REGULATION OF NOV BY WT1 - A POTENTIAL ROLE FOR NOV IN NEPHROGENESIS

The nov gene encodes a putative Insulin-like-Growth Factor-Binding Pro tein (IGFBP) of a novel type which is structurally related to a family of growth-factors likely to play a role in the control of cell prolif eration. In the kidney, nov is expressed essentially at the embryonic stage and alterations of nov expression, relative to the normal kidney , have been detected in both avian nephroblastomas and human Wilms' tu mors. The levels of human nov (novH) and WT1 mRNA in individual Wilms' tumors have been shown to be inversely correlated, suggesting that th e expression of novH could be under the negative control of WT1. We ha ve now established the nucleotide sequence of the 5' flanking region,a nd identified two transcription start sites by RNase protection assays and primer extension. We report that in transient cotransfection expe riments the transcription activity of novH promoter constructs was rep ressed by two isoforms of WT1 proteins (WT1 and WT1 + KTS). Repression of the novH promoter required both intact zinc finger regions and the NH, transcription repression domain of WT1. Inasmuch as the minimal r egion of novH promoter required to mediate WT1 repression irt vivo fai led to bind recombinant WT1 protein in in vitro footprinting assays th is repression may be mediated by either (i) low affinity sites coopera tive interactions or (ii) indirectly via protein-protein interactions with another factor(s). Furthermore, constitutive expression of wild t ype WT1 into 293 cells resulted in a decrease of endogenous NOVH prote in levels, suggesting that novH may be a physiological target for WT1. The downregulation of novH expression by WT1 might represent a key el ement in normal and tumoral nephrogenesis.