Division of Dermatology, Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710, USA. yeowe001@mc.duke.edu
Synthesis of collagen, a major component of the extracellular matrix, is increased dramatically in fibrotic conditions such as scleroderma. This overaccumulation of collagen is associated with increased pyridinoline cross-links. These cross-links are derived by the action of the alternatively spliced long form of lysyl hydroxylase 2 (LH2), a collagen telopeptide LH. As LH2 (long) is reported to be overexpressed in scleroderma fibroblasts, the regulation of LH2 splicing suggests an important step in controlling fibrosis. Using an LH2 minigene, we have compared the regulation of the alternative splicing pattern of LH2, both endogenously and in the minigene, by the RNA-binding splicing proteins TIA-1 and TIAL1 (T-cell-restricted intracellular antigens). A decrease in the ratio of LH2 (long) to LH2 (short) was observed in fibroblasts from TIAL1 knockout mice, and in HEK293 cells knocked down for TIA-1 and TIAL1. As a corollary, overexpression of TIA-1/TIAL1 in HEK293 cells resulted in an increase in LH2 (long) minigene transcripts, accompanied by a decrease in LH2 (short). In scleroderma fibroblasts, a double TIA-1/TIAL1 knockdown reduced the ratio of LH2 (long) to LH2 (short) by over fivefold compared to controls. Identification of these TIA regulatory factors therefore suggests a tool to manipulate cellular LH2 levels in scleroderma so that potential intervention therapies may be identified.