The virulence factor IpgD, delivered into nonphagocytic cells by the type III secretion system of the pathogen Shigella flexneri, is a phosphoinositide 4-phosphatase generating phosphatidylinositol 5 monophosphate (PtdIns(5)P). We show that PtdIns(5)P is rapidly produced and concentrated at the entry foci of the bacteria, where it colocalises with phosphorylated Akt during the first steps of infection. Moreover, S. flexneri-induced phosphorylation of host cell Akt and its targets specifically requires IpgD. Ectopic expression of IpgD in various cell types, but not of its inactive mutant, or addition of short-chain penetrating PtdIns(5)P is sufficient to induce Akt phosphorylation. Conversely, sequestration of PtdIns(5)P or reduction of its level strongly decreases Akt phosphorylation in infected cells or in IpgD-expressing cells. Accordingly, IpgD and PtdIns(5)P production specifically activates a class IA PI 3-kinase via a mechanism involving tyrosine phosphorylations. Thus, S. flexneri parasitism is shedding light onto a new mechanism of PI 3-kinase/Akt activation via PtdIns(5)P production that plays an important role in host cell responses such as survival.

Two isoforms of estrogen receptor (ER) have been described: ER␣ and ER␤. The initial gene targeting of ER␣, consisting in the introduction of a Neo cassette in exon 1 [␣ERKO, hereafter called ER␣-Neo KO (knockout)], was reported in 1993. More recently, another mouse deficient in ER␣ because of the deletion of exon 2 (ER␣KO, hereafter called ER␣-⌬2 KO) was generated. In ovariectomized ER␣-wild-type mice, estradiol (E2) increases uterine weight and basal production of endothelial nitric oxide (NO). Both of these effects are abolished in ER␣-⌬2 KO mice. In contrast, we show here that both of these effects of E 2 are partially (uterine weight) or totally (endothelial NO production) preserved in ER␣-Neo KO. We also confirm the presence of two ER␣ mRNA splice variants in uterus and aorta from ER␣-Neo KO mice. One of them encodes a chimeric ER␣ protein (ER␣55), partially deleted in the A͞B domain, that was detected in both uterus and aorta by Western blot analysis. The other ER␣ mRNA splice variant codes for an isoform deleted for the A͞B domain (ER␣46), which was detected in uterus of ER␣-Neo KO, and wild-type mice. This protein isoform was not detected in aorta. The identification of these two N-terminal modified isoforms in uterus, and at least one of them in aorta, probably explains the persistence of the E 2 effects in ER␣-Neo KO mice. Furthermore, ER␣-Neo KO mice may help in the elucidation of the specific functions of full-length ER␣ (ER␣66) and ER␣46, both shown to be physiologically generated in vivo.

Lineage conversion of one somatic cell type into another constitutes an attractive approach for research and clinical use. Lineage conversion can proceed in a direct manner, in the absence of proliferation and multipotent progenitor generation, or in an indirect manner, by the generation of expandable multipotent progenitor states. Here we report on the development of a combined reprogramming methodology that, transitioning through a plastic intermediate state, allows for the generation of human mesodermal progenitor cells while circumventing the traditional hallmarks of pluripotency. Converted mesodermal progenitor cells demonstrated bi-potent differentiation potential and were able to generate endothelial and smooth muscle lineages. Importantly, human fibroblasts can be converted into angioblast-like progenitor cells by non-integrative approaches. Differentiated angioblast-like cells exhibit neo-angiogenesis and anastomosis in vivo. The methodology for indirect lineage conversion to angioblast-like cells described here adds to the armamentarium of reprogramming approaches aimed at the clinical treatment of ischemic pathologies.