Type I collagen is the most abundant
protein in human body.
Fibrosis is characterized by excessive synthesis of
type I collagen in parenchymal organs. It is a leading cause of morbidity and mortality worldwide, about 45% of all natural deaths are attributable to some fibroproliferative disease. There is no cure for
fibrosis. To find specific antifibrotic
therapy targeting
type I collagen, critical molecular interactions regulating its synthesis must be elucidated. Type I and
type III collagen mRNAs have a unique sequence
element at the 5' end, the 5' stem-loop. This stem-loop is not found in any other
mRNA. We cloned LARP6 as the
protein which binds
collagen 5' stem-loop with high affinity and specificity. Mutation of the 5' stem-loop or knock down of LARP6 greatly diminishes
collagen expression. Mice with mutation of the 5' stem-loop are resistant to development of
liver fibrosis. LARP6 associates
collagen mRNAs with filaments composed of nonmuscle
myosin; disruption of these filaments abolishes synthesis of
type I collagen. Thus, LARP6 dependent
collagen synthesis is the specific mechanism of high
collagen expression seen in
fibrosis. We developed fluorescence polarization (FP) method to screen for drugs that can inhibit binding of LARP6 to 5' stem-loop
RNA. FP is high when LARP6 is bound, but decreases to low levels when the binding is competed out. Thus, by measuring decrease in FP it is possible to identify chemical compounds that can dissociate LARP6 from the 5' stem-loop. The method is simple, fast and suitable for high throughput screening.