PHI-1, an Endogenous Inhibitor Protein for Protein Phosphatase-1 and a Pan-Cancer Marker, Regulates Raf-1 Proteostasis

Authors

Jason Kirkbride, Thomas Jefferson University
Garbo Nilsson, Thomas Jefferson University
Jee In Kim, Thomas Jefferson University
Kosuke Takeya
Yoshinori Tanaka
Hiroshi Tokumitsu
Futoshi Suizu
Masumi Eto, Thomas Jefferson UniversityFollow

Document Type

Article

Publication Date

12-4-2023

Comments

This article is the author's final published version in Biomolecules, Volume 13, Issue 12, December 2023, Article number 1741.

The published version is available at https://doi.org/10.3390/biom13121741.

Copyright © 2023 by the authors

Abstract

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.

Recommended Citation

Kirkbride, Jason; Nilsson, Garbo; Kim, Jee In; Takeya, Kosuke; Tanaka, Yoshinori; Tokumitsu, Hiroshi; Suizu, Futoshi; and Eto, Masumi, "PHI-1, an Endogenous Inhibitor Protein for Protein Phosphatase-1 and a Pan-Cancer Marker, Regulates Raf-1 Proteostasis" (2023). Kimmel Cancer Center Faculty Papers. Paper 113.
https://jdc.jefferson.edu/kimmelccfp/113

Creative Commons License

This work is licensed under a Creative Commons Attribution 4.0 License.

PubMed ID

38136612

Language

English