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Cytochrome b5 domain containing 2 (CYB5D2) (neuferricin) belongs to the family of membrane-associated progesterone receptors (MAPRs). MAPRs affect multiple cellular processes, including proliferation, differentiation, and survival. Consistent with these observations, we report here that CYB5D2 enhances HeLa cells survival of etoposide (ETOP)-mediated cytotoxicity. Overexpression of CYB5D2 enhanced the survival of HeLa cells compared with HeLa cells transfected with empty vector (EV) upon ETOP treatment. As ETOP initiates ATM-dependent DNA damage response (DDR), we were able to show that CYB5D2 did not affect ETOP-induced DDR. In line with these observations, CYB5D2 did not protect HeLa cells from UV-induced cytotoxicity. Additionally, CYB5D2 had no effects on TNFα-induced apoptosis. Collectively, CYB5D2 enhances HeLa cell survival of ETOP-induced cytotoxicity with some specificity. CYB5D2 contains a cytochrome b5 (cyt-b5) domain and a transmembrane (TM) motif. Both domains are required for CYB5D2-mediated protection of HeLa cells from ETOP-induced cytotoxicity. In an effort to search for the underlying mechanisms, we have profiled gene expression between HeLa-CYB5D2 and HeLa-EV cells. Although ectopic CYB5D2 does not massively alter gene expression, the expression of several transcripts was affected more than 2-fold, suggesting that they may contribute to CYB5D2-mediated HeLa cell survival of ETOP treatment. Key words: CYB5D2/neuferricin, cytotoxicity, apoptosis, cell cycle and DNA damage response. Resume : La neuferricine (CYB5D2, acronyme de Cytochrome b5 domain containing 2) appartient a la famille des recepteurs de la progesterone associes a la membrane (MAPR). Les MAPR affectent plusieurs processus cellulaires, notamment la proliferation, la differenciation et la survie. De maniere coherente avec ces observations, nous rapportons ici que CYB5D2 augmente la survie des cellules HeLa soumises aux effets cytotoxiques de l'etoposide (ETOP). La surexpression de CYB5D2 augmentait la survie des cellules HeLa comparativement aux cellules HeLa transfectees avec un vecteur vide (VV) a la suite du traitement a l'ETOP. Puisque le l'ETOP initie une reponse aux dommages a l'ADN dependante de l'ATM, nous avons pu demontrer que CYB5D2 n'affectait pas cette reponse induite par l'ETOP. Dans la foulee de ces observations, CYB5D2 ne protegeait pas les cellules HeLa de la cytotoxicite induite par les UV. De plus, CYB5D2 n'avait pas d'effet sur l'apoptose induite par le TNF-α. En somme, CYB5D2 augmente la survie des cellules HeLa traitees a l'ETOP avec une certaine specificite. CYB5D2 contient un domaine cytochrome b5 (cyt-b5) et un motif transmembranaire. Les deux domaines sont requis a la protection conferee par CYB5D2 vis-a-vis la cytotoxicite induite par l'ETOP chez les cellules HeLa. Afin de decouvrir les mecanismes sous-jacents, nous avons dresse un profil de l'expression genique chez les cellules HeLa-CYB5D2 et HeLa-VV. Meme si CYB5D2 ne modifie pas massivement l'expression genique, les niveaux d' expression de plusieurs transcrits etaient affectes de plus de deux fois, ce qui suggere que ces derniers peuvent contribuer a la survie des cellules HeLa conferee par CYB5D2 a la suite d'un traitement a l'ETOP. Mots-cles : CYB5D2/neuferricine, cytotoxicite, apoptose, cycle cellulaire, reponse aux dommages a l'ADN. [Traduit par la Redaction], Introduction Nongenomic actions of progesterone are mediated by the membrane progesterone receptors (mPRs), which include the 7 transmembrane PRs and the single transmembrane PRs (Bramley 2003; Brinton et al. 2008; [...]

Inactivation of phosphatase and tensin homolog (PTEN) is a critical step during tumorigenesis, and PTEN inactivation by genetic and epigenetic means has been well studied. There is also evidence suggesting that PTEN negative regulators (PTEN-NRs) have a role in PTEN inactivation during tumorigenesis, but their identity has remained elusive. Here we have identified shank-interacting protein-like 1 (SIPL1) as a PTEN-NR in human tumor cell lines and human primary cervical cancer cells. Ectopic SIPL1 expression protected human U87 glioma cells from PTEN-mediated growth inhibition and promoted the formation of HeLa cell-derived xenograft tumors in immunocompromised mice. Conversely, siRNA-mediated knockdown of SIPL1 expression inhibited the growth of both HeLa cells and DU145 human prostate carcinoma cells in vitro and in vivo in a xenograft tumor model. These inhibitions were reversed by concomitant knockdown of PTEN, demonstrating that SIPL1 affects tumorigenesis via inhibition of PTEN function. Mechanistically, SIPL1 was found to interact with PTEN through its ubiquitin-like domain (UBL), inhibiting the phosphatidylinositol 3,4,5-trisphosphate (PIP3) phosphatase activity of PTEN. Furthermore, SIPL1 expression correlated with loss of PTEN function in PTEN-positive human primary cervical cancer tissue. Taken together, these observations indicate that SIPL1 is a PTEN-NR and that it facilitates tumorigenesis, at least in part, through its PTEN inhibitory function., Introduction While PTEN displays phosphatase activity for both protein and lipid substrates (1), accumulating evidence reveals that its lipid phosphatase activity, which dephosphorylates the 3'-position phosphate from the inositol ring [...]