CALRETICULIN BINDS HYRNA AND THE 52-KDA POLYPEPTIDE COMPONENT OF THE RO SS-A RIBONUCLEOPROTEIN AUTOANTIGEN/

Calreticulin (CR) is a multifunctional, calcium-binding protein that h as recently been shown to bind to and promote the replication of the r ubella virus genome in mammalian cells. While CR is now widely recogni zed as a new human autoantigen, the relationship between CR and the Ro /SS-A ribonucleoprotein (RNP) autoantigen has been somewhat controvers ial. In this work, we demonstrate that unphosphorylated human rCR bind s specifically and distinctly to in vitro transcribed forms of hYRNA, the RNA backbone of the Ro/SS-A RNP particle. This interaction appears to be mediated by binding through the N- and C-terminal domains of CR , but not by the central proline-rich domain. Furthermore, our studies indicate that CR can facilitate the binding of the 60-kDa polypeptide component of the Ro/SS-A RNP (Ro60) to hYRNA. In addition, CR and the 52-kDa Ro/SS-A polypeptide (Ro52) appear to be capable of interacting through direct protein-protein binding. These studies confirm that CR is an hYRNA-binding protein, and provide for the first time a molecul ar mechanism by which Ro52 can be linked physically to hYRNA. Through these molecular interactions and its known functional role as a chaper one, it is suggested that CR plays a supportive role in the formation of the Ro/SS-A RNP complex. The capacity of CR to interact with RNA vi ruses such as rubella provides an additional argument for an infectiou s trigger for autoantibody production against self RNP particles such as Ro/SS-A.