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Biomedical subjects

Petri Lehenkari

Publications and source records attributed to Petri Lehenkari.

8 recordsLinked to original sources
PubMed2004

Protein kinase C alpha/beta inhibitor Go6976 promotes formation of cell junctions and inhibits invasion of urinary bladder carcinoma cells.

Changes in activation balance of different protein kinase C (PKC) isoenzymes have been linked to cancer development. The current study investigated the effect of different PKC inhibitors on cellular contacts in cultured high-grade urinary bladder carcinoma cells (5637 and T24). Exposure of the cells to isoenzyme-specific PKC inhibitors yielded variable results: Go6976, an inhibitor of PKCalpha and PKCbeta isoenzymes, induced rapid clustering of cultured carcinoma cells and formation of an increased number of desmosomes and adherens junctions. Safingol, a PKCalpha inhibitor, had similar but less pronounced effects. In contrast, a PKCdelta inhibitor, rottlerin, had an opposite effect on cell clustering and caused dissociation of cell junctions. A broad-spectrum PKC inhibitor bisindolylmaleimide I did not have any apparent effect on the morphology of the cultures or on the number of cell junctions. Additional studies with Go6976 demonstrated that inhibition of PKCalpha and beta isoenzymes induced translocation of beta1-integrin from the cell-matrix junctions and that beta4-integrin was translocated to face the culture substratum. Go6976 was also highly effective in inhibiting migration of carcinoma cells and inhibited invasion through artificial basement membrane. Our results on urinary bladder carcinoma cells emphasize that Go6976 is a potential anticancer drug due to its effects on cell-cell and cell-matrix junctions, migration, and invasion. Furthermore, the results may be explained by changes in PKC activation balance promoted by inhibition of PKCalpha/beta.

Actins↗
PubMed2003

Functional diversity of endothelin pathways in human lung fibroblasts may be based on structural diversity of the endothelin receptors.

Posttranslational modifications of the endothelin receptors A and B from human lung fibroblasts were investigated before and after stimulation of the cells with (dA)(30)-5'-S-EMC-endothelin-1. The patterns of phosphorylation and palmitoylation of both receptors were much more complicated than expected. In both the stimulated and the unstimulated states, multiple isoforms differing in the number and location of posttranslational modifications were present. MS analyses suggested rapid changes in these isoforms following stimulation. Overall, the ETA receptor was modified at 20 sites (15 phosphorylation, five palmitoylation sites) and ETB at 17 sites (13 phosphorylation, four palmitoylation sites). Part of the structural diversity involved hypermodification of short sequence regions, and it is suggested that this could represent a mechanism for incremental modulation of receptor activity. It is postulated that the observed structural diversity over disparate parts of the receptor sequences forms the basis for parallel stimulation of different signaling pathways at spatially and functionally distinct ET receptors differing in posttranslational modifications.

Amino Acid Sequence↗
PubMed2003

Osteoblast recruitment from stem cells does not decrease by age at late adulthood.

This study was aimed to characterize the ability of human bone marrow mesenchymal stem cells (MSC) to differentiate into osteoblasts in vitro. Twenty-three women and 20 men at late adulthood (52-92 years of age) were selected for the study. MSCs were isolated and cultured in vitro and alkaline phosphatase (ALP) activity, secretion of amino-terminal propeptide of type I procollagen (PINP), type III procollagen (PIIINP) and osteocalcin were analyzed. Matrix mineralization was analyzed by the von Kossa staining and by calcium quantification. We found that the ALP and PINP levels compared with control increased to 2.8- and 2.9-fold, respectively, when cells were cultured for three weeks. ALP activity, PINP and calcium deposition in response to dexamethasone treatment increased by age in women and was unchanged in men. Overall our data suggests that the osteogenic potential of MSCs does not decrease by age in either women or men at late adulthood.

Age Factors↗
PubMed2003

The effects of tamoxifen and toremifene on bone cells involve changes in plasma membrane ion conductance.

Selective estrogen receptor modulators (SERMs), tamoxifen (Tam) and toremifene (Tor), are widely used in the treatment of breast cancer. In addition, they have been demonstrated to prevent estrogen deficiency-induced bone loss in postmenopausal women. These effects are thought to be caused by the interaction of the SERMs with the estrogen receptor, although SERMs have also been shown to conduct non-receptor-mediated effects such as rapid changes in membrane functions. We compared the effects of Tam, Tor, and 17beta-estradiol (E2) on the viability of rat osteoclasts and osteoblasts. Both Tam and Tor were found to cause osteoclast apoptosis in in vitro cultures, which was reversed by E2. In addition, at higher concentration (10 microM), both SERMs had an estrogen receptor-independent effect, which involved interaction with the plasma membrane as demonstrated with UMR-108 osteosarcoma cells by Tam and Tor, but not E2. A leak of protons leading to changes in intracellular pH was shown both in medullary bone derived membrane vesicles and in intact cells. These effects were followed by a rapid loss of cell viability and subsequent cell lysis. Our results show that both Tam and Tor have an ionophoric effect on the plasma membranes of bone cells and that these SERMs differed in this ability: Tor induced rapid membrane depolarization only in the presence of high concentration of potassium. These non-receptor-mediated effects may be involved in therapeutic responses and explain some clinical side effects associated with the treatment of patients with these SERMs.

Animals↗
PubMed2002

Microstructural properties of bone in rat vertebra after long-term clodronate treatment.

Bisphosphonates (BPs) are known to increase bone mineral density, but it is not known how this increase manifests at low hierarchic levels of the bone structure. The present study aimed to clarify the effects of the long-term use of clodronate on the microstructure and chemical composition of bone. The second lumbar vertebral body (L2) in growing rats, subjected to 32 weeks' treatment with clodronate at either a therapeutic dose of 2 mg/kg, or a high dose of 10 mg/kg, or physiological saline (control group), was studied by scanning electron microscopy for morphology, by backscattered electron image (BSE) for density, and by energy dispersive spectrometry for material analysis. BSE images showed that the degree of mineralization in the different areas of trabecular bone of the vertebral body varied in both the control and the study groups, but this variation seemed to be different in the control and study groups. BSE analysis showed that there was more high-density bone (white area) in the low-dose clodronate group than in the controls, but the difference between the high-dose clodronate group and the control group was not significant. The density of the white area (high-density bone) was slightly increased in the low-dose clodronate group. There were no differences in the density of the gray area (low-density bone) between the groups. Neither the distribution of Ca, P, or Mg, nor the total mineral content, was affected by the clodronate treatment. Our results indicate that long-term clodronate treatment at the therapeutic level increases the proportion of high-density bone in the vertebral body in non-osteoporotic rats.

Analgesics, Non-Narcotic↗
PubMed2002

Effect of metal alloy surface stresses on the viability of ROS-17/2.8 osteoblastic cells.

In this study we compared the effect of structural stresses and surface roughness on biocompatibility of NiTi- and Ti-alloy for ROS-17/2.8 osteoblastic cells. We suggest here that cell viability and cell attachment are linear functions of internal (structural) stress and subgrain size of the implant alloy. However, this is not the case with surface roughness. The two-phase state in these materials is characterized by different mean values of structural stresses (sigma) in alpha-martensite and beta-phase. We found a straight correlation between cell viability and sigma(beta)/sigma(alpha) ratio. Atomic force microscopy revealed that, even after equal surface polishing treatments, roughness varied significantly between the different alloys. The effect of the surface structure of the alloy on the osteoblastic ROS-17/2.8 cell survival rate was studied with combined calcein-ethidium-homodimer fluorescence labeling. The possible effects on cell attachment to substrate were studied by staining the focal contacts with paxillin antibody. All the NiTi surfaces were tolerated well and the cells attached most abundantly to the roughest NiTi surface but the smoothest Ti-alloy surface. However, other parameters of the material state, such as the surface stresses created by hot rolling seem to be responsible for some of the attachment and cell survival features observed in this study.

Alloys↗
PubMedDate not supplied

Analysis of ligand-receptor interactions in cells by atomic force microscopy.

Atomic force microscopy (AFM) increasingly has been used to analyse "receptor" function, either by using purified proteins ("molecular recognition microscopy") or, more recently, in situ in living cells. The latter approach has been enabled by the use of a modified commercial AFM, linked to a confocal microscope, which has allowed adhesion forces between ligands and receptors in cells to be measured and mapped, and downstream cellular responses analysed. We review the application of AFM to cell biology and, in particular, to the study of ligand-receptor interactions and draw examples from our own work and that of others to show the utility of AFM, including for the exploration of cell surface functionalities. We also identify shortcomings of AFM in comparison to "standard" methods, such as receptor auto-radiography or immuno-detection, that are widely applied in cell biology and pharmacological analysis.

Animals↗