Abstract A18: G1 cell cycle arrest is required for invasive behavior

Abstract

Abstract The ability for a cell to breach the surrounding basement membrane and adopt an invasive phenotype is a critical, but poorly understood step in the progression of cancer. Like many aspects of cancer cell behavior, the genetic programs that regulate invasive behavior are likely shared with normal cell biological processes, as invasion occurs during embryonic development and immune surveillance. Due to difficulties of studying this dynamic behavior in vivo, elucidating the genetic and epigenetic controls of cell invasive activity has been difficult. Our laboratory uses a unique in vivo model to examine cell invasion that combines functional genomic and genetic tools with single-cell high resolution visual analyses. We examine anchor cell (AC) invasion into the vulval epithelium during the larval development of the model roundworm, C. elegans. Our data functionally links G1 cell cycle arrest to acquisition of invasive behavior. Previously we have identified that a single transcription factor, the conserved nuclear hormone receptor nhr-67 (NR2E1/TLX) is required in the AC to prevent the invasive AC from entering the cell cycle. NHR-67 maintains the AC in G1 cell cycle arrest, in part through upregulation of the cyclin-dependent kinase inhibitor cki-1 (p21CIP1/p27Kip1). Loss of nhr-67 results in non-invasive mitotic ACs that fail to express matrix metalloproteinases (MMPs) and actin regulators or form invadopodia, F-actin rich membrane-localized protrusions that are required for invasion. Strikingly, AC invasion can be rescued through induction of G1 arrest, preventing cell division and promoting differentiation. Downstream of G1 arrest, the AC requires the activity of the conserved histone deacetylase HDA-1, a key regulator of cell differentiation, to regulate the expression of pro-invasive genes and localize invadopodia. Through loss-of-function RNA interference (RNAi) screening, we have identified new cell cycle regulatory components (lin-35/RB, skr-2/SKP1, cdc-14/CDC14A, cul-1/ Cullin-1 and cul-4/ Cullin-4B) and epigenetic modifiers (let-418/Mi-2/CHD3 and Swi/snf-components) that function with cki-1 and hda-1, respectively, to maintain G1 cell cycle arrest and differentiate the invasive phenotype. Together our results suggest that the acquisition of the invasive phenotype is a post-mitotic differentiated state, which may help explain the paradoxical reports that the invasive fronts of many metastatic cancers are non-proliferative. Citation Format: Abraham Q. Kohrman, Mana Chandhok, Wan Zhang, David Q. Matus. G1 cell cycle arrest is required for invasive behavior. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Cancer Cell Cycle - Tumor Progression and Therapeutic Response; Feb 28-Mar 2, 2016; Orlando, FL. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(11_Suppl):Abstract nr A18.