P38 Mediates Tumor Suppression through Reduced Autophagy and Actin Cytoskeleton Changes in NRAS-Mutant Melanoma

Ishani Banik; Adhideb Ghosh; Erin Beebe; Blaž Burja; Mojca Frank Bertoncelj; Christopher M Dooley; Enni Markkanen; Reinhard Dummer; Elisabeth M Busch-Nentwich; Mitchell P Levesque

doi:10.3390/cancers15030877

P38 Mediates Tumor Suppression through Reduced Autophagy and Actin Cytoskeleton Changes in NRAS-Mutant Melanoma

Cancers (Basel). 2023 Jan 31;15(3):877. doi: 10.3390/cancers15030877.

Authors

Ishani Banik^{1

2}, Adhideb Ghosh³, Erin Beebe⁴, Blaž Burja⁵, Mojca Frank Bertoncelj^{5

6}, Christopher M Dooley⁷, Enni Markkanen⁴, Reinhard Dummer^{1

2}, Elisabeth M Busch-Nentwich⁸, Mitchell P Levesque^{1

2}

Affiliations

¹ Department of Dermatology, University of Zurich Hospital, University of Zurich, 8091 Zurich, Switzerland.
² Department of Dermatology, University of San Francisco California, San Francisco, CA 94117, USA.
³ Functional Genomics Center Zurich, ETH/University of Zurich, 8057 Zurich, Switzerland.
⁴ Institute of Veterinary Pharmacology and Toxicology, Vetsuisse Faculty, University of Zurich, 8057 Zurich, Switzerland.
⁵ Center of Experimental Rheumatology, Department of Rheumatology, University Hospital Zurich, University of Zurich, 8091 Zurich, Switzerland.
⁶ Team Integrative Biology of Immune-Mediated Inflammatory Diseases, BioMed X Institute, 69120 Heidelberg, Germany.
⁷ Max Plank Institute for Heart and Lung Research, 61231 Bad Nauheim, Germany.
⁸ School of Biological and Behavioural Sciences, Queen Mary University of London, London E1 4NS, UK.

Abstract

Hotspot mutations in the NRAS gene are causative genetic events associated with the development of melanoma. Currently, there are no FDA-approved drugs directly targeting NRAS mutations. Previously, we showed that p38 acts as a tumor suppressor in vitro and in vivo with respect to NRAS-mutant melanoma. We observed that because of p38 activation through treatment with the protein synthesis inhibitor, anisomycin leads to a transient upregulation of several targets of the cAMP pathway, representing a stressed cancer cell state that is often observed by therapeutic doses of MAPK inhibitors in melanoma patients. Meanwhile, genetically induced p38 or its stable transduction leads to a distinct cellular transcriptional state. Contrary to previous work showing an association of invasiveness with high p38 levels in BRAF-mutated melanoma, there was no correlation of p38 expression with NRAS-mutant melanoma invasion, highlighting the difference in BRAF and NRAS-driven melanomas. Although the role of p38 has been reported to be that of both tumor suppressor and oncogene, we show here that p38 specifically plays the role of a tumor suppressor in NRAS-mutant melanoma. Both the transient and stable activation of p38 elicits phosphorylation of mTOR, reported to be a master switch in regulating autophagy. Indeed, we observed a correlation between elevated levels of phosphorylated mTOR and a reduction in LC3 conversion (LCII/LCI), indicative of suppressed autophagy. Furthermore, a reduction in actin intensity in p38-high cells strongly suggests a role of mTOR in regulating actin and a remodeling in the NRAS-mutant melanoma cells. Therefore, p38 plays a tumor suppressive role in NRAS-mutant melanomas at least partially through the mechanism of mTOR upregulation, suppressed autophagy, and reduced actin polymerization. One or more combinations of MEK inhibitors with either anisomycin, rapamycin, chloroquine/bafilomycin, and cytochalasin modulate p38 activation, mTOR phosphorylation, autophagy, and actin polymerization, respectively, and they may provide an alternate route to targeting NRAS-mutant melanoma.

Keywords: NRAS mutation; anisomycin; autophagy; mTOR; melanoma; p38 tumor suppressor.

Grants and funding

This research received no external funding.