Mona Johannessen

The multifunctional roles of the four-and-a-half-LIM only protein FHL2.

Abstract.Numerous cellular processes require the concerted action of multiple proteins that assemble in functional complexes. Protein-protein interaction domains allow specific proteins to combine with certain partners. Specificity of protein-protein association can be obtained by an interaction code predicted by conserved amino acid sequences. One of the protein-protein interaction motifs is the LIM domain, a conserved cysteine-rich module present in more than 100 different human proteins. The human four-and-a-half-LIM-only protein family consists of the members FHL1, FHL2, FHL3, FHL4 and ACT. They are expressed in a cell- and tissue-specific manner and participate in various cellular processes, including regulation of cell survival, transcription and signal transduction. Here, we review the current knowledge of the best-studied member of this family, FHL2. We describe the transcription regulation, the expression profile, the interaction partners, the subcellular localization, the biological functions and discuss the possible involvement of FHL2 in human diseases.

Relations between the mitogen-activated protein kinase and the cAMP-dependent protein kinase pathways: comradeship and hostility.

Inter- and intracellular communications and responses to environmental changes are pivotal for the orchestrated and harmonious operation of multi-cellular organisms. These well-tuned functions in living organisms are mediated by the action of signal transduction pathways, which are responsible for receiving a signal, transmitting and amplifying it, and eliciting the appropriate cellular responses. Mammalian cells posses numerous signal transduction pathways that, rather than acting in solitude, interconnect with each other, a phenomenon referred to as cross-talk. This allows cells to regulate the distribution, duration, intensity and specificity of the response. The cAMP/cAMP-dependent protein kinase (PKA) pathway and the mitogen-activated protein kinase (MAPK) cascades modulate common processes in the cell and multiple levels of cross-talk between these signalling pathways have been described. The first- and best-characterized interconnections are the PKA-dependent inhibition of the MAPKs ERK1/2 mediated by RAF-1, and PKA-induced activation of ERK1/2 interceded through B-RAF. Recently, novel interactions between components of these pathways and new mechanisms for cross-talk have been elucidated. This review discusses both known and novel interactions between compounds of the cAMP/PKA and MAPKs signalling pathways in mammalian cells.

Oncogenic potentials of the human polyomavirus regulatory proteins

Abstract.The polyomaviruses BK, JC and SV40 are common in the human population. Their DNA genomes encode large T-antigen, small t-antigen, agnoprotein, and the capsid proteins VP1–3. Studies with these viruses have contributed extensively to the understanding of processes such as replication, transcriptional and posttranscriptional regulation, and cell cycle control. All three viruses can transform human cells in vitro, can induce tumours in animal models, and are strongly association with certain human cancers. It is generally assumed that large T-antigen is the major protein involved in neoplastic processes and that large T-antigen predominantly exerts its effect through deregulation of the tumour suppressors p53 and the retinoblastoma family members. However, additional properties of large T-antigen as well as the other viral proteins contribute to oncogenic processes. This review presents the different mechanisms by which the polyomavirus proteins can induce transformation and discusses which mechanisms may be operational in polyomavirus-positive cancers.

Both Binding and Activation of p38 Mitogen-Activated Protein Kinase (MAPK) Play Essential Roles in Regulation of the Nucleocytoplasmic Distribution of MAPK-Activated Protein Kinase 5 by Cellular Stress

ABSTRACT The p38 mitogen-activated protein kinase (MAPK) pathway is an important mediator of cellular responses to environmental stress. Targets of p38 include transcription factors, components of the translational machinery, and downstream serine/threonine kinases, including MAPK-activated protein kinase 5 (MK5). Here we have used enhanced green fluorescent protein fusion proteins to analyze the subcellular localization of MK5. Although this protein is predominantly nuclear in unstimulated cells, MK5 shuttles between the nucleus and the cytoplasm. Furthermore, we have shown that the C-terminal domain of MK5 contains both a functional nuclear localization signal (NLS) and a leucine-rich nuclear export signal (NES), indicating that the subcellular distribution of this kinase reflects the relative activities of these two signals. In support of this, we have shown that stress-induced activation of the p38 MAPK stimulates the chromosomal region maintenance 1 protein-dependent nuclear export of MK5. This is regulated by both binding of p38 MAPK to MK5, which masks the functional NLS, and stress-induced phosphorylation of MK5 by p38 MAPK, which either activates or unmasks the NES. These properties may define the ability of MK5 to differentially phosphorylate both nuclear and cytoplasmic targets or alternatively reflect a mechanism whereby signals initiated by activation of MK5 in the nucleus may be transmitted to the cytoplasm.

Staphylococcus aureus: Determinants of human carriage

Staphylococcus aureus is a common human commensal but carriage varies between e.g. geographic location, age, gender, ethnicity and body niche. The nares, throat and perineum are the most prevalent sites for carriage in the general adult population. Other sites of the skin and the intestine are also frequently colonised. Thus, a successful establishment is dependent on multiple factors. This review describes results from observational studies of S. aureus carriage and the influence bacterial, host and environmental/modifiable factors might have on the relationship.

PKA-induced F-actin rearrangement requires phosphorylation of Hsp27 by the MAPKAP kinase MK5

Mitogen-activated protein kinase (MAPK) pathways can play a role in F-actin dynamics. In particular, the p38 MAPK/MAPK-activated protein kinase 2 (MK2)/heat shock protein 27 (Hsp27) pathway is involved in F-actin alternations. Previously, we showed that MK5 is implicated in F-actin rearrangement induced by the cAMP/cAMP-dependent protein kinase pathway in PC12 cells, while others found Hsp27 to be a good in vitro MK5 substrate. Here we demonstrate that MK5 can specifically interact with Hsp27 in vivo and can induce phosphorylation at serine residues 78 and 82 in cells. siRNA-mediated depletion of Hsp27 protein levels, as well as overexpression of the non-phosphorylatable Hsp27-3A mutant prevented forskolin-induced F-actin reorganization. While ectopic expression of a constitutive active MK5 mutant was sufficient to induce F-actin rearrangement in PC12 cells, co-expression of Hsp27-3A could ablate this process. Our results imply that MK5 is involved in Hsp27-controlled F-actin dynamics in response to activation of the cAMP-dependent protein kinase pathway. These findings render the MK5/Hsp27 connection into a putative therapeutic target for conditions with aberrant Hsp27 phosphorylation such as metastasis, cardiovascular diseases, muscle atrophy, autoimmune skin disease and neuropathology.

Protein Kinase D Induces Transcription through Direct Phosphorylation of the cAMP-response Element-binding Protein

Protein kinase D (PKD), a family of serine/threonine kinases, can be activated by a multitude of stimuli in a protein kinase C-dependent or -independent manner. PKD is involved in signal transduction pathways controlling cell proliferation, apoptosis, motility, and protein trafficking. Despite its versatile functions, few genuine in vivo substrates for PKD have been identified. In this study we demonstrate that the transcription factor cAMP-response element-binding protein (CREB) is a direct substrate for PKD. PKD1 and CREB interact in cells, and activated PKD1 provokes CREB phosphorylation at Ser-133 both in vitro and in vivo. A constitutive active mutant of PKD1 stimulates GAL4-CREB-mediated transcription in a Ser-133-dependent manner, activates CRE-responsive promoters, and increases the expression of CREB target genes. PKD1 also enhances transcription mediated by two other members of the CREB family, ATF-1 and CREM. Our results describe a novel mechanism for PKD-induced signaling through activation of the transcription factor CREB and suggest that stimulus-induced phosphorylation of CREB, reported to be mediated by protein kinase C, may involve downstream activated PKD.

Host- and microbe determinants that may influence the success of S. aureus colonization

Staphylococcus aureus may cause serious skin and soft tissue infections, deep abscesses, endocarditis, osteomyelitis, pneumonia, and sepsis. S. aureus persistently colonizes 25–30% of the adult human population, and S. aureus carriers have an increased risk for infections caused by the bacterium. The major site of colonization is the nose, i.e., the vestibulum nasi, which is covered with ordinary skin and hair follicles. Several host and microbe determinants are assumed to be associated with colonization. These include the presence and expression level of bacterial adhesins, which can adhere to various proteins in the extracellular matrix or on the cellular surface of human skin. The host expresses several antimicrobial peptides and lipids. The level of β-defensin 3, free sphingosine, and cis-6-hexadecenoic acid are found to be associated with nasal carriage of S. aureus. Other host factors are certain polymorphisms in Toll-like receptor 2, mannose-binding lectin, C-reactive protein, glucocorticoid-, and vitamin D receptor. Additional putative determinants for carriage include genetic variation and expression of microbial surface components recognizing adhesive matrix molecules and their interaction partners, as well as variation among humans in the ability of recognizing and responding appropriately to the bacteria. Moreover, the available microflora may influence the success of S. aureus colonization. In conclusion, colonization is a complex interplay between the bacteria and its host. Several bacterial and host factors are involved, and an increased molecular understanding of these are needed.

Modulation of F-actin Rearrangement by the Cyclic AMP/cAMP-dependent Protein Kinase (PKA) Pathway Is Mediated by MAPK-activated Protein Kinase 5 and Requires PKA-induced Nuclear Export of MK5

The MAPK-activated protein kinases belong to the Ca2+/calmodulin-dependent protein kinases. Within this group, MK2, MK3, and MK5 constitute three structurally related enzymes with distinct functions. Few genuine substrates for MK5 have been identified, and the only known biological role is in ras-induced senescence and in tumor suppression. Here we demonstrate that activation of cAMP-dependent protein kinase (PKA) or ectopic expression of the catalytic subunit Cα in PC12 cells results in transient nuclear export of MK5, which requires the kinase activity of both Cα and MK5 and the ability of Cα to enter the nucleus. Cα and MK5, but not MK2, interact in vivo, and Cα increases the kinase activity of MK5. Moreover, Cα augments MK5 phosphorylation, but not MK2, whereas MK5 does not seem to phosphorylate Cα. Activation of PKA can induce actin filament accumulation at the plasma membrane and formation of actin-based filopodia. We demonstrate that small interfering RNA-triggered depletion of MK5 interferes with PKA-induced F-actin rearrangement. Moreover, cytoplasmic expression of an activated MK5 variant is sufficient to mimic PKA-provoked F-actin remodeling. Our results describe a novel interaction between the PKA pathway and MAPK signaling cascades and suggest that MK5, but not MK2, is implicated in PKA-induced microfilament rearrangement.

Human polyomaviruses and cancer: expanding repertoire.

Polyomaviruses were originally isolated in mouse and in monkey (SV40) about 50 years ago. In 1971, the first human polyomaviruses BK and JC were isolated and subsequently demonstrated to be ubiquitous in the human population. Recent studies have shown that SV40 can spread between humans and led to the identification of three new human polyomaviruses (KIPyV, MCPyV, and WUPyV). BKV, JCV, and SV40 appear harmless in healthy individuals, but possess pathogenic properties in immunosuppressed patients. Moreover they may play an etiological role in human malignancies. Epidemiologic and pathogenic studies of KIPyV, MCPyC, and WUPyV are limited so far, but MCPyV may be associated with Merkel cell carcinoma, a rare but aggressive neuroendocrine skin cancer. We describe the biology of human polyomaviruses, review their non‐malignant and malignant potentials, and discuss the mechanisms by which these viruses may contribute to transformation.