Cytohesin Binder and Regulator (Cybr) is Not Essential for T- and Dendritic-Cell Activation and Differentiation

Cybr (also known as Cytip, CASP, and PSCDBP) is an interleukin-12-induced gene expressed exclusively in hematopoietic cells and tissues that associates with Arf guanine nucleotide exchange factors known as cytohesins. Cybr levels are dynamically regulated during T-cell development in the thymus and upon activation of peripheral T cells. In addition, Cybr is induced in activated dendritic cells and has been reported to regulate dendritic cell (DC)-T-cell adhesion. Here we report the generation and characterization of Cybr-deficient mice. Despite the selective expression in hematopoietic cells, there was no intrinsic defect in T- or B-cell development or function in Cybr-deficient mice. The adoptive transfer of Cybr-deficient DCs showed that they migrated efficiently and stimulated proliferation and cytokine production by T cells in vivo. However, competitive stem cell repopulation experiments showed a defect in the abilities of Cybr-deficient T cells to develop in the presence of wild-type precursors. These data suggest that Cybr is not absolutely required for hematopoietic cell development or function, but stem cells lacking Cybr are at a developmental disadvantage compared to wild-type cells. Collectively, these data demonstrate that despite its selective expression in hematopoietic cells, the role of Cybr is limited or largely redundant. Previous in vitro studies using overexpression or short interfering RNA inhibition of the levels of Cybr protein appear to have overestimated its immunological role.

Ca2+-independent phospholipase A2-dependent gating of TRPM8 by lysophospholipids

TRPM8 represents an ion channel activated by cold temperatures and cooling agents, such as menthol, that underlies the cold-induced excitation of sensory neurons. Interestingly, the only human tissue outside the peripheral nervous system, in which the expression of TRPM8 transcripts has been detected at high levels, is the prostate, a tissue not exposed to any essential temperature variations. Here we show that the TRPM8 cloned from human prostate and heterologously expressed in HEK-293 cells is regulated by the Ca(2+)-independent phospholipase A(2) (iPLA(2)) signaling pathway with its end products, lysophospholipids (LPLs), acting as its endogenous ligands. LPLs induce prominent prolongation of TRPM8 channel openings that are hardly detectable with other stimuli (e.g. cold, menthol, and depolarization) and that account for more than 90% of the total channel open time. Down-regulation of iPLA(2) resulted in a strong inhibition of TRPM8-mediated functional responses and abolished channel activation. The action of LPLs on TRPM8 channels involved either changes in the local lipid bilayer tension or interaction with the critical determinant(s) in the transmembrane channel core. Based on this, we propose a novel concept of TRPM8 regulation with the involvement of iPLA(2) stimulation. This mechanism employs chemical rather than physical (temperature change) signaling and thus may be the main regulator of TRPM8 activation in organs not exposed to any essential temperature variations, as in the prostate gland.