Deletion of the transcription factor ATF4 in a model of clear cell renal cell carcinoma.

Clear cell renal cell carcinoma (ccRCC) is the most common form of kidney cancer in adults. We generated TRAnsgenic of Cancer of the Kidney (TRACK) mice that express a triple-mutant (P402A, P564A, and N803A) human HIF1α construct specifically in their proximal tubule (PT) cells. We demonstrated that the elevated lipid content found in human ccRCCs is mimicked in these TRACK PT cells. Additionally, we reported that ATF4 (activating transcription factor 4), a transcription factor, and its target genes were highly expressed both in human ccRCCs and in TRACK PT cells. To delineate the functions of ATF4 in ccRCC we have now generated TRACK mice in which the ATF4 gene is specifically deleted in PT cells (GCREA∆T). Our genome-wide transcriptomics and proteomics studies show that expression of ∼20 % of mRNAs and proteins is significantly altered in GCREA∆T compared to TRACK kidney cortices. Gene set enrichment analyses (GSEAs) of mRNAs demonstrate that the fatty acid metabolism pathway is upregulated in TRACK vs WT and that, conversely, ATF4 deletion reduces mRNAs in the fatty acid metabolism pathway (e.g., ATP citrate lyase). Moreover, some transcripts elevated in human ccRCC are reduced in GCREA∆T vs. TRACK kidney cortices and cystic, pre-cancerous lesions are also reduced. Thus, ATF4 actions increase both lipid droplet accumulation in this ccRCC model and oncogenesis-related gene expression. These data suggest that ATF4 contributes to the formation of ccRCC tumors and may be a potential therapeutic target

Modulation of 11β-hydroxysteroid dehydrogenase expression by bombesin: A possible mechanism for glucocorticoid resistance in androgen independent prostate cancer

Treatment with glucocorticoids is one of a limited number of options for androgen independent prostate cancer. Neuroendocrine differentiation has been shown to contribute to androgen-independent prostate cancer progression. To study the potential link between neuroendocrine differentiation and the glucocorticoid action, we investigated the effects of the product of neuroendocrine differentiation - bombesin on glucocorticoid metabolizing enzymes - 11β-hydroxysteroid dehydrogenases in PC-3 cells. Our Western analysis, RT-PCR, and activity assays demonstrate that while 18-hour exposure to bombesin reduces 11β-hydroxysteroid dehydrogenases-1 profiles (activities 25% less, protein level 29% lower, mRNA levels 45% lower), contrarily it increases 11β-hydroxysteroid dehydrogenases-2 profiles (activities 34%, protein levels 100%, mRNA levels 120%). Blockade bombesin action with bombesin receptor antagonists and the enzyme degrading bombesin prevented these changes, suggesting the observed modulations were bombesin receptor-specific. In addition, bombesin increased the amounts of interleukin-8 and mRNA of vascular endothelial growth factor receptor 2, which were lowered in the presence of cortisol, suggesting that neuropeptide blockade may extend the benefits of glucocorticoids in treating androgen-independent prostate cancer