Neuroendocrine secretory protein 55 (NESP55): Alternative splicing onto transcripts of the GNAS gene and posttranslational processing of a maternallyexpressed protein

Recent studies established a novel genomically imprinted gene located 45 kb upstream of the human GNAS1 locus. This locus encoded for the Neuroendocri ne Secretory Protein with an apparent molecular weight of 55,000 (NESP55), which is transcribed exclusively from the maternal allele. We sequenced rat and human NESP55 and investigated tissue-specific splicing of its mRNA and posttranslational modifications of the protein in various tissues. Alterna tive mRNA splicing of NESP55 was analyzed by sequencing of cDNA clones, RT- PCR and Northern blotting. Two main splice variants, which were generated i n a tissue-specific manner, were identified: The open reading frame encodin g NESP55 was spliced onto exons 2-13 of Gsa in the adrenal medulla, pituita ry and the brain. In addition, in the pituitary a second shorter, prominent mRNA transcript was generated by splicing of NESP55 onto exons 2, 3 and N1 of Gs alpha. Several of the cDNA clones isolated contained inverted repeat s of 50-150 bp at their 5' or 3' termini, which might form hairpin stems an d thus alter mRNA stability. The NESP55 open reading frame encoded a hydrop hilic protein of 28,018 Da (human) and 29,218 Da (rat), respectively, which resembled the class of acidic, neuroendocrine secretory proteins collectiv ely called chromogranins. NESP55 is highly conserved among mammalian specie s. It is posttranslationally acidified by the addition of keratan sulfate g lycosaminoglycan chains and differentially processed by endopeptidases in v arious endocrine and euronal tissues. Copyright (C) 2000 S. Karger AG, Base l.