SummaryNeuregulin (NRG) signaling through the receptor tyrosine kinase, ERBB3, is required for embryonic development, and dysregulated signaling has been associated with cancer progression. Here, we show that NRG1 ⁄ ⁄ ERBB3 signaling inhibits melanocyte (MC) maturation and promotes undifferentiated, migratory and proliferative cellular characteristics. Embryonic analyses demonstrated that initial MC specification and distribution were not dependent on ERBB3 signaling. However NRG1 ⁄ ⁄ ERBB3 signaling was both necessary and sufficient to inhibit differentiation of later stages of MC development in culture. Analysis of tissue arrays of human melanoma samples suggests that ERBB3 signaling may also contribute to metastatic progression of melanoma as ERBB3 was phosphorylated in primary tumors compared with nevi or metastatic lesions. Neuregulin 1-treated MCs demonstrated increased proliferation and invasion and altered morphology concomitant with decreased levels of differentiation genes, increased levels of proliferation genes and altered levels of melanoma progression and metastases genes. ERBB3 activation in primary melanomas suggests that NRG1 ⁄ ⁄ ERBB3 signaling may contribute to the progression of melanoma from benign nevi to malignancies.We propose that targeting ERBB3 activation and downstream genes identified in this study may provide novel therapeutic interventions for malignant melanoma.

Summary The oculocerebrorenal syndrome of Lowe (Lowe syndrome) is an X‐linked disorder of phosphatidylinositol metabolism characterized by congenital cataracts, renal proximal tubulopathy and neurological deficits. The disorder is due to the deficiency of the phosphatidylinositol 4,5‐bisphosphate (PIP2) 5‐phosphatase, ocrl1. PIP2 is critical for numerous cellular processes, including cell signalling, actin reorganization and protein trafficking, and is chronically elevated in patients with Lowe syndrome. The elevation of PIP2 cells of patients with Lowe syndrome provides the unique opportunity to investigate the roles of this phospholipid in fundamental cellular processes. We previously demonstrated that ocrl1 deficiency causes alterations in the actin cytoskeleton. Since actin remodelling is strongly activated by [Ca+2], which increases in response to IP3 production, we hypothesized that altered calcium signalling might contribute to the observed abnormalities in actin organization. Here we report a specific increase in bradykinin‐induced Ca+2 mobilization in Lowe fibroblasts. We show that the abnormal bradykinin signalling occurs in spite of normal total cellular receptor content. These data point to a novel role for ocrl1 in agonist‐induced calcium release.

Melanoma tumors are heterogeneous lesions that progress through distinct cellular phenotypes exhibiting either highly proliferative or invasive cell state gene expression signatures (SOX10+ vs. TGFB+ pathways, respectively) as disease progression occurs. It is appreciated that even within a single tumor, individual cells respond to hypoxic conditions through Hypoxia Inducible Factor 1a (HIF1a) activation, leading to gene expression that promotes invasive cell properties. Regulation of gene expression integrates the binding of intrinsic cell lineage factors and general transcription machinery to key cis-regulatory DNA sequences that are epigenetically defined. In order to identify the cis-regulatory sequences that are utilized in a cell's response to HIF1a activation, we have established an integrated regulatory dataset from melan-Ink4a-ARF-/- immortalized mouse melanocytes. This dataset includes Dnase1 HS regions, enhancer regions marked by H3K4me1 and EP300 co-binding, ChIP-Seq for the transcription factors HIF1a and SOX10, and RNA-SEQ datasets under proliferative and HIF1a-activated growth conditions. We are evaluating HIF1a binding regions in order to identify the cis-regulatory sequences utilized to regulate gene expression, identify the key factors engaged at these sites, and assess the role that DNA variation has in modulating factor binding and gene transcription in the switch from proliferative to hypoxic cell signaling conditions. By identifying the epigenetic cis-regulatory interactions that occur as a result of HIF1a activation, we hypothesize that we will highlight pathways important for melanoma progression that may be relevant to future therapeutics. Citation Format: Stacie Loftus, Julie Cronin, Temesgen Fufa, Andrew McCallion, Gregory Crawford, William Pavan. Epigenetic Cis-regulatory interactions in HIF1a-activated melanocytes. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Melanoma: From Biology to Therapy; Sep 20-23, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(14 Suppl):Abstract nr A23.