Mutations in GNA11 in uveal melanoma

Abstract

Background: Uveal melanoma is the most common intraocular cancer. There are no effective therapies for metastatic disease. Mutations in GNAQ, the gene encoding an alpha subunit of heterotrimeric G proteins, are found in 40% of uveal melanomas.

Methods: We sequenced exon 5 of GNAQ and GNA11, a paralogue of GNAQ, in 713 melanocytic neoplasms of different types (186 uveal melanomas, 139 blue nevi, 106 other nevi, and 282 other melanomas). We sequenced exon 4 of GNAQ and GNA11 in 453 of these samples and in all coding exons of GNAQ and GNA11 in 97 uveal melanomas and 45 blue nevi.

Results: We found somatic mutations in exon 5 (affecting Q209) and in exon 4 (affecting R183) in both GNA11 and GNAQ, in a mutually exclusive pattern. Mutations affecting Q209 in GNA11 were present in 7% of blue nevi, 32% of primary uveal melanomas, and 57% of uveal melanoma metastases. In contrast, we observed Q209 mutations in GNAQ in 55% of blue nevi, 45% of uveal melanomas, and 22% of uveal melanoma metastases. Mutations affecting R183 in either GNAQ or GNA11 were less prevalent (2% of blue nevi and 6% of uveal melanomas) than the Q209 mutations. Mutations in GNA11 induced spontaneously metastasizing tumors in a mouse model and activated the mitogen-activated protein kinase pathway.

Conclusions: Of the uveal melanomas we analyzed, 83% had somatic mutations in GNAQ or GNA11. Constitutive activation of the pathway involving these two genes appears to be a major contributor to the development of uveal melanoma. (Funded by the National Institutes of Health and others.).

Figure 1. Anatomical Location and Mutational Status of 118 Samples of Primary Uveal Melanoma

Lesions arising in the ciliochoroidal region had an increased frequency of GNA11 mutations (P=0.048 by Fisher’s exact test).

Figure 2. Effect of Mutations in GNAQ and GNA11 on Overall and Disease-free Survival

There was no significant difference in outcome on the basis of mutational status among 81 patients with primary uveal melanomas for whom follow-up information was available. The characteristics of these patients are provided in Table 1 in the Supplementary Appendix.

Figure 3. Induction of Tumors by the GNA11 Q209L and GNA11 R183C Variants in a Mouse Model

Immortalized mouse melanocytes (melan-a cells) were transduced with GNA11 variant Q209L or R183C, wild-type GNA11, or a β-galactosidase control vector and injected bilaterally into the flank of nonobese diabetic mice with severe combined immunodeficiency and depletion of the interleukin-2 receptor γ chain. By 11 weeks, tumors developed at all 6 injection sites in 3 mice bilaterally injected with melanocytes transduced with the Q209L variant (Panel A). Tumors developed at 3 out of 8 injection sites in 4 mice bilaterally injected with melanocytes transduced with the R183C variant (Panel B). There were no tumors in 5 mice bilaterally injected with melanocytes transduced with wild-type (WT) GNA11 or 3 mice bilaterally injected with melanocytes transduced with the β-galactosidase control vector (β-gal) (Panel B). The graph in Panel B shows the combined results of two independent experiments. Tumors were heavily melanized in all the mice (Panel C). Among the 3 mice with the Q209L variant, multiple lung metastases developed in all 3 mice (Panel D), and liver metastases developed in 1 (Panel E). Tumors were composed of pigmented spindle and epithelioid melanocytes (Panel F, hematoxylin and eosin). On Western blot analysis, melan-a cells that were transduced with GNA11 Q209L, but not their wild-type counterparts, showed activation of the mitogen-activated protein kinase pathway that was similar to the results in GNAQ Q209L and mutant BRAF or NRAS samples used as positive controls (Panel G). The term pERK denotes phosphorylated extracellular signal-regulated kinase.