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M Henriksson

Publications and source records attributed to M Henriksson.

70 records · Page 4Linked to original sources
PubMed1993

Analysis of c-Myc domains involved in stimulating SV40 replication.

We have demonstrated previously that overproduction of c-Myc, N-Myc and, to a lesser extent, L-Myc facilitates the replication of simian virus 40 (SV40)-based vectors in human lymphoid cells. Using a series of c-myc deletion mutants, we investigated which c-Myc regions are important in stimulating SV40 replication. The ability of c-Myc to promote SV40 replication was significantly reduced by deletions in the second exon domain, formerly shown to be crucial for c-Myc's transforming capacity. The c-myc mutants with a disrupted basic region (b) or leucine zipper (Zip) motif were also unable to stimulate SV40 replication. These regions are implicated in protein-DNA and protein-protein interactions, respectively, suggesting that the c-Myc protein might be associated with the DNA-protein replication complex. We present data obtained from gel mobility shift assays and from an immunocomplex-binding assay substantiating this hypothesis.

Base Sequence↗
PubMed1993

Phosphorylation sites mapping in the N-terminal domain of c-myc modulate its transforming potential.

The nuclear proto-oncoprotein c-Myc is involved in the regulation of cell growth and differentiation. c-Myc is phosphorylated at multiple sites in vivo, two of which we have identified near the amino terminus. In chicken Thr-61/Ser-65 are phosphorylated, as are the comparable positions, Thr-58/Ser-62 in human c-Myc. These residues are located within a domain that is implicated in transactivation and is important for the transforming potential of the protein. Furthermore, these phosphorylation sites or nearby amino acids are frequently mutated in v-myc and in several c-myc genes from Burkitt's lymphoma cells. In vitro these two phosphorylation sites can be modified by glycogen synthase kinase 3 and mitogen activated protein kinase. To address their biological importance we mutated these amino terminal phosphorylation sites separately and together. Stably transfected Rat1A cells expressing the mutated proteins have an increased growth potential in soft agar compared to wt-c-myc transfectants. These altered transformation characteristics indicate that Myc function may be negatively regulated by the amino terminal phosphorylation.

Amino Acid Sequence↗
PubMed1993

Identification of casein kinase II phosphorylation sites in Max: effects on DNA-binding kinetics of Max homo- and Myc/Max heterodimers.

Myc proteins have been implicated in the regulation of cell growth and differentiation. The identification of Max, a basic region/helix-loop-helix/leucine zipper protein, as a partner for Myc has provided insights into Myc's molecular function as a transcription factor. Recent evidence indicates that the relative abundance of Myc and Max is important to determine the level of specific gene transcription. In this report we have identified two major in vivo phosphorylation sites in Max (Ser-2 and -11) which can be modified in vitro by casein kinase II (CKII). Phosphorylation of these sites modulates DNA-binding by increasing both the on- and off-rates of Max homo- as well as Myc/Max heterodimers. In addition, our data indicate that the steady state binding of the shorter version of Max (p21) to DNA was similar yet its rate of dissociation faster than that of longer version of Max (p22). These data argue that different Max complexes have different kinetic properties and that these can be modified by CKII phosphorylation. We propose this as an important biological mechanism by which different dimeric complexes can exchange with varying efficiencies on DNA, thereby responding to changes in cell growth conditions.

Amino Acid Sequence↗
PubMed1992

Nuclear colocalization of c-myc protein and hsp70 in cells transfected with human wild-type and mutant c-myc genes.

Using immunofluorescence and electron microscopy we have studied the localization of wild-type and mutant c-myc proteins transiently expressed in CV-1 cells. In agreement with our previous observations, wild-type c-myc protein accumulated in large amorphous globules in the nucleus. All mutant proteins tested accumulated in the nucleus as well, but gave rise to morphologically different inclusion bodies. Many small globules appeared in cells transfected with D145-262 (deletion of amino acids 145-262), while cells transfected with D371-412 or D414-433 generated structures looking like a fine network or like beads on a string. In addition, a particulate cytoplasmic staining appeared in some cells transfected with the wild-type gene and in cells transfected with mutants D145-262 or D414-433. Since the c-myc protein has been reported to stimulate expression of exogenous hsp70 protein, we also examined the intracellular distribution of hsp70 in the transfected cells. Double immunofluorescence microscopy revealed that hsp70 codistributed with the c-myc protein in distinct globules in the nucleus of many but not all myc-positive cells. However, the levels of hsp70 transcripts were not significantly raised compared to nontransfected and vector-transfected cells. Likewise, the levels of hsp70 protein did not vary significantly. These findings indicate that overexpression of c-myc stimulates translocation of preexisting hsp70 from the cytoplasm into the nucleus, rather than influencing hsp70 expression. Conceivably, this may represent one of several mechanisms whereby the cell deals with excessive amounts of c-myc protein.

Animals↗
PubMed1992

Completed suicide and recent lithium treatment.

Of 1397 completed suicides in Finland in one year, all victims (N = 20) that had used lithium in prophylaxis and treatment of a mood disorder during the three final months were carefully examined. Eight victims (40%) fulfilled the criteria of recent adequate lithium prophylaxis. Continuous or intermittent noncompliance with psychopharmacological treatment during the last two years was reported in the majority (85%) of the victims. Only two cases used lithium as a suicide method. The study suggests that problems especially in compliance but also in quality of treatment are likely to limit the usefulness of lithium treatment in suicide prevention.

Adult↗
PubMed1992

Chronic facial pain together with severe depression is responsive to electroconvulsive therapy. A case report.

Electroconvulsive therapy (ECT) is widely accepted as a treatment for severe depression, but is seldom used in the treatment of chronic pain even though chronic pain and depression frequently occur together. This study presents a case in which ECT relieved both severe depression and chronic pain. It seems that the recognition of depressive disorders merits more attention and that ECT as a treatment for chronic pain in patients with severe depression should be taken into consideration in cases in which other treatments have failed.

Amitriptyline↗
PubMed1991

Misuse of zopiclone and convulsions during withdrawal.

It has been documented that benzodiazepines have the potential to cause dependence and withdrawal reactions, including convulsions. However, the available data concerning zopiclone, a nonbenzodiazepine hypnotic, are insufficient. The present study describes the case of a 36-year-old man who repeatedly misused zopiclone, in daily doses of 60-90 mg. Furthermore, the patient suffered from convulsion on two occasions following abrupt withdrawal of zopiclone. The concomitant use of alcohol, trimipramine, and promazine may have contributed to the development of convulsions. It is concluded that zopiclone may cause problems associated with misuse and withdrawal reactions similar to those of benzodiazepines.

Adult↗
PubMed1991

Reintroduction of a normal retinoblastoma gene into retinoblastoma and osteosarcoma cells inhibits the replication associated function of SV40 large T antigen.

The product of the retinoblastoma (Rb) gene can form complexes with the transforming proteins of small DNA tumor viruses, including SV40 large T antigen (Tag), adenovirus E1A, and the human papilloma virus E7. The strong correlation between their ability to transform and their ability to bind Rb protein suggests that these oncoproteins exert their effect through blocking the Rb function. SV40 Tag causes oncogenic cell transformation of rodent cells, and it is also required for viral DNA replication. In this paper, we investigated the effect of the Rb protein on the SV40 replication associated function of Tag. We present evidence suggesting that the complex formation between Rb and Tag interferes with the viral DNA replication. In Y79 retinoblastoma and Saos-2 osteosarcoma cells, which lack functional Rb protein, a SV40 based plasmid vector, pSVEpR4, replicates well. In the same cells reconstituted for Rb expression with an intact Rb gene introduced by retroviral mediated gene transfer, pSVEpR4 replicates to a considerably lower level. The inhibitory effect of Rb protein was surmounted by increasing the intracellular level of Tag. Increasing amounts of Tag in wild-type Rb negative Y79 cells had virtually no effect on SV40 replication. Furthermore, the overexpression of Tag in Rb reconstituted Y79 cells did not alter the growth rate of the cells. These data suggest that Rb protein interacts with Tag and modulates its ability to promote SV40 DNA replication.

Antigens, Polyomavirus Transforming↗
PubMed1990

The effect of myc proteins on SV40 replication in human lymphoid cells.

We have previously demonstrated that over-expression of c-myc facilitates the replication of SV40 DNA in human Burkitt lymphoma cells (BL). In this paper we investigated the ability of N-myc and L-myc to substitute for c-myc in promoting SV40 DNA replication. Vectors expressing either a chimeric N-myc/c-myc, N-myc or L-myc gene were constructed and co-transfected with a plasmid containing the SV40 origin of replication and the early genes encoding SV40 T antigens (Tag). The chimeric N-myc/c-myc and the N-myc proteins enhance SV40 replication in the human lymphoma line BJAB at levels comparable to c-myc. The stimulative effect of N-myc is also evident in the BL cell line RAMOS. However, L-myc stimulated SV40 replication only in RAMOS cells.

DNA Replication↗
PubMed1989

Efficient retroviral transfer of a mouse c-myc construct into HL60.

We introduced an LTR-driven mouse c-myc second and third exon, Tn5Neo gene construct into the inducible human leukemia line HL60 using an amphotropic retroviral vector system. Over 90% of the cells became neo-resistant and the transfected myc gene was transcribed in several neomycin resistant clones. Making use of the simultaneous presence of the different myc genes in the same cell, we compared expression of the corresponding mRNAs after differentiation and their decay mechanisms.

Animals↗
PubMed1988

Elevated expression of c-myc and N-myc produces distinct changes in nuclear fine structure and chromatin organization.

The proto-oncogenes c-myc and N-myc encode nuclear phosphoproteins with unknown function. Here, c-myc or N-myc, or hybrid constructs of the two, were transfected into fibroblastic cells (CV-1) using SV40-based high expression vectors. The cells were studied by indirect immunofluorescence microscopy and transmission electron microscopy to determine the localization of the two myc proteins within the nucleus and their influence on nuclear fine structure and chromatin organization. In c-myc transfected cells the overproduced protein product accumulated in large amorphous globules that displaced the normal chromatin and did not stain for DNA. In N-myc transfected cells condensed chromatin loops were formed. They were attached to the nuclear envelope and by traction in the latter they may have contributed to give the nucleus its irregular shape in these cells. During mitosis the chromatin loops persisted as clearly identifiable entities within the chromosomes, suggesting a rigid conformation that did not allow normal chromosome packaging. These findings suggest that the c-myc and N-myc proteins bind to different structures and may have different functions. Observations on cells transfected with hybrid constructs indicated that both the second and third exon of c-myc were required to yield a product that behaved like the c-myc protein. In contrast, domains encoded by the second exon of N-myc were sufficient to give rise to a product that morphologically behaved like the N-myc protein.

Animals↗
PubMedDate not supplied

Inactivation of Myc-induced p53-dependent apoptosis in human tumors.

The Myc family of oncoproteins promote cell growth and are frequently overexpressed in human tumors. However, Myc can also trigger cell death by apoptosis. This is at least in part mediated via the ARF-p53 pathway. Myc activation leads to a selection for inactivation of ARF or p53, allowing cell survival and tumor progression. Restoration of p53-dependent apoptosis by various means is an attractive approach for new cancer therapy.

Apoptosis↗
PubMedDate not supplied

Elevated c-myc expression facilitates the replication of SV40 DNA in human lymphoma cells.

The v-myc oncogene can induce tumours in haematopoietic, mesenchymal and epithelial tissues. The corresponding c-myc proto-oncogene can contribute to the genesis and/or the progression of an equally wide variety of tumours when activated by retroviral insertions, chromosomal translocations or gene amplification. The c-myc gene product is a DNA-binding, nuclear phosphoprotein that is involved in the control of cell proliferation and possibly in DNA synthesis. The replication of Simian virus 40 (SV40) is a useful model system to study eukaryotic DNA replication as the virus relies almost entirely on cellular DNA replication apparatus. The SV40-based vector, pSVEpR4, replicates poorly in the human BJAB lymphoma line and in most human cells, but replicates well in Burkitt lymphoma lines, which have fused immunoglobulin and c-myc genes, resulting in high c-myc expression. Cotransfection of the BJAB cells with a c-myc-expressing construct (pI4-P6) increased the replication of pSVEpR4 tenfold. Our findings indicate that overexpression of the c-myc gene product allows the replication of SV40 in human lymphoma cells, suggesting that c-myc is involved in the control of replication.

Antigens, Viral, Tumor↗
PubMedDate not supplied

Postural control after anterior cruciate ligament reconstruction and functional rehabilitation.

Total sagittal knee laxity and postural control in the sagittal and frontal planes were measured in 25 patients at a mean of 36 months (range, 27 to 44) after anterior cruciate ligament reconstruction and in a control group consisting of 20 uninjured age- and activity-matched subjects. Body sway was measured in the sagittal plane on a stable and on a sway-referenced force plate in single-legged stance, double-legged stance, or both, with the eyes open and closed. Postural reactions to perturbations in the sagittal and frontal planes were recorded in the single-legged stance with the eyes open. Total sagittal plane laxity was significantly greater in the anterior cruciate ligament-reconstructed knee (11.2 mm; range, 6 to 15) than in the uninjured knee (8.9 mm; range, 6 to 12) or in the control group (6.0 mm; range, 5 to 8). In spite of this, the patients, in comparison with the controls, exhibited normal postural control except in two variables-the reaction time and the latency between the start of force movement to maximal sway in the sagittal plane perturbations. This supports the hypothesis that rehabilitation, with proprioceptive and agility training, is an important component in restoring the functional stability in the anterior cruciate ligament-reconstructed knee.

Adolescent↗