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A protein methyl transferase, PRMT5, selectively blocks oncogenic ras-p21 mitogenic signal transduction
Lyndon Chie1, Jeffry R Cook, Denise Chung
1Department of Pathology & Laboratory Medicine, New York Harbor VA Medical Center, Brooklyn, NY 11209, USA.
Abstract:
A Janus-2 (JAK-2) binding protein, JBP1, has been found to function as an arginine methyl transferase and is now designated PRMT5. Co-injection of plasmids encoding this protein together with oncogenic (Val 12-containing) ras-p21 protein into Xenopus leavis oocytes results in strong inhibition of oncogenic p21-induced oocyte maturation. This inhibition appears to be dependent on the methyl transferase function since a partially active R368A mutant shows diminished ability to inhibit Val 12-p21-induced oocyte maturation, and an almost totally inactive GAGRG (365-369) deletion mutant fails to inhibit Val 12-p21-induced maturation. In contrast, PRMT5 (JBP1) does not inhibit insulin-induced oocyte maturation. Since insulin-induced maturation depends on activation of cellular ras-p21, PRMT5 does not appear to inhibit the wild-type p21 protein. We also find that arginine methyl transferase inhibitors strongly block oncogenic ras-p21-activated, but not insulin-activated, wild-type ras-p21-induced oocyte maturation. Thus signaling by oncogenic p21 appears to involve methyltransferases uniquely. Surprisingly, the active site peptide, Gly-Arg-Gly, strongly suppresses insulin-induced maturation but has no effect on Val 12-p21-induced maturation. This peptide may therefore be useful in defining steps in the wild-type ras pathway.
Insights
Oncoprotein signaling involves unique arginine methyltransferases. Protein arginine methyltransferase 5 (PRMT5) inhibits oncogenic ras-p21 but not wild-type ras-p21, suggesting a specific role in cancer pathways.
Area of Science:
- Molecular Biology
- Cell Signaling
- Biochemistry
Background:
- Janus-2 (JAK-2) binding protein 1 (JBP1) identified as protein arginine methyltransferase 5 (PRMT5).
- Oncogenic ras-p21 proteins are implicated in various cancers.
- Oocyte maturation is a model system for studying cell signaling pathways.
Purpose of the Study:
- To investigate the role of PRMT5 in ras-p21 signaling.
- To determine if PRMT5's methyltransferase activity is essential for its function.
- To explore the differences between oncogenic and wild-type ras-p21 signaling.
Main Methods:
- Xenopus laevis oocyte maturation assay.
- Co-injection of plasmids encoding PRMT5 and ras-p21 variants.
- Site-directed mutagenesis to create PRMT5 mutants (R368A, GAGRG deletion).
- Use of arginine methyltransferase inhibitors and active site peptide.
Main Results:
- PRMT5 strongly inhibits oncogenic (Val 12) ras-p21-induced oocyte maturation.
- PRMT5's inhibitory effect is dependent on its methyltransferase activity.
- PRMT5 does not inhibit insulin-induced oocyte maturation, which relies on wild-type ras-p21.
- Arginine methyltransferase inhibitors block oncogenic ras-p21 signaling but not insulin-induced signaling.
- Active site peptide suppresses insulin-induced maturation but not oncogenic ras-p21-induced maturation.
Conclusions:
- Oncogenic ras-p21 signaling uniquely involves arginine methyltransferases.
- PRMT5 plays a specific role in inhibiting oncogenic ras-p21 pathways.
- The active site peptide may be a tool for dissecting wild-type ras pathways.