Evidence for two isoforms of the endoplasmic-reticulum Ca2+ pump in pig smooth muscle

Abstract

cDNA clones coding for the endoplasmic reticulum Ca2+-transport ATPase have been cloned from a pig smooth-muscle cDNA library. The transcripts can be divided into two classes which differ in their 3' ends due to alternative splicing of the primary gene transcript. The class 1 cDNA encodes a protein of 997 amino acids (Mr 110,000). The class 2 protein (1042 amino acids; Mr 115,000) is completely identical to the class 1 protein except that the four C-terminal amino acids of the class 1 protein are replaced in the class 2 protein with a tail of 49 amino acids. Comparison of these sequences with other Ca2+ pump sequences reveals that the class 1 isoform corresponds to the sarcoplasmic reticulum Ca2+ pump of slow-twitch skeletal/cardiac muscle, whereas the class 2 protein corresponds to a Ca2+ pump recently detected in non-muscle tissues.

Higher plant Ca(2+)-ATPase: primary structure and regulation of mRNA abundance by salt.

“…The greatest homology is seen with the SER Ca2+-ATPases of animals. Overall amino acid identity of LCA with animal SER Ca2+-ATPases is 50% (28,(32)(33)(34)(35)(36)(37)(38), 27-35% with three putative yeast Ca2+-ATPases (39,40), and 25-31% with all of the other P-type ATPases (19,27,(41)(42)(43)(44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54)(55)(56), including animal PM Ca2+-ATPases (57,58) (Table 1). In addition to the highly conserved functional domains of all P-type ATPases, large regions of relatively high amino acid sequence identity (>60%) are seen between LCA and the SER Ca2+-ATPase, but not between LCA and other P-type ATPases (regions A, B, and C; Fig.…”

The sarco(endo)plasmic reticulum Ca2+‐ATPase mRNA isoform, SERCA 3, is expressed in endothelial and epithelial cells in various organs

“…The SERCA 1 gene is exclusively expressed in fast skeletal muscle [4,5]. The SERCA 2 gene gives rise to two alternatively spliced transcripts, one of which, SERCA 2a, has been detected in adult cardiac muscle, in slow skeletal muscle and in some smooth muscle tissues whereas the other, SERCA 2b, is found in adult smooth muscle and in non-muscle tissues [6][7][8][9][10][11][12]. SERCA 3, originally isolated from adult rat kidney, is highly homologous to SERCA 1 and SERCA 2 mRNAs; it was shown to be expressed in a broad variety of muscle and non-muscle tissues [1] but its cellular localization remained unknown.…”

Structure of the Human Sarco/Endoplasmic Reticulum Ca2+-ATPase 3 Gene

“…The Ets-1 cis-element 5Ј-GAG-GAAG-3Ј (46) was found at position Ϫ1181 to Ϫ1175. A trinucleotide repeat (TAA) 9 is found at position Ϫ1430 to Ϫ1404. A poly(dA-dT) stretch (47), 16 bp long, was found within the Alu sequence at position Ϫ1634 to Ϫ1619.…”

“…Tissue-specific processing of the SERCA2 gene primary transcript generates up to four mRNA classes (6), which code for two isoenzymes as follows: a cardiac/ slow-twitch skeletal muscle protein (SERCA2a) and a ubiquitously expressed isoform (SERCA2b). As a result of alternative splicing, the SERCA2a-specific C terminus comprising the sequence AILE (aa 994 -997) is replaced by a variant tail of 49 or 50 amino acids in SERCA2b (7)(8)(9). This extended tail contains a very hydrophobic stretch, which is suggested to represent a possible 11th transmembrane segment (7)(8)(9).…”

“…As a result of alternative splicing, the SERCA2a-specific C terminus comprising the sequence AILE (aa 994 -997) is replaced by a variant tail of 49 or 50 amino acids in SERCA2b (7)(8)(9). This extended tail contains a very hydrophobic stretch, which is suggested to represent a possible 11th transmembrane segment (7)(8)(9). The divergence in the C-terminal part is responsible for functional differences between SERCA2a and SERCA2b (10,11); these differences were recently ascribed to the presence of the last 12 amino acids in SERCA2b (12).…”