GH4 pituitary cell variants selected as nonresponsive to thyrotropin-releasing hormone-enhanced substratum adhesion are nonresponsive to epidermal growth factor: evidence for a common signaling defect.
Thyrotropin-releasing hormone (TRH) and epidermal growth factor both enhance prolactin synthesis and substrate adhesion (a morphological change called stretching) of GH4 rat pituitary cells. We have examined TRH- and EGF-induced cell stretching using genetic and pharmacologic approaches. We selected and isolated a series of GH4 cell variants nonresponsive to TRH-induced cell stretching (str-). This selection yielded several variants that were nonresponsive to both TRH- and EGF-induced stretching but were still responsive to stretching induced by several other agents (tetradecanoylphorbol acetate [TPA], butyrate, and Neplanocin A). One of the str- variants (a14) was examined in detail. TRH, EGF, and TPA each enhanced prolactin synthesis in a14 cells, indicating that the a14 variant contained functional receptor binding sites for all 3 ligands as well as the capacity to generate those intracellular signals required for enhanced prolactin synthesis. Because the str- variants were isolated without selective pressure for EGF-induced stretching and because the possibility of more than one selectable mutation in all the variants is unlikely, we suggest that TRH and EGF share a common mechanism to induce cell stretching. We next examined whether the str- variants had a defect in a signaling pathway or in the biochemical endpoint for TRH- and EGF-induced cell stretching. A pharmacologic approach was utilized to investigate the biochemical basis for induced cell stretching. A synthetic Arg-Gly-Asp-Ser tetrapeptide (RGDS), specific for fibronectin and vitronectin adhesion receptors, inhibited TRH-, EGF-, and TPA-induced GH4 cell stretching and attachment to fibronectin- and vitronectin-coated dishes. These results suggest that the interaction between fibronectin and/or vitronectin and their receptor(s) may be a biochemical endpoint by which several agonists induced stretching of GH4 cells. Because the str- variant has RGDS-specific binding sites for fibronectin and vitronectin and responds to some agents that induce cell stretching via an RGDS receptor, we conclude that the a14 str- variant has a defect in an intracellular signaling pathway, shared by TRH and EGF, which induces cell stretching.
Ramsdell
J S
JS
Department of Anatomy and Cell Biology, Medical University of South Carolina, Charleston 29425.
Tashjian
A H
AH
D000818:Animals; D002448:Cell Adhesion / Q000187:drug effects; D002460:Cell Line; D002465:Cell Movement / Q000187:drug effects; D002469:Cell Separation; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D005353:Fibronectins / Q000378:metabolism / Q000494:pharmacology / Q000502:physiology; D014644:Genetic Variation / Q000502:physiology*; D006023:Glycoproteins / Q000378:metabolism / Q000494:pharmacology / Q000502:physiology; D013006:Growth Hormone / Q000378:metabolism / Q000502:physiology; D009842:Oligopeptides / Q000378:metabolism / Q000494:pharmacology; D010902:Pituitary Gland / Q000166:cytology* / Q000378:metabolism / Q000502:physiology; D010975:Platelet Aggregation Inhibitors / Q000378:metabolism / Q000494:pharmacology; D011388:Prolactin / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*; D019096:Vitronectin
D005353:Fibronectins; D006023:Glycoproteins; D009842:Oligopeptides; D010975:Platelet Aggregation Inhibitors; D019096:Vitronectin; D013973:Thyrotropin-Releasing Hormone; D004815:Epidermal Growth Factor; D011388:Prolactin; D013006:Growth Hormone; C046617:arginyl-glycyl-aspartyl-serine