Casein kinase II phosphorylation of caldesmon downregulates myosin-caldesmon interactions

Leupaxin stimulates adhesion and migration of prostate cancer cells through modulation of the phosphorylation status of the actin-binding protein caldesmon

The focal adhesion protein leupaxin (LPXN) is overexpressed in a subset of prostate cancers (PCa) and is involved in the progression of PCa. In the present study, we analyzed the LPXN-mediated adhesive and cytoskeletal changes during PCa progression. We identified an interaction between the actin-binding protein caldesmon (CaD) and LPXN and this interaction is increased during PCa cell migration. Furthermore, knockdown of LPXN did not affect CaD expression but reduced CaD phosphorylation. This is known to destabilize the affinity of CaD to F-actin, leading to dynamic cell structures that enable cell motility. Thus, downregulation of CaD increased migration and invasion of PCa cells. To identify the kinase responsible for the LPXN-mediated phosphorylation of CaD, we used data from an antibody array, which showed decreased expression of TGF-beta-activated kinase 1 (TAK1) after LPXN knockdown in PC-3 PCa cells. Subsequent analyses of the downstream kinases revealed the extracellular signal-regulated kinase (ERK) as an interaction partner of LPXN that facilitates CaD phosphorylation during LPXN-mediated PCa cell migration. In conclusion, we demonstrate that LPXN directly influences cytoskeletal dynamics via interaction with the actin-binding protein CaD and regulates CaD phosphorylation by recruiting ERK to highly dynamic structures within PCa cells.

Glomangioma of the nasal septum: a case report and review

Glomangioma is a painful, blue-red tumor that appears as a solitary encapsulated nodular mass, almost always on the skin. The first case of nasal glomangioma was reported in 1965. Since then, only 31 other cases have been reported in the literature. We present a new case of glomangioma of the nasal septum in a 61-year-old woman. The tumor was removed via an intranasal endoscopic excision. No recurrence was found at 3 years of follow-up. Our challenge was to distinguish the glomangioma from a true hemangiopericytoma and a paraganglioma.

cGMP-dependent protein kinase Iβ regulates breast cancer cell migration and invasion via interaction with the actin/myosin-associated protein caldesmon

The two isoforms of type I cGMP-dependent protein kinase (PKGIα and PKGIβ) differ in their first ∼100 amino acids, giving each isoform unique dimerization and autoinhibitory domains. The dimerization domains form coiled-coil structures and serve as platforms for isoform-specific protein-protein interactions. Using the PKGIβ dimerization domain as an affinity probe in a proteomic screen, we identified the actin/myosin-associated protein caldesmon (CaD) as a PKGIβ-specific binding protein. PKGIβ phosphorylated human CaD on serine 12 in vitro and in intact cells. Phosphorylation on serine 12 or mutation of serine 12 to glutamic acid (S12E) reduced the interaction between CaD and myosin IIA. Because CaD inhibits myosin ATPase activity and regulates cell motility, we examined the effects of PKGIβ and CaD on cell migration and invasion. Inhibition of the NO/cGMP/PKG pathway reduced migration and invasion of human breast cancer cells, whereas PKG activation enhanced their motility and invasion. siRNA-mediated knockdown of endogenous CaD had pro-migratory and pro-invasive effects in human breast cancer cells. Reconstituting cells with wild-type CaD slowed migration and invasion; however, CaD containing a phospho-mimetic S12E mutation failed to reverse the pro-migratory and pro-invasive activity of CaD depletion. Our data suggest that PKGIβ enhances breast cancer cell motility and invasive capacity, at least in part, by phosphorylating CaD. These findings identify a pro-migratory and pro-invasive function for PKGIβ in human breast cancer cells, suggesting that PKGIβ is a potential target for breast cancer treatment.

Prolactin-induced changes in protein expression in human pancreatic islets

Ex vivo islet cell culture prior to transplantation appears as an attractive alternative for treatment of type 1 diabetes. Previous results from our laboratory have demonstrated beneficial effects of human prolactin (rhPRL) treatment on human islet primary cultures. In order to probe into the molecular events involved in the intracellular action of rhPRL in these cells, we set out to identify proteins with altered expression levels upon rhPRL cell treatment, using two-dimensional (2D) gel electrophoresis and mass spectrometry (MS). An average of 300 different protein spots were detected, 14 of which were modified upon rhPRL treatment (p<0.01), of which 12 were successfully identified using MS and grouped according to their biological functions. In conclusion, our study provides, for the first time, information about proteins that could be critically involved in PRL's action on human pancreatic islets, and facilitate identification of new and specific targets involved in islet cell function and proliferation.

Regulation of microfilament organization by Kaposi sarcoma-associated herpes virus-cyclin.CDK6 phosphorylation of caldesmon

Kaposi sarcoma-associated herpes virus (KSHV) encodes a D-like cyclin (K-cyclin) that is thought to contribute to the viral oncogenicity. K-cyclin activates cellular cyclin-dependent kinases (CDK) 4 and 6, generating enzymes with a substrate selectivity deviant from CDK4 and CDK6 activated by D-type cyclins, suggesting different biochemical and biological functions. Here we report the identification of the actin- and calmodulin-binding protein caldesmon (CALD1) as a novel K-cyclin.CDK substrate, which is not phosphorylated by D.CDK. CALD1 plays a central role in the regulation of microfilament organization, consequently controlling cell shape, adhesion, cytokinesis and motility. K-cyclin.CDK6 specifically phosphorylates four Ser/Thr sites in the human CALD1 carboxyl terminus, abolishing CALD1 binding to its effector protein, actin, and its regulator protein, calmodulin. CALD1 is hyperphosphorylated in cells following K-cyclin expression and in KSHV-transformed lymphoma cells. Moreover, expression of exogenous K-cyclin results in microfilament loss and changes in cell morphology; both effects are reliant on CDK catalysis and can be reversed by the expression of a phosphorylation defective CALD1. Together, these data strongly suggest that K-cyclin expression modulates the activity of caldesmon and through this the microfilament functions in cells. These results establish a novel link between KSHV infection and the regulation of the actin cytoskeleton.

Role of CaM kinase II and ERK activation in thrombin-induced endothelial cell barrier dysfunction

We have previously shown that thrombin-induced endothelial cell barrier dysfunction involves cytoskeletal rearrangement and contraction, and we have elucidated the important role of endothelial cell myosin light chain kinase and the actin- and myosin-binding protein caldesmon. We evaluated the contribution of calmodulin (CaM) kinase II and extracellular signal-regulated kinase (ERK) activation in thrombin-mediated bovine pulmonary artery endothelial cell contraction and barrier dysfunction. Similar to thrombin, infection with a constitutively active adenoviral alpha-CaM kinase II construct induced significant ERK activation, indicating that CaM kinase II activation lies upstream of ERK. Thrombin-induced ERK-dependent caldesmon phosphorylation (Ser789) was inhibited by either KN-93, a specific CaM kinase II inhibitor, or U0126, an inhibitor of MEK activation. Immunofluorescence microscopy studies revealed phosphocaldesmon colocalization within thrombin-induced actin stress fibers. Pretreatment with either U0126 or KN-93 attenuated thrombin-mediated cytoskeletal rearrangement and evoked declines in transendothelial electrical resistance while reversing thrombin-induced dissociation of myosin from nondenaturing caldesmon immunoprecipitates. These results strongly suggest the involvement of CaM kinase II and ERK activities in thrombin-mediated caldesmon phosphorylation and both contractile and barrier regulation.

One-thousand-and-one substrates of protein kinase CK2?

CK2 (formerly termed "casein kinase 2") is a ubiquitous, highly pleiotropic and constitutively active Ser/Thr protein kinase whose implication in neoplasia, cell survival, and virus infection is supported by an increasing number of arguments. Here an updated inventory of 307 CK2 protein substrates is presented. More than one-third of these are implicated in gene expression and protein synthesis as being either transcriptional factors (60) or effectors of DNA/RNA structure (50) or translational elements. Also numerous are signaling proteins and proteins of viral origin or essential to virus life cycle. In comparison, only a minority of CK2 targets (a dozen or so) are classical metabolic enzymes. An analysis of 308 sites phosphorylated by CK2 highlights the paramount relevance of negatively charged side chains that are (by far) predominant over any other residues at positions n+3 (the most crucial one), n+1, and n+2. Based on this signature, it is predictable that proteins phosphorylated by CK2 are much more numerous than those identified to date, and it is possible that CK2 alone contributes to the generation of the eukaryotic phosphoproteome more so than any other individual protein kinase. The possibility that CK2 phosphosites play some global role, e.g., by destabilizing alpha helices, counteracting caspase cleavage, and generating adhesive motifs, will be discussed.

Effects of protein kinase CK2, extracellular signal-regulated kinase 2, and protein phosphatase 2A on a phosphatidic acid-preferring phospholipase A1

A soluble, phosphatidic acid-preferring phospholipase A1, expressed in mature bovine testes but not in newborn calf testes, may contribute to the formation or function of sperm. Here we incubated a recombinant preparation of the phospholipase in vitro with several enzymes including protein kinase CK2 (CK2), extracellular signal-regulated kinase 2 (ERK2), and protein phosphatase 2A (PP2A) to identify effects that might be of regulatory importance in vivo. Major findings were that 1) CK2 phosphorylated the phospholipase on serines 93, 105, and 716; 2) ERK2 phosphorylated the enzyme on serine 730; 3) there was cross-antagonism between the reactions that phosphorylated serines 716 and 730; 4) PP2A selectively hydrolyzed phosphate groups that were esterified to serines 716 and 730; 5) CK2alpha formed a stable, MgATP/MgGTP-dependent complex with the phospholipase by a novel mechanism; and 6) the complex showed reduced phospholipase activity and resembled a complex identified in homogenates of macaque testis. These results provide the first available information about the effects of reactions of phosphorylation and dephosphorylation on the behavior of the phospholipase, shed light on properties of CK2alpha that may be required for the formation of complexes with its substrates, and raise the possibility that a complex containing CK2alpha and the phospholipase may play a special biological role in the testis.