Cis- and trans-acting factors that regulate BMP processing and secretion

Cell-cell communication forms the basis for the development of all multicellular organisms, and mis-regulation of cell signalling systems is often associated with developmental defects and contributes to the onset of many kinds of cancer. The bone morphogenetic proteins (BMPs) are a class of cell signalling molecules that were initially identified by virtue of their role in bone formation in humans, but which have subsequently been shown to function throughout development, and, indeed, in all organisms in the animal kingdom. The key aim of this proposal is to identify factors that are involved in regulating BMP function. In particular, the research focuses on those factors that affect the production of the active signalling molecule. Like many signalling molecules (insulin is a good example), BMPs are not synthesized in their ?active? form, but rather as inactive ?pro-proteins? that must be cleaved by specific enzymes to produce the active peptide. The goal of this study is to characterize the various factors and processes that are involved in activation of BMPs. Different parts of the proposal focus on different aspects of the process including how BMPs interact with one another, what sites in the pro-proteins are necessary for proper cleavage, what enzymes are catalyzing this reaction, and what other proteins are involved in moving the BMP to the cell surface. Through the combination of these approaches, we will have a better understanding of the mechanisms underlying the regulation of cell-cell communication and its role in developmental processes.

Bone morphogenetic proteins (BMPs) are a class of intercellular signalling molecules that are essential for the development of all metazoans, and play key roles in fundamental cellular processes including cell specification, proliferation, differentiation and apoptosis. The BMPs fall roughly into two classes, the BMP2/4 class, which are the primary morphogenetic factors, and the less well-characterized BMP5/6/7/8 class, members of which modulate BMP2/4 function. This proposal focuses on the two Drosophila members of the BMP5/6/7/8 class, Screw (Scw) and Glass Bottom Boat (Gbb), and aims to characterize the cis- and trans- acting factors that are involved in their processing and secretion and that modulate their interactions with the BMP2/4 ortholog Decapentaplegic (Dpp). The first aim of the proposal focuses on the characterization of cis- acting elements in the Scw and Gbb precursor proteins that are responsible for their proper function and their context-specific interactions with Dpp. The second and third aims address the cis- and trans-acting factors involved in the proteolytic cleavage of the pro-protein. In particular, the second aim focuses on the identification and function of sequences in the pro-protein that are essential for proper cleavage, and the third on the genetic and molecular characterization of the Drosophila Furins, which are the enzymes likely to catalyse this cleavage. The final aim describes a whole-genome approach using RNA-interference technology to screen the genome for genes involved in BMP processing and secretion. Candidate genes identified in these screens will form the basis for further studies on the regulation of BMP processing during development. As a whole, the proposal presents an integrated genetic and biochemical dissection of BMP regulation, processing, and secretion that will provide the first detailed analysis of the regulatory elements responsible for this aspect of the BMP signalling pathway.