TRANSCRIPTIONAL STIMULATION OF THE DELTA-1-CRYSTALLIN GENE BY INSULIN-LIKE GROWTH FACTOR-I AND INSULIN REQUIRES DNA CIS ELEMENTS IN CHICKEN

Insulin-like growth factor I (IGF-I) and insulin regulate expression of the endogenous δ1-crystallin gene in embryonic lens cells that express receptors for both peptides. To further analyze the transcriptional component of this hormonal effect, transient transfections of lens cells were prepared with DNA constructs containing deletions of the δ1-crystallin promoter and the chloramphenicol acetyltransferase reporter gene. A 77-nucleotide DNA segment of the δ1-crystallin promoter from nucleotide positions -120 to -43 confers sensitivity to insulin and IGF-I. The hormonal effect is dose-dependent, and maximal stimulation of promoter activity (2- to 2.5-fold induction) is obtained with 10-8 M IGF-I and 10-7 M insulin. Mobility-shift DNA-binding analysis shows specific binding of nuclear protein(s) to the δ1-crystallin promoter DNA between positions -120 and +23, which appears to be regulated by IGF-I. An SP1-binding motif is involved in this DNA-protein interaction. The bivalent IgG fraction of an anti-insulin receptor antiserum (B-10), known to mimic insulin action in other systems, stimulates promoter activity to the same extent as insulin.