Anchorage-dependent cell growth: tyrosine kinases and phosphatases meet redox regulation

Recent data have provided new insight concerning the regulation of nontransformed cell proliferation in response to both soluble growth factors and adhesive cues. Nontransformed cells are anchorage-dependent for the execution of the complete mitotic program and cannot avoid the concomitant signals starting from mitogenic molecules, as growth factors, and adhesive agents belonging to the extracellular matrix. Protein tyrosine kinases (PTKs) and phosphotyrosine phosphatases (PTPs) together with soluble small molecules have been included among intracellular signal transducers of growth factor and extracellular matrix receptors. Reactive oxygen species retain a key role during both growth factor and integrin receptor signaling, and these second messengers are recognized to be a synergistic point of confluence for anchorage-dependent growth signaling. Redox-regulated proteins include PTPs and PTKs, although with opposite regulation of enzymatic activity. Transient oxidation of PTPs leads to their inactivation, through the formation of an intramolecular S-S bridge. Conversely, oxidation of PTKs leads to their activation, either by direct SH modification or, indirectly, by concomitant inhibition of PTPs that leads to sustained activation of PTKs. This review will focus on the redox regulation of PTPs and PTKs during anchorage-dependent cell growth and its implications for tumor biology.