Hayashi K, Yano H, Hashida T, Takeuchi R, Takeda O, Asada K, Takahashi E, Kato I, Sobue K
Department of Neurochemistry and Neuropharmacology, Osaka University Medical School, Japan.
Proc Natl Acad Sci U S A. 1992 Dec 15;89(24):12122-6. doi: 10.1073/pnas.89.24.12122.
The high molecular weight caldesmon (h-CaD) is predominantly expressed in smooth muscles, whereas the low molecular weight caldesmon (l-CaD) is widely distributed in nonmuscle tissues and cells. The changes in CaD isoform expression are closely correlated with the phenotypic modulation of smooth muscle cells. During a search for isoform diversity of human CaDs, l-CaD cDNAs were cloned from HeLa S3 cells. HeLa l-CaD I is composed of 558 amino acids, whereas 26 amino acids (residues 202-227 for HeLa l-CaD I) are deleted in HeLa l-CaD II. The short amino-terminal sequence of HeLa l-CaDs is different from that of fibroblast (WI-38) l-CaD II and human aorta h-CaD. We have also identified WI-38 l-CaD I, which contains a 26-amino acid insertion relative to WI-38 l-CaD II. To reveal the molecular events of the expressional regulation of the CaD isoforms, the genomic structure of the human CaD gene was determined. The human CaD gene is composed of 14 exons and was mapped to a single locus, 7q33-q34. The 26-amino acid insertion is encoded in exon 4 and is specifically spliced in the mRNAs for both h-CaD and l-CaDs I. Exon 3 is the exon that encodes the central repeating domain specific to h-CaD (residues 208-436) together with the common domain in all CaD (residues 73-207 for h-CaD and WI-38 l-CaDs, and residues 68-201 for HeLa l-CaDs). The regulation of h- and l-CaD expression is thought to depend on selection of the two 5' splice sites within exon 3. Thus, the change in expression between l-CaD and h-CaD might be caused by this splicing pathway.
高分子量钙调蛋白（h-CaD）主要在平滑肌中表达，而低分子量钙调蛋白（l-CaD）广泛分布于非肌肉组织和细胞中。CaD亚型表达的变化与平滑肌细胞的表型调节密切相关。在寻找人类CaD的亚型多样性过程中，从HeLa S3细胞中克隆了l-CaD cDNA。HeLa l-CaD I由558个氨基酸组成，而HeLa l-CaD II中缺失了26个氨基酸（HeLa l-CaD I的202-227位残基）。HeLa l-CaD的短氨基末端序列与成纤维细胞（WI-38）l-CaD II和人主动脉h-CaD的不同。我们还鉴定出了WI-38 l-CaD I，相对于WI-38 l-CaD II，它含有一个26个氨基酸的插入片段。为了揭示CaD亚型表达调控的分子事件，确定了人类CaD基因的基因组结构。人类CaD基因由14个外显子组成，定位于一个单一基因座7q33-q34。26个氨基酸的插入片段在外显子4中编码，并且在h-CaD和l-CaD I的mRNA中特异性剪接。外显子3是编码h-CaD特有的中央重复结构域（208-436位残基）以及所有CaD中的共同结构域（h-CaD和WI-38 l-CaD的73-207位残基，HeLa l-CaD的68-201位残基）的外显子。h-CaD和l-CaD表达的调控被认为取决于外显子3内两个5'剪接位点的选择。因此，l-CaD和h-CaD之间表达的变化可能是由这种剪接途径引起的。
