Abstract
Mutual exclusiveness of oncogenes is a general phenomenon in cancer. Specifically in melanoma BRAF and NRAS mutations do not co-exist except a few (0.7%) cases. Here, we are looking for critical exclusive common target(s) of BRAF and NRAS mutations meant for synthetic lethality in melanoma therapy. To specifically evaluate BRAF and NRAS mutation dependent gene regulation in melanoma, mRNA microarray gene expression analysis was performed in melanoma cell lines where growth suppressive and non-suppressive properties depend on mutual targets of BRAFV600E and NRASQ61R/K mutation. We identified the tumor suppressor gene SPRY4 as a novel transcriptional target of second oncogenes BRAFV600E or NRASQ61R/K responsible for suppressive growth phenotype in various melanoma cell lines. Sprouty4 (SPRY4) acts as a feedback suppressor of the receptor-transduced mitogen-activated protein kinase (MAPK) signaling pathway. It has a role in the regulation of cell growth, motility and progression of various cancer types’ breast cancer, osteosarcoma, endometrial adenocarcinoma, myeloid leukemia including melanoma. Remote inducible expression of either BRAFV600E or NRASQ61R/K enhances the expression of SPRY4 at mRNA and protein level only in poor growth cell lines such as NRASQ61R (Tet-On BRAFV600E: SKmel119, WM1361 and BRAFV600E (Tet-On NRASQ61R: Gmel and MGH-CH-1) but not in NRASQ61R (Tet-On BRAFV600E: SKmel-63), BRAFV600E (Tet-On NRASVQ61R: A375) mutation. In addition, we observed that BRAFV600E expression exhibit constitutive activation of stress pathway signaling that is presumed to induce secondary senescence, as it does in nevi or normal cells. SPRY4 modify second oncogene induced changes such as inhibition of SPRY4 rescues cell growth impaired by BRAF or NRAS mutation expression. Hence, second oncogene enhances SPRY4 expression in part through stress pathway as confirmed by phospho kinase array. These findings suggest that in SPRY4/MAPK/Stress pathway, SPRY4 as a common target of BRAF and NRAS mutations affecting melanoma growth.
Citation Format: Raj Kumar, Ching-Ni-Jenny Njauw, Zhenyu Ji, Anpuchchelvi Rajadurai, Hensin Tsao. Dissecting mutual exclusiveness of oncogenic mutations in melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-307. doi:10.1158/1538-7445.AM2017-LB-307