Four Types of Calpastatin Isoforms with Distinct Amino-Terminal Sequences Are Specified by Alternative First Exons and Differentially Expressed in Mouse Tissues

Abstract

Calpastatin, a specific inhibitor of calpain, consists of a unique N-terminal domain (domain L) and four repetitive protease-inhibitor domains (domains 1-4). The isolated cDNAs from various mammalian species have conspicuous differences in the regions encoding the N-terminal sequences and can be classified into four types. Mouse and bovine calpastatins (Type I and Type II, respectively), which also differ from each other in the uttermost N-terminal regions, possess longer domain L sequences than those of rabbit, pig, and human inhibitors (Type III). A sequence of a shorter isoform, registered in a DNA data bank, starts from a part of domain 2 with a different N-terminal sequence (Type IV). To clarify the source of this molecular diversity, we investigated the entire exon-intron organization of the mouse calpastatin gene. The previously obtained mouse calpastatin cDNA is encoded by as many as 31 exons including the first exon, designated 1xa. Three additional exons specifying the N-terminal sequences of the other types (designated exons 1xb, 1u, and 14t, respectively) were identified in the mouse genomic DNA sequence. While the mRNAs for Types I and III were expressed at high levels in liver, the Type II mRNA was abundant in heart and skeletal muscle and expressed at lower levels in liver, brain and testis. The Type IV mRNA was specifically expressed in testis among the tissues examined. These results suggest that the calpastatin isoforms possessing different N-terminal sequences are generated by alternative transcription initiation from their own promoters and skipping of the mutually exclusive exons.

Foxj1 regulates basal body anchoring to the cytoskeleton of ciliated pulmonary epithelial cells

“…1B). The 110 kDa band represents full-length calpastatin, while the 70 kDa band represents a truncated form of calpastatin found in erythrocytes (Takano et al, 2000). A 50% decrease in the 110 kDa calpastatin protein was detected in foxj1 -/-lung tissue and a 25% decrease was detected in the foxj1 +/-lung tissue compared to E15.5 wild-type lung tissue (Fig.…”

Characterization and comparative expression of zebrafish calpain system genes during early development

“…CAST is the only known specific inhibitor of typical, dimeric calpains. In mammals, multiple CAST transcripts are generated from a single gene by means of extensive alternative splicing and transcription from one of three possible promoters (Lee et al, 1992;Cong et al, 1998;Takano et al, 1999Takano et al, , 2000. Whereas each isoform has four well-conserved calpain inhibitory domains in the C-terminus, each has a divergent L-domain at the Nterminus.…”

The Ca2+‐dependent interaction of calpastatin domain L with the C‐terminal tail of the Cav1.2 channel

“…CS is composed of multiple domains, including CS XL , CS L and domains 1-4 [1,8]. During cardiac ischemia and reperfusion injury, the full-length CS may be degraded [17], and the CS L may be released.…”

“…Domains 1-4 are responsible for the inhibition of calpain; but CS L does not have calpain-inhibition activity [1,2]. Based on the N-terminal sequence, CS is classified into four types: types I-IV.…”

“…The CS L domain is present in types I, II, and III (tissue-type), but not in type IV, which is found in erythrocyte-type CS. The existence of CS L is well conserved in tissuetype CS of humans, pigs, rabbits, and other mammals [1,2], but its physiological function remains largely unknown.…”