👤 Jean-Christophe Bérubé

RAS proteins are GTPases that lie upstream of a signaling network impacting cell fate determination. How cells integrate RAS activity to balance proliferation and cellular senescence is still incompletely characterized. Here, we identify ZNF768 as a phosphoprotein destabilized upon RAS activation. We report that ZNF768 depletion impairs proliferation and induces senescence by modulating the expression of key cell cycle effectors and established p53 targets. ZNF768 levels decrease in response to replicative-, stress- and oncogene-induced senescence. Interestingly, ZNF768 overexpression contributes to bypass RAS-induced senescence by repressing the p53 pathway. Furthermore, we show that ZNF768 interacts with and represses p53 phosphorylation and activity. Cancer genomics and immunohistochemical analyses reveal that ZNF768 is often amplified and/or overexpressed in tumors, suggesting that cells could use ZNF768 to bypass senescence, sustain proliferation and promote malignant transformation. Thus, we identify ZNF768 as a protein linking oncogenic signaling to the control of cell fate decision and proliferation. Show less

Type 3 17beta-hydroxysteroid dehydrogenase (17beta-HSD) catalyzes the last step in the biosynthesis of the potent androgen testosterone (T) by selectively reducing the C17 ketone of 4-androstene-3,17-dione (delta4-dione), with NADPH as cofactor. This enzyme is thus an interesting therapeutic target for androgen-sensitive diseases. Using an efficient convergent chemical approach we synthesized a phosphorylated version of the best delta4-dione/adenosine hybrid inhibitor of type 3 17beta-HSD previously reported. An appropriately protected C2' phosphorylated adenosine was first prepared and linked by esterification to the steroid delta4-dione bearing an alkyl spacer. After three deprotection steps, the phosphorylated bisubstrate inhibitor was obtained. The inhibitory potency of this compound was evaluated on homogenated HEK-293 cells overexpressing type 3 17beta-HSD and compared to the best non-phosphorylated bisubstrate inhibitor. Unexpectedly, the phosphorylated derivative was slightly less potent than the non-phosphorylated bisubstrate inhibitor of type 3 17beta-HSD. Two hypotheses are discussed to explain this result: 1) the phosphorylated adenosine moiety does not interact optimally with the cofactor-binding site and 2) the bisubstrate inhibitors, phosphorylated or not, interact only with the substrate-binding site of type 3 17beta-HSD. Show less

Steroidogenic enzyme type 3 17beta-hydroxysteroid dehydrogenase (17beta-HSD) is an important therapeutic target for androgen-sensitive diseases. This enzyme selectively reduces the C17 ketone of 4-androstene-3,17-dione (Delta4-dione), thus producing testosterone (T) using NADPH as cofactor. Our group previously synthesized hybrid (estradiol/adenosine) inhibitors that successfully inhibit the biosynthesis of the potent estrogen estradiol by type 1 17beta-HSD. To similarly lower the level of the potent androgen testosterone, inhibitors of type 3 17beta-HSD were designed and synthesized applying the same hybrid (substrate/cofactor) strategy. Two chemical approaches were developed to join the three components of the bisubstrate inhibitor (the substrate Delta4-dione, an alkyl spacer and the cofactor moiety adenosine). An alkylation in the alpha position of steroidal 17-ketone or a cross-metathesis was used as a key step to efficiently join the substrate and the alkyl spacer, whereas an esterification was employed to link the spacer to adenosine. An enzymatic assay in homogenated HEK-293 cells overexpressing type 3 17beta-HSD revealed that the best inhibitors of that series are those bearing an alkyl side-chain spacer of 11 or 12 methylenes: inhibition of 69 and 78% at 1 microM were respectively observed. As expected, these bisubstrate inhibitors were less potent in intact cells than in homogenated cells. However, both enzymatic assays revealed that the strategy of substrate/cofactor dual inhibitors seems to work for type 3 17beta-HSD, although the inhibitors designed have not been optimized yet. Show less