KLF6/Sp1 initiates transcription of the tmsg-1 gene in human prostate carcinoma cells: an exon involved mechanism.

The tumor metastasis suppressor gene-1 (tmsg-1) was first cloned as a new tumor suppressor gene in our laboratory several years ago. Since then, however, despite the substantial progression that has been made in investigation of the biologic roles played by this gene, the manner in which it exerts its regulatory influence is still unknown. With transfection of various deletion or mutation constructs, we identified a potential enhancer and three potential silencers in the 5'-flanking region. However, it was particularly interesting to find that a region (+59 to +123 bp) of exon 1 exhibited a strong role in initiation of tmsg-1 gene transcription. Deletion of this region led to essentially complete loss of driving activity of exon-1 sequence on luciferase. Further analysis showed that transcription factors KLF6 and Sp1 are able to interact with each other and bind to their elements in this region. Co-transfection of pGL3-114/+123 with KLF6- and/or Sp1-expressing plasmids resulted in an elevation of luciferase activity and transcription level of tmsg-1, which was abolished by knockdown of KLF6 or Sp1. Analysis of metastatic capacity showed that cells with high metastatic capability exhibited a lower level of KLF6/TMSG-1 proteins with higher invasive capability and vice versa. Thus, we concluded that interaction of KLF6 and Sp1, together with their binding of elements in exon 1 are critical events in initiation of transcription of the tmsg-1 gene. These results reveal a hitherto unreported mechanism for initiation of transcription of the tmsg-1 gene.