| 1. |
- Afrakhte, Mozhgan
(författare)
-
Growth control mechanisms in normal and neoplastic mammalian cells
- 1998
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main theme of the studies presented in this thesis is, the growth control mechanisms whose loss in normal cells predispose to or cause cancer. The balance between growth inhibitory and stimulatory mechanisms is crucial for the development and maintenance of a normal animal.PDGF, a growth factor for cells of mesenchymal origin, is implicated in normal developmental processes as well as neoplasia. The alternative splicing of exon 6 in PDGF-A gene transcripts gives rise to two different proteins with different compartmentalization properties. The PDGF-A chain homodimers, PDGF-AAL, encoded PDGF A-splice variant remain associated with the cell membrane. Studies of a human fibrosarcoma cell line, U-2197, revealed a high expression level of the cell associated PDGF-AAL which upon release increased autophosphorylation of the endogenous PDGF receptors, suggesting an autocrine loop. PDGF-A gene and PDGFR-α gene found to be co-amplified in the U-2197, indicating an optimised system for growth in these cells, i.e. amplified growth factor receptor as well as a local autocrine supply of the mitogen.Members of TGFβ superfamily are potent regulators of the growth and differentiation of a wide range of cell types. Intracellular mediators of TGF-β signalling, SMADs, transduce signals from serine/threonine kinase receptors to the nucleus where they affect transcription of target genes. A new class of SMAD proteins has been identified whose members, the inhibitory SMADS, antagonise TGF-β signals by interfering with agonistic SMADs activity. Smad6 and Smad7 are two closely related TGF-β antagonists identified in mammalian cells. Overexpression of Smad7 inhibited the cellular response to TGF-β whereas expression of an anti-sense Smad7 construct showed an enhancing effect on this response. The inhibitory SMADs may act in a negative feedback loop, as their expression is induced by the same ligands whose action they antagonise.Density dependent growth inhibition is a growth control mechanism often lost in transformed and malignant cells. Cells in dense culture are refractory to the mitogen stimulation although, the mitogenic signals were shown to be processed to some extent. The expression of immediate-early genes in dense culture stimulated with mitogen was induced. The activity of cyclin dependent kinases (CDKs), the pivotal kinases in G1/S transition, showed to be density dependent and decreased by increasing cell density. pRb, a tumour suppressor and growth regulatory protein, remained unphosphorylated in mitogen treated dense culture. The cessation of CDKs kinase activity in dense cultures was shown to be accompanied with increasing expression of inhibitory proteins of these kinases, CKIs. The impaired expression of a positive regulator of CDKs, Cdc25A phosphatase, was another feature of dense cultures.
|
|
| 2. |
- Afrakhte, Mozhgan, et al.
(författare)
-
Induction of inhibitory Smad6 and Smad7 mRNA by TGF-beta family members
- 1998
-
Ingår i: Biochemical and Biophysical Research Communications - BBRC. - : Elsevier BV. - 0006-291X .- 1090-2104. ; 249:2, s. 505-11
-
Tidskriftsartikel (refereegranskat)abstract
- Smad6 and Smad7 function as intracellular antagonists in transforming growth factor-beta (TGF-beta) signaling. Here we report the isolation of human Smad6, which is closely related to Smad7. Smad6 and Smad7 mRNAs were differentially expressed in lung cancer cell lines and were rapidly and directly induced by TGF-beta1, activin and bone morphogenetic protein-7. Cross-talk between TGF-beta and other signaling pathways was demonstrated by the finding that epidermal growth factor (EGF) induced the expression of inhibitory SMAD mRNA. Moreover, whereas the phorbol ester PMA alone had no effect, it potentiated the TGF-beta1-induced expression of Smad7 mRNA. Ectopic expression of anti-sense Smad7 RNA was found to increase the effect of TGF-beta1, supporting its role as a negative regulator in TGF-beta signaling. Thus, expression of inhibitory Smads is induced by multiple stimuli, including the various TGF-beta family members, whose action they antagonize.
|
|
| 3. |
- Forsberg-Nilsson, Karin, et al.
(författare)
-
Platelet-derived growth factor induces chemotaxis of neuroepithelial stem cells
- 1998
-
Ingår i: Journal of Neuroscience Research. - 0360-4012 .- 1097-4547. ; 53:5, s. 521-530
-
Tidskriftsartikel (refereegranskat)abstract
- The ability of differentiating cells to migrate within the developing central nervous system (CNS) depends on extrinsic guidance signals, some of which are growth factors. In this study we have investigated the chemotactic response of cultured stem cells from the embryonic rat cortex to platelet-derived growth factor (PDGF). Nestin-positive stem cells from the developing CNS can be maintained and expanded in vitro under serum-free conditions in the presence of basic fibroblast growth factor (bFGF). Northern blot analysis of PDGF receptor expression revealed both α- and β-receptors on bFGF-treated neural stem cells. Both PDGF-AA and PDGF-BB readily induced directed migration of cultured neuroepithelial cells as measured in a microchemotaxis assay. Blocking of the migratory response was achieved by incubation with PDGF isoform-specific antibodies. More than 90% of the migrating cells were nestin-positive and incorporation of BrdU was also seen suggesting the cells to be immature and not yet committed to a specific cell lineage. These findings suggest a role for PDGF in cell migration in the developing cortex.
|
|
| 4. |
|
|
