The peritoneal cavity (PerC) is a unique compartment within which a variety of immune cells reside, and from which macrophages (MØ) are commonly drawn for functional studies. Here we define two MØ subsets that coexist in PerC in adult mice. One, provisionally called the large peritoneal MØ (LPM), contains approximately 90% of the PerC MØ in unstimulated animals but disappears rapidly from PerC following lipopolysaccharide (LPS) or thioglycolate stimulation. These cells express high levels of the canonical MØ surface markers, CD11b and F4/80. The second subset, referred to as small peritoneal MØ (SPM), expresses substantially lower levels of CD11b and F4/80 but expresses high levels of MHC-II, which is not expressed on LPM. SPM, which predominates in PerC after LPS or thioglycolate stimulation, does not derive from LPM. Instead, it derives from blood monocytes that rapidly enter the PerC after stimulation and differentiate to mature SPM within 2 to 4 d. Both subsets show clear phagocytic activity and both produce nitric oxide (NO) in response to LPS stimulation in vivo. However, their responses to LPS show key differences: in vitro, LPS stimulates LPM, but not SPM, to produce NO; in vivo, LPS stimulates both subsets to produce NO, albeit with different response patterns. These findings extend current models of MØ heterogeneity and shed new light on PerC MØ diversity, development, and function. Thus, they introduce a new context for interpreting (and reinterpreting) data from ex vivo studies with PerC MØ.CD11b | F4/80 | lipopolysaccharide | peritoneal cavity | thioglycolate

Although the viral genome is often quite small, it encodes a broad series of proteins. The virus takes advantage of the host-RNAprocessing machinery to provide the alternative splicing capability necessary for the expression of this proteomic diversity. Serinearginine-rich (SR) proteins and the kinases that activate them are central to this alternative splicing machinery. In studies reported here, we use the HIV genome as a model. We show that HIV expression decreases overall SR protein͞activity. However, we also show that HIV expression is significantly increased (20-fold) when one of the SR proteins, SRp75 is phosphorylated by SR protein kinase (SRPK)2. Thus, inhibitors of SRPK2 and perhaps of functionally related kinases, such as SRPK1, could be useful antiviral agents. Here, we develop this hypothesis and show that HIV expression down-regulates SR proteins in Flp-In293 cells, resulting in only low-level HIV expression in these cells. However, increasing SRPK2 function up-regulates HIV expression. In addition, we introduce SR protein phosphorylation inhibitor 340 (SRPIN340), which preferentially inhibits SRPK1 and SRPK2 and down-regulates SRp75. Although an isonicotinamide compound, SPRIN340 (or its derivatives) remain to be optimized for better specificity and lower cytotoxicity, we show here that SRPIN340 suppresses propagation of Sindbis virus in plaque assay and variably suppresses HIV production. Thus, we show that SRPK, a well known kinase in the cellular RNAprocessing machinery, is used by at least some viruses for propagation and hence suggest that SRPIN340 or its derivatives may be useful for curbing viral diseases.HIV ͉ kinase inhibitor ͉ SR protein phosphorylation inhibitor 340 H IV-1 precursor RNA transcribed from proviral DNA integrated in the host cell genome contains all of the transcribed viral reading frames (1). Alternative splicing is essential for producing mRNAs encoding various viral proteins from the limited size of a single precursor mRNA (2). In the early phase of HIV expression, eight splice acceptor sites compete for the splicing machinery to produce the vif, vpu, vpr, nef, env, tat, and rev mRNAs (3). In the late phase of the virus life cycle, singly spliced longer RNA is translated to a polyprotein and then cleaved by HIV protease to generate gag and pol proteins. Several reports show that regulation of the complex splicing pattern can dramatically affect HIV-1 infectivity and pathogenesis (4-6). However, little is known about the molecular mechanism that links this alternative splicing regulation and the dynamics of virus propagation.Alternative splicing depends on the alternative utilization of four 5Ј splice sites and eight 3Ј splice sites (3). The combination of these splice sites are regulated by cis-regulatory elements, which bind cellular heterogeneous nucleoproteins (hnRNPs) of the A, B, and H groups and serine-arginine-rich (SR) proteins (7). SR proteins are highly conserved in eukaryotes and are characterized by having one or two RNA-recognition motifs at the amino termi...

In eukaryotes, entry into M-phase of the cell cycle is induced by activation of cyclin B-Cdc2 kinase. At G2-phase, the activity of its inactivator, a member of the Wee1 family of protein kinases, exceeds that of its activator, Cdc25C phosphatase. However, at M-phase entry the situation is reversed, such that the activity of Cdc25C exceeds that of the Wee1 family. The mechanism of this reversal is unclear. Here we show that in oocytes from the starfish Asterina pectinifera, the kinase Akt (or protein kinase B (PKB)) phosphorylates and downregulates Myt1, a member of the Wee1 family. This switches the balance of regulator activities and causes the initial activation of cyclin B-Cdc2 at the meiotic G2/M-phase transition. These findings identify Myt1 as a new target of Akt, and demonstrate that Akt functions as an M-phase initiator.

We observed that mouse neural progenitor cells (NPCs) have a secretory protein profile distinct from other brain cells and modulate microglial activation, proliferation, and phagocytosis in culture and in vivo. NPC-derived vascular endothelial growth factor was necessary and sufficient to exert at least some of these effects in mice. Neural stem or precursor cells may thus not only be shaped by microglia but regulate in turn microglia functions and activity.