Targeting glycogen synthase kinase-3 (GSK-3) in human melanoma

A18

In our functional survey of specific melanoma-associated alterations, we found a surprising anti-oncogenic role of beta-catenin signaling. Introduction of a protein-stabilized form of beta-catenin antagonized oncogene (activated Ras and c-Met)-driven transformation of human epidermal melanocytes (HEMs). Tracing the canonical beta-catenin pathway identified GSK-3, a negative regulator of beta-catenin, as a potential molecular target amenable to pharmacologic inhibition in melanoma cells. Treatment of oncogene-transformed HEMs with a small molecular GSK-3 inhibitor, BIO phenocopied the inhibitory effect of beta-catenin overexpression. Whereas the growth of primary HEMs and oncogene-transduced derivatives is exquisitely sensitive to inhibition by BIO treatment, the growth of patient-derived melanoma cell lines, in contrast, showed variable sensitivities (over two orders of magnitude) to pharmacologic GSK-3 inhibition. BIO synergized with the p53-MDM2 inhibitor, Nutlin-3, in the growth inhibition of susceptible melanoma cells. In addition, cell lines harboring NRAS mutations, compared to those with BRAF mutations or WT NRAS/BRAF alleles, are associated with increased resistance to GSK-3 inhibition. Gene Ontology (GO) analysis and Gene Set Enrichment Analysis (GSEA) of genomic mRNA profiles revealed enhanced cellular autophagy to be correlated with increased resistance to BIO-mediated growth inhibition. Relative BIO-resistance correlated with increased GFP-LC3 subcellular punctate localization, a reporter for enhanced autophagolysosomal flux. Additionally, pharmacologic inhibition of the autophagolysosomal pathway enhanced BIO-mediated growth inhibition. Thus, the growth of melanoma cells displays variable sensitivities to GSK-3 inhibition, and survival of melanoma cells in response to acute GSK-3 inhibition may be partially mediated by enhanced cellular autophagy.