TRANSFORMING-GROWTH-FACTOR OR IS A TARGET FOR THE VON-HIPPEL-LINDAU TUMOR-SUPPRESSOR

The von Hippel-Lindau (VHL) tumor suppressor gene has a critical role in the pathogenesis of clear cell renal cell carcinoma (RCC), because VHL mutations have been found in both VHL disease-associated and spora dic RCC. Overexpression of transforming growth factor (TGF)-alpha has been observed in numerous RCC tumors and cell lines, and TGF-alpha has been demonstrated to support RCC cell growth through an autocrine loo p. We demonstrate here that VHL substantially decreases TGF-alpha mess age and protein by shortening TGF-alpha mRNA half-life. By Northern an alysis TGF-alpha mRNA steady-state levels mere suppressed 5-fold in pe rmanent 786-0 RCC cell lines expressing wild-type VHL compared with 78 6-0 cells expressing an empty vector or a mutant VHL protein lacking C OOH-terminal residues 116-213 (Delta VHL). By Western analysis, VHL al so substantially down-regulated the unprocessed, cell-associated M-r 2 0,000 TGF-alpha protein. Moreover, secreted TGF-alpha was undetectable in VHL-expressing cells. In contrast, VHL did not down-regulate the T GF-alpha receptor, epidermal growth factor receptor, either at the mRN A or protein in level. Nuclear run-on in vitro transcription experimen ts in 786-0 cells showed that VHL did not affect transcriptional contr ol of the endogenous TGF-alpha gene. However, actinomycin D experiment s revealed a long TGF-alpha mRNA half-life in 786-0 cells that was sig nificantly decreased by wild-type VHL but not by Delta VHL. We have, t herefore, identified TGF-alpha, an important growth factor for RCC, as a new target gene for VHL and demonstrated that VHL acts by decreasin g TGF-alpha mRNA stability.