Fibronectin gene transcription is enhanced in abnormal wound healing

Abnormal wound healing in susceptible individuals can result in the formation of keloids that have an elevated content of extracellular matrix material compared to normal scars. Keloid-derived fibroblasts exhibit as much as a four-fold increase in the rate of fibronectin biosynthesis compared to fibroblasts from normal dermis and normal scars. Altered biosynthesis is due to an increase in the steady-state level of fibronectin mRNA, and in this investigation we have identified the level of fibronectin gene expression that is responsible for this increase. The rate of fibronectin gene transcription was found to be increased as much as threefold in keloid fibroblasts when compared to normal fibroblasts. Other possible changes that could account for the elevated level of fibronectin mRNA in keloids, such as increased copy number of the fibronectin gene or decreased turnover of fibronectin mRNA were also examined. The possibility of altered gene dosage was eliminated because chromosome content, G-banding patterns, and fibronectin gene content of keloid fibroblasts were all found to be normal. Analysis of fibronectin mRNA degradation revealed a half-life of approximately 13 h, and the residual fibronectin mRNA was observed to remain full length during this time period in both keloid and normal fibroblasts. Thus, altered degradation of fibronectin mRNA is unlikely to contribute to overproduction of fibronectin in keloids. Increased translational competence of fibronectin mRNA in keloids was also eliminated as a contributing factor because fibronectin mRNA remaining after one half-life were equally available for translation in both cell types. Although stimulation of transcription may not entirely account for the increase in fibronectin biosynthesis in keloids, this mechanism is best able to account for the majority of the change.