Iws1 (Interacts with Spt6) was originally identified in Saccharomyces Cerevisiae as a binding partner of Spt6, a histone H3/H4 chaperone.As a transcription factor, Iws1 plays a key role in defining the composition of the RNA polymerase II (RNAPII) elongation complex and in modulating the production of mature mRNA transcripts.Iws1 is phosphorylated, following stimulation with growth factors, by Akt3 and Akt1 at Ser720/Thr721 in human cells (Ser667/Thr668 in the mouse).Preliminary evidence supports a critical protumorigenic role of Iws1 and its phosphorylation in several types of malignancies such as lung cancer (NSCLC), mammary adenocarcinomas and melanomas.For example, it has been shown that, while IWS1 expression in normal human lung is very low, dramatically increases in many NSCLCs. Interestingly the level of IWS1 phosphorylation is variable between tumors and correlates with Akt3 expression.Moreover data from the TCGA database show that Iws1 is expressed at higher levels in tumors than in normal mammary gland specimens and also that basal and HER-2-enriched tumors express the highest levels. The genetic depletion of Iws1 in human mammary adenocarcinoma cell lines inhibits anchorage-independent growth in soft agar and mammosphere formation and growth. Similar experiment revealed that human melanoma cells were extraordinarily sensitive to the knockdown of Iws1. These experiments identify mammary adenocarcinomas and melanomas as tumors potentially addicted to Iws1. However, Iws1 biological functions are poorly characterized and there is no reported in vivo investigation about this RNA-processing factor.To begin to shed some light on the function of this protein at organismal level, we performed a thorough analysis of the expression of Iws1 and generated Iws1-deficient mice.The systematic analysis of expression in mouse tissues shows that Iws1 is ubiquitously expressed. We also report that ablation of Iws1 causes lethality at very early stages of mouse development. In fact, Iws1-deficient mouse embryos die at pre-implantation stage. Overall, these results show that Iws1 is an essential gene for mouse development and suggest a critical function in mammary adenocarcinomas as well as in melanoma.

Citation Format: Arturo Orlacchio, Claudia Foray, Tyler Sheetz, Erika Reese, Foued Amari, Aaron E. Stark, Krista La Perle, Ioannis Sanidas, Philip N. Tsichlis, Dario Palmieri, Vincenzo Coppola. IWS1 is essential for mouse development [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 359.