Cloning and characterization of the alternative promoter regions of the human LIMK2 gene responsible for alternative transcripts with tissue-specificexpression

We previously isolated the human LIMK2 gene and identified two alternative transcripts, LIMK2a and LIMK2b, which were differentially regulated in a ti ssue-specific manner. To examine this differential tissue-specific expressi on in detail, an RNase protection assay was performed, which demonstrated t hree expression patterns of the LIMK2 isoforms. In digestive organs, the LI MK2a transcripts were preferentially expressed in fetal and adult tissues; in brain and lung, the LIMK2a transcript was predominantly expressed only i n fetal tissue, and in placenta, the LIMK2b transcript was expressed more a bundantly than that of LIMK2a. To further investigate this mechanism and th e transcription factors involved, we isolated the two distinct 5' upstream regions from the phage genomic library and found that both LIMK2a and 2b pr omoters have a single major transcription initiation site and the character istics of a TATA-less promoter. A luciferase reporter assay of the transcri ptional activity revealed positive as well as negative regulatory regions w ithin both promoters. The co-transfection assay suggested that the MZF-1 mi ght regulate the expression of the LIMK2 isoforms in a different manner. Th e ROR alpha 1 might also be involved in the transcriptional regulation of t he LIMK2b isoform. The genomic structure of the LIMK2 gene was also determi ned. These findings should lead to a better understanding of the possibly d iverse functions of the LIMK family. (C) 1999 Elsevier Science B.V. All rig hts reserved.