| Autor: |
Kirkbride JA; Department of Molecular Physiology and Biophysics, and Kimmel Cancer Center, Jefferson Medical College, Thomas Jefferson University, 1020 Locust Street, Philadelphia, PA 19107, USA., Nilsson GY; Department of Molecular Physiology and Biophysics, and Kimmel Cancer Center, Jefferson Medical College, Thomas Jefferson University, 1020 Locust Street, Philadelphia, PA 19107, USA., Kim JI; Department of Molecular Physiology and Biophysics, and Kimmel Cancer Center, Jefferson Medical College, Thomas Jefferson University, 1020 Locust Street, Philadelphia, PA 19107, USA.; Department of Molecular Medicine, Keimyung University School of Medicine, Daegu 42601, Republic of Korea., Takeya K; Department of Veterinary Medicine, Faculty of Veterinary Medicine, Okayama University of Science, Imabari 794-8555, Ehime, Japan., Tanaka Y; Department of Veterinary Medicine, Faculty of Veterinary Medicine, Okayama University of Science, Imabari 794-8555, Ehime, Japan., Tokumitsu H; Applied Cell Biology, Graduate School of Interdisciplinary Science & Engineering in Health Systems, Okayama University, Okayama 700-8530, Okayama, Japan., Suizu F; Oncology Pathology, Department of Pathology and Host-Defense, Faculty of Medicine, Kagawa University, Kita-gun 761-0793, Kagawa, Japan., Eto M; Department of Molecular Physiology and Biophysics, and Kimmel Cancer Center, Jefferson Medical College, Thomas Jefferson University, 1020 Locust Street, Philadelphia, PA 19107, USA.; Department of Veterinary Medicine, Faculty of Veterinary Medicine, Okayama University of Science, Imabari 794-8555, Ehime, Japan. |
| Abstrakt: |
Raf-1, a multifunctional kinase, regulates various cellular processes, including cell proliferation, apoptosis, and migration, by phosphorylating MAPK/ERK kinase and interacting with specific kinases. Cellular Raf-1 activity is intricately regulated through pathways involving the binding of regulatory proteins, direct phosphorylation, and the ubiquitin-proteasome axis. In this study, we demonstrate that PHI-1, an endogenous inhibitor of protein phosphatase-1 (PP1), plays a pivotal role in modulating Raf-1 proteostasis within cells. Knocking down endogenous PHI-1 in HEK293 cells using siRNA resulted in increased cell proliferation and reduced apoptosis. This heightened cell proliferation was accompanied by a 15-fold increase in ERK1/2 phosphorylation. Importantly, the observed ERK1/2 hyperphosphorylation was attributable to an upregulation of Raf-1 expression, rather than an increase in Ras levels, Raf-1 Ser338 phosphorylation, or B-Raf levels. The elevated Raf-1 expression, stemming from PHI-1 knockdown, enhanced EGF-induced ERK1/2 phosphorylation through MEK. Moreover, PHI-1 knockdown significantly contributed to Raf-1 protein stability without affecting Raf-1 mRNA levels. Conversely, ectopic PHI-1 expression suppressed Raf-1 protein levels in a manner that correlated with PHI-1's inhibitory potency. Inhibiting PP1 to mimic PHI-1's function using tautomycin led to a reduction in Raf-1 expression. In summary, our findings highlight that the PHI-1-PP1 signaling axis selectively governs Raf-1 proteostasis and cell survival signals. |
