Integrin is the ab heterodimeric cell surface receptor for extracellular matrix (ECM) and an excellent model to investigate the function of conserved tyrosine (Y) phosphorylation motif, NPXY. The b integrin possesses two NPXY motifs, Y792 and Y804, in the cytoplasmic tail, and the phosphorylation of NPXY mediates interaction to a protein with phosphotyrosine binding (PTB) domain. Cell culture analyses suggested that Y to phenylalanine (F) mutation caused mild defects while Y to alanine (A) abolished cellular function of b integrins. We characterized the activation of NPXY using
bpat-3 integrin of the nematode Caenorhabditis elegans and generated a tyrosine (Y) to glutamate (E) mutant.
bpat-3(Y804E), a transgenic mutant carrying a phosphomimetic mutation in the second NPXY motif of the
bpat-3 cytoplasmic tail, showed defective muscles, abnormal gonad migration and tail morphology, ineffective mating, and high incidence in male. Some phenotypes of
bpat-3(Y804E) parallel those of
him-4/hemicentin, an ECM molecule similar to human fibulin-5, leading us to hypothesize that defective
him-4 causes phosphorylation in NPXY motifs of
bpat-3 cytoplasmic tail. Thus, we introduced the
bpat-3 non-phosphorylatable mutation,
bpat-3(YYFF), in the
him-4 background. Phenotypic analyses of
bpat-3(YYFF);
him-4 double mutant indicated that
bpat-3(YYFF) mutation suppressed ineffective mating, high incidence in male, and egg-laying defects of
him-4 males and hermaphrodites. This suggested that one of the functions of
him-4/hemicentin is to prevent phosphorylation of
bpat-3 NPXY. Further analysis will provide valuable information on the function of NPXY motifs in b integrin regulation and will enable us to interpret integrin signaling in other species.