Germ Line Gain of Function with SOS1 Mutation in Hereditary Gingival Fibromatosis

• Published in: The Journal of biological chemistry Vol. 282; no. 28; pp. 20245 - 20255
• Main Authors: Jang, Shyh-Ing, Lee, Eun-Jin, Hart, P. Suzanne, Ramaswami, Mukundhan, Pallos, Debora, Hart, Thomas C.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 13.07.2007; American Society for Biochemistry and Molecular Biology
• Subjects: Cell Membrane - genetics; Cell Membrane - metabolism; Cell Membrane - pathology; Cells, Cultured; Cyclins - biosynthesis; E2F Transcription Factors - biosynthesis; Early Growth Response Protein 1 - biosynthesis; Early Growth Response Protein 1 - genetics; Extracellular Signal-Regulated MAP Kinases - metabolism; Fibroblasts - metabolism; Fibroblasts - pathology; Fibromatosis, Gingival - genetics; Fibromatosis, Gingival - metabolism; Fibromatosis, Gingival - pathology; G1 Phase - genetics; Humans; MAP Kinase Signaling System - genetics; Phosphorylation; Proliferating Cell Nuclear Antigen - biosynthesis; Proliferating Cell Nuclear Antigen - genetics; Protein Processing, Post-Translational - genetics; Protein Transport - genetics; Retinoblastoma Protein - genetics; Retinoblastoma Protein - metabolism; RNA, Small Interfering - genetics; RNA, Small Interfering - pharmacology; S Phase - genetics; SOS1 Protein - antagonists & inhibitors; SOS1 Protein - genetics; SOS1 Protein - metabolism; Up-Regulation - genetics
• DOI: 10.1074/jbc.M701609200
• ISSN: 0021-9258

Mutation of human SOS1 is responsible for hereditary gingival fibromatosis type 1, a benign overgrowth condition of the gingiva. Here, we investigated molecular mechanisms responsible for the increased rate of cell proliferation in gingival fibroblasts caused by mutant SOS1 in vitro. Using ectopic expression of wild-type and mutant SOS1 constructs, we found that truncated SOS1 could localize to the plasma membrane, without growth factor stimuli, leading to sustained activation of Ras/MAPK signaling. Additionally, we observed an increase in the magnitude and duration of ERK signaling in hereditary gingival fibromatosis gingival fibroblasts that was associated with phosphorylation of retinoblastoma tumor suppressor protein and the up-regulation of cell cycle regulators, including cyclins C, D, and E and the E2F/DP transcription factors. These factors promote cell cycle progression from G1 to S phase, and their up-regulation may underlie the increased gingival fibroblast proliferation observed. Selective depletion of wild-type and mutant SOS1 through small interfering RNA demonstrates the link between mutation of SOS1, ERK signaling, cell proliferation rate, and the expression levels of Egr-1 and proliferating cell nuclear antigen. These findings elucidate the mechanisms for gingival overgrowth mediated by SOS1 gene mutation in humans.