CHARACTERIZATION OF BETA-PAT-3 HETERODIMERS, A FAMILY OF ESSENTIAL INTEGRIN RECEPTORS IN C-ELEGANS

Members of the integrin family of cell surface receptors have been sho wn to mediate a diverse range of cellular functions that require cell- cell or cell-extracellular matrix interactions. We have initiated the characterization of integrin receptors from the nematode Caenorhabditi s elegans, an organism in which genetics can be used to study integrin function with single cell resolution. Here we report the cloning of a n integrin beta subunit from C. elegans which is shown to rescue the e mbryonic lethal mutation pat-3(rh54) and is thus named beta pat-3. Ana lysis of the deduced amino acid sequence revealed that beta pat-3 is m ore similar to Drosophila integrin beta PS and to vertebrate integrin beta(1) than to other integrin beta subunits. Regions of highest homol ogy are in the RGD-binding region and in the cytoplasmic domain. In ad dition, the 56 cysteines present in the majority of integrin beta subu nits are conserved. A major transcript of similar to 3 kilobase pairs was detected by RNA blot analysis. Immunoblot analysis using a polyclo nal antiserum against the cytoplasmic domain showed that beta pat-3 mi grates in SDS-PAGE with apparent M(r) of 109 k and 120 k under nonredu cing and reducing conditions, respectively. At least nine protein band s with relative molecular weights in the range observed for known inte grin alpha subunits coprecipitate with beta pat-3, and at least three of these bands migrate in SDS-PAGE with increased mobility when reduce d. This behavior has been observed for a majority of integrin alpha su bunits. Immunoprecipitations of beta pat-3 from developmentally staged populations of C elegans showed that the expression of several of the se bands changes during development. The monoclonal antibody MH25, whi ch has been postulated to recognize the transmembrane component of the muscle dense body structure (Francis, G. R., and R. H. Waterston. 198 5. Muscle organization in Caenorhabditis elegans: localization of prot eins implicated in thin filament attachment and I-band organization. J . Cell Biol. 101:1532-1549), was shown to recognize beta pat-3. Finall y, immunocytochemical analysis revealed that beta pat-3 is expressed i n the embryo and in many cell types postembryonically, including muscl e, somatic gonad, and coelomocytes, suggesting multiple roles for inte grin heterodimers containing this beta subunit in the developing anima l.