Abstract: The invention provides methods and compositions for treating diseases and conditions, which are associated with an abnormal PDGF level or response, such as cell proliferation, cell migration, extracellular matrix synthesis and secretion, and cell contraction. Exemplary diseases or disorders include cell proliferative diseases and fibrotic diseases. Exemplary fibrotic diseases include those resulting from a wound healing process, such as excessive scarring and PVR. Generally, the method comprise administering to a subject in need thereof a pharmaceutically efficient amount of a nucleic acid encoding a mutated PDGFR. The invention further provides gel contraction assays for identifying compounds for treating or preventing the development of diseases involving cell contraction, e.g., fibrotic diseases.