo id fibroblasts, phosphorylation studies were performed using three differen t keloid (n = 3) and normal human dermal (n = 3) fibroblast cell lines. The se studies were undertaken to elucidate whether keloid and normal human der mal fibroblasts exhibit different tyrosine kinase activity. Initially, dist inct tyrosine phosphorylation patterns of keloid and normal human dermal fi broblasts were demonstrated, Next, the phosphorylation patterns were correl ated with known molecules that may be important to keloid pathogenesis. On the basis of molecular weight, it was hypothesized that the highly phosphor ylated bands seen in keloid fibroblasts represented epidermal growth factor receptor (EGFR); discoidin domain receptor 1 (DDR1); and Shc, an adaptor p rotein known to bind many tyrosine kinases, including EGFR and DDR1. Indivi dual immunoblotting using EGFR, DDR1, and Shc antibodies revealed greater e xpression in keloid fibroblasts compared with normal human dermal fibroblas ts. These data substantiate for the first time the finding of greater phosp horylation by the above-mentioned molecules, which may be important in kelo id pathogenesis.