Abstract 3428: Genome-stabilizing functions of NM23 in metastatic melanoma

Abstract

Abstract The metastasis suppressor protein NM23-H1 exhibits two enzymatic activities in vitro with potential roles in the maintenance of genomic integrity: a nucleoside diphosphate kinase (NDPK) activity that maintains balance in nucleotide pools and a 3′-5′ exonuclease (3′-5′ EXO) activity that could provide proofreading during DNA repair and replication. Studies were conducted in cell culture and in vivo to determine the extent to which NM23-H1 expression contributes to maintenance of genomic integrity, as well as suppression of melanoma initiation and progression. Expression of NM23-H1, and possibly NM23-H2, was shown to be necessary for timely repair of UVR-induced (6-4) photoproducts (6-4PP) in melanoma cell lines, as well as in transgenic mouse-derived melanocytes and embryo fibroblasts, as determined by immunoslot-blot assay. NM23 protein expression also suppressed the incidence of both spontaneous and UVR-induced mutations as determined using the 6-thioguanine resistance colony-forming assay. Point mutations that either selectively or tandemly disrupted the NDPK and 3′-5′ EXO activities of NM23-H1 exhibited compromised DNA repair and mutation-suppressing activities, consistent with contributions of both enzymatic functions. UVR induced rapid (< 5 min) translocation of NM23-H1 to the nucleus, where it colocalized closely in concert with 6-4PPs, strongly suggesting direct participation in the repair of those lesions. Consistent with this proposed function, transgenic mice engineered to be hemizygous-null in expression of both NM23-M1 and NM23-M2 (the mouse homologs of NM23-H1 and NM23-H2, respectively) were rendered susceptible to UVR-induced melanoma and epithelioid follicular cyst formation. Moreover, this NM23-deficient genotype conferred an aggressively metastatic phenotype to the HGF-expressing transgenic mouse model of UVR-inducible melanoma. Metastasis of highly-pigmented cells to draining lymph nodes and the lungs was seen in most cases, with lesions also occasionally seen in liver, brain and bone. Taken together, these results demonstrate a critical role for NM23 proteins in DNA repair and suppressing mutations under basal and genotoxic conditions. Importantly, they highlight for the first time a tumor suppressor function in the context of UVR-induced melanoma in vivo, and suggest a novel metastasis suppressor activity through suppression of metastasis-driving mutations. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3428. doi:1538-7445.AM2012-3428