Liver fibrosis caused by chronic alcohol abuse represents a worldwide medical problem with a high mortality rate. In the United States, chronic liver fibrosis associated with ethanol abuse is one of the top causes of death among alcoholics. Fibrosis is characterized by excessive synthesis of type I collagen. Despite the medical advances, there are no known anti fibrotic drugs available. Activated hepatic stellate cells (HSCs) are the primary cells responsible for excess collagen synthesis during liver injury. Steady state level of collagen mRNAs is dramatically increased in fibrosis and efficient translation of these mRNAs results in secretion of high levels of collagen protein. Therefore, understanding the regulation of translation of collagen mRNAs may lead to development of novel antifibrotic drugs. Collagen mRNAs have a unique 5'stem loop structure (5'SL) and our lab has recently characterized a new protein, La ribonucleoprotein domain family member 6 (Larp6), that binds 5'SL and regulates translation. We have identified two additional proteins which participate in translation of collagen mRNAs;RNA helicase A (RHA), and FK506 Binding Protein 3 (FKBP3). RHA facilitates translation of mRNAs with structured 5'end, but has not been associated with translation of collagen mRNAs. Because of the 5'SL, the 5'UTR of collagen mRNAs is structured;it is thus likely that RHA may enhance their translation.
Specific aim 1 of this proposal will address this hypothesis. FKBP3 belongs to the immunophillin class of proteins which bind immunosuppressants (FK506 and rapamycin) with high affinity. So far FKBP3 has been poorly characterized and its biological function is unclear. When we overexpressed FKPB3 in HSCs they failed to synthesize type I collagen. Overexpression of FKBP3 in lung fibroblasts resulted in secretion of homotrimers of collagen 11(I) chains, while the secretion of 12(I) chain was abolished. Normally, collagen protein is always secreted as heterotrimer of two 11(I) and one 12(I) chains. This indicates that FKBP3 may regulate coordinated synthesis and folding of collagen polypeptides. When we treated the cells with rapamycin, which shows strong affinity for FKBP3, the same result was obtained. This indicates that rapamycin, or other related immunosuppressant drugs, may have antifibrotic properties. These are novel findings and I will characterize the effect of FKBP3 and immunosuppressant drugs on collagen expression in the specific aim 2 of this proposal. Overall, I believe that the proposed experiments will help elucidate the mechanism of translation of collagen mRNAs during chronic ethanol fibrogenesis and discover specific and critical molecular interactions which may be targets for future development of antifibrotic drugs.
This project will take a closer look into translational factors RNA Helicase A, and FK506 Binding Protein 3 involved in regulation of type I collagen expression during liver damage caused by chronic ethanol consumption. Detailed understanding of these factors could lead to their uses as potential targets of antifibrotic therapy.
|Manojlovic, Zarko; Earwood, Ryan; Kato, Akiko et al. (2014) RFX7 is required for the formation of cilia in the neural tube. Mech Dev 132:28-37|
|Manojlovic, Zarko; Blackmon, John; Stefanovic, Branko (2013) Tacrolimus (FK506) prevents early stages of ethanol induced hepatic fibrosis by targeting LARP6 dependent mechanism of collagen synthesis. PLoS One 8:e65897|
|Manojlovic, Zarko; Stefanovic, Branko (2012) A novel role of RNA helicase A in regulation of translation of type I collagen mRNAs. RNA 18:321-34|