Inhibition of the phosphatidylinositol-3-kinase pathway abrogates polyinosinic:polycytidylic acid-stimulated hyaluronan-mediated human mucosal smooth muscle cell binding of U937 monocytic cells

The state of CD44 activation in cancer progression and therapeutic targeting

CD44, a non-kinase transmembrane glycoprotein, is ubiquitously expressed on various types of cells, especially cancer stem cells (CSCs), and has been implicated in cancer onset and aggressiveness. The major ligand for the CD44, hyaluronan (HA), binds to and interacts with CD44, which in turn triggers downstream signaling cascades, thereby promoting cellular behaviors such as proliferation, motility, invasiveness and chemoresistance. The CD44-HA interaction is cell-specific and strongly affected by the state of CD44 activation. Therefore, the binding of HA to CD44 is essential for the activation of CD44 during which the detailed regulatory mechanism needs to be clarified. Different CD44 activation states distribute in human carcinoma and normal tissue; however, whether CD44 activation is a critical requirement for tumor initiation, progression and notorious CSC properties remains to be clarified. A deeper understanding of the regulation of CD44 activation may facilitate the development of novel targeted drugs in the future. Here, we review the current findings concerning the states of CD44 activation on the cell surface, the underlying regulatory mechanisms of CD44 activation, the known role for CD44 activation in tumor progression and CSC hallmarks, as well as the potential of HA-coated nanoparticle for targeting activated CD44 for cancer therapy.

Selective killing of breast cancer cells expressing activated CD44 using CD44 ligand-coated nanoparticles in vitro and in vivo

The cell surface glycoprotein CD44 is expressed in cancer cells and has been used as a therapeutic target in preclinical studies. However, the ubiquitous expression of CD44 in numerous cell types, including hematopoietic cells, has hindered its application in targeted therapy. Here, we demonstrated that CD44 was activated on breast cancer cells but was inactive on normal cells in vitro and in vivo. We analyzed 34 clinical primary tumor and normal breast tissues and demonstrated that CD44 was in an active state on breast cancer cells but in an inactive state on normal cells. Furthermore, based on the binding property of CD44 with its ligand hyaluronan (HA), we self-assembled HA-coated nanoparticles and studied their selective targeting efficacy. Our results indicate that HA-coated nanoparticles bearing the CD44 ligand selectively targeted cancer cells both in vitro and in vivo, killing breast cancer cells while sparing normal cells. Our study suggested that the active state of CD44 plays a crucial role in the selective targeting of breast cancer cells by avoiding nonspecific toxicity to CD44-quiescent normal cells. These findings may provide a new idea for the selective targeting of cancer cells in other human cancers.

Periostin induces intracellular cross-talk between kinases and hyaluronan in atrioventricular valvulogenesis

Periostin (PN), a novel fasciclin-related matricellular protein, has been implicated in cardiac development and postnatal remodeling, but the mechanism remains unknown. We examined the role of PN in mediating intracellular kinase activation for atrioventricular valve morphogenesis using well defined explant cultures, gene transfection systems, and Western blotting. The results show that valve progenitor (cushion) cells secrete PN into the extracellular matrix, where it can bind to INTEGRINs and activate INTEGRIN/focal adhesion kinase signaling pathways and downstream kinases, PI3K/AKT and ERK. Functional assays with prevalvular progenitor cells showed that activating these signaling pathways promoted adhesion, migration, and anti-apoptosis. Through activation of PI3K/ERK, PN directly enhanced collagen expression. Comparing PN-null to WT mice also revealed that expression of hyaluronan (HA) and activation of hyaluronan synthase-2 (Has2) are also enhanced upon PN/INTEGRIN/focal adhesion kinase-mediated activation of PI3K and/or ERK, an effect confirmed by the reduction of HA synthase-2 in PN-null mice. We also identified in valve progenitor cells a potential autocrine signaling feedback loop between PN and HA through PI3K and/or ERK. Finally, in a three-dimensional assay to simulate normal valve maturation in vitro, PN promoted collagen compaction in a kinase-dependent fashion. In summary, this study provides the first direct evidence that PN can act to stimulate a valvulogenic signaling pathway.

TLR3 activation evokes IL-6 secretion, autocrine regulation of Stat3 signaling and TLR2 expression in human bronchial epithelial cells

Human bronchial epithelial cells exposed to synthetic double-stranded RNA (poly I:C) exhibited increased IL-6 and RANTES secretion and TLR2 expression that was inhibited following TLR3 silencing. Increased NF-κB and Stat3 phosphorylation were detected after poly I:C exposure and pretreatment with neutralizing antibody targeting IL-6 receptor α (IL-6Rα -nAb) or blocking Jak2 and Stat3 activity inhibited Stat3 phosphorylation. TLR2 up-regulation by poly I:C was also reduced by IL-6Rα-nAb and inhibitors of Jak2, Stat3 and NF-κB phosphorylation, whereas RANTES secretion was unaffected, but abolished following NF-κB inhibition. Treatment with exogenous IL-6 failed to increase TLR2. These findings demonstrate that TLR3 activation differentially regulates TLR expression through autocrine signaling involving IL-6 secretion, IL-6Rα activation and subsequent phosphorylation of Stat3. The results also indicate that NF-κB and Stat3 are required for TLR3-dependent up-regulation of TLR2 and that its delayed expression was due to a requirement for IL-6-dependent Stat3 activation.