Identification and localization of a neurally expressed member of the plakoglobin/armadillo multigene family

Abstract

The plakoglobin/armadillo multigene family comprises many proteins widely differing in sizes and functions which have in common a variable number of tandemly repeated arm sequences of about 42 amino acids (aa). In a search for proteins with sequence homology to the desmosomal-plaque-associated arm-repeat-containing protein, plakophilin 1, we have identified a novel plakoglobin/armadillo protein. This new member of the multigene family is predominantly, if not exclusively, expressed in neural and neuroendocrine tissues, hence the name neural plakophilin-related arm-repeat protein (NPRAP). The murine cDNA codes for a protein of 1247 aa, with a predicted molecular weight of 135 kDa and a pI of 7.57. The orthologous human protein differs only in a few aa, indicative of the evolutionary stability of NPRAP. In human and murine cDNAs, we have found different transcripts of the NPRAP gene, suggesting that in each species the protein exists in at least two isoforms. The NPRA protein contains three different regions: a 528-aa amino-terminal "head" domain, including a potential coiled-coil-forming alpha-helix segment, a central domain with 10 imperfect arm-repeat units, and a 212-aa carboxy-terminal "tail" domain. By aa sequence, NPRAP is highly homologous to three proteins: p120cas, p0071 and ARVCP, which represent a distinct subgroup within the plakoglobin/armadillo family. By in situ hybridization and immunofluorescence microscopy using NPRAP-specific antibodies, we have demonstrated NPRAP and its mRNA in the perikarya of various kinds of CNS neurons in embryonic and adult mice, but minimal amounts have also been detected by immunoblot analysis in some other tissues containing neural or neuroendocrine elements. We have not seen significant enrichment of NPRAP at cell junctions or in nuclei. Possible NPRAP functions are discussed and the correlation of NPRAP synthesis with neuronal differentiation processes is emphasized.