HOXA1 drives melanoma tumor growth and metastasis and elicits an invasion gene expression signature that prognosticates clinical outcome.

Melanoma is a highly lethal malignancy notorious for its aggressive clinical course and eventual resistance to existing therapies. Currently, we possess a limited understanding of the genetic events driving melanoma progression, and much effort is focused on identifying pro-metastatic aberrations or perturbed signaling networks that constitute new therapeutic targets. In this study, we validate and assess the mechanism by which homeobox transcription factor A1 (HOXA1), a pro-invasion oncogene previously identified in a metastasis screen by our group, contributes to melanoma progression. Transcriptome and pathway profiling analyses of cells expressing HOXA1 reveals upregulation of factors involved in diverse cytokine pathways that include the transforming growth factor beta (TGFß) signaling axis, which we further demonstrate to be required for HOXA1-mediated cell invasion in melanoma cells. Transcriptome profiling also shows HOXA1's ability to potently downregulate expression of microphthalmia-associated transcription factor (MITF) and other genes required for melanocyte differentiation, suggesting a mechanism by which HOXA1 expression de-differentiates cells into a pro-invasive cell state concomitant with TGFß activation. Our analysis of publicly available data sets indicate that the HOXA1-induced gene signature successfully categorizes melanoma specimens based on their metastatic potential and, importantly, is capable of stratifying melanoma patient risk for metastasis based on expression in primary tumors. Together, these validation data and mechanistic insights suggest that patients whose primary tumors express HOXA1 are among a high-risk metastasis subgroup that should be considered for anti-TGFß therapy in adjuvant settings. Moreover, further analysis of HOXA1 target genes in melanoma may reveal new pathways or targets amenable to therapeutic intervention.

Coordinate phosphorylation of multiple residues on single AKT1 and AKT2 molecules.

Aberrant AKT activation is prevalent across multiple human cancer lineages providing an important new target for therapy. Twenty-two independent phosphorylation sites have been identified on specific AKT isoforms likely contributing to differential isoform regulation. However, the mechanisms regulating phosphorylation of individual AKT isoform molecules have not been elucidated because of the lack of robust approaches able to assess phosphorylation of multiple sites on a single AKT molecule. Using a nanofluidic proteomic immunoassay (NIA), consisting of isoelectric focusing followed by sensitive chemiluminescence detection, we demonstrate that under basal and ligand-induced conditions that the pattern of phosphorylation events is markedly different between AKT1 and AKT2. Indeed, there are at least 12 AKT1 peaks and at least 5 AKT2 peaks consistent with complex combinations of phosphorylation of different sites on individual AKT molecules. Following insulin stimulation, AKT1 was phosphorylated at Thr308 in the T-loop and Ser473 in the hydrophobic domain. In contrast, AKT2 was only phosphorylated at the equivalent sites (Thr309 and Ser474) at low levels. Further, Thr308 and Ser473 phosphorylation occurred predominantly on the same AKT1 molecules, whereas Thr309 and Ser474 were phosphorylated primarily on different AKT2 molecules. Although basal AKT2 phosphorylation was sensitive to inhibition of phosphatidylinositol 3-kinase (PI3K), basal AKT1 phosphorylation was essentially resistant. PI3K inhibition decreased pThr451 on AKT2 but not pThr450 on AKT1. Thus, NIA technology provides an ability to characterize coordinate phosphorylation of individual AKT molecules providing important information about AKT isoform-specific phosphorylation, which is required for optimal development and implementation of drugs targeting aberrant AKT activation.