The human sef-a isoform utilizes different mechanisms to regulate receptor tyrosine kinase signaling pathways and subsequent cell fate.
Negative feedback is among the key mechanisms for regulating receptor tyrosine kinase (RTK) signaling. Human Sef, a recently identified inhibitor of RTK signaling, encodes different isoforms, including a membrane spanning (hSef-a) and a cytosolic (hSef-b) isoform. Previously, we reported that hSef-b inhibited fibroblast proliferation and prevented the activation of mitogen-activated protein kinase (MAPK), without affecting protein kinase B/Akt or p38 MAPK. Conflicting results were reported concerning hSef-a inhibition of MAPK activation, and the effect of hSef-a on other RTK-induced signaling pathways is unknown. Here we show that, in fibroblasts, similar to hSef-b, ectopic expression of hSef-a inhibited fibroblast growth factor-induced cell proliferation. Unlike hSef-b, however, the growth arrest was mediated via a MAPK-independent mechanism, and was accompanied by elevated p38 MAPK phosphorylation and inhibition of protein kinase B/Akt. In addition, hSef-a, but not hSef-b, mediated apoptosis in fibroblast growth factor-stimulated cells. Chemical inhibitor of p38 MAPK abrogated the effect of hSef-a on apoptosis. In epithelial cells, ectopic expression of hSef-a inhibited the activation of MAPK, whereas down-regulation of endogenous hSef-a significantly increased MAPK activation and accelerated growth factor-dependent cell proliferation. These results indicate that hSef-a is a multifunctional negative modulator of RTK signaling and clearly demonstrate that hSef-a can inhibit the activation of MAPK, although in a cell type-specific manner. Moreover, the differences between the activities of hSef-a and hSef-b suggest that hSef isoforms can control signal specificity and subsequent cell fate by utilizing different mechanisms to modulate RTK signaling.
Ziv
Inbal
I
Department of Biology, Technion Institute of Technology, Haifa 32000, Israel.
Fuchs
Yaron
Y
Preger
Ella
E
Shabtay
Ariel
A
Harduf
Haggar
H
Zilpa
Tal
T
Dym
Naama
N
Ron
Dina
D
D000818:Animals; D017209:Apoptosis; D049109:Cell Proliferation; D004847:Epithelial Cells / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D020935:MAP Kinase Signaling System; D051379:Mice; D041681:NIH 3T3 Cells; D020033:Protein Isoforms; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*; D018123:Receptors, Interleukin / Q000737:chemistry / Q000502:physiology*; D015398:Signal Transduction; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
C477526:IL17RD protein, human; D020033:Protein Isoforms; D018123:Receptors, Interleukin; D020794:Receptor Protein-Tyrosine Kinases; D051057:Proto-Oncogene Proteins c-akt; D048051:p38 Mitogen-Activated Protein Kinases