ABSTRACT
Contact inhibition is a crucial mechanism regulating proliferation in vitro and in vivo. Despite its generally accepted importance for maintaining tissue homeostasis knowledge about the underlying molecular mechanisms of contact inhibition is still scarce. Since the MAPK ERK1/2 plays a pivotal role in the control of proliferation, we investigated regulation of ERK1/2 phosphorylation which is downregulated in confluent NIH3T3 cultures. We found a decrease in upstream signaling including phosphorylation of the growth factor receptor adaptor protein ShcA and the MAPK kinase MEK1/2 in confluent compared to exponentially growing cultures whereas involvement of ERK1/2 phosphatases in ERK1/2 inactivation is unlikely. Treatment of confluent, serum-deprived cultures with PDGF-B resulted in similar phosphorylation of ERK1/2 and induction of DNA-synthesis as detected in sparse, serum-deprived cultures. In contrast, ERK1/2 phosphorylation and DNA-synthesis could not be stimulated in confluent, serum-deprived cultures exposed to EGF. Our data indicate that PDGFR- and EGFR signaling are differentially inhibited in confluent cultures of NIH3T3 cells.
Subject(s)
Cell Communication , Cell Proliferation , Mitogen-Activated Protein Kinase 1/metabolism , Mitogen-Activated Protein Kinase 3/metabolism , Animals , Down-Regulation , ErbB Receptors/metabolism , Fibroblasts/drug effects , Fibroblasts/enzymology , Fibroblasts/physiology , Mice , NIH 3T3 Cells , Phosphorylation , Receptor, Platelet-Derived Growth Factor beta/pharmacology , Receptors, Platelet-Derived Growth Factor/metabolismABSTRACT
Proliferation of non-transformed cells is regulated by cell-cell contacts, which are referred to as contact-inhibition. Vice versa, transformed cells are characterised by a loss of contact-inhibition. Despite its generally accepted importance for cell-cycle control, little is known about the intracellular signalling pathways involved in contact-inhibition. Unravelling the molecular mechanisms of contact-inhibition and its loss during tumourigenesis will be an important step towards the identification of novel target genes in tumour diagnosis and treatment. To better understand the underlying molecular mechanisms we identified the transcriptional programme of contact-inhibition in NIH3T3 fibroblast using high-density microarrays. Setting the cut off: >or=1.5-fold, P Subject(s)
Cell Cycle Proteins/genetics
, Contact Inhibition/genetics
, Fibroblasts/metabolism
, Gene Expression Profiling
, Animals
, Blotting, Western
, Cell Cycle/genetics
, Cell Cycle Proteins/metabolism
, Fibroblasts/cytology
, Flow Cytometry
, Mice
, NIH 3T3 Cells
, Oligonucleotide Array Sequence Analysis
, Reverse Transcriptase Polymerase Chain Reaction
, Signal Transduction/genetics
