Sarcomeric TPM3 expression in human heart and skeletal muscle.

In mammals, four tropomyosin genesTPM1,TPM2,TPM3, andTPM4are known. One isoform of theTPM3gene, encoding 285 amino acid residues designated as TPM3 alpha, has been reported. TPM3 alpha protein expression in human hearts is not definitively established. We have cloned from human heart and skeletal muscle transcripts of TPM3 alpha and three novel TPM3 isoforms, TPM3 nu, TPM3 xi, and TPM3 omicron. TPM3 nu and TPM3 omicron are alternatively spliced RNAs with different 3 '-UTRs encoding an identical novel protein with 285 amino acid differing from TPM3 alpha and TPM3 xi in exon 6 only. TPM3 alpha and TPM3 xi, which have different 3 ' UTRs, also encode an identical protein. qRT-PCR data show that the transcripts of TPM3 alpha, TPM3 nu, TPM3 xi, and TPM3 omicron are expressed in both heart and skeletal muscle. We have evaluated the expression of various TPM proteins in fetal and adult human hearts, and also in skeletal muscle samples. Western blots using CG3 antibody show a stronger signal of TPM3 protein in fetal heart and adult skeletal muscle compared to adult heart. LC-MS/MS studies with the protein spots separated and identified by CH1 antibody after 2D Western blot analyses, confirm the expression of TPM3 alpha/TPM3 xi in heart, but some peptides detected could be either TPM3 alpha or TPM3 nu. In heart samples, TPM1 protein was the dominant with varying amount of TPM2 and TPM3, while TPM4 expression was not observed. In skeletal muscles, TPM2 was the majority TPM protein expressed. The biological consequences of these varying expression of individual tropomyosin proteins are yet to be established.