PI3K/AKT signaling determines a dynamic switch between distinct KSRP functions favoring skeletal myogenesis

Skeletal myogenesis is orchestrated by distinct regulatory signaling pathways, including PI3K/AKT, that ultimately control muscle gene expression. Recently discovered myogenic micro-RNAs (miRNAs) are deeply implicated in muscle biology. Processing of miRNAs from their primary transcripts is emerging as a major step in the control of miRNA levels and might be well suited to be regulated by extracellular signals. Here we report that the RNA binding protein KSRP is required for the correct processing of primary myogenic miRNAs upon PI3K/AKT activation in myoblasts C2C12 and in the course of injury-induced muscle regeneration, as revealed by Ksrp knock-out mice analysis. PI3K/AKT activation regulates in opposite ways two distinct KSRP functions inhibiting its ability to promote decay of myogenin mRNA and activating its ability to favor maturation of myogenic miRNAs. This dynamic regulatory switch eventually contributes to the activation of the myogenic program.

KSRP, many functions for a single protein

KSRP is a single-strand nucleic acids binding protein that affects RNA fate at multiple levels. KSRP modular structure and its complex pattern of post-translational modifications underpin the interaction with a wide spectrum of RNA target sequences, as well as with other RNA-binding proteins and molecular adaptors. These interactions are important to the regulation of different steps of mRNA metabolism and, in turn, modulate several aspects of cellular proliferation and differentiation. In this review we will discuss in detail KSRP ability to i) promote decay of labile mRNAs interacting with some components of the mRNA decay machinery and ii) favor the maturation of a select group of microRNA precursors.

Bone morphogenetic protein/SMAD signaling orients cell fate decision by impairing KSRP-dependent microRNA maturation

MicroRNAs (miRNAs) are essential regulators of development, physiology, and evolution, and their biogenesis is strictly controlled at multiple levels. Regulatory proteins, such as KSRP, modulate rates and timing of enzymatic reactions responsible for maturation of select miRNAs from their primary transcripts in response to specific stimuli. Here, we show that KSRP silencing in mesenchymal C2C12 cells produces a change in the transcriptome largely overlapping that induced by bone morphogenetic protein 2 (BMP2) signaling activation. This induces osteoblastic differentiation while preventing myogenic differentiation. KSRP silencing- and BMP2-dependent myogenic miRNA (myomiR) maturation blockade is required for osteoblastic differentiation of C2C12 cells. Our results demonstrate that phosphorylated R-SMAD proteins, the transducers of BMP2 signal, associate with phosphorylated KSRP and block its interaction with primary myomiRs. This abrogates KSRP-dependent myomiR maturation, with SMAD4, SMAD5, and SMAD9 silencing being able to rescue KSRP function. Thus, SMAD-induced blockade of KSRP-dependent myomiR maturation is critical for orienting C2C12 cell differentiation toward osteoblastic lineage.

KSRP silencing favors neural differentiation of P19 teratocarcinoma cells

Understanding the molecular mechanisms that control the balance between multipotency and differentiation is of great importance to elucidate the genesis of both developmental disorders and cell transformation events. To investigate the role of the RNA binding protein KSRP in controlling neural differentiation, we used the P19 embryonal carcinoma cell line that is able to differentiate into neuron-like cells under appropriate culture conditions. We have recently reported that KSRP controls the differentiative fate of multipotent mesenchymal cells owing to its ability to promote decay of unstable transcripts and to favor maturation of selected micro-RNAs (miRNAs) from precursors. Here we report that KSRP silencing in P19 cells favors neural differentiation increasing the expression of neuronal markers. Further, the expression of two master transcriptional regulators of neurogenesis, ASCL1 and JMJD3, was enhanced while the maturation of miR-200 family members from precursors was impaired in KSRP knockdown cells. These molecular changes can contribute to the reshaping of P19 cells transcriptome that follows KSRP silencing. Our data suggests that KSRP function is required to maintain P19 cells in a multipotent undifferentiated state and that its inactivation can orient cells towards neural differentiation.

The crystal structure of kukisvumite, Na6ZnTi4(Si2O6)4O4 · 4H2O

The crystal structure of kukisvumite, a rare mineral from Kola peninsula, Russia, has been refined in the Pccn space group with X-ray single-crystal data to R = 0.055. Kukisvumite, ideally Na6ZnTi4(Si2O6)4O4.4H2O, has a = 29.029(4) Å, b = 8.595(1) Å, c = 5.209(1) Å, and Z = 2. Its crystal structure is closely related to that of lintisite; the latter mineral is obtained from kukisvumite through the substitution Zn2+ ∀ = 2 Li+. In the Pccn space group an average structural model is realized, resulting in columns of half-occupied [ZnO4] tetrahedra and in zig-zag chains of half-occupied Na-centered octahedra. The actual structure of kukisvumite would imply a concerted ordering of zinc and sodium in neighbour cells. The polysomatic relationships of kukisvumite with the minerals of the lintisite family are shortly outlined.

1,2,3-Triazole[4,5-d]pyridazines--II. New derivatives tested on adenosine receptors

This paper reports the synthesis and biological evaluation towards A1 and A2 adenosine receptors of new 1,2,3-triazole[4,5-d]pyridazines bearing lipophilic substituents in the 1 position. Some 1-benzyl-4-substituted amino derivatives were prepared and the cyclohexylamino-, anilino- and p-toluidino- derivatives showed an interesting moderately selective activity on the A1 receptor.

The crystal structure of barstowite, Pb4Cl6(CO3) · H2O, determined on crystals from Etruscan slags and from a Late-Hellenistic shipwreck

Crystals of the rare lead mineral barstowite, Pb4Cl6(CO3) · H2O, were found on a lead object from a Late-Hellenistic shipwreck and within Etruscan iron slags. Its crystal structure was determined and refined to R = 0.023. Barstowite crystallizes in the monoclinic space group P21/m with a = 4.2043(8) Å, b= 9.199(2) Å, c= 16.663(3) Å, β = 91.82(1)°. The lead atoms are nine-fold coordinated in form of tricapped trigonal prisms by chlorine and oxygen atoms. The polyhedra, through sharing of faces, edges and corners, define structural layers which are linked together in a three-dimensional framework. Oxygen atoms belonging to the water molecules form hydrogen bonds with oxygens of the carbonate groups. The relationship of barstowite with cotunnite and phosgenite is shortly discussed.