Characterization of tissue-specific LIM domain protein (FHL1C) which is analternatively spliced isoform of a human LIM-only protein (FHL1)

We have cloned and characterized another alternatively spliced isoform of t he human four-and-a-half LIM domain protein 1 (FHL1), designated FHL1C. FHL 1C contains a single zinc finger and two tandem repeats of LIM domains at t he N-terminus followed by a putative RBP-J binding region at the C-terminus . FHL1C shares the same N-terminal two-and-a-half LIM domains with FHL1 but different C-terminal protein sequences. Due to the absence of the exon 4 i n FHL1C, there is a frame-shift in the 3' coding region. Sequence analysis indicated that FHL1C is the human homolog of murine KyoT2. The Northern blo t and RT-PCR results revealed that FHL1 is widely expressed in human tissue s, including skeletal muscle and heart at a high level, albeit as a relativ ely low abundance transcript in brain, placenta, lung, liver, kidney, pancr eas, and testis. in contrast, FHL1C is specifically expressed in testis, sk eletal muscle, and heart at a relatively low level compared with FHL1. The expression of FHL1C transcripts was also seen in aorta, left atrium, left, and right ventricles of human heart at low level. Immunoblot analysis using affinity-purified anti-FHL1C antipeptide antibodies confirmed a 20 kDa pro tein of FHL1C in human skeletal muscle and heart. Unlike FHL1 B, which is a nother FHL1 isoform recently reported by our group and localized predominan tly in the nucleus [Lee et al., 1999], FHL1C is localized both in the nucle us and cytoplasm of mammalian cell.